Abstract
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 (σ°) 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 σ°-values (a difference lower than 0.3 dB). The mean σ°-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 σ°-values that are higher than those from RS-2 by roughly 1 dB.
Highlights
Synthetic Aperture Radar (SAR) space-borne sensors have been widely used for soil and vegetation parameters estimation
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
Aboard Sentinel-1 is a C-band (~5.4 GHz) SAR sensor that facilitates high-resolution image acquisition according to four standard operational modes: the Strip Map (SM), Interferometric Wide swath (IW), Extra Wide swath (EW), and WaVe (WV) modes
Summary
Synthetic Aperture Radar (SAR) space-borne sensors have been widely used for soil and vegetation parameters estimation. SAR data of radiometric stability and quality are essential to accurate surface monitoring [1,2]. An expected gain imbalance on acquired S-1A data was reported during the commission phase. This gain imbalance generated an overall gain offset of roughly 0.666 dB for all polarization and imagining modes [4]. The goal of the paper is to investigate the radiometric stability and quality of S-1A signals using a times series of S-1A images acquired over continental areas. The second section of the paper describes the SAR images and studied areas.
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