Sensor Description

SSM/I was first launched on board the Defense Meteorological Satellite Program (DMSP) F8 satellite in June of 1987. The DMSP series satellites are in sun-synchronous polar orbits at an altitude of approximately 830 km. The instrument is a seven channel linearly polarized passive microwave radiometer operating at frequencies of 19.35, 22.235, 37.0, and 85.5 GHz. Detailed specifications for the spacecraft and instrument are given by Hollinger et al. [1987] and Hollinger [1989, 1991].

SSM/I channel characteristics:

Center Frequencies (GHz) 19.35 19.35 22.235 37.0 37.0 85.5 85.5
Polarization V H V V H V H
Bandwidth (MHz) 250 250 250 1000 1000 1500 1500
Sensitivity (K) 0.6 0.6 0.6 0.6 0.6 1.1 1.1
EFOV (km x km) * 69 x 43 69 x 43 60 x 40 37 x 28 37 x 29 15 x 13 15 x 13
Sampling Interval (km x km) * 25 x 25 25 x 25 25 x 25 25 x 25 25 x 25 12.5 x 12.5 12.5 x 12.5
Integration Time (msec) 7.95 7.95 7.95 7.95 7.95 3.89 3.89
Main Beam Efficiency (%) 96.1 96.5 95.5 91.4 94.0 93.2 91.1
Beamwidth (half-power, degrees) 1.87 1.87 1.65 1.10 1.10 0.43 0.45

* EFOV and Sampling Interval values are km along track x km across track. Note that the effective field-of-view for the 22 GHz channel is wrongly reported in the SSM/I Users Guide Table 2.1 as 50 x 40 km. The actual FOV is 60 x 40 km, as reported in the SSM/I User's Interpretation Guide.

Channel characteristics shown above are from:

Local observing times:

  Geolocation

The original SSM/I pixel geolocation is based on predicted spacecraft ephemeris. For the FCDR data we recompute the spacecraft ephemeris using orbital element information contained in two-line element (TLE) files produced by the North American Aerospace Defense Command (NORAD). Using this updated spacecraft ephemeris along with software to compute the pixel geoleocation based on the geometry of the sensor, we perform an examination of geolocation errors and the subsequent impact on the view angle, or Earth incidence angle (EIA). Given that the observed Tb are highly sensitive to the view angle, properly accounting for changes in EIA across an orbit and over time is an important step that must be addressed before attempting to intercalibrate the sensors. Using a previously developed coastline analysis technique, estimates of changes in the spacecraft attitude including deviations in roll, pitch, and yaw have been computed for the life of each of the SSM/I sensors. Applying these corrections results in an improved pixel geolocation, but more importantly provides accurate estimates of the EIA across the scan and throughout each orbit. An analysis of uncertainties in the calculation of EIA shows mean errors within 0.1 degrees, which translates to errors in the calibration of less than 0.2 K for all channels. Equally important, is the availability of improved geolocation and EIA estimates for algorithm developers using the SSM/I data, which is critical for producing unbiased estimates of geophysical parameters for use in climate applications.

Additional Information on Geolocation

  Intercalibration

Intercalibration of the SSM/I sensors (including F08, F10, F11, F13, F14, and F15) has been done using multiple techniques. The reason for using several difference approaches is both to quantify calibration differences beween sensors over radiometrically cold (i.e. ocean) and warm (i.e. land) scenes as well as the uncertainty in the resulting calibration differences. Given the lack of an absolute calibration target for the microwave frequencies employed on SSM/I and SSMIS, using multiple approaches provides confidence in the results and a reasonable estimate of the uncertainties. The techniques that have currently been used include the following.

Additional Information on Intercalibration

  Data

Get Data

Data Availability

Format Specifications

BASE Files
FCDR Files

  Software

Code to read FCDR files is available in the following languages:

  Documentation

CSU FCDR Documentation
SSM/I Documentation from other Sources