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19990423: 19990416: GOES-7 Question

Terence,

The image you mention below, which I downloaded, is a GOES-7 image that
has the "raw" bit set in the AREA file header- however the values appear to
be in the range of a calibrated GOES-7 Image.

Gempak has a table that specifies the expected range for values in an
image. The table that is distributed has expected raw values for IR in the 
range of 1280 to 18000....instead of the calibrated range of 0 to 255,
so what you likely see is all you values are down at the bottom end of the 
scale and all show up black.

The Gempak table you need to edit is $GEMTBL/sat/imgtyp.tbl. For
The GOES-7 IR image, change:

GOES7-RAW            IR         1280  18000     33    128      1 ir_sab.tbl
to
GOES7-RAW            IR            0    255     33    128      1 lingray.tbl

The 0-255 range is the stretch over which the range of values in the
image is mapped to the colors in the color table. I set the default
colortable to lingray.tbl which is probably a better default.
Similarly, the VIS and WV ranges will probably be in the 0-255 range
as well for those entries in the table.

Once you have modified the table, you should be able to view the image
in the normal colortable range, eg:
 
 MAP      = 3
 GAREA    = dset
 PROJ     = sat
 SATFIL   = 199107280001.goes7ir
 RADFIL   =
 LATLON   = 0
 PANEL    = 0
 TITLE    = 6
 TEXT     = 1
 CLEAR    = YES
 DEVICE   = gf|goes7.gif
 LUTFIL   = default
 STNPLT   =
 GEMPAK-GPMAP>r

I placed the output above at:
http://www.unidata.ucar.edu/staff/chiz/gifs/goes7.gif

Steve Chiswell
Unidata User Support



>From: Terence Kung <address@hidden>
>Organization: .
>Keywords: 199904231513.JAA20383

>Steve,
>
>Thanks for your reply. The satellite imagery I have was obtained from Dr. Luis
>Farfan of the U. of Arizona. We found that while the images can be displayed b
> y
>McIDAS, they cannot be displayed by gempak 5.4. I am really not too familiar
>with the format of the files. But if you could help me look into it, they are
>now located in a ftp area in cirrus.mit.edu. They are in the directory
>/pub/KUNG, and can be obtained by anonymous ftp. An eg. of the files I have is
>  
>199107280001.goes7ir. 
>
>Thanks.
>
>Terence
>