6
Human Health and Security
OVERVIEW
Virtually every aspect of human health and well-being is linked to Earth, be it through the air we breathe, the climate or weather we experience, the food we eat, the water we drink, or the environs in which we live, work, or play. Diverse environmental factors affect the distribution, diversity, incidence, severity, and persistence of diseases and other health effects—something that has been recognized for millennia. Yet in the United States today, an estimated 1.8 to 3.1 years of life are lost to people living in the most polluted cities because of chronic exposure to air pollutants (Pope, 2000). Roughly 9 million cases of waterborne disease occur in the United States each year (Rose et al., 2001). Exposure to ultraviolet (UV) radiation may be the most important preventable factor in a person’s risk of skin cancer in the United States (American Academy of Dermatology, 2006); more than 1 million new cases occur each year (American Cancer Society, 2006). The 1995 heat wave in Chicago caused nearly 700 excess deaths (Whitman et al., 1997), and perhaps as many as 15,000 people died in 2003 during a prolonged heat wave in France (Fouillet et al., 2006). The annual number of industrial accidents involving the release of hazardous substances from facilities required to have risk management plans ranged from 225 to more than 500 over the 9-year period ending in 2003 (EPA, 2005). Although diseases transmitted by arthropod vectors (mosquitoes, sand flies, and so on) may be less important in the United States than elsewhere in the world, they still present an important health concern. In developing countries, malaria kills 1 million to 2 million people each year, and dengue fever afflicts as many as 80 million people globally each year (Pinheiro and Corber, 1997). Those are several of the important examples identified by the Panel on Human Health and Security and discussed later in this chapter. The examples critically link observations of Earth’s environment to human health and security risks, and indicate the opportunities that space-based observations offer to better assess and manage those risks.
The current unprecedented rate of global environmental change and the growing rates of global population growth and resource consumption indicate that analyses of such changes are important to human well-being. Global movement of people, pollutants, and lifestyles has exacerbated the role of environmental factors that affect human health. The urgency of obtaining global data—often obtained via space-
based methods—on land-use changes, climate changes, weather extremes, episodes of atmospheric and surface water pollution, and other observations has become critical to understanding how population and economic changes throughout the globe affect our common well-being. The panel considered issues of environmental factors pertinent to its charge, identified various kinds of human health and security risks, and then evaluated how remote sensing data from space might contribute to a better understanding of relationships between those factors and risks.
Over the past couple of decades, health and environmental scientists have used remote sensing data in diverse analyses of how environmental factors have altered the risk of various health effects in time and space, and how these insights might eventually be used to make observations and evaluate and manage risk. The basis for such research is the long-term availability of remote sensing data, combined with in situ observations (such as disease surveillance and reporting) that permit analyses necessary to uncover patterns and develop forecasts (NRC, 2007). Such research is impossible without continued capture and dissemination of remote sensing data, information that has served as the basis for understanding many larger-scale spatial environmental patterns. These data, combined with in situ epidemiological observations of disease morbidity and mortality, have served as the mainstay of research on environmental factors and disease and recommendations related to human health and security. Many studies successfully demonstrate the application of remote sensing data to identification of spatial or temporal variation in disease incidence or to assessment of the quantity or quality of air, food, and potable water, for example. The aim of such studies typically is to enhance forecasts of future outbreaks or to understand pathways by which environmental features are linked to increased health risks. Although the research being undertaken has been productive in identifying environmental links to human health risk, the confidence with which most diseases and other health effects can be forecast is still very weak. For this reason, the continued availability of space-based observations of land use and land cover, oceans, weather and climate, and atmospheric pollutants is critical to further enhancing the understanding of links to diseases and to expanding capacity for early warning of times and places where risk is elevated. Only through analyses of long-term time series will such patterns be understood and capabilities developed that will be useful to risk managers and health responders.
In general, knowledge of changing risk across regions and habitats, or over weeks to a few years, should improve forecasts, and hence detection capabilities and possible interventions and adaptation. For example, new higher-spatial-resolution satellite data may increase understanding of some infectious diseases whose risk to people is influenced by changes in microhabitat conditions. Also, such data can enhance understanding of relationships between human health effects and UV radiation dosage levels. Likewise better remote sensing capabilities should enhance the capacity to detect and track risk agents, including local drought conditions, harmful algal blooms, regional air pollution, and many acute releases of environmental contaminants. Anticipated health and security benefits currently drive most of the basic research agenda that employs space-based observations, yet public health practitioners and risk managers are only slowly expanding their use of these results. Future research is more likely to be useful if it is closely linked with the needs of the public health community, risk mangers, emergency responders, and specific components of human well-being.
Prioritization of Needs
The approach taken by this panel differed somewhat from that of most other panels, in that it intentionally began by identifying important health threats that are related to environmental factors and desired health outcomes (societal benefits). The panel then identified the kinds of Earth observation parameters and variables (environmental data) it considered important to informing relevant research and applications, and finally determined which platforms, sensors, and remote sensing data could provide the appropriate
data (missions). Thus, the panel’s discussions focused on various kinds of health effects and the Earth environmental factors and contaminants that might contribute to those effects. The discussions also focused on determining which people are at risk, and where and when. Thus, mission recommendations from this panel correspond to those of many of the other panels, in that climate, weather, ecosystems, and water resources, in particular, directly and indirectly affect the range of human health and security issues identified here. This approach led to the following considerations:
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Setting priorities among the sensors, platforms, or missions essential to human health and security is difficult. The importance of existing and future sensors depends on the environmental health effects that society considers to be of greatest concern, which in turn determines the environmental data that best inform exposure and risk assessments, and efforts to predict and prevent or mitigate health effects.
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At a minimum, continuity of existing sensors is critical to developing observational and forecast capabilities for most diseases and other health risks. Although environmental links with more direct, short-term health effects are reasonably well understood (e.g., temperature and heat stress or atmospheric pollutants and some respiratory symptoms), many other environment-disease associations involve complex pathways requiring extensive analyses of time series to develop sound predictive associations.
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Continued research is needed to firmly establish the predictive relationships between remotely sensed environmental data and patterns of environmentally related health effects. Beyond these research needs, preservation of existing sensors (e.g., AVHRR/MODIS, Landsat) will permit continued development and implementation of early warning or detection capacity for some better-understood limits between environmental exposures and health effects.
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The research agenda of many human health and environmental scientists who analyze remote sensing data and in situ data increasingly involves time-space modeling and statistical analysis of associations, suggesting that federal agencies should vigorously support such efforts. Accordingly, enhanced funding for research on and application of space-based observations to health problems should be an important part of NASA’s and NOAA’s missions to achieve societal benefits.
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Field evaluation of analytic results and forecasts is important to developing more comprehensive and accurate models of diverse complex environment-disease dynamics. Such efforts may eventually serve as a basis for developing improved observation systems.
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The need for higher-spatial-resolution data depends on the health problems to be addressed. Exceptions might occur where global transport of risk agents (by water or air plumes or the migration of birds) could be monitored by multiple sensors over large areas. Many health applications of remote sensing data will use data relevant to applications identified by other panels. There is an important synergy between many of the data needs identified by this panel and by other panels.
Overarching Issues
The World Health Organization defines health as “a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.” Thus, human health and security should be thought of in the larger context of multiple factors that affect people through various direct and indirect pathways. The Earth sciences agenda that relates to human health involves at least how environmental factors affect the more limited notion of human health. However, the manner in which those factors help to shape and define social, economic, and psychological aspects of people’s existence also alters their health. Thus, the value of remote sensing data cannot be considered independently of the more encompassing meaning of health and security, nor of data coming from other sources—demographic, occupational, insurance, housing, and other surveys and analyses.
The panel therefore considered the overarching issues to involve much more than the more narrow conceptions of human health. Indeed, it considered that the societal benefits accruing through improved human health should be fundamental to defining the research and applications goals of the Earth science agenda, including the need for an intellectual framework that directs bridging research between the Earth system framework and the public-health response and decision-maker community. It is critical for Earth scientists to interact more openly and effectively with public health and security officials, to help determine the needed understanding, the desired analyses, and the applications through which remote sensing data can contribute to prediction, detection, and mitigation of threats to health and security. With such conceptual, research, planning, and policy interactions, the Earth science community, and NASA and NOAA, will be better able to contribute to improving human health and security, thus achieving the desired societal benefits. Developing such a reliable observational and predictive capacity, based on remote sensing data used in the context of human health risk, should be a goal of future space mission decisions and agency responsibilities.
Critical Questions
Given these contextual issues, the panel discussed the following questions, among others that were part of its charge:
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How can remote sensing data be enhanced to assist detection and prediction of the places where disease risk is elevated or times when disease outbreaks are likely?
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Might such data enhance the rapid detection of events that threaten health or security?
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How can risk maps derived from space-based observations be used to enhance public-health efforts directed at education and prevention?
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What new exchanges can expand interactions between remote sensing system designers and public-health analysts that will help identify spatial and temporal risk patterns?
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What new understanding derived from remote sensing data can be used to target interventions aimed at reducing the vulnerability of human communities to health risks?
