Combined radiometric calibration and multilooking

Microwave Toolbox
2

This is a task perfectly suited for the graph processing capabilities of SNAP, which allows you to efficiently chain multiple processing steps together.

Here is a sample of a graph you might want to use to generate calibrated, multilooked and terrain-corrected images from S1 GRDs. Remove/add any steps and modify any parameters as you see fit.

preprocess.xml (4.7 KB)

<graph id="Graph">
    <version>1.0</version>
    <node id="Read">
        <operator>Read</operator>
        <sources/>
        <parameters>
            <file>${inFile}</file>
        </parameters>
    </node>
    <node id="Subset">
        <operator>Subset</operator>
        <sources>
            <sourceProduct refid="Read"/>
        </sources>
        <parameters>
            <sourceBands/>
            <region/>
            <geoRegion>${georegion}</geoRegion>
            <subSamplingX>1</subSamplingX>
            <subSamplingY>1</subSamplingY>
            <tiePointGridNames/>
            <copyMetadata>true</copyMetadata>
        </parameters>
    </node>
    <node id="Apply-Orbit-File">
        <operator>Apply-Orbit-File</operator>
        <sources>
            <sourceProduct refid="Subset"/>
        </sources>
        <parameters>
            <orbitType>Sentinel Precise (Auto Download)</orbitType>
            <polyDegree>3</polyDegree>
        </parameters>
    </node>
    <node id="Calibration">
        <operator>Calibration</operator>
        <sources>
            <sourceProduct refid="Apply-Orbit-File"/>
        </sources>
        <parameters>
            <sourceBands/>
            <auxFile>Product Auxiliary File</auxFile>
            <externalAuxFile/>
            <outputImageInComplex>false</outputImageInComplex>
            <outputImageScaleInDb>false</outputImageScaleInDb>
            <createGammaBand>false</createGammaBand>
            <createBetaBand>false</createBetaBand>
            <selectedPolarisations/>
            <outputSigmaBand>false</outputSigmaBand>
            <outputGammaBand>false</outputGammaBand>
            <outputBetaBand>true</outputBetaBand>
            <outputDNBand>false</outputDNBand>
        </parameters>
    </node>
    <node id="Multilook">
        <operator>Multilook</operator>
        <sources>
            <sourceProduct refid="Calibration"/>
        </sources>
        <parameters>
            <sourceBands/>
            <nRgLooks>10</nRgLooks>
            <nAzLooks>10</nAzLooks>
            <outputIntensity>false</outputIntensity>
            <grSquarePixel>false</grSquarePixel>
        </parameters>
    </node>
    <node id="Terrain-Flattening">
        <operator>Terrain-Flattening</operator>
        <sources>
            <sourceProduct refid="Multilook"/>
        </sources>
        <parameters>
            <sourceBands/>
            <demName>SRTM 1Sec HGT</demName>
            <demResamplingMethod>BICUBIC_INTERPOLATION</demResamplingMethod>
            <externalDEMFile/>
            <externalDEMNoDataValue>0.0</externalDEMNoDataValue>
            <outputSimulatedImage>false</outputSimulatedImage>
        </parameters>
    </node>
    <node id="Terrain-Correction">
        <operator>Terrain-Correction</operator>
        <sources>
            <sourceProduct refid="Terrain-Flattening"/>
        </sources>
        <parameters>
            <sourceBands/>
            <demName>SRTM 1Sec HGT</demName>
            <externalDEMFile/>
            <externalDEMNoDataValue>0.0</externalDEMNoDataValue>
            <demResamplingMethod>BICUBIC_INTERPOLATION</demResamplingMethod>
            <imgResamplingMethod>BICUBIC_INTERPOLATION</imgResamplingMethod>
            <pixelSpacingInMeter>50.0</pixelSpacingInMeter>
            <pixelSpacingInDegree>-1</pixelSpacingInDegree>
            <mapProjection>${projection}</mapProjection>
            <nodataValueAtSea>true</nodataValueAtSea>
            <saveDEM>false</saveDEM>
            <saveLatLon>false</saveLatLon>
            <saveIncidenceAngleFromEllipsoid>false</saveIncidenceAngleFromEllipsoid>
            <saveLocalIncidenceAngle>false</saveLocalIncidenceAngle>
            <saveProjectedLocalIncidenceAngle>false</saveProjectedLocalIncidenceAngle>
            <saveSelectedSourceBand>true</saveSelectedSourceBand>
            <applyRadiometricNormalization>false</applyRadiometricNormalization>
            <saveSigmaNought>false</saveSigmaNought>
            <saveGammaNought>false</saveGammaNought>
            <saveBetaNought>false</saveBetaNought>
            <incidenceAngleForSigma0>Use projected local incidence angle from DEM</incidenceAngleForSigma0>
            <incidenceAngleForGamma0>Use projected local incidence angle from DEM</incidenceAngleForGamma0>
            <auxFile>Latest Auxiliary File</auxFile>
            <externalAuxFile/>
        </parameters>
    </node>
    <node id="Write">
        <operator>Write</operator>
        <sources>
            <sourceProduct refid="Terrain-Correction"/>
        </sources>
        <parameters>
            <file>${outFile}</file>
            <formatName>BEAM-DIMAP</formatName>
        </parameters>
    </node>
</graph>

To apply it to input images, you can use either the SNAP’s batch processing tool or the GPT command-line utility. I personally prefer the GPT.

For example, you could run the above graph with the following parameters from the command line, which will generate “preprocessed.dim” as the output.

gpt preprocess.xml "-Pgeoregion=Polygon ((26.894 57.939, 27.403 57.913, 27.3
35 57.596, 26.754 57.623, 26.629 57.819, 26.894 57.939))" -Pprojection=EPSG:3301 "-PinFile=S1A_IW_GRDH_1SDV_20150603T042552_20150603T042617_006204_00817F_C6A2.zip" -PoutFile=preprocessed
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