SSM/I Temperature Data Record (TDR) Data Sets

TABLE OF CONTENTS

1.0     Introduction
2.0     Special Sensor Microwave Imager
2.1     Instrument Description
2.2     Scan Geometry
2.3     Antenna Beam Characteristics
3.0     SSM/I TDR Data Set
3.1     File Naming Conventions
3.2     Data Set Format
4.0     References
 

1.0     Introduction

This README file contains information on the Special Sensor Microwave
Imager (SSM/I) Temperature Data Record (TDR) data sets.  Brief
descriptions of the Defense Meteorological Satellite Program (DMSP)
satellites, the SSM/I instrument, the computation of antenna
temperatures and brightness temperatures and the format of the data
sets are included.  Included is the source code for three software
programs. The first program, ssmitdrlatlon.c, extracts the portion of
the daily file which contains a user specified latitude/longitude
range.  The second program, ssmitdrta.c, reads a NESDIS SSM/I TDR data
file and outputs antenna temperatures.  The third program, ssmitdrtb.f,
converts the antenna temperatures produced by the second program into
brightness temperatures.  Pertinent scientific references are also
included.

The Defense Meteorological Satellite Program (DMSP) is a Department of
Defense program which is responsible for designing, building, launching
and operating polar orbiting meteorological satellites.  The SSM/I was
first launched on June 19, 1987 aboard the DMSP Block 5D-2 Spacecraft
F8.  Since that time, additional launches have been made aboard DMSP
Block 5D-2 Spacecraft F10 and DMSP Block 5D-2 Spacecraft F11.  The F10
and F11 Spacecrafts are both still operational but the F8 Spacecraft
has completed it's mission as of July 31, 1994.  The launch
aboard DMSP Block 5D-2 Spacecraft F13 was made in March 1995. Additionally
the launch aboard DMSP Block 5D-2 Spacecraft F14 was made in early 1997.

Note:  From March 19, 1997 - April 20, 1997 the F11 satellite was not 
operational.

The satellites can broadcast visual, infrared and microwave imagery
directly to transportable tactical sites around the world.  The data is
also stored for transmission to the Navy's Fleet Numerical Meteorology
and Oceanography Center (FNMOC) and to the Air Force Global Weather
Central (AFGWC). The Naval Oceanography Command (NOC) and the Air
Weather Service process the SSM/I data to obtain near real-time global
maps of cloud water, rain rates, water vapor over oceans, marine wind
speeds, sea ice location, age and concentration, snow water content and
land surface type, moisture and temperature.

Each of the DMSP satellites fly in a sun-synchronous, near-polar orbit.
For a satellite in sun synchronous orbit, the ascending equatorial
crossing time remains relatively constant with respect to the local
time throughout the lifetime of the satellite.  The table below
summarizes the orbits for each spacecraft (valid for the orbit shown).

Spacecraft              F-10               F-11               F-13
Launch Date             1 Dec 1990         28 Nov 1991        24 Mar 1995
Information Valid For   Rev 719            Rev 1276           Not Available
Ascending Equator
Crossing                19:42              17:04              17:36
Time (Local Time)
Inclination             98.8 Deg           98.8 Deg           98.8 Deg
Degrees Period          100.7 Min          101.9 Min          101.9 Min
Maximum Altitude        853 Km             878 Km             875 Km
Minimum Altitude        740 Km             841 Km             840 Km
Eccentricity            0.00814            0.00129            0.00075
Semi Major-Semi Minor   238 Meters         6 Meters           5 Meters
Distance                117 Km             19 Km              Not Available

2.0  Special Sensor Microwave Imager (SSM/I)

The information in this section is quoted from the DMSP Special Sensor
Microwave /Imager Calibration/ Validation Report, Volume I, Hollinger,
et al. (1989) and the DMSP SSM/I Calibration/Validation Report, Volume II,
Hollinger, et al. (1990).

The SSM/I is a seven-channel, four-frequency, linearly-polarized,
passive microwave radiometric system.  The SSM/I receives both
horizontally and vertically linearly polarized radiation at 19.3,37.0,
and 85.5 GHz and vertical only at  22.2 GHz.  The following table
summarizes satellite specific instrument details.