STATUS AND REQUIREMENTS
Status of Current Understanding and Strategic Thinking
To illustrate the importance of space-based observations in addressing human health and security, this section provides a few examples of past efforts, discusses the need to assimilate space-based observations with data from other sources, identifies the role of spatial and temporal scale, and stresses the importance of moving research toward operations.
Uses of Space-based Observations to Address Human Health Concerns
In addressing human health and security concerns, space-based observations are most useful when used along with many other sources of data. Public-health and risk management decision making has benefited from space-based technologies, and can benefit further with improvements in these technologies, through applications that include:
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Prediction of occurrence of disease or disease outbreaks. Space-based observations provide spatial and temporal data on environmental changes that affect the conditions related to disease occurrence and can be combined within predictive frameworks to forecast health emergencies.
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Rapid detection and tracking of events. Given sufficient temporal or spatial detail, space-based observations can provide data to support rapid detection of environmental changes or pollution events that affect human health.
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Construction of risk maps. The spatial extent of space-based observations provides a means to identify spatial variability in risk, potentially improving the scale of environmental observations so that they match the scale of activities in human communities.
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Targeting interventions. Activities to reduce the vulnerability of human communities to health risks, including environmental, behavioral, educational, and medical interventions, can be guided, improved, and made more efficient by use of available and proposed space-based observational systems.
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Enhancing knowledge of human health-environment interactions. Basic research on the causes of disease is ongoing, and remote sensing of environmental parameters that affect health is crucial for investigations that improve understanding of the spatial and temporal dynamics of health risk.
Assimilation of Space-based Observations with Other Data Sources and Models
Space-based observations are most effective as inputs to public-health decision making when they are used in concert with other data systems, including ground-based observations of environmental and epidemiological conditions, demographic data, data collected from aircraft, and outputs from numerical models.1 Investments are needed for the coordination of data collection efforts from multiple sources for specific purposes. Specifically, research on public-health decision support systems needs to address the limitations in how current data systems interface, and the opportunities for coordinating observations.
The Importance of Appropriate Spatial and Temporal Resolution
Effective incorporation of remote sensing data into public-health and risk management practices requires measurements that are at spatial and temporal resolutions appropriate to the scale of the problems at hand. That often means that data are needed at more finely detailed spatial and temporal resolutions than current technology allows. When rapid response to events is required or continuous monitoring can be used to identify anomalous environmental conditions, fine temporal resolution is required. Accuracy of measurements can also be improved through aggregation of multiple observations over time; frequent observations can be used for this purpose as well. Experience with risk management applications (e.g., warnings on harmful algal bloom and famine early-warning systems) suggests that fine-spatial-resolution data are required to target forecasts and warnings to specific geographical locations; such targeted warnings have been shown to be more effective than blanket warnings over entire regions, as discussed later in this chapter.
The Importance of Moving Toward Operational Systems
To realize the potential benefits of space-based operations for improving human health, remote sensing has to move from research to operations. Making the data collection operational, in the service of improving
BOX 6.1 LESSONS FROM LANDSAT The history of the Landsat program provides useful lessons on how long-term data continuity and user training affect the application of satellite data to real-world problems. As the Landsat technology evolved from the late 1970s to the late 1980s, the scientific literature based on Landsat data increased and its user community grew in size and expertise. By the mid-1990s it had a very large base of knowledgeable users and formed a central theme of much of the teaching about remote sensing at universities. Despite later setbacks (privatization in the late 1980s, the loss of Landsat 6 on launch, and scan-line corrector problemson Landsat 7), it continued its dominance into the new century, including an increase in interdisciplinary applications, such as health, demographics, and geology. At this writing however, the Landsat era is threatened. With only Landsat 5 still operating properly and no replacement expected to be ready in the near future, Landsat dominance in high-resolution environmental monitoring may be over. University training programs are redoing their teaching materials to focus on new sensors. Change-detection research programs are experiencing difficulties as new sensors are not back-compatible with Landsat. Interdisciplinary research scientists now find that their hard-won expertise in Landsat data analysis is obsolete, and they must seek out new collaborators with expertise in new systems. |
human health and security, requires that they be used to address the five sets of activities listed above and that accurate information products be delivered to public-health practitioners, risk managers, emergency responders, and the public in a timely manner. The data also have to be analyzed so that they are understandable in the context of the problems faced by decision makers and on the scale of human decision making. The data need to be reliably available so that they can be evaluated sufficiently to be trusted by the public-health community and other users and relied on as tools for supporting decisions that have life-and-death consequences. The panel believes that emphasis on three key investments would improve the benefits of remote sensing for this purpose, as well as the development of new sensing systems.
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First, continuity of systems that provide data to health-related programs and research is important. The existing base of users of space-based observations in the health community has experience with such sensor systems as Landsat, AVHRR, and MODIS, and the availability of these data products is necessary to ensure that the users have access to data they understand (see Box 6.1). Research and applications in public health often require long time series of data to evaluate or predict how environmental changes affect health. Sensor systems with a long-term archive of observations are most useful in such cases.
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Second, when new sensing systems are brought online, the public-health community, risk mangers, and emergency responders have to be trained to make the best possible use of them.
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Third, research that develops decision-making frameworks, tools to analyze space-based observations, and tests of efficacy in the context of real-world health interventions are all needed.
Status of Existing and Planned Products and Needed Improvements
Many, but not all, of the desired satellite sensors relevant to human health and security already exist. However, because the sensors are beginning to fail, plans should be devised for, at a minimum, maintaining these sensors (or their equivalents) so that long-term, time-series research linking environmental processes to health risks or disease patterns can be continued. In addition, these time-series data maintained into the
future will be critical for early warning of when and where risk mitigation efforts are warranted. As has been pointed out in other parts of this report, existing sensors are becoming nonfunctional, and replacement of equivalent or enhanced satellites and sensors is in some cases highly uncertain. The need for continued availability of the kinds of atmospheric and surface environmental data that have proved so valuable for understanding health linkages cannot be overstated. New sensors are being recommended—including some that will gather similar data at a higher spectral resolution or over a different horizontal span or time frequency.
PRIORITY OBSERVATIONS, MEASUREMENTS, AND TECHNOLOGY DEVELOPMENT
This section identifies various needs for space-based observational data that will help to address human health problems in six areas of application:
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Ultraviolet radiation and cancer,
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Heat stress and drought,
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Acute toxic pollution releases,
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Air pollution and respiratory/cardiovascular disease,
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Algal blooms and water-borne infectious diseases, and
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Vector-borne and zoonotic disease.
These are linked to the missions (Table 6.1) that are discussed in detail elsewhere in this report. The rationale and means for application of data and information for societal benefits are outlined in each of these health domains.
Ultraviolet Radiation and Cancer
Mission Summary—Ozone Processes: Ultraviolet Radiation and Cancer
Variables: |
Stratospheric ozone; water vapor; short-lived reactive species (OH, HO2, NO2, CIO, BrO, IO, HONO2, HCI, and CH2O); isotope observations (HDO, H218O, H2O); benchmark tracer data (O3, CO2, CO, HDO/H2O, NOy, N2O, CH4, halogen source molecules); spectrally resolved radiance; cloud and aerosol particles |
Sensor: |
Spectrally resolved radiometer (200–2,000 cm−1) |
Orbit/coverage: |
LEO/global |
Panel synergies: |
Climate, Ecosystems, Weather |
Background and Importance
The need to forecast ultraviolet (UV) dosage levels at Earth’s surface is a first-order public-health issue, as skin cancer occurs with a high frequency and is also a form of cancer with an increasing incidence of occurrence despite the efforts of medical research. The American Cancer Society (2006) estimated that, in 2006, more than 1 million new cases of basal and squamous cell cancers would be diagnosed. In addition, 60,000 cases of melanoma, the most serious form of skin cancer, are diagnosed each year.
The catalytic destruction of ozone that has been observed to occur predominantly in the lower stratosphere at high- and midlatitudes over highly populated regions is extremely sensitive to temperature through the potential catalytic conversion of inorganic halogens to free-radical form on cold aerosols and ice particles. Recognition of that sensitivity has created a strong mechanistic link between the forcing of
climate by increases in CO2 and H2O that radiatively cool the lower stratosphere, and studies of the loss of ozone by free-radical catalysis. The strong links between skin cancer incidence, ozone loss by catalytic destruction in the stratosphere, and the response of the climate system to CO2 forcing has linked research communities in the pursuit of global UV dosage forecasts.
Role of Remotely Sensed Data
The panel considered in three parts the problem of understanding and forecasting human health effects of UV. First, it addressed the mechanisms that control catalytic destruction of ozone in the stratosphere (Figure 6.1). That region of the atmosphere is important because evidence gathered over the last 30 years has shown that it has experienced the greatest loss. Second, it considered the impact that climate change will have on the processes that control ozone. Third, it reviewed what is known about the human response to increasing UV dose.
