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[McIDAS #POV-692867]: Area to netcdf



Hi Cory,

re:
> I put my sample file at ftp://ftp.rap.ucar.edu/pub/cwolff/NETCDF0001.nc
> Please let me know if you can't get it.

Got it, thanks.

re:
> That file was created using
> McIDAS.

Yup, one of the global attributes is 'auditTrail' which contains the McIDAS
IMGCOPY invocation used to create the image:

auditTrail =
 "11238 140335 IMGCOPY AGOES12/ALL.79 CASES/NETCDFGRID.1 DAY=11138 BAND=4 
SIZE=SAME GAU=5"

Furthermore, the sensorID = 78 shows that it is a GOES-12 imager image;
BAND=4 for GOES-12 is the 10.7 um channel; it is the same size (same
number of lines and elements) as the original image; and the images is
for 21:58:00 for 2011138 (May 18, 2011).

re:
> It looks very similar to the example file that you have on the
> website I mentioned in my initial post.  That example file has a minimum
> value of 0 and a maximum of 23328 but is called IMAGE0002.nc.  What you
> said about values from 0 - 255 makes sense but it appears that these
> files have much larger ranges.

The values in your file are each represented by 4-byte integers (dataWidth=4,
lineRes=4, elemRes=4).

The McIDAS HELP for IMGCOPY indicates that one should include the UNIT=
keyword when creating output netCDF files.  However, it also indicates
that if UNIT= is not specified (which it is not for your image), then
the primary calibration unit in source image will be used.  The primary
calibration unit in the image from which your image was created is most
likely RAW.

re:
> The file I have contains GOES 10.7 micron data but the values are all
> between 400 and 20000, which doesn't make sense to me.

I believe that the values stored in your image are the raw counts, and
that those counts have been shifted by 5 bits.  Unshifted RAW counts should
range from 0-1024.  Shifting them by 5 bits will change the range to
0-32768.  Dividing by 32 (2**5) should return the stored values back
to RAW counts.

Next, is how to convert the counts to radiance or temperature.  The following
link should be helpful in this:

Conversion of GVAR Infrared Data to Scene Radiance or Temperature
http://www.oso.noaa.gov/goes/goes-calibration/gvar-conversion.htm

Question:

- does the person/group who created your netCDF image file still
  have the original image?

  If yes, it would be easy using McIDAS to output an image that
  has values of radiance or temperature.

Please let me know if the above helped in any way...

Cheers,

Tom
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Ticket Details
===================
Ticket ID: POV-692867
Department: Support McIDAS
Priority: Normal
Status: Closed


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