NISAR L-band Radar Pointing Bias Estimation and Verification During Commissioning Phase

The commissioning phase of dual L-S band NASA-ISRO synthetic aperture radar (NISAR) mission started in August and ended in October 2025. Estimating and correcting the radar pointing bias has been one of the key commissioning-phase activities of NISAR mission. This task is crucial for successful onboard digital beamforming (DBF), high-quality SAR image formation, and generation of radiometrically calibrated science products on the ground. This paper briefly covers some novel data-driven radar pointing estimation methodologies with emphasis on elevation direction from multi-channel SweepSAR NISAR L-band raw products. The algorithms and NISAR pointing products are illustrated via NISAR-like L-band simulation performed prior to the launch. The very first NISAR radar pointing results obtained from analyzing real NISAR L-band products during commissioning-phase are presented for the first time. The verification of estimated pointing bias via SAR image formation with antenna calibration of multi-channel SweepSAR L-band product is also demonstrated here. The spacecraft orientation is mechanically adjusted for the estimated bulk bias around -215 milli-degrees in elevation. This is a common bias among L-band and S-band instruments. Finally, the residual pointing bias is also extracted from later L-band raw products for further confirmation