Ozone (O3) is controlled in an important way by transport processes that move it poleward and downward at low latitudes. This large-scale transport is summarized in Figure 6.2, which shows convective injection of tropospheric air into the tropical lower stratosphere and into the midlatitude lowermost stratosphere (or “middle world”). Although this illustrates meridional transport, there are also important longitudinal variations coupled to such large-scale events as monsoon structures and seasonal oscillation. The longitudinal variations tend to drive gyres that bring lower stratospheric air masses to amplify catalytic activity.
Those observations, of highly increased water convected in the cold lower stratosphere, raise the obvious potential of amplifying the destruction of O3 by catalytic loss. An example of the water-vapor observations is shown in Figure 6.3.
The key concern that emerges from the observations is that the combination at lower temperatures and high water-vapor concentrations can dramatically enhance the CIO concentration in particular. That effect is captured in Figure 6.4 (from Kirk-Davidoff et al., 1999), which plots the logarithmic increase in the reaction rate converting HCI and ClONO2 to Cl2 (and then to CIO) and HONO2.
CIO is amplified by heterogeneous conversion of HCI and ClONO2 to Cl2 and HONO2, but the mechanism may well not be capable of sufficiently amplifying ozone loss (Smith et al., 2001). However, the link between the BrO and CIO cycles, rate-limited by the reaction CIO+BrO→Cl+Br+O2 (McElroy et al., 1986) may provide an explanation. As Figure 6.1 reveals, small increases in BrO resulting from direct injection of short-lived organic bromines or BrO itself may well provide the solution to the puzzle of what has controlled changes in the ozone column concentration over the last two decades. Figure 6.5 (from Salawitch et al., 2005) shows the impact of small additional amounts of BrO on the loss of ozone column resulting from the addition of aerosol precursors into the stratosphere by volcanic injection. Only with the addition of BrO at 8 ppt can the large losses observed in the ozone column be quantitatively explained.
Panel’s Recommended Objectives for UV Dosage Forecasting
Those observations provide the foundation of a strategy needed for the forecast of UV dosage at Earth’s surface over the next decades. The following objectives must be achieved:
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Catalytic destruction of O3 under conditions of low temperature and increased water vapor by the combination of chlorine, bromine, and iodine must be defined by observing the CIO, BrO, and IO concentrations in the lower stratosphere in the presence of increased water-vapor concentrations.
TABLE 6.1 Human Health and Security Panel Priorities (Unranked) and Associated Space-based Missions
Summary of Mission Focus |
Variables |
Type of Sensor(s) |
Coverage |
Spatial Resolution |
Frequency |
Synergies with Other Panels |
Related Planned or Integrated Space-based Missions |
Ozone processes: Ultraviolet radiation and cancer |
Stratospheric ozone; water vapor; short-lived reactive species (OH, HO2, NO2, ClO, BrO, IO, HONO2, HCl, and CH2O); isotope observations (HDO, H218O, H2O); benchmark tracer data (O3, CO2, CO, HDO/H2O, NOy, N2O, CH4, halogen source molecules); spectrally resolved radiance; cloud and aerosol particles |
Spectrally resolved radiometer (200-2,000 cm–1) |
Global |
5 km horizontal; 2-3 km vertical |
TBD |
Climate Ecosystems Weather |
GACM |
ACE ASCENDS CLARREO GEO-CAPE GPSRO |
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Heat stress and drought |
Rainfall; soil moisture; vegetation state; temperature |
Microwave sensors, radar, hyperspectral, imagers |
Global |
1 km |
Twice daily |
Ecosystems Weather Climate |
DESDynI GEO-CAPE HyspIRI LIST PATH SMAP |
GPM LDCM NPP/NPOESS |
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Acute toxic pollution releases |
Visible atmospheric or hydrospheric plumes; ocean color; particle size; gross vertical structure |
High-resolution imager (multispectral: UV-near-IR) |
Geostationary for Western Hemisphere |
1 km (aerosols, ocean state, surface layers) |
Daily |
Ecosystems |
GEO-CAPE ACE GACM |
|
|
|
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1–20 m (multispectral, high resolution) |
Multi-day |
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GOES-R |
|
|
|
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30–50 m (high resolution, particles) |
15 min. |
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![](/https/nap.nationalacademies.org/openbook/0309103878/xhtml/images/p200131deg162001.jpg)
FIGURE 6.1 Ozone photochemistry. Enhanced bromine: increased ozone (O3) depletion due mainly to BrO+CIO cycle. BrO+HO2 cycle becomes a significant O3 sink below 16 km (BrO+HO2 does not drive O3 depletion if BryTrop is constant. In the left-most panel, BRyTrop=0 ppt; in the middle panel, BRyTrop=8 ppt. SOURCE: Salawitch et al. (2005). Copyright 2005 American Geophysical Union. Reproduced by permission of American Geophysical Union.
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Mechanisms controlling the dynamic coupling between the troposphere and stratosphere must be established with a combination of in situ isotopes, long-lived tracers, and reactive intermediates to establish how the irreversible flux of water vapor into the stratosphere will change, given increased forcing of the climate system by CO2, methane, and so on.
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The role of convective injection of short-lived compounds through the tropical tropopause and by convection at midlatitude continental sites must be established.
Those objectives require the following combination of high-spatial-resolution observations:
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The short-lived reactive species OH, HO2, NO2, CIO, BrO, IO, HONO2, HCI, and CH2O to pin down the chemical-catalytic-transport structure of the TTL and the injection of short-lived species into the overworld and middleworld from the troposphere;
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Isotope observations of HDO, H2O obtained simultaneously in the condensed and vapor phases;
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Benchmark tracer data (O3, CO2, CO, HDO/H2O, NOy, N2O, CH4, and halogen source molecules) to quantify the extent of horizontal mixing and entrained ambient air and to establish the spatial pattern of the age of the air;
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Benchmark water vapor and total water based on instruments capable of measuring water-vapor mixing ratios accurately and precisely both outside and inside clouds. Uncertainties in measurements of relative humidity are directly proportional to uncertainties in measurements of water vapor;
![](/https/nap.nationalacademies.org/openbook/0309103878/xhtml/images/p200131deg163001.jpg)
FIGURE 6.2 Convective injection of tropospheric air into various portions of the stratosphere.
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Absolute, spectrally resolved radiance—upwelling and downwelling—throughout the thermal infra-red (IR) (200–2,000 cm–1), with a spectral resolution of ~1 cm−1 and an accuracy (absolute) of 0.1 K in brightness temperature; and
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Particle composition and number density based on instruments capable of determining in a single-particle or ensemble mode the chemical composition (preferably in a quantitative or stoichiometric way) of cloud particles and interstitial aerosols.
A crucial aspect related to the forecasting of UV dosage over the coming decades is the determination of the impact of increased UV on human morbidity and mortality. Given that the incidence of skin cancer has continued to grow despite improving medical knowledge, a bridge must be built that encourages the atmospheric science community to interact more effectively with the public-health community to evaluate human responses to UV more accurately. This is a recommendation of the human health panel for the next decade. The primary scientific questions that are directly linked to societal objectives include these:
![](/https/nap.nationalacademies.org/openbook/0309103878/xhtml/images/p200131deg164001.jpg)
FIGURE 6.3 Observations of highly increased water convected in the cold lower stratosphere. SOURCE: Sherwood and Desslert (2004). Copyright 2004 American Geophysical Union. Reproduced by permission of American Geophysical Union.
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Which mechanisms are responsible for the continuing erosion of ozone over midlatitudes of the Northern Hemisphere?
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Will rapid loss of ozone over the Arctic in late winter worsen? Are these large losses coupled to losses in midlatitudes?
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How will the catalytic loss of ozone respond to changes in boundary conditions of water and temperature forced by increasing CO2, CH4, and so on?
![](/https/nap.nationalacademies.org/openbook/0309103878/xhtml/images/p200131deg165001.jpg)
FIGURE 6.4 Logarithmic increase in the reaction rate converting HCI and CIONO2 to Cl2 (and then to CIO) and HONO2. SOURCE: Reprinted by permission from Macmillan Publishers Ltd. from Kirk-Davidoff et al. (1999). Copyright 1999.
![](/https/nap.nationalacademies.org/openbook/0309103878/xhtml/images/p200131deg165002.jpg)
FIGURE 6.5 Impact of small additional amounts of BrO on the loss of O3 column resulting from the addition of aerosol precursors into the stratosphere by volcanic injection. SOURCE: Salawitch et al. (2005). Copyright 2005 American Geophysical Union. Reproduced by permission of American Geophysical Union.
Heat Stress and Drought
Mission Summary—Heat Stress and Drought
Variables: |
Rainfall, soil moisture, vegetation state, temperature |
Sensors: |
Microwave sensors, radar, hyperspectral imagers |
Orbit/coverage: |
Multiple/global |
Panel synergies: |
Ecosystems, Weather, Climate |
Background and Importance
Current global-warming scenarios indicate an increasingly frequent occurrence of regional droughts and heat waves over the next several decades (IPCC, 2001). Those events have a substantial effect on human health, agriculture, and the natural environment. They often require an emergency health response similar to that to a disease outbreak. Important components of society’s preparation for a warming climate are improved prediction, monitoring, response, and postevent analysis of these extreme events. Satellite sensing of temperature, moisture, and vegetation will play a key role in this work, especially in down-scaling the spatial analysis of heat and drought to the human scale of a few kilometers. Recent research has demonstrated the utility of remote sensing data for regional heat and drought analysis and put scientists in a good position to suggest satellite-based monitoring and research strategies.
