Investigations on the Radiometric Performance of Sentinel-1: Comparing Point and Distributed Target Results and Analyzing Beam-to-Beam Gain Offsets in Overlap Regions

Abstract

This paper presents a detailed radiometric performance assessment of the Sentinel-1 SAR constellation, focusing on absolute calibration factor estimation using reference point targets, analysis of gamma profiles over the Ama-zon rainforest, and beam-to-beam gain offset evaluation in sub-swath overlap regions. The study utilizes data from S1A and S1C, including recent results from in-orbit commissioning as well as routine operations. Reference point targets at the DLR calibration site provide high-precision absolute calibration benchmarks, while the Ama-zon rainforest serves as a stable distributed calibration target to assess relative radiometric accuracy and antenna pattern consistency. Results show strong agreement between point target and distributed target methods, with ab-sCal deviations closely clustered around zero and gamma profiles reflecting stable backscatter levels with some elevation-dependent variations. Beam-to-beam offset analysis reveals low standard deviations, particularly in IW mode, with a few sub-swath transitions indicating localized calibration adjustments. Overall, Sentinel-1 demon-strates robust and stable radiometric calibration across multiple satellites and acquisition modes, supporting its reliable contribution to quantitative Earth observation applications.