CryoSat-2 range, datation and interferometer calibration with Transponder

Adrián Flores (isardSAT, Spain)

CoAuthors

Albert Garcia-Mondéjar (isardSAT, Spain); Mònica Roca (isardSAT, Spain); Marco Fornari (European Space Agency/ESTEC, Netherlands); Jerome Bouffard (European Space Agency/ESRIN, Italy)

Event: 2020 Ocean Surface Topography Science Team Meeting (virtual)

Session: Regional and Global CAL/VAL for Assembling a Climate Data Record

Presentation type: Type Forum

The CryoSat mission is designed to determine fluctuations in the mass of the Earth’s land and the marine ice fields. Its primary payload is a radar altimeter that operates in different modes optimised depending on the kind of surface: Low resolution mode (LRM), SAR mode (SAR) and SAR interferometric mode (SARin). This radar is named SIRAL: Synthetic aperture interferometer radar altimeter.

ESA has deployed a transponder available for the CryoSat project (a refurbished ESA transponder developed for the ERS-1 altimeter calibration). It is deployed at the KSAT Svalbard station: SvalSAT. Another transponder has been deployed in Greece Technical University of Crete for the Sentinel 3 calibration.

Transponders are commonly used to calibrate absolute range from conventional altimeter waveforms because of it characteristic point target radar reflection. The waveforms corresponding to the transponder distinguish themselves from the other waveforms resulting from natural targets, in power and shape.

We are using the transponder to calibrate SIRAL’s range, datation, and interferometric baseline (or angle of arrival) to meet the missions requirements. In these calibrations, we are using 3 different type of data: the raw Full Bit Rate data, the stack beams before they are multi-looked (stack data) in the Level 1b processor, and the Level 1b data itself.

Ideally the comparison between (a) the theoretical value provided by the well-known target, and (b) the measurement by the instrument to be calibrated; provides us with the error the instrument is introducing when performing its measurement. When this error can be assumed to be constant regardless the conditions, it will provide the bias of the instrument. And if the measurements can be repeated after a certain period of time, it can also provide an indication of the instrument drift.

This poster presents the analysis and results of this calibration. The work presented here has been carried out under an ESTEC/ESA contract, to calibrate CryoSat-2 during the Commissioning phase. It was later extended with an ESRIN/ESA contract, for continue monitoring and including further analysis.
 
Adrián Flores
isardSAT
Spain
adrian.flores@isardsat.cat