For purposes of this discussion, a drought is defined as an extended period of low precipitation or high evapotranspiration that affects natural vegetation and agriculture. A heat wave is an extended period during which the air or ground temperature is high (e.g., above 32°C [90°F] in temperate regions) and well above the seasonal average. Those two types of events are often coincident; both are associated with warm winds, clear skies, increased evapotranspiration rates, and a shift in the nature of the heat budget of Earth’s surface. As soil moisture becomes depleted, the fraction of the Sun’s irradiance that is balanced by evaporative cooling diminishes. A greater fraction of the Sun’s heat goes into heating the lower atmosphere.
The effects of drought and heat on agriculture may be rapid or slow, but the human impact is often delayed until harvest time (Table 6.2). The direct impact of a heat wave on human physiology is much quicker. Heat-stress-induced illnesses and deaths may begin to climb within just a few days after the start of extreme conditions. The sensitivity of humans to heat stress varies with genetics, age, and type of shelter, but large segments of society are susceptible to extreme combinations of heat and humidity. Typically, heat-stress problems mount rapidly as the dew point climbs above 25°C (77°F). The ability of the human body to thermoregulate is compromised beyond dew points of 30°C (86°F). High dew points slow the evaporation of moisture that the body uses to cool the skin. In affluent areas, those effects can be mitigated
TABLE 6.2 Some Recent Heat Waves and Droughts
Event |
Year |
Location |
Impact |
Heat wave |
1987 |
Athens |
~900 deaths |
Heat wave |
1995 |
Chicago |
~700 deaths |
Heat wave and drought |
2002 |
Australia |
Poor crop yield |
Drought |
2002 |
Southwest United States |
Poor crop yield |
Heat wave and drought |
2003 |
France |
~1 5,000 deaths, poor crop yield |
Drought |
2005 |
Illinois |
Poor crop yield |
by air conditioning. The analyses of risk can be enhanced if they combine spatially explicit observations of potential heat stress with spatial data on at-risk populations.
Role of Remotely Sensed Data
Many aspects of heat and drought can be monitored with conventional meteorological networks of surface and upper-air stations. The networks vary greatly in their density and efficacy around the world, however, and are generally insufficient for accurate monitoring on scales less than 100 km. One issue is that the spatial pattern of a heat wave usually has a small-scale component driven by patterns of vegetation, terrain, water bodies, and urban surfaces that are unresolved with conventional climatologic methods (Box 6.2). A second issue is that conventional measurements do not monitor the state of the vegetation or soil moisture that may be responding or contributing to the heat and moisture anomaly. Neither soil moisture nor surface radiative temperature is routinely monitored.
To supplement conventional observations, space-based monitoring methods have made major strides over the last 20 years (Kogan, 1997). With AVHRR and MODIS reflective bands, time series of NDVI were generated to evaluate the state of vegetation relative to other years. Surface albedo and its impact on local climate can also be determined. The same satellite sensor systems include thermal sensors that can measure the surface radiative temperature and emissivity both day and night. The 1-km spatial resolution of these sensors far exceeds the spatial resolution of weather-station networks. Column-integrated water vapor can also be inferred, giving qualitative indications of humidity under clear-sky conditions.
A successful program for operational monitoring of drought conditions is the Famine Early Warning System run by the U.S. Agency for International Development, NOAA, and other agencies (http://www.fews.net/) and focused primarily on Africa. This system integrates satellite data (primarily AVHRR) with conventional climate data, meteorological models, and crop reports to issue regional watch, warning, and emergency drought notices (Buchanan-Smith, 1994; Herman et al., 1997). It is also used in the prediction of disease outbreaks that are environmentally triggered.
Finer-scale aspects of heat waves have been studied with Landsat and ASTER (see Box 6.2), satellites that have much higher spatial resolution in both their reflective and thermal channels. They allow surface vegetation and temperature to be mapped down to the scale of cities, towns, agricultural fields, and forest patches (1 km), revealing important relationships between heat and land use. The urban “heat island” and the cooling effects of forests have also been mapped in this way (Lo et al., 1997). However, those satellite or sensor systems have poor return times, typically 18 days or more, which limit their usefulness for monitoring.
Satellite-derived land-cover patterns are increasingly used as inputs to high-resolution physical models of regional climates. Satellites help in prediction, down-scaling, model verification, and real-time monitoring of heat waves.
Future Needs
To maintain and enhance the ability to monitor heat waves and drought from space, the panel recommends the following future efforts and needed new sensor capabilities:
-
Develop new high-resolution satellite observations of rainfall and soil moisture, extending TRMM-type measurements to high latitudes and advance microwave sensors, such as SMOS (2007 launch scheduled) and HYDROS (2009 launch planned but unlikely).
BOX 6.2 EUROPEAN HEAT WAVE The European heat wave during the summer of 2003 included small-scale features that could be resolved only with satellite remote sensing. By August, a coupled pattern of high temperature and vegetation loss was evident over central France, controlled in part by terrain and land-use factors. The anomalies in vegetation index and surface temperature derived from MODIS are shown in Figures 6.2.1 and 6.2.2. On a smaller scale, ASTER images reveal that pastures and active agricultural fields have lost their vegetation and heated substantially and forests and inactive fields have a small temperature anomaly (Figure 6.2.3). ![]() FIGURE 6.2.1 Vegetation-index anomaly from MODIS in France for August 13–28, 2003, compared with the same dates in 2000–2002 and 2004. Yellow pixels are unchanged; brown pixels have decreased the index by 0.4. Solid lines demarcate conventional climate zones. SOURCE: Figure 2D, p. 749, in Zaitchik et al. (2006). Copyright 2006 Royal Meteorological Society. ![]() FIGURE 6.2.2 Similar to Figure 6.2.1 but for surface-temperature anomaly. Gray areas are slightly cooler, yellow is unchanged, and red is hotter by as much as 20°C (68°F). SOURCE: Figure 6D, p. 753, in Zaitchik et al. (2006). Copyright 2006 Royal Meteorological Society. |
To enhance the operational capabilities and use of the sensor data, the panel recommends the following actions:
-
Develop new strategies for increasing the revisit frequency of high-resolution sensors.
-
Maintain the growth and use of the MODIS and ASTER archives.
![]() FIGURE 6.2.3 Small-scale vegetation and temperature differences associated with the heat wave of 2003; seen from ASTER. A and B, false color images for August 2000 and 2003, with vegetation in red and bare soil in pale blue. C and D, emission temperature for the same two dates (see color bar). The scale bar in the lower right has a length of 500 m. The forest patch on the right stayed relatively cool while the affected agricultural fields heated significantly. This scene location is part of the ASTER footprint shown in Figures 6.2.1 and 6.2.2. SOURCE: Figure 10, p. 756, in Zaitchik et al. (2006). Copyright 2006 Royal Meteorological Society. |
-
Continue development and operationalization of the VIIRS sensor for long-term monitoring of MODIS-type information
-
Implement an effective Landsat-7 follow-on program, including a slightly enhanced reflective-channel selection and an effective thermal-band selection (on the basis of recent experience with the ATLSS (airborne), ASTER, and Hyperion sensors).
Finally, the availability and use of remote sensing for drought and heat-wave mitigation would benefit from additional support for research on heat waves and droughts that makes use satellite data from GOES, AVHRR, MODIS, Landsat, ASTER, and new sensors and from in situ sensors.
Acute Toxic Pollution Releases
Mission Summary—Acute Toxic Pollution Releases
Variables: |
Visible atmospheric or hydrospheric plumes, ocean color, particle size, gross vertical structure |
Sensor: |
High-resolution imager (multispectral: UV-near-IR) |
Orbit/coverage: |
GEO/regional |
Panel synergy: |
Ecosystems |
Background and Importance
Acute pollution events are short-lived aperiodic events that discharge and disperse large amounts of anthropogenic or natural toxicants or other hazardous substances into and through the environment. They may result from natural phenomena such as wildfires; from industrial accidents such as freight-train derailments, oil spills at sea, and refinery fires; or from terrorist acts that release radiological, biological, or chemical agents into the air or water supply. The incidents can range from the microscale (tens of meters and tens of minutes) in the case of some tanker-truck chemical spills to the mesoscale (tens of kilometers and hours) in the case of some refinery fires to the macroscale (months to years and hundreds to thousands of square kilometers) in the case of red tide or volcanic eruptions. The frequency of the events also varies widely, although detailed statistical summaries and analyses are lacking. The Environmental Protection Agency reports that the annual number of industrial accidents involving the release of hazardous substances from facilities that are required to have risk-management plans ranged from 225 to more than 500 over the 9-year period ending in 2003 (EPA, 2005). The U.S. Coast Guard’s National Response Center (www.nrc.uscg.mil/nrchp.html) reports that spill incidents of all types in the United States numbered more than 35,000 in 2005. Between 1973 and 2001, the number of oil spills in and around U.S. waters (www.uscg.mil.hq/g-m/nmc/response/stats/aa.htm) ranged from about 5,000 in the late 1980s to about 10,500 in 1978. Environment Canada (www.etc-cte.ec.gc.ca) reports that there were 742 large oil-tanker spills worldwide for the period 1974–1997; a “large” spill is one that involves over 1,000 barrels (136 metric tons) of oil released per event in a nonwartime incident.
