NetCDF Packed Byte data
Charles Seman
Charles.Seman at NOAA.GOV
Sat Nov 4 16:01:34 EST 2006
M. Mahakur,
Have you checked out this web site?
http://www.iges.org/grads/gadoc/descriptorfile.html#unpack
Not sure why 'sea_ice_fraction' is not displayed... 16 characters is
GrADS limit...
http://www.iges.org/grads/gadoc/descriptorfile.html#VARS
I hope this helps,
Chuck
M.Mahakur wrote:
> Respected GrADS users:
>
> How can I open the packed netcdf byte data (ncdumped headers of a single
> file I am pasting here)? I could display the variable 'sst_foundation'
> using sdfopen. I guess GrADS is taking care of off_set and scale_factor.
> But I could not do for the other variables (i.e.. analysis_error, bias,
> sea_ice_fraction and mask), which are packed bytes.
>
> Secondly, variable 'sea_ice_fraction' is getting truncated to
> 'sea_ice_fractio'!!
>
> Thanks in advance.
>
> With Regards,
>
> M. Mahakur
>
> ---------------------------------------------------
> ga-> q file
> File 1 : OSTIA Sea Surface Temperature Analysis
> Descriptor: 20060101-UKMO-L4UHfnd-GLOB-v01.nc
> Binary: 20060101-UKMO-L4UHfnd-GLOB-v01.nc
> Type = Gridded
> Xsize = 7200 Ysize = 3600 Zsize = 1 Tsize = 1
> Number of Variables = 5
> sst_foundation 0 -999 foundation sea surface temperature
> analysis_error 0 -999 error estimate from the analysis
> bias 0 -999 analysis error bias
> sea_ice_fractio 0 -999 sea ice fraction
> mask 0 -999 mask
>
>
> ---------Headers from ncdump------------------------------------
> netcdf 20060101-UKMO-L4UHfnd-GLOB-v01 {
> dimensions:
> lon = 7200 ;
> lat = 3600 ;
> time = 1 ;
> variables:
> int time(time) ;
> time:long_name = "reference time of sst field" ;
> time:units = "seconds since 1981-01-01 00:00:00" ;
> float lat(lat) ;
> lat:long_name = "latitude" ;
> lat:units = "degrees_north" ;
> float lon(lon) ;
> lon:long_name = "longitude" ;
> lon:units = "degrees_east" ;
> short sst_foundation(time, lat, lon) ;
> sst_foundation:long_name = "foundation sea surface
> temperature" ;
> sst_foundation:units = "kelvin" ;
> sst_foundation:_FillValue = -32768s ;
> sst_foundation:add_offset = 273.15f ;
> sst_foundation:scale_factor = 0.01f ;
> sst_foundation:valid_min = -32767s ;
> sst_foundation:valid_max = 32767s ;
> sst_foundation:standard_name = "sea_surface_temperature" ;
> byte analysis_error(time, lat, lon) ;
> analysis_error:long_name = "error estimate from the
> analysis" ;
> analysis_error:units = "kelvin" ;
> analysis_error:_FillValue = -128b ;
> analysis_error:add_offset = 0.f ;
> analysis_error:scale_factor = 0.05f ;
> analysis_error:valid_min = -127b ;
> analysis_error:valid_max = 127b ;
> byte bias(time, lat, lon) ;
> bias:long_name = "analysis error bias" ;
> bias:units = "kelvin" ;
> bias:_FillValue = -128b ;
> bias:add_offset = 0.f ;
> bias:scale_factor = 0.01f ;
> bias:valid_min = -127b ;
> bias:valid_max = 127b ;
> byte sea_ice_fraction(time, lat, lon) ;
> sea_ice_fraction:long_name = "sea ice fraction" ;
> sea_ice_fraction:units = "1" ;
> sea_ice_fraction:_FillValue = -128b ;
> sea_ice_fraction:add_offset = 0.f ;
> sea_ice_fraction:scale_factor = 0.01f ;
> sea_ice_fraction:valid_min = -127b ;
> sea_ice_fraction:valid_max = 127b ;
> sea_ice_fraction:standard_name = "sea_ice_area_fraction" ;
> sea_ice_fraction:comment = "Data derived from OSI-SAF
> sea ice product" ;
> byte mask(time, lat, lon) ;
> mask:long_name = "mask" ;
> mask:comment = "b0: 1=sea ; b1: 1=land ; b2: 1=lakes ;
> b3: 1=ice" ;
>
> // global attributes:
> :Conventions = "CF-1.0" ;
> :title = "OSTIA Sea Surface Temperature Analysis" ;
> :DSD_entry_id = "UKMO-TSANAL-v01-GLOB" ;
> :references = "None" ;
> :institution = "UK Met Office" ;
> :contact = "john.stark at metoffice.gov.uk" ;
> :GDS_version_id = "v1.0-rev1.5" ;
> :netcdf_version_id = "3.6.0-p1 of Jul 4 2005 16:41:16
> $" ;
> :creation_date = "2006-01-02 14:00 UTC" ;
> :product_version = "0.1" ;
> :history = "Created from sst:temperature from
> /data/local/frhn/OSTIA/analysis/20060102_UKMO_L4UHfnd_GLOB_v01.nc;
> error:; bias:; sea ice:" ;
> :grid_resolution = " 0.05000 degree" ;
> :comment = "WARNING Some applications are unable to
> properly handle signed byte values. If values are encountered > 127,
> please substract 256 from this reported value" ;
> :start_date = "2006-01-01 UTC" ;
> :start_time = "00:00:00 UTC" ;
> :stop_date = "2006-01-02 UTC" ;
> :stop_time = "00:00:00 UTC" ;
> :southernmost_latitude = -90.f ;
> :northernmost_latitude = 90.f ;
> :westernmost_longitude = -180.f ;
> :easternmost_longitude = 180.f ;
> :file_quality_index = "0" ;
> data:
>
> time = 788961600 ;
>
> lat = -89.975, -89.925, -89.875, -89.825, -89.775, -89.725, -89.675,
> -89.625, -89.575, -89.525, -89.475, -89.425, -89.375, -89.325,
> -89.275,
--
Please note that Charles.Seman at noaa.gov should be considered my NOAA
email address, not cjs at gfdl.noaa.gov.
********************************************************************
Charles Seman Charles.Seman at noaa.gov
U.S. Department of Commerce / NOAA / OAR
Geophysical Fluid Dynamics Laboratory voice: (609) 452-6547
201 Forrestal Road fax: (609) 987-5063
Princeton, NJ 08540-6649 http://www.gfdl.noaa.gov/~cjs/
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