Unzipping Level 3 files

The level 3b (mapped) hyperspectral files are delivered as zipped files to save space. Depending on the orientation of the flightline the zipped files are often significantly smaller than the unzipped bil files. This is because areas outside the flightline with no data can be compressed well but ENVI files are uncompressed so areas with no data take up the same amount of space as those areas with data. If the lines are flown diagonal there are a lot of pixels in the image which contain no data.

Large file sizes reported in Windows

The uncompressed file size is sometimes reported incorrectly in Windows as being much larger than it actually is, preventing the file from being unzipped to to available free space.

For example in the screenshot below Windows reports the unzipped filesize as 734 PB rather than the actual size of 7.66 GB, as reported in 'unzipped_filesize.csv'. It is therefore recommended to use another unzipping program for Windows such as ​7-zip or to unzip on a Linux machine.