NISAR SweepSAR Data Processing

NASA ISRO Synthetic Aperture Radar (NISAR) is a joint SAR mission between NASA and ISRO having the capability to image a wide swath at high resolution using the SweepSAR technique. NISAR aims to provide high quality SAR data with systematic coverage for entire globe at 12 days repeat cycle catering to various science disciplines such as deformation, ecosystem, cryosphere, agriculture and oceanic studies. Shorter repeat period enables NISAR data to be useful for time series analysis. The NISAR SweepSAR imaging makes use of Digital Beam Forming (DBF) to generate 240 km ground swath data with uniform radiometry. Large receive data window compared to Pulse Repeat Interval (PRI) results in dead range gaps in data. The uniform distribution of dead range gaps across swath is achieved by staggering (dithering) the PRI. It allows the estimation of dead range gaps using correlation based estimators. Estimation of dead range gaps in stagger PRI case results in improvement of contrast of images by decreased ambiguity levels. The wide swath images thus generated are free from dead range gaps effects. Range Doppler Algorithm (RDA) is baselined for NISAR S-SAR data processing necessitating resampling of staggered PRI data to uniform PRI. This paper discusses about NISAR data processing strategy adopted for Range Doppler and Geocoded product generation. Additionally, implementation of NISAR specific features have been deliberated.