As for natural events, there has been an average of one red tide outbreak in Florida alone per year for the last three decades (see section below titled “Algal Blooms and Waterborne Infectious Diseases” for discussion of the detection of harmful algal blooms and waterborne pathogens by remote sensing). Apart from natural and accidental incidents, the potential for large-scale terrorist actions has received much attention, and considerable research and planning are aimed at thwarting these actions and minimizing their impacts. It is widely recognized that terrorist actions could involve spatial and temporal scales not dissimilar to those of industrial accidents and natural phenomena. Planning for possible terrorist actions has focused on the release of chemical, biologic, and radiological agents.
Although some chemical agents (see Table 6.3) may be observed from space (although not detected in the analytic sense), biological, radiological, and most chemical agents will not be observable from space or with imaging systems operated from aircraft. But it is likely that accompanying fires and explosions will release particulate matter or hydrometeors that will be visible from space.
The panel recommendations offered below pertain to high-impact pollution events involving visible plumes with lateral scales of at least several hundred meters and longitudinal scales of at least several
TABLE 6.3 Types and Properties of Chemical Agents
Agents |
Symbol |
Boiling Point |
Appearance |
|
Nerve agents |
|
|
|
|
|
Sarin |
GB |
158 |
Clear, colorless |
|
Soman |
GD |
198 |
Clear, colorless |
|
Tabun |
GA |
240 |
Clear, colorless |
|
GF |
GF |
239 |
N/A |
|
VX |
VX |
298 |
Clear, amber-colored oil |
Choking agents |
|
|
|
|
|
Chlorine |
Cl |
-34 |
Amber liquid,green vapor |
|
Phosgene |
CX |
7.6 |
Clear, colorless |
Blood agents |
|
|
|
|
|
Hydrogen cyanide |
AC |
25.7 |
Colorless |
|
Cyanogen chloride |
CK |
12.8 |
Colorless |
Blister agents |
|
|
|
|
|
Distilled mustard |
HD |
215–217 |
Clear, amber-colored |
|
Lewisite |
L |
197 |
Dark-colored, oily |
|
Phosgene oxime |
CX |
53–54 |
Clear, colorless crystalline or liquid |
SOURCE: Data from Adams (2002). |
kilometers. Small-scale events, such as tanker truck spills or explosions, are not within the scope of these suggestions, nor are very-large-scale events, such as large wildfires. The latter are already well documented by MODIS (http://maps.geog.umd.edu/) and other moderate-resolution imagers. Nonetheless, the high-resolution imagery would probably be highly beneficial to wildfire responders and researchers. This discussion reflects input from the National Atmospheric Release Advisory Center (Lundquist et al., 2006) at Lawrence Livermore National Laboratory and the National Center for Atmospheric Research Workshop on Air Quality Remote Sensing from Space: Defining an Optimum Observing Strategy, February 21–23, 2006 (Edwards et al., 2006).
Role of Remotely Sensed Data
A moderately high-resolution imaging capability in geostationary orbit can serve a multitude of emergency-response applications: inland and coastal oil spills and algal blooms, industrial accidents, severe weather, and discharges of hazardous agents resulting from terrorist actions. Satellite imagery is an important but partial solution to the emergency-response observation challenge; the total solution requires an integrated approach that blends satellite observations with surface and airborne observations. Previous National Research Council (NRC) reports have identified the nation’s needs related to the threat of terrorist activities. In particular, NRC (2003) recommended deployment of both permanent and rapid-response meteorological and plume-monitoring systems.
The challenge is to identify satellite-based systems that can provide the imagery that is invaluable for responders and health officials charged with managing and minimizing the impacts of natural and anthropogenic incidents when such incidents involve visible atmospheric or hydrospheric plumes. Both meteorologic and plume observations are critical for analyzing and predicting atmospheric dispersion and deposition of gases and particles in an acute pollution event. The measurements needed include wind speed and direction, temperature, humidity, precipitation type and intensity, mixing height, turbulence, and energy fluxes. Table 6.4 summarizes the measurement requirements according to the associated dispersion and meteorologic variables. The specific variables that must be measured may also depend on the
TABLE 6.4 Candidate Meteorologic and Plume-Observing Systems
algorithms and parameterizations used in the dispersion model. Because of their height variability in the boundary layer, vertical profiles of many parameters are important. In the same way, spatial variability of the dispersion variables may necessitate multiple observing sites or spatial imagery. Table 6.5 expands on the applicability of high-resolution satellite imagery. The ideal yet pragmatic solution is a geostationary imaging spectroradiometer in space that has the following characteristics:
-
Moderately high spatial resolution to capture plume horizontal structure;
-
Moderate view area to ensure that the visible plume can be observed in its entirety to quantify transport;
-
Pointing capability to ensure capturing scenes within the useful surface geometry viewed by the satellite;
-
Rapid refresh rate to map the temporal evolution of the plume and estimate the horizontal diffusivity (atmospheric and hydrospheric plumes have different requirements); and
-
Multiple channels to observe ocean color, estimate particle size, and estimate gross vertical structure (such as plume penetration of the inversion capping the surface-based mixed layer).
Figures 6.6 and 6.7 show images of two large acute pollution events taken from two different satellites. The particle plume from the collapse of the World Trade Center on September 11, 2001, is seen in Figure 6.6 from a 20-m-resolution image taken by the French SPOT polar-orbiting satellite. About 3 km downwind of the World Trade Center, the visible plume is about 1 km wide. The 20-m-resolution image is able to depict much of the turbulent structure of the plume. Figure 6.7 is an image of the February 21, 2003, oil-terminal fire on Staten Island, New York, as observed by the Sea-viewing Wide Field-of-view
TABLE 6.5 Applicability of Satellite Imagery to Plume Mapping and Characterization for Emergency Response to Large Singular Events
Plume Attribute or Feature |
Prioritya |
Feasibilityb |
Comments |
Vertical resolution |
3 |
3 |
Terrestrial observations likely to be more effective |
Vertical extent |
2 |
2 |
Does the plume penetrate into the free troposphere? |
Horizontal resolution |
1 |
1 |
Coparamount with “coverage” |
Horizontal extent or coverage |
1 |
1 |
Plume transport direction is the most important measure |
Temporal resolution or refresh rate |
1 |
1 |
High temporal resolution is important for diffusion,and moderate temporal resolution is valuable for transport |
Particle sizing |
4 |
3 |
Terrestrial observations likely to be more effective |
Species identification |
5 |
3 |
Terrestrial observations more effective |
Diurnal observations |
1 |
1 |
Important, but nocturnal observations will have reduced resolution |
a1, highest; 5, lowest. b1, highest; 3, lowest. |
Sensor (SeaWiFS), a Sun-synchronous orbiting satellite with 24-hour revisit time and 1.13-km resolution at nadir. Figure 6.6 illustrates the vastly improved quantitative information obtained from the high-resolution SPOT imagery in comparison with the nominal 1-km imagery of GOES and SeaWiFS. The images also suggest that moderately high-resolution—say, around 50 m—is a reasonable compromise of cost and the monitoring demands imposed by large-impact events, such as refinery and chemical-plant fires. A precise specification for horizontal resolution remains to be developed.
Panel’s Recommendation for a Special-Events Imager
A special-events imager instrument in geostationary orbit would be invaluable for observing the time evolution of coastal and ocean pollution sources, tidal effects, and high-frequency eddy currents; the origin and evolution of aerosol plumes; and the tropospheric ozone. The imager requires a wide range of wavelengths (18 channels from the UV to the near-IR), spatial resolution of about 50 meters, and high temporal resolution (less than 1 minute per image). The frequent observations will reveal currently hidden processes and relationships in Earth’s oceans, on land surfaces, and in the atmosphere. This type of time-resolved data is currently not available from any satellite observations.
Such a special-events imager would meet all of the requirements for observing very large acute events, including wildfires and very large refinery fires, and the harmful algal blooms discussed later in this chapter. The imager would also meet the more demanding requirements for supporting emergency response dispersion modeling of the more common large acute events associated with train accidents, chemical upsets, oil spills, terrorist actions, and the like. Recent discussions with the co-investigator responsible for the design of an imager with more limited spatial resolution2 indicate that achieving the more rigorous requirements for a special-events imager is feasible with today’s technologies.
