Frequently Asked Questions

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Question:
What are the differences between the earlier Thompson Ramo Woolridge (TRW) products and the new USGS Hyperion products?

Answer:
The USGS has created a new Hyperion product format. There are packaging and data differenced between the 2 sets of code explained below:

The USGS products are packaged in Hierarchical Data Format (HDF) with the datasets being image data, spectral center wavelengths, spectral bandwidths, gain coefficients and a flag mask. The previous TRW was image data with separate files for other ancillary details. The file naming conventions are different as well; the USGS utilizes an entitiy ID target versus the data capture time utilized by TRW.

Comparisons of the data show that the USGS products are very comparable to the TRW products. For most bands the radiometric differences are within 1%. Some differences to note are:
      1) Dead detectors are not corrected or interpolated in USGS products, thus
           vertical stripes will be visible where these known dead detectors exist;
       2) Radiometric differences may be greater because of the known dead
           detectors not being interpolated in USGS products.
       3) An additional scan line in the USGS products accommodates for the
            SWIR shift
       4) The first scan line in USGS products is not corrected for echo,
            since echo correction requires information from the preceding line;
       5) For the spectral center wavelengths, USGS products represent means
           across all detectors for each band while the TRW products represented the wavelength at field of view pixel 128.