The NASA-Indian Space Research Organization (ISRO) Synthetic Aperture Radar (NISAR) Mission Team has released 25 new NISAR sample data products — the first public release of NISAR Level 1 to Level 3 L-band data.
Now users are able to test accessing the data and metadata for each data product type and get to know the characteristics of the L-band data (data and ancillary data layers, metadata and product specifications, noise levels, resolution, etc.). These sample data are intended to help users prepare for managing NISAR’s large data volumes and refine processing pipelines as the archive grows.
The NISAR project is still undergoing early-stage refinement and the data products are not fully calibrated. Through processing of the global data, the project has revealed unique characteristics of this first-of-a-kind radar system and identified required algorithm updates. As a result, while some limitations and artifacts have been identified in the data, a number of these are expected to be improved in future releases.
Known data product limitations in this release:
- Radiometric banding across the swath caused by incomplete calibration.
- Inter-beam channel calibration: Onboard digital beamforming uses amplitude and phase weights for each receive channel that have not yet been updated using diagnostic mode analysis. Expected adjustments are very small and would provide only minor improvements to signal-to-noise ratio and phase variability. Beamforming performance is otherwise nominal.
- Antenna pattern calibration: Calibration is ongoing and still being refined.
- Low-amplitude radiometric ripple aligned with the azimuth direction. The effect is visible only in some radar-dark areas and at spatial scales of about 600 meters and shorter. Efforts are underway to improve radiometric uniformity at this level, but some SNR banding at this scale may persist.
- Polarimetric channel imbalance: Polarimetric calibration and estimation of channel imbalances have not yet been performed because of highly active ionospheric conditions. These steps will follow completion of the radiometric corrections.
- Quad-polarimetric (QP) product noise layers: In QP data products, the noiseEquivalentBackscatter layer for the horizontal transmit, horizontal receive (HH) channel is incorrectly populated with zeros. The corresponding layers for the horizontal transmit, vertical receive (HV) and vertical transmit, vertical receive (VV) channels contain correct but uncalibrated values.
Known limitations in the Geocoded Unwrapped (GUNW) interferogram data product:
- The wrapped interferogram layer is incorrectly georeferenced. This issue does not affect other layers in the GUNW product.
- The boundary of the ionospheric phase layer contains edge-effect artifacts that will be reduced in a future release.
- Interferogram generation does not yet use the full “rubbersheeting” algorithm to estimate local image distortions caused by deformation. While this capability is important for fast-moving regions in global production, it is not critical for the current sample data products, which show modest deformation. Current coregistration relies on geometry-based offsets refined with a polynomial fit to dense offsets derived from amplitude cross-correlation.
We look forward to sharing the upcoming release of a larger volume of global data products around the end of February 2026. Fully calibrated and algorithmically improved global data products are anticipated for release around May/June 2026.