Spacecraft                      F-10            F-11            F-13
Launch Date                     1 Dec 1990      28 Nov 1991     24 Mar 1995
Information Valid For           Rev 719         Rev 1276        Not Available
Instrument Viewing Direction    Forward         Forward         Forward
Maximum Swath Width             1427 Km         1483 Km         Not Available
Minimum Swath Width             1226 Km         1414 Km         Not Available
Maximum Incidence Angle         53.29 Deg       53.56 Deg       Not Available
Minimum Incidence Angle         52.10 Deg       53.16 Deg       Not Available
Maximum Incidence Angle
 Change for All Orbits          1.4 Deg         0.5 Deg         Not Available

2.1     Instrument Description

The information in this section is quoted from the DMSP Special Sensor
Microwave /Imager Calibration/ Validation Report, Volume I, Hollinger,
et al. (1989) and the DMSP SSM/I Calibration/Validation Report, Volume II,
Hollinger, et al. (1990).

The SSM/I instrument consists of an offset parabolic reflector with
dimensiions of 61 by 66 cm.  This reflector is illuminated by a
corrugated, broad-band, seven-port horn antenna.  The feed-horn antenna
and the reflector are mounted on a drum which contains the radiometers,
digital data subsystem, mechanical scanning subsystem, and power
subsystem. The entire feed-horn, reflector and drum assembly rotate
about the axis of the drum by a coaxially mounted bearing and power
transfer system (BAPTA).  All data, commands, power, timing and
telemetry signals pass through the BAPTA on slip ring connectors to
the rotating assembly.

A small mirror and a hot reference absorber are mounted on the BAPTA
and do not rotate with the drum assembly. They are positioned off axis
such that they pass between the feed horn and the parabolic reflector,
occulting the feed horn once each scan. The mirror reflects cosmic
background radiation (3 K) into the feed horn thus serving, along with
the hot reference absorber, as calibration references for the SSM/I.
This scheme provides an overall end-to-end absolute calibration which
includes the feed horn. The combination of the calibration scheme and
the use of total power radiometers greatly improve the SSM/I
performance in comparison with previous spaceborne radiometeric
systems.  Corrections for spillover and antenna pattern effects from
the parabolic reflector are incorporated in the data processing
algorithms.

The SSM/I employs a total-power radiometer configuration.  A balanced
mixer down-converts the output of the feed horn and amplifies it. Then
a square-law detector converts that output to a video voltage.  A
bandpass filter defines the receiver passband and improves the
out-of-band rejection.  The component of receiver output due to
receiver noise is removed through the amplification and offset of the
detected video signal.  The output of the video amplifier is integrated
by an integrate and dump filter for 7.95 msec for all frequencies,
except the 85.5 GHz frequency which is integrated for 3.89 msec.
Following this integration, the output is delivered to the data
processing system. The time between samples is the same for all
frequencies (12.5 msec) except for the 85.5 GHz frequency (4.22 msec).

The data processor uses an anolog multiplexer to multiplex the seven
radiometer output signals.  The data processor then samples and holds
the signals prior to them being digitized into 12-bit words.  Twelve
channels, which contain three hot target temperature measurements, two
temperature sensor measurements within the radiometer, reference
voltage, and reference return data, are multiplexed with radiometer
data.

A microprocessor supervises instrument timing, control, and data
buffering with the DMSP Operational Line Scanner (OLS) instrument
(collocated on the satellite) which records all SSM/I data.  The
average data rate of the SSM/I including zeros required to match the
OLS interface is 3276 bps.

2.2     Scan Geometry

The information in this section is quoted from the DMSP Special Sensor
Microwave /Imager Calibration/ Validation Report, Volume I, Hollinger,
et al. (1989) and the DMSP SSM/I Calibration/Validation Report, Volume II,
Hollinger, et al. (1990).

The SSM/I continuously rotates about an axis paralled to the local
spacecraft vertical at 31.6 rpm.  The SSM/I measures, over an angular
section of 102.4 degrees about the sub-satellite track, the upwelling
scene brightness temperatures.  When looking in the forward direction
of the spacecraft, the scan is directed from left to right with active
scene measurements lying 51.2 degree about the forward direction.  The
resulting swath width is 1400 km, which results in 24 hour global
coverage.  The spacecraft sub-satellite point travels 12.5 km during
the 1.9 second period.  For each scan, 128 uniformly spaced 85.5 GHz
scene data are taken over a 102.4 degree scan region.  The sampling
interval is 4.22 msec and equals the time for the beam to travel 12.5
km in the cross track direction. Radiometer data at the remaining
frequencies are sampled every other scan with 64 uniformly spaced
samples being taken and have an 8.44 msec interval. Scan A denotes scans
in which all channels are sampled and Scan B denotes scans in which only
85.5 GHz data  are taken.  The start and stop times of the integrate and
dump filters at 19.35, 22.235, and 37.0 GHz are selected to maximize the
radiometer integration time and achieve concentric beams for all sampled
data.  The effect of the radiometer integration times isto increase the
effective along scan beam diameter and make the beams at 37 and 85 GHz
nearly circular.

