Fifteen Years of Cal/Val Service to Reference Altimetry Missions: Calibration of Satellite Altimetry at the Permanent Facilities in Gavdos and Crete, Greece
Abstract
:1. Introduction
2. The Permanent Facility for Altimeter Calibration
2.1. Infrastructure and Instrumentation
2.1.1. The Gavdos Cal/Val Site
2.1.2. The CRS1 Cal/Val Site
2.1.3. The RDK1 Cal/Val Site
2.1.4. The CDN1 Transponder Cal/Val Site
2.1.5. The GNSS Monitoring Network
2.1.6. The Operations Control Center
2.2. Regional Models and Reference Surfaces
3. Sea-Surface Calibration Results
4. Transponder Calibration Results
4.1. Transponder Versus Sea-Surface Biases: Jason-2 and Jason-3
4.2. Tandem Mission for Jason-2 and Jason-3
5. Crossover Calibration Results
6. Conclusions
- Jason-1 has produced a sea-surface height bias of +3.5 cm and +4.7 cm along the ascending and the descending orbits, respectively, around Gavdos. The mean value of this Jason-1 altimeter comes to +4.1 cm based on cycles 70 to 100 and the GRD-E data products.
- Jason-2 exhibits an altimeter bias in determining sea-surface heights of +0.33 cm (ascending No. 109) and to a value of +0.63 cm for its descending orbit No. 18. Hence, the mean value for Jason-2 comes to almost zero (i.e., +0.48 cm). These results were based on the Gavdos Cal/Val, and Cycles 2–303 with GDR-D data products for Jason-2.
- The transponder at CDN1 Cal/Val facility has produced a range bias for Jason-2 of −1.2 cm for Cycles 267–303 with SGDR-D and Level-2 data products. The associated SSH bias of Jason-2 along Pass No. 18 for the same cycles amounts to +1.7 cm based on Gavdos Cal/Val facility. Biases derived using transponder and sea surface techniques exhibited absolute values of about the same magnitude but with opposite signs. These results back each other up as they are determined by diverse calibration techniques, different locations, settings, and instrumentation;
- Jason-3 demonstrated a bias at determining sea-surface heights of −0.50 cm along the ascending orbit and −0.74 cm along its descending orbit, as determined by the Gavdos Cal/Val site. Results were based on GDR-D products and its first 80 cycles of Jason-3. The mean value of the SSH bias of Jason-3 came to −0.62 cm when averaged over the ascending and its descending pass.
- The transponder at the CDN1 Cal/Val site demonstrated a range bias of +0.76 cm for Jason-3, based on Cycles 5–80 with S-GDR products and precise orbits.
- During the tandem mission, the offset in biases of Jason-3 with respect to Jason-2 for the SSH came to −2.66 cm, while it became +1.77 cm when ranges were directly evaluated with the transponder. The average bias offset of Jason-3 with respect to Jason-2 amounted to +2.21 cm (mean of transponder and SSH);
- Sentinel-3A appeared to exhibit a relative offset in sea surface heights of +4 cm with respect to Jason-3 with crossover analysis. This value was also confirmed using a simultaneous transponder pass over the CDN1 Cal/Val site on 11 November 2016, where a range bias of −2.5 cm (i.e., opposite sign when compared to SSH bias) was determined.
- Relative calibration of HY-2A against Jason-2 with crossover analysis at sea shows that HY-2A displayed a performance that looks like a linear downward trend in bias, starting from +60 cm at Cycle 23 and reaching about −60 cm at Cycle 98. This kind of behavior might be explained by realizing it was generated by a satellite clock defect (oscillation) onboard HY-2A. Comparable bias results for HY-2A have been verified with cross over analysis at sea north of western Crete (Figure 31).
