Terrain Flatten function

Available with Image Analyst license.

Overview

Corrects the input synthetic aperture radar (SAR) data for radiometric distortions due to topography.

Notes

The input radar data must first be calibrated to beta nought. Use the Sentinel-1 Radiometric Calibration function or the Radar Calibration function to calibrate SAR data to beta nought.

If the input DEM does not span the entire SAR dataset, the tool will output NoData values for the pixels outside of the DEM extent for gamma nought and sigma nought.

The input DEM must be in the WGS84 (EPSG:4326) geographic coordinate system.

Parameters

Parameter	Description
Raster	The input radar data. This raster must first be radiometrically calibrated to beta nought.
DEM	The input DEM. The DEM is used to estimate the local illuminated area.
Geoid	Specifies whether the vertical reference system of the input DEM will be transformed to ellipsoidal height. Most elevation datasets are referenced to sea level orthometric height, so a correction is required in these cases to convert to ellipsoidal height. Checked—A geoid correction will be made to convert orthometric height to ellipsoidal height (based on EGM96 geoid). This is the default. Unchecked—No geoid correction will be made. Use this option only if the DEM is expressed in ellipsoidal height.
Calibration Type	Specifies whether the output is terrain flattened using Sigma nought or Gamma nought. Gamma nought—The beta nought backscatter is normalized using the unit area of a plane locally tangent to the DEM, commonly known as the local incidence angle. This is the default. Sigma nought—The beta nought backscatter is normalized using a DEM to compute the area.