Appendix A:

Importing SSM/I Data into Terascan

Introduction

This appendix describes importing SSM/I data into the image processing package Terascan from Seaspace. SSM/I data were received from two different sources; (1) Defense Meteorological Satellite Program (DMSP) data archive at the National Geophysical Data Center (NGDC) and (2) The Hydrologic Cycle DAAC at Marshall Space Flight Center (MSFC). The NGDC data are easier to import into Terascan, but we found that the NGDC data contained gaps that are not found in the MSFC data. When comparing images from NGDC and MSFC it was found that the brightness temperatures may differ by as much as seven degrees in some channels. I believe that these differences are due to the use of different algorithms to convert from level 1B sensor counts data to brightness temperature data. Currently, these different algorithms are being compared and revised. For future studies, it is my recommendation that data from the MSFC be used. The MSFC SSM/I l1b data is currently free of charge and is received on 8 mm tapes within one week of ordering.

NGDC Data

Information on ordering SSM/I data from NGDC is available on the "How to Order DMSP DATA from NGDC" Web page at http://www.ngdc.noaa.gov/dmsp/order.html. Currently, NGDC allows orders of SSM/I brightness temperature data by orbit or day. SSM/I data for the Rabaul and Klyuchevskoi eruptions were received from NGDC using ftp and stored on 8 mm tapes. The following are the steps to take to retrieve an orbital file from tape and import it into Terascan. For this example, the filename is "F1114654.MI.Z" which is file number 42 on the tape.

  1. nrst1 asf 42
    nrst1 is aliased to mt -f /dev/nrst1 !*
  2. tar xvf /dev/nrst1 F1114654.MI.Z
    /dev/nrst1 is the device name for the 8 mm tape drive.
    The archive tape case contains a list of file numbers and names.
    A full orbital file is about 6-8 Mbytes.
  3. uncompress F1114654.MI.Z
  4. xdrdmsp
    xdrdmps is a Terascan command that was written for us to import the xdr formatted NGDC SSM/I data.
  5. fastreg
    fastreg is a Terascan command that registers the SSM/I data to a map projection.

MSFC Data

To order Level 1b SSM/I data from MSFC send email to msfc@eos.nasa.gov. The MSFC archive consist of a tar file of orbital files for each day. The 8 mm tapes received from MSFC contained one large tar file of all the daily tar files ordered. A backup tape was made where each days data was written to a separate file. The following are the steps to take to get a file off the backup tape and imported into Terascan. For this example, the filename is "sc11mi94.273_nesdis_swath.tar" which is file number 5 on the tape.

  1. nrst1 asf 5
    nrst1 is aliased to mt -f /dev/nrst1 !*
  2. tar xvf /dev/nrst1 sc11mi94.273_nesdis_swath.tar
    /dev/nrst1 is the device name for the 8 mm tape drive.
    The archive tape case contains a list of file numbers and names.
  3. tar xvf sc11mi94.273_nesdis_swath.tar
  4. inview
    inview is a Terascan command that is used to find out what time a satellite is over an area.
    Choose an orbital file that is over your area of interest (i.e. S5.D94273.S2000.Z).
  5. uncompress S5.D94273.S2000.Z
    The filename contains the year (94), day (273) and time (20:00:00 GMT) of the observation.
  6. ssmil1bta.o S5.D94273.S200 S5.D94273.S2000.TA
    ssmil1bta.o is a C excutable that converts l1b data to antenna temperature data.
  7. ssmilb.exe
    Input file: S5.D94273.S2000.TA
    Output file: S5.D94273.S2000.TB
    "ssmil1btb.exe" is a FORTRAN excutable that converts antenna temperature data to brightness temperature data. The source codes, "ssmil1bta.c" and "ssmil1btb.f", are received from the MSFC when ordering SSM/I l1b data.
  8. impssmi
    Input File Name: S5.D94273.S2000.TB
    Number of lines to process: "800" (Gets the first 800 lines in the file)
    impssmi is an IDL subroutine that converts the brightness temperature data into a file that Terascan can read. Note that impssmi creates a output file called "data.out"
  9. impasc
    impasc is a Terascan surboutine to import ascii data.
  10. satmaster
    satmaster is a Terascan subroutine to create a master file from the satellite position.
    Note that the time is just taken off of the filename, which is close and will be adjusted later.
  11. copyxfm
    copyxfm is a Terascan subroutine to copy the master file to the imported file.
  12. The Terascan file can be displayed by using "Image/Display" from the "xvu" display widget. The outline of the cost can be adjusted using "Image/Navigate" from the "xvu" display widget. The time variable should be adjusted until the water/land interface is correct.