Remote Sensing tips and tricks

Pansharpening with a handy GDAL tool

I found this set of GDAL tools recently which I’ve found to be really useful. I thought it would be good to show some of these in action.

gdal_landsat_pansharp is one of these tools and allows easy and effective pansharpening of Landsat ETM images (I haven’t tried it on images from other sensors). It’s handy as it allows quick pansharpening even if you haven’t composited bands from a freshly downloaded Landsat image, for example:

gdal_landsat_pansharp -rgb band3.tif -rgb band2.tif -rgb band1.tif \
    -lum band4.tif 0.52 -lum band3.tif 0.23 -lum landsat2.tif 0.25 \
    -pan band8.tif -ndv 0 -o outimage.tif

The -rgb option is used for each input band, the -lum option is used to simulate a low resolution panchromatic band, each band requires a weighting (0-1). -pan is needed to select the panchromatic band (band 8 for Landsat ETM), -ndv to specify a no data value and finally -o to give an output filename.

Alternatively, if you already have a true colour (bands 3, 2, 1) composite:

gdal_landsat_pansharp -rgb rgbimage.tif \
    -lum band2.tif 0.25 -lum band3.tif 0.23 -lum landsat4.tif 0.52 \
    -pan band8.tif -ndv 0 -o outimage.tif

It also works nicely to quickly pansharpen false colour composites, using the same -lum settings. For example, for a 432 composite:

gdal_landsat_pansharp -rgb band4.tif -rgb band3.tif -rgb band2.tif \
    -lum band4.tif 0.52 -lum band3.tif 0.23 -lum landsat2.tif 0.25 \
    -pan band8.tif -ndv 0 -o outimage.tif

A quick read of the tools wiki page points us to this paper in order to derive the weightings for the low resolution simulated image. I also refer you to the wiki page for further information on the maths behind the technique.

Here’s some results:

A true colour (bands 3, 2, 1) image of Abisko National Park in Sweden, 30m spatial resolution

Landsat RGB image

The panchromatic band, 15m spatial resolution

Landsat panchromatic image

And the pansharpened image

Landsat pansharpened RGB image

Finally, a false colour (bands 4, 3, 2) pansharpened image

Landsat pansharpened FCC image Landsat scene ID: LE71980121999227SGS00 date: 15/08/1999

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