A transponder calibration tool based on FFSAR: results for CryoSat from 10 years of operations

Michele Scagliola (Aresys, Italy)


Marco Fornari (RHEA for ESA, The Netherlands); Marco Meloni (Serco for ESA, Italy); Jerome Bouffard (ESA, Italy); Tommaso Parrinello (ESA, Italy)

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

Session: Instrument Processing: Measurement and Retracking

Presentation type: Type Forum

External calibration of satellite altimeters is commonly used to assess the errors introduced by the instrument when performing its measurements. The on-ground processing of the altimeter acquisitions over an external calibrator is a key step to assess these errors starting from the knowledge of the exact location of the external calibrator and its characterization.
Starting from the new capabilities provided by FFSAR, a tool was developed for the transponder calibration of a high PRF altimeter. The tool needs as input the FBR or L1A product for the acquisition over the transponder and auxiliary information about the transponder characterization as well as atmospheric corrections. Starting from the inputs above and exploiting algorithms in [1] and [2], the tool allows to estimate the following parameters
- Datation bias
- Range bias
- FFSAR point target response characterization (e.g. along- and across-track resolution, Peak-to-Side Lobe ratio, ecc.)

The tool was exploited to process all the CryoSat acquisition in SAR and SARin mode over the Svalbard and Crete CDN1 transponder starting from Baseline-D FBR products. The long-term analysis of the transponder calibration parameters allowed to verify the quality of the CryoSat Baseline-D FBR products and to observe the stable performance of the SIRAL instrument from the beginning of the Mission. The long term transponder calibration parameters for SARin acquisition over Svalbard transponder are shown in the following figures.

[1] A. Egido and W. H. F. Smith, "Fully Focused SAR Altimetry: Theory and Applications," in IEEE Transactions on Geoscience and Remote Sensing, vol. 55, no. 1, pp. 392-406, Jan. 2017, doi: 10.1109/TGRS.2016.2607122.
[2] M. Scagliola and P. Guccione, "Datation and Range Calibration of Radar Altimeter Exploiting Fully Focused SAR Processing," in IEEE Geoscience and Remote Sensing Letters, doi: 10.1109/LGRS.2020.2980635

A transponder calibration tool based on FFSAR: results for CryoSat from 10 years of operations
Michele Scagliola