20090828: MODIS on Aqua question (cont.)

Hi Sheila,

re:
> I would like to use chlorophyll a concentration data from MODIS on  
> Aqua at 0.05 km resolution from the site
> http://las.pfeg.noaa.gov/oceanWatch/oceanwatch_safari.php?dsetinit=MH1&hab=0&varinit=chla&currentvarindex=0&compinit=mday&reginit=c&modeinit=u#
>  
> However, I have been unable to determine from the metadata the  
> exact geolocation of the data. For instance, if the ASCII output  
> gives me latitude, longitude, and chla, would this data point be  
> centered on the given latitude or longitude or offset to say the  
> southeast  corner of the described grid cell.
>
> In advance, thank you for your help.

I assume that you mean you want to use the 0.05 degree (which is
nominally 5.55 km) MODIS on Aqua Chlorophyll-A data (8 day or monthly
composite...

I don't believe that there is any way to know apriori which portion of
the grid cell the location represents as this will be a function of the
way the data was processed from the original satellite scans.  Since
the original pass data has been remapped into a LatxLon projection, I
would assert that treating the location as the center of the grid cell
is as valid as anywhere else.

You may be able to get a more definitive answer from the person cited
as contributing the data (the person listed in the Data courtesy of:
reference on the top left portion of the page you included a URL for):

G. Feldman - NASA GSFC

A Google search for G. Feldman got me this reference:

http://www1.whoi.edu/mzweb/ssc-all.html

Gene C. Feldman
    NASA/GSFC 
    Code 970.2, Bldg. 28, Rm. W161B 
    Goddard Space Flight Center 
    Greenbelt, MD 20771 
    Tel: 301 286-9428 
    Fax: 301 286-1775 
    E-mail: address@hidden 

I suggest contacting him for additional information about this dataset.

Cheers,

Tom Yoksas
Unidata User Support

Dan Holloway wrote:
>
>         Sheila,
>
>         One place to start would be to look at the metadata in the  
>datafile, you can find that thru the LAS interface after selecting the  
>data/variable of interest and then following the OPeNDAP - info link.
>
>         That information shows that the data was written using the  
>CF-1.0 convention.  The metadata unfortunately only states the  
>coordinate system and grid spacing and not the cell methods  
>specifically, so you'd need to cross-reference the CF-1.0 guide to  
>determine in cases like this whether the lat/lon for each grid cell  
>represents the location of the center of the cell.  Typically that  
>would be my assumption if the metadata did not explicitly state  
>otherwise.
>
>        Another venue for your question could be the CF-1.0 list,  
>though I suspect 'support@unidata' will answer your question shortly.
>
>              Dan
>
>>
>> Sheila
>>
>> -- 
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~
>> Sheila Walsh
>> Center for Marine Biodiversity and Conservation
>> Scripps Institution of Oceanography
>> Hubbs Hall, Rm 2175
>> 8750 Biological Grade
>> La Jolla, CA 92037
>> Phone: (858) 344-7182
>> Fax: (858) 822-1267
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~
>> _______________________________________________
>> Support mailing list
>> address@hidden
>> http://mailman.opendap.org/mailman/listinfo/support

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