Re: [cf-satellite] very rough draft of way to represent band

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On Jul 26, 2011, at 3:05 PM, John Caron wrote:

> On 7/26/2011 12:26 PM, Tom Rink wrote:
>> Upendra,
>> 
>> On 7/26/11 1:07 PM, Upendra Dadi wrote:
>>> Jim,
>>>   Could you please clarify how to represent data which contain bands 
>>> with multiple spatial resolutions using you scheme? I am thinking of 
>>> MODIS data:
>>> 
>>> http://en.wikipedia.org/wiki/Moderate-Resolution_Imaging_Spectroradiometer#MODIS_Bands
>>> As you can see, not all the bands have same spatial resolution (or 
>>> spatial dimensions), even though all of them have same units. Could 
>>> we even store all the bands in the same variable?
>> 
>> I think multiple resolutions in same variable would be difficult and 
>> impracticable,
>> the CF conventions for defining Projections, analytic or lat/lon, 
>> don't work like
>> this.  You'd probably have to define another dimension to index the 
>> different
>> resolutions for the data, lon and lat variables.  I would think this 
>> would be
>> pretty messy.
>> 
>> Tom
> 
> Correct, you need seperate variables for different resolutions. However, 
> theres no problem with having multiple coordinate systems in the same 
> file. So if you chose, you would create multiple groups of variables, 
> each group with their own coordinates.
> 

The HDF files for MODIS currently do separate the resolutions into different 
variables.  However, MODIS presents some other issues, such as having both 
low-gain and high-gain versions of the same band in the same 3D variable.  
Currently, they handle this inside the file by calling one band "13" and 
another "13.5", but this is a bit opaque.  I can never remember which is low 
and which is high.

There are also two bands (21 and 22) with different band "numbers" but the same 
bandwidth (different Spectral Reflectance).

I have been mentally struggling to understand how these would fit in the 
various "band" dimension/coordinate proposals.

Would it be useful to begin a set of examples for actual instruments so that 
the less CF-savvy amongst us could see the implications?
--
Dr. Christopher Lynnes     NASA/GSFC, Code 610.2    phone: 301-614-5185




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