It may also be possible to achieve higher resolution with a post-processing technique called super-resolution, or through a combination of improved optics and postprocessing. Super-resolution imaging (see summaries by Borman and Stevenson, 1998; Park et al., 2003; Vandewalle et al., 2006) constructs a high-resolution image from a set of low-resolution images that are taken from almost the same point of view. Super-resolution techniques can be used to reconstruct an image with a spatial resolution greater
![](/https/nap.nationalacademies.org/openbook/0309103878/xhtml/images/p200131deg174001.jpg)
FIGURE 6.6 SPOT multispectral image with 20-m resolution taken 87 minutes after the collapse of the North Tower of the World Trade Center and 110 minutes after the collapse of the South Tower, clearly showing the particle plume transport to the southeast. Approximately 3 km from the source, the visible plume is about 1 km wide. SOURCE: Courtesy of SPOT Image Corporation, 2007.
than the typical diffraction limit of the telescope. Figure 6.8 illustrates the technique as applied by Emery (2003) to 1 km AVHRR images of the Death Valley region. In this reconstruction, later AVHRR passes sample the scene from slightly different locations. This can also be done in real time from geostationary orbit by oversampling in the image backplane and reconstructing the enhanced image.
The panel recommends that NASA assign priority to the development and launch of a special-events imager mission to provide the capability needed by federal, state, and local emergency managers to best respond to a plethora of natural, accidental, and overt environment emergencies. The mission is feasible and would provide a valuable service to the nation.
![](/https/nap.nationalacademies.org/openbook/0309103878/xhtml/images/p200131deg175001.jpg)
FIGURE 6.7 SeaWiFS image of the visible plume from the Staten Island oil-terminal fire (arrow points to fire site). This true-color image of the U.S. northeastern coastline was acquired on February 21, 2003, by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) several hours after the explosion. The dark smoke can be seen clearly in contrast with the whiter clouds in the area and the snow-covered landscape. In this scene, the smoke plume stretches about 150 km (93 miles) to the east-southeast of the fire. SOURCE: Courtesy of the SeaWiFS Project, NASA Goddard Space Flight Center, and GeoEye.
Air Pollution and Respiratory and Cardiovascular Diseases
Mission Summary—Air Pollution and Respiratory and Cardiovascular Diseases
Variables: |
Aerosol composition and size; NO2, HCHO, VOCs, CO, SO2; tropospheric ozone |
Sensors: |
Multispectral UV/visible/near-IR/thermal IR, lidar |
Orbit/coverage: |
LEO and GEO/regional and global |
Panel synergy: |
Climate |
Background and Importance
Air pollution, particularly in the lower troposphere, is a major cause of cardiovascular and respiratory disease (EPA, 2004, 2006). The main harmful pollutants are ozone and fine particles (aerosols) produced by chemical reactions involving nitrogen oxides (NOX=NO+NO2), volatile organic compounds (VOCs), carbon monoxide (CO), and sulfur dioxide (SO2). Table 6.6 lists air-quality standards in the United States
![](/https/nap.nationalacademies.org/openbook/0309103878/xhtml/images/p200131deg176001.jpg)
FIGURE 6.8 Comparison of enhanced-resolution AVHRR image with a high-resolution Landsat MSS image (centered at 36.5°N, 117.5°W): (a) Superresolution reconstruction; (b) Landsat MMS Channel 1 image sampled; and (c) original AVHRR 1-km image (180-m resolution) of AVHRR 1-km near-IR image to 180-m resolution (April 25, 1992) sampled at 180 m (22:27 GMT, May 7, 1992). SOURCE: Courtesy of William Emery, University of Colorado, Boulder.
and Europe. The United Sates has an 8-hour standard for ozone and 1-day and 1-year standards for airborne particulate matter (also referred to as aerosols). By those standards, one-third of the U.S. population is breathing unhealthful air (EPA, 2003). Europe has much tighter ozone standards (which are routinely exceeded). Air quality in China, India, and other rapidly industrializing nations is worse than in the United States or Europe.
TABLE 6.6 Ozone and Aerosol Air-Quality Standards in the United States and Europe
Pollutant of Concern |
Ambient Air-Quality Standard |
|
United States |
European Union |
|
O3 |
84 ppbv (8 hour average) |
55 ppbv (8 hour average) AOT40 (seasonal total)a |
PM2.5b |
15 µg m−3 (annual) 65 µg m−3 (24 hour average) |
—c |
PM10b |
50 µg m−3 (annual) 150 µg m−3 (24 hour average) |
40 µg m–3 (annual) 50 µg m–3 (24 hour average) |
aNo more than 5,000 ppbv-hours in excess of 40 ppbv during daytime hours in April-September. This corresponds roughly to a 43-ppbv daytime average. bParticulate matter less than 2.5 µm radius (PM2.5) or 10 µm in radius (PM10). cSee at http://europa.eu.int/comm/environment/air/cafe/pdf/cafe_dir_en.pdf a proposal for a European Union Directive on Clean Air for Europe with respect to exposures to particulate matter. |
Role of Remotely Sensed Data
Recent advances in tropospheric remote sensing have revealed the potential for applying satellite observations to air-quality issues. Observations of NO2 and formaldehyde (HCHO) from GOME, SCIAMACHY, and OMI have been used to place top-down constraints on sources of NOx and VOCs. Observations of CO from MOPITT and AIRS have been used to constrain CO sources and to track the intercontinental transport of pollution. Combined observations of ozone and CO from TES and MLS have mapped the continental outflow of ozone pollution. Aerosol optical depth (AOD) observations from MODIS and MISR have been used to infer surface air concentrations of aerosols. Assimilation of MODIS AOD observations and OMI ozone is being implemented in air-quality analyses and forecasts.
Mercury is a neurotoxin and a major public health concern. It is transported on a global scale in the atmosphere, depositing and accumulating far from its sources. Sources from combustion have been declining in North America and Europe due to regulation but have been rising rapidly in Asia, and so the global mercury pool in the environment continues to increase. Attempts at international agreements have been thwarted on a scientific level by poor understanding of the atmospheric redox Hg(O)/Hg(II) chemistry, which determines mercury deposition as Hg(II), and by the role of re-emission from surface reservoirs. Improved and expanded atmospheric observations are critically needed to expand the current knowledge base through the testing of models. Although mercury is not directly observable from space, an effective observational strategy should integrate in situ measurements from the surface and from aircraft with satellite observations of correlated species (e.g., CO from combustion).
Also of considerable interest are LEO satellite observations of tropospheric BrO by solar backscatter, given that Br atoms could represent a major global oxidant for Hg(0). Tropospheric BrO retrievals are available from OMI and its predecessors (GOME, SCIAMACHY) but have yet to be validated with aircraft observations. They suggest that elevated levels of BrO, known to occur acutely in the Arctic spring and to be responsible for enhancing mercury deposition there, could in fact be found ubiquitously in the troposphere. This represents an important case study for the effective combination of aircraft, satellite, and modeling studies that are delineated in Figure 6.9. Particularly in the case of human health, the critical importance of innovative coupling between in situ and remote observations requires fundamental restructuring of the Earth sciences in service to society.
![](/https/nap.nationalacademies.org/openbook/0309103878/xhtml/images/p200131deg178001.jpg)
FIGURE 6.9 A key link between scientific development and the accomplishment of societal objectives is the effective integration of satellite, aircraft, and modeling studies. An important example for human health in the tracking and diagnosis of the chemistry linking mercury release and the reactions of halogen compounds that sequester heavy metals at high latitudes of the northern hemisphere.
However, the instruments now in space have serious limitations for air-quality applications (they were not, in general, designed for that purpose). Developing an improved capability for air-quality observations from space was the focus of the recent community Workshop on Air Quality Remote Sensing from Space (NCAR, 2006). The workshop identified future satellite observations as crucial for air-quality management, involving four axes of application: (1) forecasting and monitoring of pollution episodes, (2) emissions of ozone and aerosol precursors, (3) long-range transport of pollutants extending from regional to global scales, and (4) large releases from short-duration environmental disasters. It was strongly stated that there is a need for a new generation of satellite missions as part of an integrated observing system including surface air monitoring networks, in situ research campaigns, and three-dimensional chemical transport models.
Panel’s Recommended Measurements
Top-priority measurements from space for which capabilities have been demonstrated (but still need improvement) include tropospheric ozone, CO, NO2, HCHO, SO2, and aerosols. A high priority is to improve the ability to observe aerosol composition and size distribution from space.
Resolution requirements for air-quality observations from space include a horizontal pixel size of 1–10 km with continental to global coverage, ability to observe the boundary layer, and a return time of a few hours or less. Those requirements are defined by the need to observe the development of pollution episodes, the variation of emissions, and the state of atmospheric composition for purposes of forecasting. Hourly resolution in polluted regions is highly desirable, inasmuch as it matches the temporal resolutions of surface monitoring data, regional models, and the metrics used in air-quality standards. Outside these regions, temporal resolution can be relaxed to a few times per day for observation of long-range transport. For trace gases, multispectral methods combining UV/visible, near-IR, and thermal IR can offer boundary-layer information at least for ozone and CO. Active (lidar) observations can provide high vertical resolution for aerosols and ozone but with sparse horizontal coverage compared with passive techniques.
