Mission Specifications

A NASA-ISRO Collaboration

NISAR is a joint Earth-observing mission between NASA and the Indian Space Research Organization (ISRO) with the goal to make global measurements of the causes and consequences of land surface changes using advanced radar imaging. This mission concept and the resulting partnership are in response to the National Academy of Science’s 2007 survey of Earth observational priorities for the next decade, known as the decadal survey. One of the top priorities identified in this survey was to gain data and insight in three Earth science domains: ecosystems, deformation of Earth's crust and cryospheric sciences.

As NASA and ISRO discussed the possibility of a joint radar mission, it became clear that this goal was of great interest to the ISRO science community. ISRO identified science and applications that were complementary to the primary mission objectives: agricultural monitoring and characterization, landslide studies, Himalayan glacier studies, soil moisture, coastal processes, coastal winds, and monitoring hazards. A second radar frequency was added to the mission to better fulfill these science requirements. NISAR will be the first satellite mission to use two different radar frequencies (L-band and S-band) to measure changes in our planet's surface less than a centimeter across. The partnership with India has been key to preserving as much science as possible.

NISAR will monitor earthquakes, volcanic activity, land deformation, and environmental changes, providing critical data for hazard assessment, disaster response, and resource management. It will operate in L- and S-band with Single, Dual, Circular, QQP, and Quad Polarization (LSAR only) combinations, enabling high-resolution tracking of surface moisture, forest biomass, crop areas, mangroves, and wetlands. The mission also supports urgent response by expediting data acquisition and delivery following disasters for timely, informed decision-making.

SweepSAR requires the ability to receive the echoed signal on each element independently, such that localized echoes from the ground can be tracked as they propagate at the speed of light across the swath. As an echo moves from receive element to receive element, the signals from neighboring elements must be combined to form a continuous record of the echo. Given the width of the swath (~244 km), returns from two or more echoes must be processed simultaneously. This operation is best performed using digital combining techniques, so the received echo is digitized immediately upon reception, filtered, decimated, and then sent to a signal combiner.

On transmit, the entire radar feed aperture is illuminated, which creates a narrow strip of radiated energy on the 12-m reflector that illuminates the full 242 km swath on the ground. On receive, the echo illuminates the entire reflector, and that energy is focused down to a particular location on the radar feed aperture depending on the timing of the return. The narrowness of the receive beam on the ground (due to the wide reflector illumination) minimizes ambiguity noise so that individual pulses can be tracked separately as they sweep across the feed.

With SweepSAR, the entire incidence angle range is imaged at once as a single strip-map swath, at full resolution depending on the mode, and with full polarization capability if required for a given area of the interest. Azimuth resolution is determined by the 12-m reflector diameter and is of order 8 m