How do I use the MODIS Reprojection Tool (MRT) with MODIS Level-3 Snow Cover Products?

There are several things to consider when using MRT with MODIS Level-3 Snow Cover Products. The following questions and answers should guide you through using MRT with MODIS Level-3 Snow Cover Products.

  1. Will the data be resampled if the original (native) projection is changed?

    Yes, the data will be resampled in some way. For example, nearest neighbor, bilinear, cubic, etc.
  2. When inputting into MRT, why are the native data that have a sinusoidal projection and WGS84 datum being forced into NODATUM and thus a spherical projection with radius 6371007.181 m?

    MRT does not recognize that the datum spheroid, such ast the WGS84 ellipsoid, is different from the sinusoidal projection spheroid. A sphere of radius 6371007.181 m.
  3. How can you create a GeoTIFF out of MODIS Level-3 Sinusoidal data using MRT?

    Change the projection from sinusoidal to UTM with a WGS84 datum. You will end up with gridded data for which both the geographic coordinate system and the projected coordinate system are defined in terms of the WGS84 ellipsoid. You can then use MRT to create a valid GeoTIFF that all software packages should be able to interpret correctly.
  4. If the HDF-EOS data files were not reprojected to UTM WGS84 prior to creating the GeoTIFF, is it possible to reproject the GeoTIFF output file from sinusoidal NODATUM format to sinusoidal WGS84 datum?

    No. MRT can not reproject data into an ellipsoid sinusoidal projection. Thus, it can not create a sinusoidal GeoTIFF that refers to the WGS84 datum. Any particular GeoTIFF can specify one and only one spheroid to be used for both the geographical coordinate system and the projected coordinate system.