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In a Sentinel-1 Level 1 Ground Range Detected SAR data product, Intensity = Amplitude * Amplitude.

Should the intensity image or the amplitude image be used for radiometric calibration when using the ESA Sentinel-1 Toolbox software? The ultimate purpose is the classification of geophysical features, e.g. land, water, etc.

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The intensity image should be used for calibration and subsequent classification of geophysical features. To radiometrically calibrate the intensity, use the Calibrate tool in the Sentinel-1 Toolbox (SAR Processing > Radiometric > Calibrate). The S-1 Level 1 GRD product includes several Look-Up Tables (LUTs) to convert intensity values into sigma or gamma naught values. Use these LUTs as the processing parameters for the Calibration tool.

Using amplitude would produce a calibration result of a lower magnitude than using intensity because intensity equals amplitude squared. The calibration is applied using the equation

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For more information about the calibration process see the ESA Sentinel-1 Technical Guide.

Intensity depends on the scattering properties of surfaces (if the spatial extent of the scattering medium is large relative to the signal wavelength) or objects (if the spatial extent of the scattering medium is smaller than the signal wavelength). The effectiveness of a scatterer is determined by the radar cross section (RCS). Many parameters influence the RCS: surface roughness, local geomorphology, scatterer density, 3-D distribution of scatterers, and the dielectric properties of the scene. These variables can help classify features in an intensity image.

  • I meant for a level-1 Ground Range Detected Sentine-1 product (which has been multilooked and projected to ground geometry), so the phase information has been lost (conversely to Single Look Complex products). What would be the difference between classifiying on the amplitude and the intensity image. – Hakim Oct 23 '15 at 18:21
  • Yes the calibration is working well using Sentinel-1 Toolbox and the Sigma0 band has been generated (using the Amplitude band as input), but I was just wondering how the result of the calibration will be if I use the Intensity band instead. Will the use of the Intensity instead of the Amplitude influence the calibration? – Hakim Oct 23 '15 at 18:50
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    I don't think the calibration will be influenced, because the calibration is applied using the equation !equation so the values are squared, which to me indicates that using amplitude or intensity shouldn't matter. I believe you should use intensity for calibration and classification as this is the intention of the Sentinel-1 Toolbox. – Charlie Parr Oct 23 '15 at 18:59
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    Check out the Sentinel-1 Toolbox Help section for the Calibration Operator (Help > SAR Operators > Calibration). The documentation references converting intensity values into sigma or gamma naught values. I can't find references to using amplitude. You could also test it out! Try one workflow using intensity, try another using amplitude, and compare the results. – Charlie Parr Oct 23 '15 at 19:15
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    I've applied the same graph process (including a Calibration step) on the Intensity and the Amplitude and the results are exactly the same. In fact, using the Band math operator to perform the difference between the two resulting calibrated bands yield a black map (0 = no change between the two bands). – Hakim Oct 25 '15 at 11:36

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