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[McIDAS #POV-692867]: Area to netcdf

Hi Cory,

> This is kind of a netcdf question too, but I was looking at the sample
> McIDAS file that you have on 
> http://www.unidata.ucar.edu/software/netcdf/examples/files.html.
> It is called IMAGE0002.nc and looks very similar to a file I was given for
> a project I'm on.  The data are unitless so I'm wondering how I can get the
> satellite values from a file like this or if that is even possible.

Without seeing your file or knowing how it was created, I can not say if it
would be possible to extract calibrated values from what is stored.  If, on the
other hand, your netCDF image file was created by McIDAS, the values in it
should represent brightnesses (values from 0 - 255), or it could contain
calibrated values (like temperature).  If your netCDF was created by McIDAS
and if it is for an IR channel from GOES and if it contains brightnesses, you
can use the "standard" two-slope brightness<->temperature relationship for

Temp[K]     Brigtness[count]
-----       ------
 163           255
 241.9999      177
 242           176
 330           0

> I have very little knowledge of McIDAS but I was told that my file was 
> converted
> from an area file into a netcdf "image" type file.  How does that differ from 
> a
> "grid" or "point" file?

A netCDF image file created by McIDAS has values as I indicated above.  A GRID
file has values on a regular lattice; a POINT file has information for 
locations which may not be on a regular lattice.

> I can't seem to find much information on those file types.

You can find more information on McIDAS data files in:

Unidata HomePage



      Documentation and Training

Unidata McIDAS Users Guide

SSEC's McIDAS programmer's manual

> 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.

This sounds more like raw counts

> My only theory at this point is that those value represent an image
> color at a given point and have nothing to do with the actual satellite data.

I don't think so (but I could be wrong).

> I would appreciate any help you can provide.  Thank you.

Can you provide a file for me to grab so I could take a look?  If yes,
I would greatly appreciate you putting the file out on an FTP server
that I can access.  If it is a large file, please do not send it as
an email attachment.


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

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