Ground Range Detected (GRD) radar imagery is a Level-1 product that has been derived from Level 0 (raw data) SLC SAR data by a Processing Facility via the application of a processing software. GRD products usually consist of focused SAR data that has been detected, multi-looked and projected to ground range using an Earth ellipsoid model. Focused SAR data are generated in a raw data processing step. During focusing, the two-dimensional signal energy of a point target that is spread in range and azimuth direction is aggregated and put into a single image pixel in the output data set. Detected means that the complex numbers representing phase and amplitude values in the original data set have been converted to real numbers by taking their absolute square (or complex conjugate). In the resulting image data, the phase information is not present any longer and only amplitude information remains as the pixel value. The SAR imagery in GRD radar data is given in ground range geometry, which differs from the slant geometry of the SLC data. In ground range geometry, the spacing between the image objects at the Earth’s surface is in direct proportion to their real distance along a hypothetical flat ground surface. Here, image coordinates are oriented along ground range and flight direction. This means that they do not show the distorted appearance of an SLC image.
Discuss advantages and disadvantages of different SAR data formats
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