What Happens When Reading MODIS Level 1 Data

Posted by GIS talk On Thursday, June 16, 2011
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This is what happens when reading MODIS Level 1 data. I took this solution from the ENVI help and inforest.gr forum.

* MODIS: Reads MODISModerate Resolution Imaging Spectroradiometer; a NASA EOS sensor aboard the Aqua and Terra satellites. Level 1B, 2, 3, or 4 files (MODIS products MOD02-MOD44 and MYD02-MYD44). The gainIn ENVI, a value that is multiplied by the pixel value to scale it into physically meaningful units of radiance: radiance = DN * gain + offset and offsetIn the context of remote sensing: A correction value added
to or subtracted from every pixel in an image, typically by using image arithmetic (Band Math in ENVI). A variable added to the gain in a regression equation for sensor calibration. The number of bytes of embedded header information present in the file (ENVI skips these bytes when reading the file).

Values are also extracted from the HDF metadata. These values are automatically applied when ENVI converts the 16-bit data in the input file to calibrated floating-point data. The resulting emissive and reflectance data are unitless. The units of the radiance data are W/m2/m/sr. You can disable applying gains and offsets information with the Auto-Correct ASTER/MODIS preference.

Note: For EOS MODIS Level 1B files, values greater than 32767 (which indicate invalid data) are replaced by -1 when applying the gains and offsets. The data ignore value in the ENVI header is also set to -1.

To open MODIS products M*D08*, M*D27HV, M*D27W, M*D43B1, M*D43B1C, M*D43B2, M*D43B2C, M*D43B3, M*D43B3C, M*D43C2, M*DATML2, use File > Open External File > Generic Formats > HDF.


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