Conference Agenda

This work presents the results of the assessment of the radiometric stability of the BIOMASS mission, a key step in validating the performance of its P-band radar instrument. The evaluation of stability relies on the exploitation of Permanent Scatterers (PSs), which are assumed to be radiometrically stable over time, though their reflectivity varies spatially from scatterer to scatterer. In contrast, any residual radiometric gains are expected to remain spatially constant but vary temporally, making PSs an ideal reference for disentangling temporal instrument variations from scene-dependent effects.

The proposed approach involves a two-stage processing framework. In the first stage, PSs are detected using a stack of radar images, where the reliability of detection increases with the number of images. During the BIOMASS Commissioning Phase, however, the available acquisitions per site were limited to between 7 and 11 images, depending on location. Consequently, the initial part of this study focused on evaluating the probability of false alarms and missed detections as a function of the number of images and the Signal-to-Noise Ratio (SNR) of the PSs. Simulation results demonstrated that, even under these constraints, PSs can be detected with satisfactory reliability.

The second part of the analysis focused on evaluating the performance of the estimator for the residual radiometric gains. Since BIOMASS is the first mission operating at P-band, no prior information was available on the expected density of PSs within a scene. To address this uncertainty, extensive simulations were conducted by varying the number of PSs from as few as 10 to several hundred. The results indicated that the estimator remains robust even with a relatively small number of PSs, provided that the average SNR is sufficiently high to ensure stable estimates.

Following the satellite launch, the algorithm was tested on multiple sites worldwide, encompassing a wide range of topographies, vegetation types, levels of Radio Frequency Interference (RFI), and the presence or absence of urban areas. The analysis revealed that PSs are more abundant at P-band than initially expected, disproving earlier assumptions of their scarcity. The results on radiometric stability consistently confirmed excellent instrument performance, with observed variations remaining below 0.2 dB across all test sites. These findings validate both the robustness of the proposed PS-based method and the outstanding radiometric stability of the BIOMASS sensor.