The ESA Permanent Facility for Altimetry Calibration in Crete: Advanced Services and the Latest Cal/Val Results

• Published in: Remote sensing (Basel, Switzerland) Vol. 16; no. 2; p. 223
• Main Authors: Mertikas, Stelios P., Donlon, Craig, Kokolakis, Costas, Piretzidis, Dimitrios, Cullen, Robert, Féménias, Pierre, Fornari, Marco, Frantzis, Xenophon, Tripolitsiotis, Achilles, Bouffard, Jérôme, Di Bella, Alessandro, Boy, François, Saunier, Jerome
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01-01-2024
• Subjects: Altimeter; Altimeters; Altimetry; Artificial satellites in remote sensing; Bias; Calibration; Climate change; Construction sites; Infrastructure; Methods; Modernization; Mountains; Oceanography; Orbits; Radar; Radio altimeters; satellite altimetry; Sea level; sea surface; Sentinel-3; Sentinel-6 MF; Technology application; Transponders; Greece; United States > US; Crete
• ISSN: 2072-4292; 2072-4292
• DOI: 10.3390/rs16020223

Two microwave transponders have been operating in west Crete and Gavdos to calibrate international satellite radar altimeters at the Ku-band. One has been continuously operating for about 8 years at the CDN1 Cal/Val site in the mountains of Crete, and the other at the GVD1 Cal/Val site on Gavdos since 11 October 2021. This ground infrastructure is also supported at present by four sea-surface Cal/Val sites operating, some of them for over 20 years, while two additional such Cal/Val sites are under construction. This ground infrastructure is part of the European Space Agency Permanent Facility for Altimetry Calibration (PFAC), and as of 2015, it has been producing continuously a time series of range biases for Sentinel-3A, Sentinel-3B, Sentinel-6 MF, Jason-2, Jason-3, and CryoSat-2. This work presents a thorough examination of the transponder Cal/Val responses to understand and determine absolute biases for all satellite altimeters overflying this ground infrastructure. The latest calibration results for the Jason-3, Copernicus Sentinel-3A and -3B, Sentinel-6 MF, and CryoSat-2 radar altimeters are described based on four sea-surface and two transponder Cal/Val sites of the PFAC in west Crete, Greece. Absolute biases for Jason-3, Sentinel-6 MF, Sentinel-3A, Sentinel-3B, and CryoSat-2 are close to a few mm, determined using various techniques, infrastructure, and settings.