The objective of SAR calibration is to provide imagery in which pixel values can be directly related to the radar backscatter of the scene. Though uncalibrated SAR imagery is sufficient for qualitative use, calibrated SAR images are essential to quantitative use of SAR data.
Typical SAR data processing, which produces Level 1 images, does not include radiometric corrections and significant radiometric bias remains. Therefore, it is necessary to apply radiometric correction to SAR images so that the pixel values of the images truly represent the radar backscatter of the reflecting surface. Radiometric correction is also necessary for the comparison of SAR images acquired with different sensors, or acquired from the same sensor at different times, in different modes, or processed by different processors.
This raster function performs three different calibrations for Sentinel-1 datasets, including beta nought and gamma, and outputs the calibrated dataset.
Sigma nought—calibrates the backscatter returned to the antenna from a unit area on the ground, and is related to ground range. Because the imagery is calibrated, it can be directly compared with different radar images collected from the same or a different sensor. Scientists tend to use sigma nought to interpret surface scattering and reflection, and surface properties.
Beta nought—produces a dataset containing the radar brightness coefficient, which is the ratio between the power transmitted and received by the antenna. It is related to slant range, and is dimensionless.
Gamma—is typically used when calibrating the antenna. Since each range cell is equally distant from the satellite, near range and far range are equally bright, which is helpful in determining the antenna pattern in the output dataset.
None—Do not apply any correction.
The Sentinel-1 Level-1 GRD or SLC input raster you want to process.
The function will use the LUT file either to apply the thermal correction or to remove the correction, depending on the contents of the LUT.
Select one of four calibration types: