Sam Murphy

Imagery from polar orbiting satellites can be used to mitigate global hazards from wildfires and volcanoes. An incipient constellation of moderate spatial resolution sensors (i.e. Landsat 8 and Sentinel 2) will provide an unprecedented combined spatial and temporal resolution of imagery with 20 to 30 m pixels and a revisit period of 2 to 4 days. This data stream could provide an invaluable contribution to existing hot target monitoring systems. We developed hot target detection algorithms for… Show more

Imagery from polar orbiting satellites can be used to mitigate global hazards from wildfires and volcanoes. An incipient constellation of moderate spatial resolution sensors (i.e. Landsat 8 and Sentinel 2) will provide an unprecedented combined spatial and temporal resolution of imagery with 20 to 30 m pixels and a revisit period of 2 to 4 days. This data stream could provide an invaluable contribution to existing hot target monitoring systems. We developed hot target detection algorithms for both daytime and nighttime imagery using Landsat 8 data. Performance was compared to existing state-of-the-art methods for daytime detection using a global database of active wildfires. The new approach was able to detect 80% of hot pixels (i.e. compared to 50 to 80% detected by the previous approaches) with a low false alarm rate (i.e. < 10%) and fast processing speed (i.e. orders of magnitude faster than one of the previous approaches). The new detection algorithms put forward here could form the basis of the first, moderate spatial resolution, global hot target detection system. This vision is currently being realized through development of the Hotmap software within the Grid Processing on Demand (G-POD) environment of the European Space Agency (ESA). Show less

Hot surfaces associated with volcanoes, wildfires and geothermal areas are often thermally heterogeneous with respect to the spatial resolution of satellite sensors. A single pixel temperature derived from a satellite image can therefore represent a continuum of surface temperatures that may vary by hundreds of degrees Celsius. For thermally mixed pixels it is therefore more meaningful to estimate radiantflux [Watts] and/or radiant exitance [Watts per metre squared]. Here we introduce a new… Show more

Hot surfaces associated with volcanoes, wildfires and geothermal areas are often thermally heterogeneous with respect to the spatial resolution of satellite sensors. A single pixel temperature derived from a satellite image can therefore represent a continuum of surface temperatures that may vary by hundreds of degrees Celsius. For thermally mixed pixels it is therefore more meaningful to estimate radiantflux [Watts] and/or radiant exitance [Watts per metre squared]. Here we introduce a new method for calculating radiantflux from thermally heterogeneous surfaces with temperatures in the 100 to 1100 °C range. It involves modelling radiance spectra using a spectral library. Two spectral libraries were created to represent two different sensor configurations i) a VNIR–SWIR imaging spectrometer and ii) a two channel SWIR imager, both characterized by a 30 m spatial resolution. We compare our approach against that of the“dual-band method”. The spectral library approach was able to calculate radiantflux to within 30% of the actual value for targets radiating at or above 0.7 MW (i.e. when using an imaging spectrometer) or 7.1 MW(i.e. when using just two SWIR wavebands). The dual-band approach, on the other hand, required targets to be radiating at least 12 MW before a 30% accuracy level could be obtained. All of the approaches could accuratelyfit the spectral radiance values that they modelled. However, they could not reliably determine subpixel temperature distributions. This indicates that it might never be possible to retrieve subpixel temperature distributions reliably using short-wave infrared spectra alone. This finding has significant implications for the remote sensing of hot targets. Show less

Volcanic activity is diverse in its manifestations and spans wide temporal and spatial scales. Monitoring volcanoes with any single sensor system can only provide a limited perspective on the nature of such activity because of trade-offs between spatial, temporal and spectral resolution. Spaceborne observations of volcanoes are thus optimized by utilizing data from different and complementary remote sensing instruments. This study examines the combined use of the Moderate Resolution Imaging… Show more

Volcanic activity is diverse in its manifestations and spans wide temporal and spatial scales. Monitoring volcanoes with any single sensor system can only provide a limited perspective on the nature of such activity because of trade-offs between spatial, temporal and spectral resolution. Spaceborne observations of volcanoes are thus optimized by utilizing data from different and complementary remote sensing instruments. This study examines the combined use of the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) for analyzing thermal anomalies from four separate volcanoes. Show less

Measuring temperatures on volcanoes from space provides important constraints on the transfer of mass and heat to the Earth's surface. Time series of multispectral infrared images, acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) between 2000 and 2009, were inspected to investigate fluctuations in thermal anomalies at both Mount Erebus (Antarctica) and Láscar volcano (Chile). Several thermal metrics were explored: i) maximum pixel temperatures above… Show more

Measuring temperatures on volcanoes from space provides important constraints on the transfer of mass and heat to the Earth's surface. Time series of multispectral infrared images, acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) between 2000 and 2009, were inspected to investigate fluctuations in thermal anomalies at both Mount Erebus (Antarctica) and Láscar volcano (Chile). Several thermal metrics were explored: i) maximum pixel temperatures above background, ii) the spatial extent of low, moderate and high temperature anomalies, and iii) the spatial extent of short-wave infrared anomalies. The maximum pixel temperature metric correlated to eruptive events at Láscar volcano yet displayed significant scatter at Erebus. The spatial extent of both temperature and short-wave infrared anomalies correlates well with eruptive activity at both volcanoes.

Limited variation in the size of thermal anomalies was observed at Erebus throughout the time series due to the stability of a long-lived lava lake, with the exception of a seasonal expansion in low temperature anomalies associated with localized snow-melt at the peak. This finding has implications for the interpretation of low temperature anomalies at other volcanoes. At least two different types of precursory signals are identified at Láscar: i) a gradual increase and ii) a dip, in the size and intensity of thermal anomalies. These thermal precursors appear to be associated with different eruptive styles. The former precedes a relatively shallow, short lived eruption; the later a prolonged eruptive period. Such thermal precursors could therefore help to constrain not only the timing but also the style and duration of an imminent eruptive episode. Show less