Day 4

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Paper title Towards FRM Standards with the CDN1 altimetry Cal/Val transponder in Crete
Authors
  1. Stelios Mertikas Technical University of Crete Speaker
  2. Craig James Donlon ESA - ESTEC
  3. Constantin Mavrocordatos ESA/ESTEC, Noordwijk, Netherlands
  4. Dimitrios Piretzidis Space Geomatica P.C.
  5. Konstantinos (Costas) Kokolakis Space Geomatica P.C., Technical University of Crete
  6. Demetrios Matsakis Masterclock Inc.
  7. Franck Borde ESA - ESTEC
  8. Robert Cullen ESA - ESTEC
  9. Marco Fornari Rhea System S.A. for European Space Agency
  10. François Boy CNES
  11. Achilles Tripolitsiotis Space Geomatica P.C.
  12. Thierry Guinle Centre National d’Etudes Spatiales (CNES)
  13. Xenophon Frantzis Technical University of Crete
  14. Berthyl Duesmann European Space Agency/ESTEC
Form of presentation Poster
Topics
  • B1. Calibration, validation and data quality, FRM
    • B1.01 SI-Traceable Satellites - a Gold Standard for Climate and Intercalibration
Abstract text A microwave range transponder has been operating at the CDN1 Cal/Val site on the
mountains of Crete for about 6 years, to calibrate international satellite radar altimeters
in the Ku-band. This transponder is part of the European Space Agency Permanent
Facility for Altimetry Calibration, and has been producing a continuous time series of
range biases for Sentinel-3A, Sentinel-3B, Jason-2, Jason-3 and CryoSat-2 since
2015. As of 18-Dec-2020, the CDN1 transponder has allowed calibration of the new
operational altimeter of Sentinel-6A satellite as it flies in tandem with Jason-3. This
work investigates range biases derived from the long time series of Jason-3 (and
subsequently that of Sentinel-6 since both follow the same orbit) and tries to isolate
systematic and random constituents in the produced calibration results of the
transponder. Systematic components in the dispersion of transponder biases are
identified as of internal origin, coming from irregularities in the transponder instrument
itself and its setting, or of external cause arising from the altimeter, satellite orbit,
Earth’s position in space, geodynamic effects and others. Performance characteristics
of the CDN1 transponder have been examined. Draconic harmonics, principally the 58-
day period, play a significant role in the transponder results and create cyclic trends in
the calibration results. The attitude of the satellite body as it changes for solar panel
orientation contributes an offset of about 7 mm when yaw rotation is off its central
position, and the atmospheric, water mass and non-tidal ocean loadings are
responsible for an annual systematic signal of 10 mm. At the time of writing, all other
constituents of uncertainty seem random in nature and not significantly influential,
although humidity requires further investigation in relation to the final transponder
calibration results.