Another objective of the SeRAC project is to refurbish and upgrade the existing ESA sigma-0 transponder for calibrating now the backscatter coefficient of Sentinel-3 SRAL instruments. That old ESA sigma-0 transponder had been used in the past to calibrate the Envisat Radar Altimeter 2(RA-2) (https://doi.org/10.1016/j.asr.2012.12.014).

Fig.1: The sigma0 transponder of ESA in June 2019

Refurbishment has been carried out by the Radio Analog Micro Electronics (RAME, https://ramesrl.it), Rome, Italy and completed in 2019. Final, Factory Acceptance Tests had been carried out in May 2019 in RAME, Rome, Italy.

Eight (8) field tests of the refurbished sigma0 transponder have been carried out in Tuscany, Italy under a crossover of Sentinel-3A Pass No. 193 and Sentinel-3B Pass No. 214.

Fig.2: The location of the crossover of Sentinel-3A and Sentinel-3B for the field testing of the sigma0 transponder
of ESA in Tuscany, Italy. Test sites are indicated by SP1A and SP1B.

 The first field test was held on 29-Jan-2020, during which the transponder was placed on truck and above the SP1A reference benchmark (Fig. 2 and 3). 

Fig.3: The field testing of the sigma0 transponder of ESA in Tuscany, Italy in January 2020 over the SP1A test site.

A series of six Sentinel-3A and two Sentinel-3B follow-on field tests have been carried out in the period January – September 2020. The Sentinel-3A signal as recorded by the sigma-0 transponder in September 2020 is shown in Fig. 4.

Fig.4: The received power of Sentinel-3A as captured during the field testing in September 2020 (Credit: RAME).