Analysis of Sentinel-1 Radiometric Stability and Quality for Land Surface Applications

Land monitoring using temporal series of Synthetic Aperture Radar (SAR) images requires radiometrically well calibrated sensors. In this paper, the radiometric stability of the new SAR Sentinel-1A S-1A sensor was first assessed by analyzing temporal variations of the backscattering coefficient (sigma degrees) returned from invariant targets. Second, the radiometric level of invariant targets was compared from S-1A and Radarsat-2 RS-2 data. The results show three stable sub-time series of S-1A data. The first (between 1 October 2014 and 19 March 2015) and third (between 25 November 2015 and 1 February 2016) sub-time series have almost the same mean sigma degrees-values (a difference lower than 0.3 dB). The mean sigma degrees-value of the second sub-time series (between 19 March 2015 and 25 November 2015) is higher than that of the first and the third sub-time series by roughly 0.9 dB. Moreover, our results show that the stability of each sub-time series is better than 0.48 dB. In addition, the results show that S-1A images of the first and third sub-time series appear to be well calibrated in comparison to RS-2 data, with a difference between S-1A and RS-2 lower than 0.3 dB. However, the S-1A images of the second sub-time series have sigma degrees-values that are higher than those from RS-2 by roughly 1 dB.