WP-3D Stepped Frequency Microwave Radiometer (SFMR)
Measurement of the hurricane surface wind field, and in particular the estimation of wind maxima, has long been a requirement of the Tropical Prediction Center/OAR. The NOAA/Hurricane Research Division's Stepped-Frequency Microwave Radiometer (SFMR) is the prototype for a new generation of airborne remote sensing instruments designed for operational surface wind estimation in hurricanes.
The SFMR has a downward pointing antenna which passively reads the microwave radiation coming from the ocean surface. By making assumptions about the vertical structure of the atmosphere together with sea surface temperature measurements by a downward-looking airborne infrared radiometer, reasonable estimates of the ocean surface brightness temperature can be made at six frequencies between 4.6 and 7.2 GHz. Wind speeds are then calculated assuming linear increase in wind speed with these brightness temperatures. Since some of the frequencies are more attenuated by rainfall than others, an estimate of the rainfall rate below the airplane can also be made.
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