With the successful launch of the NASA-ISRO Synthetic Aperture Radar (NISAR) mission on 30^th July 2025 from ISRO Satish Dhawan Space Centre (SDSC) SHAR, Sriharikota, a new era of SAR dual/multi-frequency SAR missions has begun. NISAR is a jointly developed SAR mission with L-Band (24 cm wavelength) developed by NASA and S-band (9.4 cm wavelength) developed by ISRO. The most unique technology of the NISAR satellite is the novel SweepSAR mode of data acquisition, which enables the NISAR satellite to acquire the SAR data in a wide swath without compromising the SAR azimuth resolution. In SweepSAR mode, a wide beam will be transmitted that illuminates the entire desired swath with the help of a 12m reflector antenna, and 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. NISAR operates at 747 Km with a swath of 240 km and repeativity of 12 days. The major specifications of the NISAR satellite are given below in Table 1:

Table 1: Major Specifications of NISAR Satellite

The penetration capability of SAR depends on the wavelength of the transmitted signal and thus, dual dual-frequency NISAR satellite will help to understand the different Earth’s features at two different penetration levels. NISAR has interferometric and polarimetric capability to map the Earth’s Surface for various applications like deformation studies, ecosystem disturbances, flood mapping, soil moisture estimations, sea-ice dynamics, and ocean applications. NISAR can acquire the data in single, dual, quad, and compact polarimetric modes and can be used for various ecosystem applications and classification of the various features. The interferometric mode of NISAR is mainly utilized for deformation studies by generating the interferograms and displacement maps of Earth’s surface with a 12-day repeat pass orbit. The simulated interferograms in L-band and S-band data of the terrain of Alwar, Rajasthan, India, are shown in Figure 1. The simulated Interferograms have been generated using the ephemeris of ISRO’s EOS-4 SAR satellite. Simulated Interferograms show the differences in the fringe patterns due to the difference in the wavelength of L-band (24 cm) and S-band (9.4 cm).

Figure 1: Simulated L & S Band Interferograms for Alwar, Rajasthan, India

The various levels of NISAR products can be provided to the users freely, which include level-0, level-1, and level-2 products. The Level-1 products will be in the radar’s range Doppler coordinate system, and the Level-2 products will be produced over geocoded map coordinate systems. The level-0 products will be raw SAR signal data products in which unprocessed data are available to the users for developing the SAR focusing algorithms. The Level-1 products will be processed products in the SAR slant range geometry, which include Range-Doppler Single Look Complex (RSLC), Range-Doppler Wrapped Phase Interferogram (RIFG), Range-Doppler Unwrapped Interferogram (RUNW), and Range-Doppler Pixel Offsets (ROFF). The Level-2 products are the geocoded products projected on the Earth geometry, which include the Geocoded SLC (GSLC), Geocoded Polarimetric Covariance (GCOV), Geocoded Unwrapped (GUNW) interferograms, and Geocoded Pixel Offsets (GOFF). All the NISAR products are available in the Hierarchical Data Format (HDF5) and can be accessed through the NASA Alaska SAR facility (ASF) and ISRO Bhoonidhi data portals. Some of the simulated products of L-band SAR of NISAR are available on NASA’s website and can be visualized in Figure 2:

Figure 2: NISAR L-Band Simulated Raw and Processed Products

The major application areas of NISAR are: Ecosystems, Solid Earth, Cryosphere, Disaster, Coastal & Oceanography. Ecosystem applications include crop monitoring, crop biomass, forest biomass, soil moisture, wetland mapping, and related applications. Solid Earth applications include Volcanic deformation, seismic activities monitoring, Land subsidence & Aquifer systems monitoring. Cryosphere applications include monitoring of Himalayan glacier dynamics, polar ice, sea-ice types & thickness, and related applications. Disaster applications include monitoring of floods, forest fires, oil spills, and earthquakes. Ocean applications include surface wind speed, coastal bathymetry & cyclone monitoring.

References :

1. https://www.isro.gov.in/NISARSatellite.html
2. P. A. Rosen et al., “The NASA-ISRO SAR Mission: A summary,” in IEEE Geoscience and Remote Sensing Magazine, doi: 10.1109/MGRS.2025.3578258.
3. https://assets.science.nasa.gov/content/dam/science/missions/nisar/nisar-jpl/pdf/NISAR_FINAL_9-6-19.pdf