All the above requirements cannot be met from a single platform. Within the framework of existing or readily developable technology, the highest priority is for a GEO mission, with North America being of prime domestic interest. The satellite should have spectral observation capabilities ranging from the UV-A to the thermal IR. Two shortcomings of GEO are lack of global coverage and limited vertical resolution. Those shortcomings should be overcome with a companion LEO platform that include a high-spectral-resolution lidar for vertical resolution of the boundary-layer aerosol and free tropospheric plumes and multispectral passive sensors ranging from the UV-A to the thermal IR for global observation of pollutant transport.
Algal Blooms and Waterborne Infectious Diseases
Mission Summary—Algal Blooms and Waterborne Infectious Diseases
Variables: |
Coastal ocean color, sea-surface temperature, atmospheric correction, coastal ocean phytoplankton, river plumes |
Sensor: |
Multispectral |
Orbit/coverage: |
GEO/regional |
Panel synergies: |
Ecosystems, Water |
Background and Importance
The rapid proliferation of toxic or nuisance algae, termed harmful algal blooms (HABs), can occur in marine water, estuarine waters, and freshwaters and are among the scientifically most complex and most economically significant water issues facing the United States. HAB toxins can cause human illness and death, halt the harvesting and sale of fish and shellfish, alter marine habitats, and adversely affect fish, endangered species, and other marine organisms. Previously, only a few regions of the United States were affected by HABs, but now virtually every coastal state reports major blooms (Ecological Society of America, 2005) (Figure 6.10). Economic losses associated with HABs are expected to exceed $1 billion over the next several decades, and a single HAB event can cause millions of dollars in damages in coastal economies through direct and indirect effects (Anderson et al., 2000).
In addition to HABs, waterborne pathogens cause human disease and are transmitted in drinking water, through recreational exposure to contaminated water, and through ingestion or inhalation (NRC, 2004). More than 9 million cases of waterborne diseases are estimated to occur in the United States each year (Rose et al., 2001). Most waterborne pathogens are enteric and spread through fecal-oral pathways from animal and human fecal sources and are introduced to waterways through sewage discharges, urban and agricultural runoff, and vessel ballast. Some of the more severe waterborne diseases are hepatic, lymphatic, neurologic, and endocrinologic diseases, including infection with Vibrio cholerae (Lobitz et al., 2000). To develop microbial risk-assessment models for water-borne diseases, it is necessary to study the fate and transport of these pathogens, or the conditions that promote them, across the landscape via aquatic
![](/https/nap.nationalacademies.org/openbook/0309103878/xhtml/images/p200131deg180001.jpg)
FIGURE 6.10 Harmful algae. Global distribution of harmful algae from the early 1970s to 2005. The red lines indicate areas where harmful algal blooms have been documented. SOURCE: Courtesy of Daniel G.Baden, University of North Carolina at Wilmington and of NOAA National Ocean Service.
systems. Table 6.7 lists selected events demonstrating the use of remote sensing to detect and monitor harmful algal blooms (red tides) and waterborne pathogens.
Role of Remotely Sensed Data
Chief among the needs to mitigate the effects of HABs and waterborne pathogens is the ability to detect, monitor, and forecast them in a cost-effective and timely manner to protect human health. Ocean-color and sea-surface temperature satellite imagery are useful for detecting and tracking HABs (Stumpf and Tomlinson, 2005; Tang et al., 2003). In ocean-color imagery, algal blooms are detected on the basis of differential absorption and backscatter of irradiance; some species are more amenable to detection because of reflectance characteristics of the cells (Carder et al., 1986). A new operational HAB forecast has been used in the Gulf of Mexico since 2004; it provides twice-a-week or daily forecasts, if conditions warrant, of bloom intensity and location (Stumpf, 2001; Stumpf et al., 2003). Information is relayed via a bulletin (www.csc.noaa.gov/crs/habf/) to local managers who use it to optimize sampling locations, focus resources, and notify the public of potential bloom conditions (Backer et al., 2003) (see Box 6.3).
Detection of phytoplankton blooms with remote sensing relies on the spectral quality, thermal signature, and hydrographic features of the waters surrounding them. Blooms are often found along frontal zones, and these hydrographic features may be coherent over scales of 102–103 km2. The physical and biological factors affecting bloom dimensions are critical because resolution of patches smaller than about 5–10 km2 is generally not possible with current technology. Major ocean-current systems are often implicated in the transport of harmful algal blooms and indicative of conditions that support Vibrio cholerae. Those currents can be tracked most simply and reliably with thermal AVHRR imagery (Lobitz et al., 2000; Tester and Steidinger, 1997). Remote sensing is most commonly used to track the transport and dispersion
TABLE 6.7 Selected Events Demonstrating the Use of Remote Sensing to Detect and Monitor Harmful Algal Blooms (Red Tides) and Waterborne Pathogens
Year |
Eventa |
1975–1986 |
Five citations of papers on remote sensing and red tides |
1975 |
First use of thermal imagery to identify ocean frontal zones where harmful algae were concentrated (Murphy et al., 1975) |
1987–1996 |
28 citations of papers on remote sensing and red tides |
1987 |
First use of thermal imagery to track oceanic currents responsible for the transport of harmful algae (Tester et al., 1991) |
1988–1990 |
NOAA’s Coastwatch Program developed to provide timely access to nearly real-time satellite data for U.S. coastal regions (http://coastwatch.noaa.gov/) |
1997–2006 |
76 citations of papers on remote sensing and red tides |
2000 |
Use of remote sensing for detection of Vibrio cholerae by indirect measurement (Lobitz et al., 2000) |
2001 |
Experimental forecast of harmful algal blooms (Stumpf et al., 2003) |
2006 |
First operational forecast of harmful algal bloom (www.csc.noaa.gov/crs/habf/; see also Box 6.3) |
aSource of citations is Cambridge Abstracts-Aquatic Sciences, Cambridge University Library, Cambridge, United Kingdom. |
of waterborne pathogens by using storm-water runoff plumes as surrogates for direct detection. Thermal, ocean-color, Landsat Thematic Mapper (TM) and synthetic-aperture radar imagery has successfully tracked storm-water plumes (DiGiacomo et al., 2004; Nichol, 1993), but remote sensing imagery is not yet widely used in public-health programs.
Panel’s Recommendations for Satellite Detection of HABs
Public-health officials and marine-resource managers expect regional HAB forecasts to be available for all coastal areas in the United States within a decade. To accomplish that, additional sensors, missions, and resources are needed. The GOES-R Coastal Water Imager (https://osd.goes.noaa.gov/coastal_waters.php) may be the most important advance for satellite detection of HABs in coastal and estuarine waters; the GOES-R platform offers frequent repeated views of an area to reduce the effects of cloud cover. The coastal zone needs higher resolution than the 1 km produced by MODIS and the proposed roughly 0.7 km of VIIRS (Visible Infrared Spectrometer) on NPOESS (see http://www.ipo.noaa.gov/Technology/viirs_summary.html). Typically, the first two pixels nearest the shoreline are lost, so with VIIRS scenario the proposed resolution of GOES-R is about 0.3 km at the equator, which means 0.4–0.45 km for most U.S. coastal waters.
The detection of blooms along the coast in turbid, pigment-rich water requires more information than is available from SeaWiFS, MODIS, and the proposed VIIRS. Atmospheric correction is extremely difficult in coastal areas and requires more bands than are currently planned. The set of ocean-color instruments—Sea WiFS, MODIS, and VIIRS—were designed for open-ocean work. They have two near-IR bands for atmospheric correction and most bands in the blue, where the open ocean (“blue water”) changes color substantially. Along the coast, three near-IR bands are needed for atmospheric correction. Red bands are needed to identify algae and separate them from turbidity and tannic acids. At least 10 bands are needed for an effective coastal sensor (three blue, two green, two red, and three near-IR); a 12-band sensor would be optimal (three blue, three green, three red, and three near-IR).
In summary, more frequent imagery (GOES-R with a coastal sensor) with higher resolution and sensors with additional bands specifically for resolving chlorophyll signals in coastal waters would be optimal.
Vector-borne and Zoonotic Disease
Mission Summary—Vector-borne and Zoonotic Disease
Variables: |
Meteorological conditions (surface temperature, precipitation, wind speed); soil moisture; land-cover status; vegetation state |
Sensors: |
Hyperspectral; high-resolution multispectral, radar, lidar |
Orbit/coverage: |
Multiple/global |
Panel synergies: |
Ecosystems, Weather, Water |
Background and Importance
Infectious diseases still account for more than 25 percent of deaths globally. Remote sensing at moderate to coarse spatiotemporal resolution focused on the visible and near-IR portion of the spectrum has shown exceptional promise in applications in many aspects of public health, especially in risk assessment related to infectious diseases caused by pathogens transmitted to people by arthropods (such as insects and ticks) or animals (as in mammal or bird reservoirs). Those diverse and widespread infectious diseases are grouped here into the broad category of vector-borne and zoonotic (VBZ) diseases.
