Transponder Calibration in SAR altimetry: from CryoSat-2 to Sentinel-3

Albert Garcia-Mondejar (isardSAT Ltd., United Kingdom)


Marco Fornari (RHEA / ESA, The Nederthlands); Jérôme Bouffard (RHEA / ESA, Italy); Pierre Féménias (ESRIN / ESA, Italy); Mònica Roca (isardSAT Ltd., United Kingdom)

Event: 2016 Ocean Surface Topography Science Team Meeting

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

Presentation type: Type Poster

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.

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 by Technical University of Crete for the Sentinel 3 calibration in the island of Crete.

For CryoSat-2 [1], we are using the transponder to calibrate SIRAL’s range, datation, and interferometric baseline (or angle of arrival) to meet the missions requirements [2].
For Sentinel-3 we are using the transponder to calibrate SRAL’s range, datation to meet the missions requirements [3].

In these calibrations, we are using 3 different type of data: the raw L1A data, the stack beams before they are multi-looked (L1BS), and the multi-looked waveform products (L1B) [4].

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 [5]. 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.

The performances of the CryoSat-2 altimeter, the SIRAL (Synthetic aperture interferometer radar altimeter), have been monitored since 2010 with the Transponder measurements. The range and datation biases from the processor have been corrected in the initial Baselines and now with the Baseline C the long-term trends can be performed in order to evaluate the aging of the instrument.
For Sentinel-3 altimeter, the first data with the Crete TRP have been analysed and the first performances assessment will be made before the end of the Commissioning Phase.

On this presentation the main results with the CryoSat-2 and Sentinel-3 altimeters will be shown.

[1] C.R. Francis, “CryoSat Mission and Data Description”, CS-RP-ESA-SY-0059.
[2] CryoSat Science and Mission Requirements Document, CS-RS-UCL-SY-001.
[3] D.J.Wingham, et al.: “CryoSat: A mission to determine the fluctuations in Earth’s land and marine ice fields”, Advances in Space Research 37 (2006) 841–871.
[4] Sentinel-3 Mission Requirements Document, EOP-SMO/1151/MD-md.
[5] SIRAL2 Calibration using TRP: Detail Processing Model – DPM; ISARD_ESA_CR2_TRP_CAL_DPM_030.

Poster show times:

RoomStart DateEnd Date
Grande Halle Thu, Nov 03 2016,11:00 Thu, Nov 03 2016,18:00
Albert Garcia-Mondejar
isardSAT Ltd.
United Kingdom