Re: Problems reading QuikSCAT hdf file

Hi Andrea

I did not find any attached script. I did not have any problem.

I downloaded and unzipped

ncl 0> f = addfile ("QS_XWGRD3_2000001.20070371658.hdf", "r")

ncl 1> q = f->asc_time_frac

ncl 2> print(q)

ncl 3> print("min(q)="+min(q)) ; ===> 0

ncl 4> print("max(q)="+max(q)) ; ===> 28078

ncl 6> print(q*q_at_scale_factor) ; q_at_scale_factor ===> 2e-05

ncl 7> qq = q*q_at_scale_factor

ncl 8> print("min(qq)="+min(qq)) ; 0

ncl 9> print("max(qq)="+max(qq)) ; 0.56156

=========================================================
Please note for future reference.

netCDF: The COARDS and CF convention for scale_factor and add_offset

                  xFloat = xShort*scale_factor + add_offset

                 See:
http://www.cgd.ucar.edu/cms/eaton/netcdf/CF-20010629.htm#pack

                 NCL:
http://www.ncl.ucar.edu/Document/Functions/Contributed/short2flt.shtml

HDF: The NASA/HDF conventions seems to be:

                  xFloat = (xShort- add_offset)*scale_factor

                  NCL:
http://www.ncl.ucar.edu/Document/Functions/Contributed/short2flt_hdf.shtml

Andrea Hahmann wrote:
> Hi!
>
> I am having some troubles reading a QuikSCAT hdf file using ncl. I
> read a couple of "16-bit unsigned integers" fields from an HDF4 file:
> "asc_avg_wind_speed" and "asc_time_frac". asc_avg_wind_speed has all
> positive values between 0. and 50., as it should, being wind speed.
> But when I read asc_time_frac it contains both positive and negative
> values. According to the "guide document" this field should be
> between 0. and 1.
>
> My script is attached. Files can be obtained from:
> ftp://podaac.jpl.nasa.gov/pub/ocean_wind/quikscat/L3/data/2000/
>
> Any help will be appreciated!
> Thanks,
> Andrea
>

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Received on Mon May 05 2008 - 15:31:22 MDT