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Question:

Why are there two thermal band 6 files with the Landsat 7 data I downloaded?

Answer:

The Landsat 7 thermal band 6 data files refer to the gain settings of which the band is acquired. Since band 6 is acquired in both high and low gain, the gain settings are provided as two separate band files. Additional details about Gain States can be found in the Landsat 7 Data Users Handbook.

FILE_NAME_BAND_6_VCID_1 (band 61 or 6L) provides an expanded dynamic range and lower radiometric resolution (sensitivity), with less saturation at high Digital Number (DN) values.

FILE_NAME_BAND_6_VCID_2 (band 62 or 6H) has higher radiometric resolution (sensitivity), although it has a more restricted dynamic range.