Re: plotting QuikSCAT L2B

From: David Brown <dbrown_at_nyahnyahspammersnyahnyah>
Date: Tue Jul 12 2011 - 17:33:25 MDT

Hi Paula,
Just to add a bit to what Dennis wrote. I downloaded a sample of data similar to what you describe from http://podaac-www.jpl.nasa.gov/dataset/QSCAT_LEVEL_2B_COMP_12?ids=Measurement&values=Ocean%20Winds. It has the same variable and dimension names. The data and coordinates in this file are stored as shorts. The latitude is called wvc_lat and the longitude is wvc_lon. The values need to be scaled by 0.01 to give normal lat/lon values. Also non-valid locations are given the value '0'. This seems to be true for the data as well.

For plotting the important thing is to set trGridType to "TriangularMesh"; the default transformation methods do not handle missing values in the coordinate arrays.
 -dave

On Jul 12, 2011, at 2:57 PM, Dennis Shea wrote:

> You do not have to regrid the data.
>
> http://www.ncl.ucar.edu/Applications/HDF.shtml
> See examples 4, 5
>
> v = f->v
>
> lat2d = f->Latitude
> lon2d = f->Longitude
>
> v@lon2d = lon2d
> v@lat2d = lat2d
>
> Draw the map and plot
>
>
>
> On 07/12/2011 02:51 PM, Paula Doubrawa Moreira wrote:
>> Hi, all -
>>
>> I am trying to plot QuikSCAT L2B winds. These are swath (orbit) files,
>> one orbital revolution per file (not gridded!).
>>
>> Since it is not gridded, so I'm having trouble *assigning coordinate
>> variables to plot it over a map*. I can't find much help on the QuikSCAT
>> manual about how to interpret the variable dimensions in the file, so
>> I'm writing for some advice.
>>
>> The variables look like this:
>>
>> *Variable: v*
>> *Type: float*
>> *Total Size: 1974784 bytes*
>> * 493696 values*
>> *Number of Dimensions: 2*
>> *Dimensions and sizes:[Wind_Vector_Cell_Row | 3248] x [Wind_Vector_Cell
>> | 152]*
>> *Coordinates: *
>> *Number Of Attributes: 9*
>> * _FillValue :1e+20*
>> * long_name :wind_speed_selection*
>> * units :m/s*
>> * SDS_type :Single*
>> * scale_factor_err : 0*
>> * add_offset_err : 0*
>> * calibrated_nt :1*
>> * hdf_name :wind_speed_selection*
>> * valid_range :( 0, 50 )*
>>
>> 3248 is number of rows and 152 is number of columns, so I have created
>> regular lat/lon coordinates using these numbers and the functions
>> latGlobeF and lonGlobeF.
>>
>> I successfully plotted the data over a map, but I don't think this is
>> correct. I have checked the values for the assigned lats/lons for some
>> points and they don't match to the original file. Creating a regular
>> grid may not be the best approach. Any hints?
>>
>> Thanks a lot!
>> Paula
>>
>> --
>> *Paula Doubrawa Moreira*/
>> /Graduate Student - Research Assistant
>> International Arctic Research Center
>> University of Alaska Fairbanks
>>
>>
>>
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>
>
> --
> ======================================================
> Dennis J. Shea tel: 303-497-1361 |
> P.O. Box 3000 fax: 303-497-1333 |
> Climate Analysis Section |
> Climate & Global Dynamics Div. |
> National Center for Atmospheric Research |
> Boulder, CO 80307 |
> USA email: shea 'at' ucar.edu |
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Received on Tue Jul 12 17:33:35 2011

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