I will be using GRASS on OSX to classify Landsat 8 geotiff images to create a vegetation map for a study site that happens to fall over 2 separate Landsat scenes.

I seek advice about which route to take and I'm not able to find any other information about this elsewhere:

1.) Should I FIRST find a way to combine the 2 scenes together (which presumably would require combining the 2 scenes of each channel separately - would that be right?), and then cut out the small area covered by my study site and THEN start the classification process.


2.) Should I conduct image classification on the 2 adjacent Landsat scenes separately and then combine right at the end? (Although I'm worried this will take much longer, not to mention use up more memory - the study site I am working with is only 1400 km2)


Anytime imagery was acquired at different time periods you will always need to do atmospheric correction. In GRASS you can use the i.atcorr tool to perform the atmospheric correction.

Once the scenes are atmospherically corrected, you can proceed with your image classification knowing that atmospheric effects such as Rayleigh scattering will be minimized.

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