[Numpy-discussion] Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data

Nicolas nicolas.fauchereau@gmail....
Fri Feb 26 07:06:54 CST 2010


Hello

a VERY specific question, but I thought someone in the list might have
used this dataset before and could give me some advice

I am trying to read the daily Antarctic Sea Ice Concentrations from
Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data, as provided by
the national snow and ice data center (http://nsidc.org), more
specifically, these are the files as downloaded from their ftp site
(ftp://sidads.colorado.edu/pub/DATASETS/seaice/polar-stereo/nasateam/final-gsfc/south/daily)

they are provided in binary files (e.g. nt_19980101_f13_v01_s.bin for
the 1st of Jan. 1998)

the metadata information
(http://nsidc.org/cgi-bin/get_metadata.pl?id=nsidc-0051) gives the
following information (for the polar stereographic projection):
"""
Data are scaled and stored as one-byte integers in flat binary arrays

geographical coordinates
N: 90°     S: 30.98°     E: 180°     W: -180°

Latitude Resolution: 25 km
Longitude Resolution: 25 km

Distribution Size: 105212 bytes per southern file
"""

I am unfamiliar with non self-documented files (used to hdf and netcdf
!) and struggle to make sense of how to read these files and plot the
corresponding maps, I've tried using the array module and the
fromstring function

file=open(filename,'rb')
a=array.array('B',file.read())
var=numpy.fromstring(a,dtype=np.int)

or directly the fromfile function
var = numpy.fromfile(filename,np.int)

with various array types and numpy.dtypes, but I dont make sense of
these values, anyone has read those files before and plot the fields
using python / numpy / matplotlib ?

I am using python2.6 / numpy 1.3.0 /

thanks in advance

Nicolas


-- 
_/\/¯¯¯¯¯¯\/\_ 33º49'45.24"S & 18º28'45.60"E
Dr. Nicolas Fauchereau
Senior Researcher
CSIR - NRE
Research Group: Ocean systems and climate
15 Lower Hope street, Rosebank 7700
South Africa
tel: 021 658 2764
_/\/¯¯¯¯¯¯\/\_ 33º49'45.24"S & 18º28'45.60"E


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