2.3     Antenna Beam Characteristics

The information in this section is quoted from the DMSP Special Sensor
Microwave /Imager Calibration/ Validation Report, Volume I, Hollinger,
et al. (1989) and the DMSP SSM/I Calibration/Validation Report, Volume II,
Hollinger, et al. (1990).

The data in Table 2.1 apply to the S/N 002 Sensor on F-10 and F-11 and
represents measurements of the instantaneous field of view (IFOV)3 dB
beamwidths of the secondary radiation patterns as a function of the
channel frequency and polarization for SSM/I.  The data are based on
measurements, taken prior to launch, of antenna temperatures which were
averaged over the RF bands.  An effective field of view (EFOV) can be
defined for each sampled radiometer brightness temperature that takes
into account the integration time.  For the along-track direction, the
IFOV and the EFOV are basically the same but in the cross track
direction, or H-plane direction, the IFOV is signficantly smaller than
the EFOV.  Table 2.1 provides information on both the EFOV 3-dB
beamwidths and the IFOV beamwidths to allow for intercomparison.  The
table also provides the along-track and cross track dimensions of the
EFOV beamwidths as projected onto the surface of the Earth.

Table 2.1.  SSM/I Antenna Beamwidths (S/N 002)

Channel    Pol.  IF Pass-Band           Beamwidth (Deg)         EFOV on Earth Surface
Frequency  (V/H)  (MHz)         E-Plane   H-Plane  H-Plane      Along-     Cross-
(GHz)                           IFOV      IFOV      EFOV        Track      Track

19.35        V    10-250         1.86      1.87      1.93         69 km    43 km
19.35        H    10-250         1.88      1.87      1.93         69 km    43 km
22.235       V    10-250         1.60      1.65      1.83         60 km    40 km
37.0         V    100-1000       1.00      1.10      1.27         37 km    28 km
37.0         H    100-1000       1.00      1.10      1.31         37 km    29 km
85.5         V    100-1500       0.41      0.43      0.60         15 km    13 km
85.5         H    100-1500       0.42      0.45      0.60         15 km    13 km

The main beam efficiency is an important parameter in the antenna
performance.  The main beam efficiency is defined as the percentage of
energy received within the main beam of the far-field radiation pattern
in the desired polarization within the prescribed bandwidth to the
total energy received.

Another important antenna performance parameter is the main beam
efficiency which is defined as the percentage of energy received within
the main beam of the far-field radiation pattern in the desired
polarization within the prescribed bandwidth to the total energy
received.  The far-field antenna pattern is the combination of the
radiation patterns of the feedhorn antenna and the parabolic reflector
antenna. The antenna beam efficiencies as a function of channel
frequency and polarization for the S/N 002 instrument are provided in
Table 2.2.  The data are based upon the S/N 002 instrument antenna range
measurements of both the feedhorn patterns and the radiation patterns
from the reflector. The antenna sidelobe column denotes the percentage of
energy lying outside 2.5 times the 3-dB beamwidth of the far-field
pattern when normalized to the sum of the co- and cross-polarization
energies. The cross-polarization column is defined as the percentage of
cross-polarized energy appearing at the output of the feedhorn and
includes contributions from the reflector and feedhorn. The feedhorn
spillover factor refers to the loss of the energy in the far-field
pattern which is not intercepted by the reflector. Thus, in the
computation of beam efficiency, the feedhorn spillover loss is a
multiplicative factor.

