There are a range of data products generated by the NISAR mission team that are archived and available for immediate use, from raw data to analysis-ready products.
One of the most exciting aspects of the NISAR mission is that it generates a number of analysis-ready SAR datasets. These Level 2 (Geocoded) and Level 3 (Geophysical) products are archived and freely available to the public. This allows users without the software or expertise necessary to process SAR data easy access to products that can be used in analysis workflows.
For SAR scientists and those who want to generate products to their own specifications, the Level 0 (Raw) data and Level 1 (Range-Doppler) products are also available.
NISAR Product Levels¶
The NASA processing levels used for SAR have somewhat different meanings than those used for multi-spectral (optical) imagery. We will summarize these processing levels and the specific products generated by the mission at each level and provide links to additional information about each product type.
Figure 2 illustrates the products that will be generated in association with the NISAR mission, indicating the products used as input. Level 0 through Level 2 products will be produced directly by the mission and archived at ASF, as will the Level 3 Soil Moisture products.
The remaining Level 3-4 products in the figure will be produced by the NISAR science team, but only for specific areas used for calibration and validation activities. Some of these cal/val products may be archived and available to the public. The processing workflows for these higher-level products will be made available as Python notebooks as they are validated, allowing users to generate these scientific products themselves for other locations.
Figure 2:NISAR Data Product Levels
Level 0: Unfocused Raw Products¶
Level 0 products are unprocessed instrument data. L0A products are the received raw data, which are archived for reference but are not of use to the scientific community. L0B products have been processed to remove transmission artifacts, and are the starting point for processing all additional mission products. They are generally only of interest to SAR scientists.
The Radar Raw Signal Data (RRSD) L0B product contains corrected, aligned radar pulse data.
Level 1: Range-Doppler Products¶
Level 1 products are processed instrument data, focused to full resolution complex images. They are time referenced and annotated with ancillary information, including radiometric and relevant geometric calibration coefficients and georeferencing parameters (i.e. platform ephemeris). Level 1 products are in natural radar coordinates, and cannot be directly overlaid on a map.
The Range-Doppler Single Look Complex (RSLC) product contains focused SAR images in range-Doppler coordinates. Other pair-based Level 1 products are derived from this product.
The Range-Doppler Interferogram (RIFG) product represents the ellipsoid height-corrected, wrapped interferogram generated from two RSLCs in range-Doppler coordinates. The RIFG product is primarily meant for detecting grounding lines.
The Range-Doppler Pixel Offsets (ROFF) product represents a collection of dense pixel offsets layers obtained from applying speckle tracking to a pair of coarsely coregistered RSLCs in range-Doppler coordinates. The ROFF product is primarily meant for cryosphere applications.
The Range-Doppler Unwrapped Interferogram (RUNW) product represents the unwrapped, multi-looked differential interferogram generated from two RSLCs in range-Doppler coordinates. The RUNW product primarily supports the solid earth requirement of ground surface displacement measurements.
Level 2: Geocoded Products¶
Level 2 products are derived from Level 1 products, resampled and geocoded to a geographic grid. They can be directly overlaid on a map and combined with other data in geographic coordinates.
The Geocoded Single Look Complex (GSLC) product represents the single look complex signal return for each polarization in geographic coordinates. The GSLC product enables users to perform backscatter amplitude analysis, and can be combined with other similar GSLC products to derive interferograms and change maps.
The Geocoded Pixel Offsets (GOFF) product represents a collection of dense pixel offsets layers obtained from applying speckle tracking to a pair of coarsely coregistered RSLCs in geographic coordinates. The GOFF product is primarily meant for cryosphere applications.
The Geocoded Polarimetric Covariance Matrix (GCOV) product provides radiometrically terrain corrected SAR backscatter data to primarily support the NISAR ecosystem requirements of biomass estimation, soil moisture estimation, disturbance detection, inundation mapping, and crop area delineation.
The Geocoded Unwrapped Interferogram (GUNW) product represents the unwrapped, multi-looked differential interferogram generated from two RSLCs in geographic coordinates. The GUNW product primarily supports the solid earth requirement of ground surface displacement measurements.
Level 3: Geophysical Products¶
Level 3 products represent geophysical parameters derived from radar-specific parameters and geocoded to a geographic grid.
The Soil Moisture (SME2) product contains soil moisture estimates derived from NISAR data using three different algorithms at agricultural field-scale (200m) posting for most regions (the Sahara Desert will be at 500m). Soil moisture information can be used for reservoir management, early warning of droughts, irrigation scheduling, and crop yield forecasting.
Summary¶
The table below summarizes the characteristics of NISAR data products.
Table 1:NISAR data product overview
| Product | Ground spacing [m] | Interferometric | Geocoded | Layers | Additional layers | Comments |
|---|---|---|---|---|---|---|
| RSLC | NA | individual binary raster layers representing complex signal return for each polarization layer | 2D LUTs provided to convert from digital numbers to beta-naught, sigma-naught, and gamma-naught | zero-Doppler geometry, constant azimuth time interval and one-way slant range spacing | ||
| GSLC | 5 to 40* | ✔ | input RSLC into a geocoded map coordinate system | 2D LUTs provided to convert from digital numbers to beta-naught, sigma-naught, and gamma-naught; mask layer indicating water bodies and shadow-layover | flattened with respect to the orbit used in the RSLC processing, which eliminates the topographic phase contribution in the GSLC | |
| ROFF | 90 | ✔ | along-track offset, slant range offset (three layers) | offset variances, correlation surface peak, cross offset variance, signal-to-noise ratio | distributed without performing any conventional post-processing operation i.e., layers might contain offsets outliers and are not low pass filtered to reduce noise in the data | |
| GOFF | 80 | ✔ | ✔ | along-track offset, slant range offset (three layers) | offset variances, correlation surface peak, cross offset variance, signal-to-noise ratio | distributed without performing any conventional post-processing operation i.e., layers might contain offsets outliers and are not low pass filtered to reduce noise in the data |
| RIFG | 30 | ✔ | wrapped interferogram | coherence magnitude | ellipsoid and topography flattened, multi-looked | |
| RUNW | 80 | ✔ | unwrapped interferogram | coherence magnitude, connected components, ionospheric phase screen, ionospheric phase screen uncertainty | ellipsoid- and topography-flattened, multi-looked | |
| GUNW | 80 | ✔ | ✔ | unwrapped interferogram | coherence magnitude, connected components, ionospheric phase screen, ionospheric phase screen uncertainty | interpolation method during geocoding depends on layer data type |
| 80 | ✔ | ✔ | wrapped interferogram | |||
| GCOV | 20 | ✔ | polarimetric covariance terms | mask, number of looks, RTC gamma to sigma factor | radiometrically terrain-corrected gamma-naught | |
| SME2 | 200 | ✔ | three soil moisture estimates: disaggregation (DSG), physical model inversion (PMI), time series ratio (TSR) | soil moisture uncertainty, DSG algorithm parameters, PMI crop type and vegetation water content, TSR algorithm parameters |
depending on range bandwidth