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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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