Application of Radiometric Calibration LUT
The objective of SAR calibration is to provide imagery in which the pixel values can be directly related to the radar backscatter of the scene. To do this, the output scaling applied by the processor must be undone and the desired scaling must be reintroduced. Level-1 products provide four calibration Look Up Tables (LUTs) to produce ß0i, σ0i and γi or to return to the Digital Number (DN). The LUTs apply a range-dependent gain including the absolute calibration constant. For GRD products a constant offset is also applied.
The radiometric calibration is applied by the following equation:
where, depending on the selected LUT,
Bi-linear interpolation should be used for any pixels that fall between points in the LUT.
Application of De-noise LUT
Level-1 products provide a noise LUT for each measurement data set. The values in the de-noise LUT, provided in linear power, can be used to derive calibrated noise profiles matching the calibrated GRD data. The de-noise LUT must be calibrated matching the radiometric calibration LUT applied to the DN:
where, depending on the LUT selected to calibrate the image data,
The calibrated noise profile can then be applied to the data to remove the noise by subtraction. Application of the radiometric calibration LUT and the calibrated de-noise LUT can be applied in one step as follows: