Terrain Flatten function

Available with Image Analyst license.


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


The input radar data must first be calibrated to beta nought. Use the Apply Radiometric Calibration tool to calibrate radar 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, sigma nought, scattering area, and geometric distortion outputs. For the geometric distortion mask output, the tool will output undetermined values for pixels outside of the DEM extent.

The input DEM must be in the WGS 1984 (EPSG:4326) geographic coordinate system.




The input radar data.

This raster must first be radiometrically calibrated to beta nought.


The input DEM.

The DEM is used to estimate the local illuminated area.


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 will be terrain flattened using Sigma nought or Gamma nought.

  • Gamma nought—The beta nought backscatter will be 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 will be normalized using a DEM to compute the area.

Related topics

In this topic
  1. Overview
  2. Notes
  3. Parameters