Using IDL to Manipulate SSM/I HDF Data

Reading SSM/I HDF Data into IDL

The idea is to

• read the header info in the HDF file to get reference numbers for the various SDS (Scientific Data Sets) contained within;
• execute a separate IDL procedure (e.g., get19h.pro) for each band desired, and output a binary file for each band as something like h19.bin;
• cat the binary files together to make one file containing a multiband SSM/I image (this is optional but useful);
• import the binary file into ENVI for display and processing.

hdf_info.pro: Getting HDF Header Information

IDL has a procedure called hdf_info.pro which reads the header information in (almost?) any HDF file. Sequence:
IDL>.run hdf_infocompile the procedure
IDL>hdfinfo,'filename.hdf'execute the procedure (Note: this is a quirk in this program. Normally, execution would be done by typing the filename, i.e., IDL>hdf_info,'filename.hdf', but this one is strange...). Execution returns a listing of the HDF file contents (MSFC version). contents.

The screen output describes the contents of the HDF data set.

Executing get19h.pro

There are seven getn,p.pro files, one for each band (. I'll use get19h.pro as an example here.

Getting HDF SSM/I Data from MSFC FTP site

ftp to microwave.msfc.nasa.gov
cd data/ssmi-f13/current-tb/hdf/ (home) | pub / \ data browse / \ / \ ssmi-f10 ssmi-f13 ssmi-f10 ssmi-f13 | | | | current-tb current-tb current-tb current-tb | | / | \ / | \ hdf hdf hdf gif hdf-raster hdf gif hdf-raster | | (10) | | (10) | | yy.ddd yy.ddd yy.ddd yy.ddd yy.ddd yy.ddd (10) (10) (30) (30) (30) (30)

IDL> .run getssmi_85v % Compiled module: GETSSMI_85V. IDL> getssmi_85v,ssmi,tb,lat,lon,sds_id_tb,sds_id_lat,sds_id_lon How big is the array? Data-Set-8 2 INT 3

DIMS = 64 806 long_name= F13_H37_96108_11A units= Kelvin format= Int*2 (*100) Data-Set-9 2 INT 3 DIMS = 128 1612 long_name= F13_V85_96108_11A units= Kelvin format= Int*2 (*100) :q

Point of contact: Drew Pilant anpilant@mtu.edu