Dear members,

I'm sorry for my recurring question. But I'm doing my first steps in satellite imaging and I have several questions:
1. In some protocols about creation of MODIS true-color images I found information that for Red band I supposed to use nLw_667, for Green nLw_551, for Blue nLw_488. But in L1A product I found EV_667, EV_488, but no 551, just EV_531 and EV_547. How I should understand, EV is the same as nLw? Or what kind of bands should I use?
2. How should I choose slopes and intercepts?
I was trying to perform it with Unix commands as it is explained in this forum, but I stuck under the command "make true-color PPM file".

Thank you for the answers
Diana

EV is 'earth view' 
551nm was renamed to 547 in order to correct a long standing mis-reporting of the wavelength

SeaDAS distributes two programs for producing true color images, l1brsgen (for satellite coordinates - i.e. not map projected) or l1mapgen for a Plate Carre projected  true color image.  The programs output PPM formatted image files (although, l1brsgen outputs an HDF file by default).  If you use the programs, you need not worry about the details of which bands to use or what scaling to apply.

Regards,

Sean

Usage: l1brsgen argument-list

The argument-list is a set of keyword=value pairs. The arguments can
be specified on the commandline, or put into a parameter file, or the
two methods can be used together, with commandline over-riding.

The list of valid keywords follows:

   par=input parameter file

   ifile=input L1 file name
   geofile=input L1 geolocation file name (MODIS only)
   ofile=output file name

   spixl=start pixel number (default=1)
   epixl=end pixel number (default=the last pixel)
   sline=start line number (default=1)
   eline=end line number (default=the last line)
   subsamp=subsampling interval (default=10)
   resolution=define the processing resolution (MODIS only)
       -1: standard ocean 1km processing, limited band set
     1000: 1km resolution including aggregated 250 and 500m land bands.
      500: 500m resolution including aggregated 250 land bands and replication
          for lower resolution bands.
      250: 250m resolution with replication for lower resolution bands.

   outmode=defines output format (default=0)
       0 = 8bit HDF
       1 = 24bit HDF
       2 = PPM (portable pixmap)
       3 = flat binary

   rgb=bands to use for red, green and blue (default=sensor specific)
   atmocor=use surface reflectance (default=0, use top of atmosphere reflectance)
   datamin=minumum reflectance for scaling (default=0.01)
   datamax=minimum reflectance for scaling (default=0.9)
   stype=set scaling type (default=0)
       0 = log scaled between datamin and datmax
       1 = linearly scaled between datamin and datmax

The default band combination produces a "true-color" image
Other combinations may be chosen with the "rgb=" option.  The expected
argument to this option is a comma separated string of wavelengths that specifies
the desired bands in red-green-blue order.  For example, to produce a false
color SeaWiFS output image using 865, 670 and 555 nm
as the red, green, and blue values respectively, the option would be specified
as "rgb=865,670,555".



Usage: l1mapgen argument-list

The argument-list is a set of keyword=value pairs. The arguments can
be specified on the commandline, or put into a parameter file, or the
two methods can be used together, with commandline over-riding.

The list of valid keywords follows:

   par=input parameter file

   ifile=input L1 file name
   geofile=input L1 geolocation file name (MODIS only)
   ofile=output file name
   resolution=define the processing resolution (MODIS only)
       -1: standard ocean 1km processing, limited band set
     1000: 1km resolution including aggregated 250 and 500m land bands.
      500: 500m resolution including aggregated 250 land bands and replication
          for lower resolution bands.
      250: 250m resolution with replication for lower resolution bands.

   north=northern limit for output image (-90.0 to 90.0)
   south=southern limit for output image (-90.0 to 90.0)
   east=eastern limit for output image (-180.0 to 180.0)
   west=western limit for output image (-180.0 to 180.0)
   width=width of output image in pixels (default=600)
   threshold (0.1 [default])
   rgb=bands to use for red, green and blue (default=sensor specific)
   atmocor=use surface reflectance (default=0, use top of atmosphere reflectance)
   datamin=minumum reflectance for scaling (default=0.01)
   datamax=maximum reflectance for scaling (default=0.9
   stype=set scaling type (default=0)
       0 = log scaled between datamin and datmax
       1 = linearly scaled between datamin and datmax

This program produces a PPM-formatted output image rendered in a
Plate Carree projection.

The default band combination produces a "true-color" image
Other combinations may be chosen with the "rgb=" option.  The expected
argument to this option is a comma separated string of wavelengths that specifies
the desired bands in red-green-blue order.  For example, to produce a false
color SeaWiFS output image using 865, 670 and 555 nm
as the red, green, and blue values respectively, the option would be specified
as "rgb=865,670,555".

Ana,

You'll get the message: "Error opening geolocation file" if you did not provide the geolocation file as input.

You must specify the geolocation file, e.g.:

l1mapgen ifile=A2002234115000.L1B_LAC geofile=A2002234115000.GEO ofile=A2002234115000_TC.ppm resolution=250

Also, resolution selection is done via the resolution parameter.  We have eliminated the use of the 250 (QKM) and 500m (HKM) L1B files
as valid input options.

Sean

Sorry, it works!
Thanks

Ana