[GRASS-user] any tips/advice for workign with MODIS data?

[Ivan Shmakov]

>>>>> mhall at berkeley.edu writes:

 > Hi,

 > I've been trying for 2 or 3 days now to get some nice looking images
 > out of MODIS TERRA/AQUA 500m land products (ie 7 bands).  I've seen
 > the screen shots and see the quality of the images that can be
 > obtained--but at best I some very faded/obscured images.  I've loaded
 > the data into GRASS using HEGTool to convert the HDF file to separate
 > bands.  I've then loaded that and tired combining Bands 143 (RGB)
 > using r.composite.  I've tried using r.colors' standard grey scale
 > and grey.eq before making the composite image.  My values for the
 > images ranges from -28672

        I guess it may be a fill (``null'') value of the source data
        set.  Try to eliminate it with, e. g.:

$ r.null map=BAND setnull=-28672

        and check the range afterwards.  You may eliminate HEG's own
        fill value as well with $ ... setnull=0.

 > to approx. 9000 .

 > I've tried rescaling the data to get it between 0 and 255, and the
 > resulting image quality is equally bad.

 > Any suggestions on what to try next?

        In the ``Tutorial on Producing MODIS True Color Images'' [1],
        authors suggest a table to be used for translating MODIS
        reflectances into RGB values.  You may apply this table to each
        of the bands (via $ r.colors ... color=rules) prior to using
        `r.composite'.  IIRC, the result was about of the same quality
        as the example in the tutorual when I've last tried that.

 > I've checked the data out in other programs that are in other
 > research groups and the data makes nice RGB images--so nothing wrong
 > with the source data.

PS.  May be a wiki [2] page for MODIS-related issues?

[1] ftp://ftp.ssec.wisc.edu/pub/IMAPP/MODIS/TrueColor/
[2] http://grass.gdf-hannover.de/wiki/