Table 2.2.  SSM/I Beam Efficiencies (S/N 002)

Channel         Pol. (V/H)      Antenna         Cross-          Feedhorn        Beam
Frequency                       Sidelobe        Polarization    Spillover       Efficiency
(GHz)                           (%)             (%)             Factor          (%)

19.35              V            0.8             0.35            0.969           96.1
19.35              H            0.4             0.30            0.969           96.5
22.235             V            2.0             0.65            0.974           95.5
37.0               V            7.3             1.80            0.986           91.4
37.0               H            4.7             1.20            0.986           94.0
85.5               V            5.7             0.60            0.988           93.2
85.5               H            7.8             1.40            0.988           91.1

The loss in beam efficiency due to small scale surface roughness is
very small at all frequencies and was therefore not included in Table
3.2.  The rms surface roughness, which is less than 0.025 mm,
translates to a loss of less than 0.15% all frequencies except the 85.5
GHz frequency which has a loss of less than 0.8%.

3.0     SSM/I TDR Data Set Summary

3.1     File Naming Conventions

The FNMOC TDRs provided by the GHRC are in a file containing a
day's worth of orbit files.  The daily files are named
tallmiyy.jd_ds_daily.tar, where ta = abbreviation for antenna
temperatures, ll=satellite number (10 for F-10, 11 for F-11), mi =
abbreviation for sensor SSM/I, yy = the year of the century, jd =
julian day of the year, ds = data source (i.e., fnmoc), and daily.tar =
the file type where all information has been put together in one file
and tarred.  A sample file name for the data from the F-10 sensor for
julian day 364 in 1994 would be:  ta10mi94.364_fnmoc_daily.tar.

Each orbit file concatenated into the daily tar file follows the NESDIS
file naming convention of NSS.TDRR.Sx.Dyyddd.Shhmm.Ehhmm.Annnnnnn,
where S = "satellite", x = the satellite identification number minus 6,
D = "day", yy = the year of the century, ddd = the Julian day of the
year, S = "orbit file start time", hh = start hour of orbit file, mm =
start minute of orbit file, E = "orbit file end time", hh = end hour of
orbit file, mm = end minute of orbit file, and A = the processing
sequence designator.  The satellite identification numbers for F-8,
F-10, and F-13 are, respectively, 2, 4, and 7.  The processing sequence
designator in either an "A" or a "B".

Note that the orbit file names are generated by NESDIS using the
information found in the file header.  The file header is created by
FNMOC and does not always accurately reflect the start and end times of
the data in the file.

3.2     Data Set Format

***************************PLEASE NOTE***********************
NESDIS TDR format has changed.  Each A-B scan pair now occupies one
record of 3604 bytes.  The data records are preceded by a 3604-byte
header record.  Here are the record layouts.  Lengths are in bytes.
At the GHRC, the new format begins with the May 1997 data (D97121).

                      ---------------
                       HEADER RECORD
                      ---------------

          Length       Type
          ----------------------------------------
             28   Product ID Block
             32   Data Sequence Block
            190   Pass HDR  Data Description Block
            370   Scan HDR1 Data Description Block
           1138   Scan HDR2 Data Description Block
            370   TDR       Data Description Block
             30   Pass HDR  Data Block
           1446   Fill (X'00')
          ----------------------------------------

                       -------------
                        DATA RECORD
                       -------------

          Length       Type
          ----------------------------------------
             76   Scan HDR1 Data Block
            194   Scan HDR2 Data Block
           3334   TDR       Data Block
          ----------------------------------------

**********************************************************

The TDR files are stored in the Shared Processing Network Data Exchange Format
(SPN DEF).  This format consists of data description (DD) blocks and data
blocks.  All blocks begin with a block identification and a block length
and end with a checksum.  The data description blocks are used to store
acronyms, start bytes, lengths, units, signs, and exponents
for the corresponding data blocks. There are 7 nonrepeating header
blocks, three repeating scan blocks, and a nonrepeating trailer block.
Table 3.1 lists the blocks in the order that they appear in the file.
The data blocks will be described in subsequent sections.  For detailed
information on all the blocks, please refer to the SSM/I Data Requirements
Document (Hughes Aircraft, 1986) and the software in Appedices A, B, and C.

Table 3.1  TDR Blocks

Product Identification Block                            (nonrepeating)
Data Sequence Block                                     (nonrepeating)
Revolution Header Data Description (DD) Block           (nonrepeating)
Scan Header #1 DD Block                                 (nonrepeating)
Scan Header #2 DD Block                                 (nonrepeating)
Scan Data DD Block                                      (nonrepeating)
Revolution Header Data Block                            (nonrepeating)
Scan Header #1 Data Block                               (repeating)
Scan Header #2 Data Block                               (repeating)
Scan Data Block                                         (repeating)
End of Product Block                                    (nonrepeating)

3.2.1  Revolution Header Data Block

This block contains the spacecraft identification, the revolution
number, the data start time, the data end time, and the nearest
ascending node time.  The times are stored as Julian Day, hours,
minutes, seconds.