- SARAL/AltiKa displays a bias in sea surface height determination which was larger than that of Jason-2.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Altimetric Mission | Specifications for Sea-Surface Height | Actual SSH | Specifications for Altimeter | Actual Altimeter Noise |
---|---|---|---|---|
Jason-2 and Jason-3 | ±3.4 cm | ±2.5 cm | ±1.7 cm | ±1.5 cm |
SARAL/AltiKa | ±3.2 cm | ±3.2 cm | ±1.5 cm | ±1.0 cm |
HY-2A | ±10 cm | ±5.0 cm | ±4 cm | ±2 cm |
Sentinel-3A | ±2.94 cm | ±3.0–5.0 cm | ±1.3 cm | ±3.0 cm |
Site | Latitude (Deg) | Longitude (Deg) | Ell.Height (m) | σ(lat) (mm) | σ(lon) (mm) | σ(h) (mm) | Time Span (Years) |
---|---|---|---|---|---|---|---|
CDN0 | N 35 20 16.024403 | E 23 46 46.854649 | 1049.5183 | 1.9 | 2.5 | 7.6 | 2014.49–2018.44 |
CDN2 | N 35 20 16.291142 | E 23 46 46.829187 | 1050.4080 | 1.7 | 1.9 | 8.0 | 2016.40–2018.44 |
CRS1 | N 35 18 12.649002 | E 23 31 17.263955 | 21.2075 | 2.0 | 1.8 | 5.4 | 2008.18–2018.44 |
GVD0 | N 34 50 18.578282 | E 24 6 31.908077 | 123.8719 | 2.2 | 1.6 | 5.6 | 2003.04–2017.35 |
GVD7 | N 34 50 52.744567 | E 24 7 11.205655 | 20.1685 | 1.5 | 1.8 | 5.8 | 2009.37–2018.44 |
GVD8 | N 34 50 52.612206 | E 24 7 11.399223 | 22.2757 | 1.6 | 1.9 | 6.2 | 2010.50–2018.44 |
IMS1 | N 35 22 12.547506 | E 24 28 20.982681 | 35.9138 | 1.8 | 1.6 | 5.0 | 2010.19–2015.19 |
MEN2 | N 35 40 12.897887 | E 23 44 26.308798 | 265.7064 | 2.9 | 3.1 | 5.9 | 2013.26–2018.25 |
RDK1 | N 35 11 15.375737 | E 24 19 6.539699 | 25.5337 | 3.7 | 1.9 | 9.0 | 2009.18–2017.44 |
SELI | N 35 21 14.334437 | E 23 50 22.305407 | 1038.0693 | 1.9 | 2.1 | 4.7 | 2009.52–2013.80 |
TUC2 | N 35 31 59.482697 | E 24 4 14.015013 | 160.8894 | 2.0 | 1.9 | 4.6 | 2004.47–2018.44 |
Site | vN (m/Year) | vE (m/Year) | vUP (m/Year) | σvN (m) | σvE (m) | σvUP (m) | Time Span (Years) |
---|---|---|---|---|---|---|---|
CDN0 | −0.0129 | 0.0092 | 0.0009 | 0.0003 | 0.0005 | 0.0015 | 2014.49–2018.44 |
CDN2 | −0.0129 | 0.0063 | 0.0002 | 0.0007 | 0.0006 | 0.0036 | 2016.40–2018.44 |
CRS1 | −0.0124 | 0.0068 | −0.0011 | 0.0002 | 0.0001 | 0.0003 | 2008.18–2018.44 |
GVD0 | −0.0128 | 0.0081 | 0.0000 | 0.0002 | 0.0001 | 0.0004 | 2003.04–2017.35 |
GVD7 | −0.0138 | 0.0086 | −0.0004 | 0.0001 | 0.0002 | 0.0005 | 2009.37–2018.44 |
GVD8 | −0.0143 | 0.0082 | −0.0007 | 0.0002 | 0.0002 | 0.0007 | 2010.50–2018.44 |
IMS1 | −0.0131 | 0.0078 | −0.0004 | 0.0002 | 0.0002 | 0.0006 | 2010.19–2015.19 |
MEN2 | −0.0146 | 0.0058 | −0.0001 | 0.0005 | 0.0005 | 0.0007 | 2013.26–2018.25 |
RDK1 | −0.0128 | 0.0081 | 0.0010 | 0.0004 | 0.0002 | 0.0009 | 2009.18–2017.44 |
SELI | −0.0112 | 0.0077 | −0.0010 | 0.0004 | 0.0005 | 0.0009 | 2009.52–2013.80 |
TUC2 | −0.0124 | 0.0075 | −0.0006 | 0.0001 | 0.0001 | 0.0002 | 2004.47–2018.44 |
Satellite | Jason-1 | Jason-2 | Jason-3 | |
---|---|---|---|---|
Product | GDR-E | GDR-D | GDR-D | |
Cycles | 70–100 | 2–303 | 1–80 | |
SSH bias | Pass No. 18, Descending | +4.70 cm (±1.3 cm) | + 0.63 cm (±0.3 cm) | −0.74 cm (±0.4 cm) |
Pass No. 109 Ascending | +3.50 cm (±1.3 cm) | +0.33 cm (±0.2 cm) | −0.50 cm (±0.4 cm) | |
Average | +4.10 cm | +0.48 cm | −0.62 cm |
SSH Bias (cm) | Satellite | Jason-1 | Jason-2 | Jason-3 | JA3 − JA2 Offset |
---|---|---|---|---|---|
Product | GDR-E | GDR-D | GDR-D | ||
Cycles | 70–100 | 2–303 | 1–80 | ||
No. 18 (descending) | +4.7 cm ± 1.3 cm | +0.63 cm ± 0.3 cm | −0.74 cm ± 0.4 cm | −1.37 cm | |
