Abstract

The Special Sensor Microwave Water Vapor Sounder (SSM/T-2) is a five-channel passive microwave instrument aboard recently launched spacecraft of the Defense Meteorological Satellite Program (DMSP). Rather than address the primary purpose of the SSM/T-2, which is to retrieve atmospheric moisture, this paper examines its ability to sense precipitation as shown by images of a frontal system off the west coast of the United States. Images from the three SSM/T-2 183-GHz channels depict large regions of upper-level water vapor as evidenced by depressed brightness temperatures. Within the moist regions, even lower brightness temperatures at 183 GHz mark embedded precipitation due to volume scattering by precipitation-sized ice particles. Images of the SSM/T-2 channels at 150 and 92 GHz show ice-phase precipitation marked by low brightness temperatures and, over the ocean, low-level clouds and water vapor, both marked by warming with respect to the radiometrically cold background.

This paper compares images of precipitation from the SSM/T-2 with a coincident visible image from the DMSP Operational Line Scanner (OLS) sensor and passive microwave images from the DMSP Special Sensor Microwave/Imager (SSM/I). The discussion emphasizes potential applications to operational workstation users who are increasingly able to produce real-time SSM/T-2 images by processing direct readout telemetry. The ability to produce useful images from the 92-, 150-, and 183-GHz microwave frequencies will increase substantially when the new DMSP Special Sensor Microwave/Imager Sounder (SSM/IS) replaces the SSM/I, the SSM/T-1 (for temperature sounding), and SSM/T-2 sensors later this decade.

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