Chandrayaan-2 Dual-Frequency SAR (DFSAR): Performance Characterization and Initial Results

TL;DR

The paper presents the calibration, performance evaluation, and initial findings of Chandrayaan-2's Dual-Frequency SAR system, demonstrating its capability to characterize lunar surface features and compare with theoretical models.

Contribution

This work provides the first calibration and performance analysis of DFSAR data, enabling lunar surface characterization at multiple wavelengths and polarimetric modes.

Findings

Crater regions show consistent anomalous CPR at both L- and S-bands.

Material properties at crater interiors and ejecta are decoupled.

Comparison with models suggests potential for studying crater evolution.

Abstract

The Dual-Frequency synthetic aperture radar (DFSAR) system manifested on the Chandrayaan-2 spacecraft represents a significant step forward in radar exploration of solid solar system objects. It combines SAR at two wavelengths (L- and S-bands) and multiple resolutions with several polarimetric modes in one lightweight ($\sim$ 20 kg) package. The resulting data from DFSAR support calculation of the 2$\times$2 complex scattering matrix for each resolution cell, which enables lunar near surface characterization in terms of radar polarization properties at different wavelengths and incidence angles. In this paper, we report on the calibration and preliminary performance characterization of DFSAR data based on the analysis of a sample set of crater regions on the Moon. Our calibration analysis provided a means to compare on-orbit performance with pre-launch measurements and the results matched with the pre-launch expected values. Our initial results show that craters in both permanently shadowed regions (PSRs) and non-PSRs that are classified as Circular Polarization Ratio (CPR)-anomalous in previous S-band radar analyses appear anomalous at L-band also. We also observe that material evolution and physical properties at their interior and proximal ejecta are decoupled. For Byrgius C crater region, we compare our analysis of dual-frequency radar data with the predicted behaviours of theoretical scattering models. If crater age estimates are available, comparison of their radar polarization properties at multiple wavelengths similar to that of the three unnamed south polar crater regions shown in this study may provide new insights into how the rockiness of craters evolves with time.