NISAR S-SAR Data Products Release
S-band sample data through Bhoonidhi Data Portal
The NASA–ISRO Synthetic Aperture Radar (NISAR) mission, a joint Earth observation initiative of ISRO and NASA, was successfully launched onboard GSLV-F16 on 30 July 2025 from Satish Dhawan Space Centre (SDSC-SHAR). NISAR is the world's first spaceborne SAR mission employing dual-frequency radar instrumentation, comprising NASA's L-band SAR and ISRO's S-band SAR, operating with the advanced SweepSAR acquisition technique to enable wide-swath, high-resolution imaging. The satellite has been placed in a 747 km altitude Polar Sun-synchronous orbit with an inclination of 98°, facilitating global repeat observations. With a nominal 12-day repeat cycle, NISAR enables systematic monitoring of Earth system processes including natural hazards, ecosystem dynamics, agricultural monitoring, cryosphere evolution and surface deformation.
NISAR Sample Data Collection
ISRO has released a limited set of NISAR S-band SAR sample data products through Bhoonidhi data portal. The datasets cover multiple regions across the Indian landmass, along with selected global locations representing diverse NISAR science themes. The release includes RSLC (Single Look Slant Range Complex), GSLC (Ground Range Single Look Complex), and GCOV (Ground Covariance) products to facilitate evaluation and application development. The datasets provide users with an opportunity to understand the data structure, product format, and characteristics of NISAR SSAR observations including science data layers, ancillary layers, metadata content, product specifications, noise characteristics, and spatial resolution attributes. These products are intended to familiarize the user community with the data access and dissemination mechanisms, while enabling the development, testing, validation, and optimization of processing workflows, analytical tools, and application pipelines in preparation for the substantial data volumes expected during routine mission operations. In addition, some of the released products span multiple acquisition cycles, offering multi-temporal datasets that support a broad spectrum of thematic applications, temporal change detection studies, time-series analyses, and InSAR-based investigations by the user community.
RSLC
Range-Doppler Single Look Complex
Standard L1 product that will be used to generate all higher level products.
GSLC
Geocoded SLC
Geocoded L1 SLC product using the MOE (Medium Orbit Ephemeris) state vectors and a DEM
GCOV
Geocoded Polarimetric Covariance Matrix
Geocoded polarimetric covariance matrix (1, 3, or 6 layers) using the MOE state vectors and a DEM
Calibration Status
S-band SAR products are currently in the calibration and validation phase. Fully calibrated products will released in near future. NISAR represents the first operational implementation of a dual-frequency SweepSAR radar system. As experience is gained through global data processing, calibration and algorithm improvements continue to be incorporated to further enhance the quality and utility of the released data products. Users may observe residual radiometric noise across the swath resulting in banding in the imagery over low SNR targets, Radio Frequency Interference (RFI), residual phase artifacts and related processing effects. Ongoing calibration, validation and algorithm refinement activities are expected to mitigate these issues in future releases.
Adapting to Sweep-SAR Data
NISAR is the first operational mission implementing SweepSAR technology. One of the primary advantages of SweepSAR imaging is wide-swath imaging with fine resolution. SweepSAR imaging enables wide-swath observations by extending the radar echo reception interval to accommodate returns from a large range extent. As a consequence, radar pulse transmissions may occur while echoes from previously transmitted pulses are still being received. Since the SweepSAR architecture utilizes a common reflector for both transmit and receive operations, echo reception is temporarily interrupted during pulse transmission intervals. These interruptions result in localized regions of missing observations within the receive window, commonly referred to as transmit gaps or dead ranges.
Fixed PRF Mode vs Dithered PRF Mode
Fig 1: NISAR SSAR Image acquired in Fixed PRF mode, showing transmit gaps
Pulse Repetition Frequency (PRF) determines the time difference between two transmitted chirps (which are high BandWidth frequency modulated signals transmitted and its echo is received). In Fixed PRF mode, the timing between two subsequent pulses throughout the duration of imaging is constant. This causes the Transmit Gaps to occur at the same position in the reception window. During Image Focusing operation, the alignment of dead-ranges in range time causes a black (low backscatter) region to appear at the same swath location in range direction. Since, all the pulses have the dead-range in the same location, it appears as a black-band spanning in the azimuth direction.
Fig 2: NISAR SSAR Image acquired in Dithered PRF Mode of Imaging, mitigating transmit gaps
The Dead Range in between the images are mitigated with an innovative combination of System Engineering and Signal Processing. The PRF is not maintained uniform but rather it is modified in a pattern of fixed repetition length. This causes the Transmit gaps of each corresponding line to be not aligned with the transmit gap of the previous line. This process is called dithering, and using Best Linear Unbiased Estimation technique, due to availability of adjacent pixel information in azimuth direction, and the nature of RAW signal property, the dead range pixel information can be estimated. This provides a final image after focusing without transmit gaps in this mode of imaging as shown above.
