Linear opacity transform

The following example XML shows a reanalysis of sea surface temperature as a colour map. The analysis error is represented by a linear opacity transform. The more uncertain an area is the more transparent it appears. The opacity transform only applies to the layer.

<?xml version="1.0" encoding="ISO-8859-1"?>
<StyledLayerDescriptor version="1.1.0" xsi:schemaLocation="http://www.opengis.net/sld
StyledLayerDescriptor.xsd" xmlns="http://www.opengis.net/sld" xmlns:ogc="http://www.opengis.net/ogc" xmlns:se="http://www.opengis.net/se" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:resc="http://www.resc.reading.ac.uk">
  <NamedLayer>
    <se:Name>OSTIA/analysed_sst</se:Name>
    <UserStyle>
      <se:Name>Red-blue palette showing SST</se:Name>
      <se:CoverageStyle>
        <se:Rule>
          <se:RasterSymbolizer>
            <resc:OpacityTransform>
              <se:Interpolate fallbackValue="1.0">
                <se:LookupValue>OSTIA/analysis_error</se:LookupValue>
                <se:InterpolationPoint>
                  <se:Data>0.0</se:Data>
                  <se:Value>1.0</se:Value>
                </se:InterpolationPoint>
                <se:InterpolationPoint>
                  <se:Data>2.5</se:Data>
                  <se:Value>0.0</se:Value>
                </se:InterpolationPoint>
              </se:Interpolate>
            </resc:OpacityTransform>
            <se:ColorMap>
              <resc:Segment fallbackValue="transparent">
                <se:LookupValue>Rasterdata</se:LookupValue>
                <resc:BelowMinValue>extend</resc:BelowMinValue>
                <resc:ValueList>
                  <se:Name>div-BuRd2</se:Name>
                </resc:ValueList>
                <resc:AboveMaxValue>extend</resc:AboveMaxValue>
                <resc:Range>
                  <resc:Minimum>270.0</resc:Minimum>
                  <resc:Maximum>310.0</resc:Maximum>
                  <resc:Spacing>linear</resc:Spacing>
                </resc:Range>
                <resc:NumberOfSegments>250</resc:NumberOfSegments>
              </resc:Segment>
            </se:ColorMap>
          </se:RasterSymbolizer>
        </se:Rule>
      </se:CoverageStyle>
    </UserStyle>
  </NamedLayer>
</StyledLayerDescriptor>

The resulting output image and its legend are shown below: