Connection Time out during Terrain Correction in Snap gpt command line process - Sentinel 1

Question

I am processing Sentinel-1 using the Snap command line gpt. The xml file i am using was produced using the graph builder within the SNAP software, and slightly modified to suit my needs. Please see below:

<graph id="Graph">
  <version>1.0</version>
  <node id="Read">
    <operator>Read</operator>
    <sources/>
    <parameters class="com.bc.ceres.binding.dom.XppDomElement">
      <file>$file</file>
    </parameters>
  </node>
  <node id="Calibration">
    <operator>Calibration</operator>
    <sources>
      <sourceProduct refid="Read"/>
    </sources>
    <parameters class="com.bc.ceres.binding.dom.XppDomElement">
      <sourceBands/>
      <auxFile>Product Auxiliary File</auxFile>
      <externalAuxFile/>
      <outputImageInComplex>false</outputImageInComplex>
      <outputImageScaleInDb>false</outputImageScaleInDb>
      <createGammaBand>false</createGammaBand>
      <createBetaBand>false</createBetaBand>
      <selectedPolarisations>VH,VV</selectedPolarisations>
      <outputSigmaBand>true</outputSigmaBand>
      <outputGammaBand>false</outputGammaBand>
      <outputBetaBand>false</outputBetaBand>
    </parameters>
  </node>
  <node id="Multilook">
    <operator>Multilook</operator>
    <sources>
      <sourceProduct refid="Calibration"/>
    </sources>
    <parameters class="com.bc.ceres.binding.dom.XppDomElement">
      <sourceBands>Sigma0_VH,Sigma0_VV</sourceBands>
      <nRgLooks>1</nRgLooks>
      <nAzLooks>1</nAzLooks>
      <outputIntensity>true</outputIntensity>
      <grSquarePixel>true</grSquarePixel>
    </parameters>
  </node>
  <node id="Speckle-Filter">
    <operator>Speckle-Filter</operator>
    <sources>
      <sourceProduct refid="Multilook"/>
    </sources>
    <parameters class="com.bc.ceres.binding.dom.XppDomElement">
      <sourceBands>Sigma0_VH,Sigma0_VV</sourceBands>
      <filter>Boxcar</filter>
      <filterSizeX>5</filterSizeX>
      <filterSizeY>5</filterSizeY>
      <dampingFactor>2</dampingFactor>
      <estimateENL>true</estimateENL>
      <enl>1.0</enl>
      <numLooksStr>1</numLooksStr>
      <windowSize>7x7</windowSize>
      <targetWindowSizeStr>3x3</targetWindowSizeStr>
      <sigmaStr>0.9</sigmaStr>
      <anSize>50</anSize>
    </parameters>
  </node>
  <node id="Terrain-Correction">
    <operator>Terrain-Correction</operator>
    <sources>
      <sourceProduct refid="Speckle-Filter"/>
    </sources>
    <parameters class="com.bc.ceres.binding.dom.XppDomElement">
      <sourceBands>Sigma0_VH,Sigma0_VV</sourceBands>
      <demName>SRTM 3Sec</demName>
      <externalDEMFile/>
      <externalDEMNoDataValue>0.0</externalDEMNoDataValue>
      <externalDEMApplyEGM>true</externalDEMApplyEGM>
      <demResamplingMethod>BILINEAR_INTERPOLATION</demResamplingMethod>
      <imgResamplingMethod>BILINEAR_INTERPOLATION</imgResamplingMethod>
      <pixelSpacingInMeter>10.0</pixelSpacingInMeter>
      <pixelSpacingInDegree>8.983152841195215E-5</pixelSpacingInDegree>
      <mapProjection>GEOGCS[&quot;WGS84(DD)&quot;, &#xd;
  DATUM[&quot;WGS84&quot;, &#xd;
    SPHEROID[&quot;WGS84&quot;, 6378137.0, 298.257223563]], &#xd;
  PRIMEM[&quot;Greenwich&quot;, 0.0], &#xd;
  UNIT[&quot;degree&quot;, 0.017453292519943295], &#xd;
  AXIS[&quot;Geodetic longitude&quot;, EAST], &#xd;
  AXIS[&quot;Geodetic latitude&quot;, NORTH]]</mapProjection>
      <alignToStandardGrid>false</alignToStandardGrid>
      <standardGridOriginX>0.0</standardGridOriginX>
      <standardGridOriginY>0.0</standardGridOriginY>
      <nodataValueAtSea>true</nodataValueAtSea>
      <saveDEM>false</saveDEM>
      <saveLatLon>false</saveLatLon>
      <saveIncidenceAngleFromEllipsoid>false</saveIncidenceAngleFromEllipsoid>
      <saveLocalIncidenceAngle>false</saveLocalIncidenceAngle>
      <saveProjectedLocalIncidenceAngle>false</saveProjectedLocalIncidenceAngle>
      <saveSelectedSourceBand>true</saveSelectedSourceBand>
      <outputComplex>false</outputComplex>
      <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="LinearToFromdB">
    <operator>LinearToFromdB</operator>
    <sources>
      <sourceProduct refid="Terrain-Correction"/>
    </sources>
    <parameters class="com.bc.ceres.binding.dom.XppDomElement">
      <sourceBands>Sigma0_VH,Sigma0_VV</sourceBands>
    </parameters>
  </node>
  <applicationData id="Presentation">
    <Description/>
    <node id="Read">
            <displayPosition x="9.0" y="9.0"/>
    </node>
    <node id="Calibration">
      <displayPosition x="45.0" y="114.0"/>
    </node>
    <node id="Multilook">
      <displayPosition x="145.0" y="192.0"/>
    </node>
    <node id="Speckle-Filter">
      <displayPosition x="240.0" y="228.0"/>
    </node>
    <node id="Terrain-Correction">
      <displayPosition x="339.0" y="275.0"/>
    </node>
    <node id="LinearToFromdB">
      <displayPosition x="493.0" y="326.0"/>
    </node>
  </applicationData>
</graph>

and i am left with the following reoccurring error message:

It shows the error occurs when it is retrieving the elevation data (SRTM3Sec)

If it helps, this is the command i run from the SNAP Command-Line:

gpt 'C:\Path_to_Graph_Xml.xml' -Pfile=C:\Path_to_Sentinel_Image.SAFE\manifest.safe -t C:\Output_path\Output_name

Initially i thought it was a Proxy issue, but this is not the case. Has anyone experienced the same issue, and if so, how has it been resolved?

Answer 1

When using the Terrain-Correction tool it will attempt to download the corresponding SRTM 3Sec DEM tile for your product. If it's timing out during this download you can manually download the DEM tile zip file and put it in your snap user folder /.snap/auxdata/dem/SRTM 3Sec (or C:\Users\username\.snap\auxdata\dem\SRTM 3Sec on Windows). Tiles can be downloaded from https://dwtkns.com/srtm/