INFORMATION

Reading binary data NSIDC Sea Ice Concentrations into GeoTIFF raster with Python

I need to read NSIDC sea ice concentration charts from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data into a raster file. These files are according to the documentation "scaled, unsigned flat binary with one byte per pixel, and therefore have no byte order, or endianness. Data are stored as one-byte integers representing scaled sea ice concentration values.[...] The file format consists of a 300-byte descriptive header followed by a two-dimensional array of one-byte values containing the data."

The blog entry, which helped med finding out how to do this is this one but it had to be modified for my files.


Part One uses the Python struct command to unpack he binary file into a tuple

import struct, numpy, gdal

#Dimensions from https://nsidc.org/data/docs/daac/nsidc0051_gsfc_seaice.gd.html
height = 448
width = 304

#for this code, inspiration found at https://stevendkay.wordpress.com/category/python/
icefile = open(r"U:SSMI
t_20120101_f17_v01_n.bin", "rb")
contents = icefile.read()
icefile.close()

# unpack binary data into a flat tuple z
s="%dB" % (int(width*height),)
z=struct.unpack_from(s, contents, offset = 300)

nsidc = numpy.array(z).reshape((448,304))
nsidc = numpy.rot90(nsidc, 1)

The "unpack_from" considers the offset of the header bytes and the tuple "z" contains now all the values in one long row of values -- this one-dimensional string of values is converted into an array and the reshaped according to the dimensions of the raster. Now I have my values in a two-dimensional array, the next part of the code writes it into a GeoTIFF file:

#write the data to a Geotiff
driver = gdal.GetDriverByName("GTiff")
outraster = driver.Create(C:UsersmaxDesktop\test4.tif, height, width, 1, gdal.GDT_Int16 )
raster = numpy.zeros((width, height), numpy.float) 
outraster.GetRasterBand(1).WriteArray( raster )

outband = outraster.GetRasterBand(1)

#Write to file     
outband.WriteArray(nsidc)
outband.FlushCache()

#Clear arrays and close files
outband = None
iceraster = None
outraster = None
outarray = None

This then is the resulting and imported image: