SAR processing levels

Processing is essential for transforming raw geospatial data into meaningful imagery. Each processing level represents a different stage in the data processing chain, from raw radar signals to fully calibrated and geocoded imagery. To assess the quality and suitability of SAR data for specific needs, it is important to understand the characteristics and limitations of each processing level.

SAR imagery falls into three processing levels: complex, detected, and geocoded.

Complex SAR imagery includes both the amplitude and phase of the received radar signals in the slant range. It’s represented as complex numbers, with the real part showing the amplitude or signal strength and the imaginary part showing the phase or signal timing. During processing, coherence and sensor platform movement are corrected.

• Single Look Complex (SLC)

  SLC (or SCS or SSC) provides complex SAR data in a relatively raw data format. It is suited for interferometry, polarimetry, change detection, and further processing. This level will be delivered in either GeoTIFF, HDF5, or COSAR file formats.

• Sensor Independent Complex Data (SICD)

  SICD provides complex SAR data and associated metadata in a standardized data format. It is suited for further processing, and when interoperability and metadata are important. This level will be delivered in the NITF file format.

• Compensated Phase History Data (CPHD)

  CPHD provides complex SAR data as phase history information in a standardized data format. It is suited for studying terrain elevation changes, target motion, and other dynamic phenomena. This level will be delivered in the CPHD file format.

Detected SAR imagery provides the amplitude information of the received radar signals in the ground range. It removes background noise to highlight the detected terrain, buildings, and other features.

• Ground Range Detected (GRD)

  GRD (or MGD) provides detected SAR data in a relatively raw data format. It is suited for mapping, land cover classification, and infrastructure monitoring. This level will be delivered in either GeoTIFF or HDF5 file formats.

• Sensor Independent Derived Data (SIDD)

  SIDD provides detected SAR data and associated metadata in a standardized data format. It is suited for when interoperability and additional metadata is important. This level will be delivered in the NITF file format.

Geocoded SAR imagery represents the amplitude information of the received radar signals in the ground range. It is then mapped to a coordinate reference system to allow for accurate georeferencing and better integration with other imagery.

• Geocoded Earth Corrected (GEC)

  GEC provides geocoded SAR data that is projected to a coordinate reference system. It may contain terrain-induced distortions. It is suited for basic visualization, large-scale mapping, and time series analysis. This level will be delivered in either GeoTIFF or HDF5 file formats.

• Geocoded Terrain Corrected (GTC)

  GTC (or GEO or EEC) provides geocoded SAR data that is projected to a coordinate reference system and then terrain-corrected using a DEM. It is suited for precise quantitative analysis, topographic mapping, and environmental monitoring. This level will be delivered in either GeoTIFF or HDF5 file formats.

SICD, SIDD, and CPHD files aren’t compatible with most GIS software. To view and analyze these files, use open-source software such as Sentinel Application Platform (SNAP), or Python libraries like PySAR and H5Py.

• How persistent scatterer interferometry is used to predict and prevent infrastructure damage
• Compensated Phase History Data (CPHD)
• Sensor Independent Complex Data (SICD)
• Sensor Independent Derived Data (SIDD)