VBZ diseases—such as malaria, dengue, and filariasis—are believed responsible for millions of deaths and tens of millions of illnesses each year. The introduction and spread of West Nile virus through North America by mosquitoes during the last 5 years and recent concerns about the worldwide dissemination of H5N1 avian influenza are key recent examples of how human populations have come to be at risk for VBZ diseases over extensive geographic regions in short periods. The recent appearance and spread of Chikungunya virus by mosquitoes among the islands of southeast Africa and the Indian Ocean demonstrate the explosive growth of vector-borne diseases under permissive environmental conditions (http://www.who.int/csr/don/2006_03_17/en/). During a 1-year period (March 2005 to March 2006), it is estimated that 204,000 of La Reunion’s population of 770,000 became ill from this mosquito-borne virus. Similar epidemics occurred during the same time in Mayotte, Seychelles, and other islands throughout the region, and the illness was exported to at least five European countries by travelers. Even in the absence of high mortality, morbidity associated with explosive epidemics taxes the health-care and economic infrastructures of affected regions. The very suspicion of vector-borne disease outbreaks often engenders substantial economic losses; the report of bubonic plague around Surat, India, in 1994 was estimated to cost the government $600 million in lost revenues from lost exports, tourism, and jobs.
Attempts to control VBZ disease epidemics with available resources are hindered by lack of ability to set priorities among areas and target them for intervention. From a practical perspective, satellite observations offer an important opportunity to assess the likelihood of spatial diffusion of disease and to monitor its timing and pattern. Identifying and validating the relationship between remote sensing data and health outcomes remain a major public-health research focus. Space-based applications to VBZ diseases run the gamut from basic research to identify environmental-risk signatures to strategies for integrating remote sensing data into operational decision-support systems. The major goal of such efforts is to establish relationships between environmental conditions, as monitored by satellites, and risk to human populations from VBZ diseases. That requires improved characterization of land use, ecological changes, and changing weather at finer spatial and temporal scales.
Role of Remotely Sensed Data
Some of the earliest attempts to use remote sensing data were nearly 25 years ago, when satellite sensors were used to identify breeding sites of mosquito species responsible for VBZ diseases. For example, Linthicum et al. (1999) used AVHRR data to locate increased breeding and later Rift Valley fever (RVF) virus activity in East African mosquitoes. RVF poses both a human and an agricultural risk. Washino and Wood (1993) demonstrated that Landsat could identify agricultural sites that were most likely to produce mosquito vectors of malaria. The underlying rationale for using remote sensing data to examine VBZ disease patterns is that environment, land use and land cover, weather, and human behavior determine the distribution and spread of many of the most important infectious agents. Environmental structure and meteorologic conditions affect the distribution and abundance of humans, environmental sources, arthropod vectors, and animal reservoirs of infectious agents. Each of those interacting components can be analyzed with statistical or simulation monitoring of case data and enhanced by using remote sensing land-use pattern data that are integrated with other in situ data.
Environmental conditions have been characterized with satellite observations primarily by monitoring reflectance patterns in the visible and near-IR spectrum. Spectral resolution has been coarse, historically relying on Landsat TM, MSS, AVHRR, and SPOT sensors for environmental monitoring. However, empirical studies indicate substantial success in characterizing environmental conditions conducive to disease transmission. For example, Beck and colleagues (1997) used Landsat TM data to identify localized areas, on the basis of vegetation and soil-moisture characteristics, that were at risk for Lyme disease in a spectrally complex residential environment. Radar and lidar have received substantially less evaluation in this field, although their potential utility in complex environments that experience substantial cloud cover during times of interest (such as tropical regions) has been recognized.
Imagery with moderate (over 20 m) to low (100–1,000 m) spatial resolution has been most commonly used to characterize environmental conditions, including land cover, elevation, temperature, and vegetation condition. Higher-resolution imagery (less than 10 m) offers utility to identify individual features, especially those related to human activities, and has been used to document the spatial distribution of human populations in regions undergoing rapid, often undocumented, development and land-cover change. Temporal resolution of 1–16 days has proved satisfactory for many of the disease systems studied; in part, this reflects the biological processes associated with pathogen amplification and the population-growth time frame for insect vectors and other animals. Typically, a sufficient environmental signal has been detected to distinguish sites with increased likelihood of disease. An intraday repeat interval for meteorological variables has been assessed with in situ monitoring systems for environmental conditions. Also, satellite-observation capabilities, in combination with in situ observations, allow for an integrated observational approach for use by emergency responders.
Future Needs
Future applications will require sensors that characterize meteorological conditions (at least maximumal and minimumal surface temperature, daily precipitation, and wind speed) and soil moisture two to four times per day; these appear to be major drivers of short-term vector and animal demographic responses. Those data serve as inputs to calibrate models of VBZ disease dynamics to identify time and space of risk. Many VBZ diseases (such as the Chikungunya virus) begin in tropical and subtropical regions and can spread globally. Those regions often have substantial cloud cover, which makes space-based monitoring of meteorological conditions difficult. Hyperspectral monitoring of land cover is needed to improve characterization of vegetation classes and condition. Repeat coverage on a weekly to about semi-monthly basis is
appropriate in that target populations typically respond to changing land-cover conditions relatively slowly. For both types of data streams, moderate spatial resolution (20–500 m) captures much of the information needed for study on regional scales, although 20–100 m would be preferable to resolve spatial details needed for calibration with VBZ disease models. A high-resolution sensor (less than 5 m) with multispectral capability to distinguish general land-cover characteristics is needed to identify detailed patterns of human land use and distribution and locate at-risk populations. Such a system would need a low return rate (less than monthly) to characterize changes in human population occupancy and use patterns.
OTHER IMPORTANT ISSUES
In addition to the specific mission recommendations, the panel discussed the importance of funding for research and applications aimed at societal benefits that are not specifically related to sensors, satellites, new remote sensing data, or particular missions. It identified the importance of support for capture, synthesis, and analysis of remote sensing data aimed at understanding health and security problems. The principal U.S. government agency charged with human health research, the National Institutes of Health, focuses more on the fundamental determinants of causation and risk than on the environmental causes that the panel considers critical. Even the Environmental Protection Agency has little research funding available for investigation of remote sensing data that might affect human health. The Centers for Disease Control and Prevention encourages studies that are aimed at applications of remote sensing data to specific diseases, but historically it has not had extensive extramural funds for such research. The panel considers the role of NASA, NOAA, and other partner agencies to be critical in funding environment and health scientists in the use of remote sensing data. The societal benefits that we all seek may not be achieved, even if remote sensing data are obtained, unless substantial and sustained support is provided for identifying Earth science determinants of the diverse health risks that can be understood.
Another aspect of the broad study charge is to enhance epidemiological and disease surveillance efforts that use remote sensing data in a research or early-warning program. The panel believes that the societal value of such data will be enormously increased if support is offered to health scientists who acquire and study remote sensing data, because they understand how such insights can be used to analyze and anticipate disease outbreaks. Those scientists lack adequate support because they too often fall between the cracks of intellectual domains, research activities, and associated funding. There is an important opportunity for NASA and NOAA to expand their research and application focus to explicitly involve studies of human health and security to a much greater extent. Investment in research on these societal benefits will expand and enhance the value of the agencies to meeting the needs of citizens of the United States and the world.
Related to those suggestions, which are critical to the panel’s discussions but not an explicit part of the study charge, is the role of aircraft (for example in Europe’s MOSAIC program) and other nonsatellite sensors in providing data for human health research and disease prevention. Such data sources were not explicitly identified in any of the six disease categories, but they are important for understanding patterns of other human health and security risks. Data collected through the use of aircraft supplement satellite imagery in important ways: they are used for prelaunch sensor tests, postlaunch ground truth, annual high-resolution state surveys, emergency high-resolution mapping (e.g., for observations of chemical spills, ocean blooms, and forest fires). Ground- and ice-penetrating sensors, below-cloud surveys, and special field projects with combined flight-level data and airborne remote sensing also illustrate the importance of aircraft as platforms for the collection of remote sensing data. The aircraft facilities and trained personnel must be maintained and enhanced if the space-borne and airborne environmental monitoring system is to be flexible and resilient.
SUMMARY
The overall recommendations of the Panel on Human Health and Security are presented in Table 6.1 above. The panel identified many aspects of human health and security that would be enhanced by the availability, analysis, and application of remote sensing data. It considered six broad categories of health-effects mitigation that have been enhanced by application of space-based observations to such diverse health risks. Maintaining the types of remote sensing data that have allowed identification of environment-disease links, in time and space, is critical for future understanding and forecasting of U.S. and global risks. In addition, new sensors that have finer spatial or spectral resolution have been identified and justified for the scientific and social benefits that will probably accrue. Relevant agencies should consider how to engage health and social scientists who are using satellite observations in a manner that encourages analyses that produce societal benefits. Such efforts should also promote interdisciplinary exchanges of data and analytic methods.
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