Overview: NISAR L-Band SAR Instrument Verification, Calibration and Validation

NISAR Science Payload consists of an L-band SAR instrument and an S-band SAR instrument share-use a 12m reflector with each own feed. The instrument design, based on “SweepSAR” architecture for wide-swath coverage, is essentially a multiple channel-beam polarimetric system employing on-board time-to-angle digital beam forming technique. The instrument exhibits a few “features” that are not present in the conventional SAR system that utilizing a rectangular phased-array antenna and electronically steering the antenna beam in “ScanSAR” operation mode. The most prominent feature is the large reflector-feed antenna, whose geometry is more susceptible to on-orbit thermal environment influence. And when the geometry gets changed thermally, the mechanical boresight will be perturbed, and the antenna patterns will be distorted. For NISAR science objectives, the instrument measurements can be used as a repeat-pass interferometer and the instrument also required to have polarimetric capability; Science imposed a set of “Performance” requirements and a set of “Pointing” requirements on L-SAR and these two sets are inter-related. The large reflector-feed antenna cannot be tested with the instrument in a deployed configuration and is the driver several test-as-you-fly exceptions. To verify the system meeting project requirements before launch and to understand what’s expected once on-orbit, a set of inter-related system models were developed and used to evaluate L-SAR’s sensitivity when the radar antenna is subject to on-orbit thermal environment influences affecting pointing and performance. The results from these models run as a whole, portends what to expect during the mission and the results also used to certify L2 requirements