3.2.2  Scan Header #1 Data Block

This block contains the parameters listed in Table 3.2 for the respective
scan data block. The Scan Header #1 block is repeated at the beginning of
every new scan A/B pair.

Table 3.2  Scan Header #1

Scan number of current scan
Scan start time for the current B-scan
Position vector time
Position vector latitude
Position vector longitude
Position vector altitude
Thermistor Hot Load Temperature Sample #3
Thermistor Hot Load Temperature Sample #2
Thermistor Hot Load Temperature Sample #1
Calibration Reference Voltage Sample #1
Calibration Reference Voltage Sample #2
RF Mixer Temperature
Forward Radiator Temperature
Scan Automatic Gain Control (AGC) Setting #1 for A Scan
Scan AGC Setting #2 Setting #2 for A Scan
Scan AGC Setting #3 Setting #3 for A Scan
19V Slope
19V Offset
19H Slope
19H Offset
22V Slope
22V Offset
37V Slope
37V Offset
37H Slope
37H Offset
85V Slope
85V Offset
85H Slope
85H Offset

3.2.3  Scan Header #2

This block contains the parameters listed in Table 3.3 for the respective
scan data block. The Scan Header #2 block is repeated at the beginning of
every new scan A/B pair.

Table 3.3  Scan Header #2

Scan number of current scan
Five 19V Cold Calibration Counts for A Scan
Five 19H Cold Calibration Counts for A Scan
Five 22V Cold Calibration Counts for A Scan
Five 37V Cold Calibration Counts for A Scan
Five 37H Cold Calibration Counts for A Scan
Five 85V Cold Calibration Counts for A Scan
Five 85H Cold Calibration Counts for A Scan
Five 19V Hot Calibration Counts for A Scan
Five 19H Hot Calibration Counts for A Scan
Five 22V Hot Calibration Counts for A Scan
Five 37V Hot Calibration Counts for A Scan
Five 37H Hot Calibration Counts for A Scan
Five 85V Hot Calibration Counts for A Scan
Five 85H Hot Calibration Counts for A Scan
Scan AGC Setting #1 for B Scan
Scan AGC Setting #2 for B Scan
Scan AGC Setting #3 for B Scan
Five 85V Hot Calibration Counts for B Scan
Five 85H Hot Calibration Counts for B Scan

3.2.4  Scan Data Block

This block contains the latitude (LAT), longitude (LON), surface type (SFT),
pixel number, and antenna temperature data listed in Table 3.4 for an A/B
scan pair.

Table 3.4

A Scan Odd  Pixels: LAT LON 19V  19H  22V  37V  37H  85V  85H  SFT Pixel#
A Scan Even Pixels: LAT LON                          85V  85H  SFT Pixel#
B Scan Odd  Pixels: LAT LON                          85V  85H  SFT Pixel#
B Scan Even Pixels: LAT LON                          85V  85H  SFT Pixel#

4.0  References

Special Sensor Microwave/Imager (SSM/I) Data Requirements Document,
Department of the Air Force, Headquarters, February, 1986.

Hollinger, J., et al., Special Sensor Microwave / Imager User's Guide,
Naval Research Laboratory, Washington, D. C., 14 September 1987.

Hollinger, J., et al., DMSP Special Sensor Microwave / Imager
Calibration / Validation Final Report Volume I, Naval Research
Laboratory, Washington, D. C.,20 July 1989.

Lee, S. O., SSM/I Level 1b Interface Control Document, NOAA/NESDIS,
Suitland, Maryland, 20233, June 15, 1993.

Wentz, F. J., Measurement of Oceanic Wind Vector Using Satellite
Microwave Radiometers, RSS Technical Report 051591, 33 pp, Remote
Sensing Systems, Santa Rosa, CA, 15 May 1991.

Wentz, F. J., User's Manual SSM/I Antenna Temperature Tapes (Revision
1), RSS Technical Report 120191, 70 pp, Remote Sensing Systems, Santa
Rosa, CA, 1 December 1991.

 
Last Updated: May 23, 1997