Observatory

The NISAR spacecraft will accommodate two fully capable synthetic aperture radar (SAR) instruments. The radars are designed to work independently or together and are self-contained units up to the point of radiating energy (sending a signal) to the shared reflector.

The focus of NASA's science goals for NISAR is the 24-cm-wavelength, side-looking, fully polarimetric, interferometric L-SAR supplied by JPL. The L-SAR will be used globally to meet all of NASA’s science requirements. Current mission observing scenarios call for the instrument to be on while collecting data for 45 to 50% of each orbit on average, with peaks as high as 70%.

The L-SAR is capable of 242-kilometer swaths with 7-meter resolution along track (the direction of travel) and 2- to 8-m resolution cross-track, depending on the viewing mode. This radar comprises 24 L-band transmit/receive array elements in 2 rows, 12 per polarization.

From the NISAR science orbit, the instrument’s pointing accuracy is such that the L-SAR data can be used to produce repeat-pass interferograms sensitive to large-scale land deformation rates as small as 4 mm/year. To meet the requirements of all science disciplines, the L-SAR radar instrument is designed to deliver fast sampling, global access and coverage, at full resolution and with polarimetric diversity. The technological innovation that allows this performance is the scan-on-receive “SweepSAR” design.

The 12cm wavelength S-SAR supplied by ISRO is the secondary radar and is composed of 48 S-band transmit/receive array elements in 2 rows, 24 per polarization. The S-SAR will be used to produce data over science areas of interest to India that are above and beyond the NASA requirements. The areas include coastal bathymetry (depth of water) and ocean winds, geology over India, and coastal shoreline studies. The S-band is also sensitive to light vegetation and will be used in polar regions, as its signal is less sensitive to ionospheric disturbances.