Gapless Imaging with the NASA-ISRO SAR (NISAR) Mission: Challenges and Opportunities of Staggered SAR

Abstract

The NASA-ISRO SAR (NISAR) is a science and applications mission that will map the Earth’s surface every 12 days by using a reflector-feed system with scan-on-receive (“SweepSAR”) capability. Gapless imaging of a swath of over 240 km at fine resolution, however, requires staggered SAR operation of the radar instrument, i.e., continuous variation of the pulse repetition interval (PRI). While NISAR presents a challenge in that the system’s size is constrained by available resources, and it is planned to operate with lower pulse rate than would be optimum, interesting opportunities arise from subaperture processing and adaptive spectral estimation techniques that greatly improve the image quality at the cost of modestly more computationally intensive image processing