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