No. 109 (ascending) | +3.5 cm ± 1.3 cm | +0.33 cm ± 0.2 cm | −0.50 cm ± 0.4 cm | −0.83 cm | |
Average Bias | +4.10 cm | +0.48 cm | −0.62 cm | ||
Tandem Bias (cm) | Satellite | Jason-2 | Jason-3 | JA3 − JA2 Offset | |
Product | GDR-D/SGDR-D | GDR-D/SGDR-D | |||
Cycles | 285–303 | 5–23 | |||
Sea-Surface Height | No.18 (descending) | +2.70 cm ± 0.9 cm | +0.27 cm ± 0.9 cm | −2.43 cm | |
No. 109 (ascending) | +1.62 cm ± 0.9 cm | −0.98 cm ± 0.9 cm | −2.60 cm | ||
Transponder | No. 18 (descending) | −0.40 cm ± 0.6 cm | +1.30 cm ± 0.5 cm | +1.70 cm | |
Range Bias | Satellite | Jason-2 | Jason-3 | JA3 − JA2 Offset | |
Product | SGDR-D | GDR-D | |||
Cycles | 267–303 | 1–80 | |||
Transponder | Descending | −1.20 cm ± 0.6 cm | +0.76 cm ± 0.4 cm | +1.96 cm |
Standard Uncertainty | Uncertainty Estimates | Divisor | Standardized Uncertainty | Sensitivity Coefficient | Uncertainty Component | Degrees of Freedom |
---|---|---|---|---|---|---|
GPS Height Processing | 0.14 mm | 1 | 0.14 mm | 1 | 0.14 mm | 1759 |
GPS Receiver Manufacturer | 6.0 mm | 3.5 mm | 1 | 3.5 mm | 50 | |
GPS Antenna Reference Point, Lab Calibration | 2.0 mm | 1 | 2.0 mm | 1 | 2.0 mm | ∞ |
Water Level Observations | 1.3 mm | 1 | 1.3 mm | 1 | 1.3 mm | 19 |
Tide Gauge Zero Offset | 5.0 mm | 2.9 mm | 1 | 2.9 mm | 2 | |
Tide Gauge Vertical Misalignment | 2.4 mm | 1.4 mm | 1 | 1.4 mm | 50 | |
Tide Gauge Calibration Certificate | 5.5 mm | 1 | 5.5 mm | 1 | 5.5 mm | ∞ |
Spirit Levelling | 0.13 mm | 1 | 0.13 mm | 1 | 0.13 mm | 15 |
GNSS and Tide Gauge Thermal Expansion | 1.1 mm | 0.6 mm | 1 | 0.6 mm | 50 | |
Spirit Levelling Target Misalignment | 1.0 mm | 0.6 mm | 1 | 0.6 mm | 50 | |
Observer’s Experience | 1.0 mm | 0.6 mm | 1 | 0.6 mm | 50 | |
Spirit Levelling Instrument | 1.0 mm | 0.6 mm | 1 | 0.6 mm | ∞ | |
Water Level at Tide Pole | 1.0 mm | 0.6 mm | 1 | 0.6 mm | ∞ | |
MSS/Geoid Models | 5.8 mm | 1 | 5.8 mm | 1 | 5.8 mm | 8 |
Cal/Val Processing and Transformations | 0.5 mm | 0.3 mm | 1 | 0.3 mm | 50 | |
Geoid Slope | 10.0 mm | 5.8 mm | 1 | 5.8 mm | 50 | |
Unaccounted Uncertainty | 50.00 mm | 28 mm | 1 | 28 mm | 50 | |
Root Sum Square | 52 mm | 31.0 mm | 1 | 31 mm | 50 |
© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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Mertikas, S.P.; Donlon, C.; Féménias, P.; Mavrocordatos, C.; Galanakis, D.; Tripolitsiotis, A.; Frantzis, X.; Tziavos, I.N.; Vergos, G.; Guinle, T. Fifteen Years of Cal/Val Service to Reference Altimetry Missions: Calibration of Satellite Altimetry at the Permanent Facilities in Gavdos and Crete, Greece. Remote Sens. 2018, 10, 1557. https://doi.org/10.3390/rs10101557
Mertikas SP, Donlon C, Féménias P, Mavrocordatos C, Galanakis D, Tripolitsiotis A, Frantzis X, Tziavos IN, Vergos G, Guinle T. Fifteen Years of Cal/Val Service to Reference Altimetry Missions: Calibration of Satellite Altimetry at the Permanent Facilities in Gavdos and Crete, Greece. Remote Sensing. 2018; 10(10):1557. https://doi.org/10.3390/rs10101557
Chicago/Turabian StyleMertikas, Stelios P., Craig Donlon, Pierre Féménias, Constantin Mavrocordatos, Demitris Galanakis, Achilles Tripolitsiotis, Xenophon Frantzis, Ilias N. Tziavos, George Vergos, and Thierry Guinle. 2018. "Fifteen Years of Cal/Val Service to Reference Altimetry Missions: Calibration of Satellite Altimetry at the Permanent Facilities in Gavdos and Crete, Greece" Remote Sensing 10, no. 10: 1557. https://doi.org/10.3390/rs10101557