relationship between wind speed (>7 m s ) and enhanced brightness 

 temperature exists. Sea surface winds of 20 m s produce a 15 K 

 increase in brightness temperature for nadir viewing. Preferred fre- 

 quencies are 10 to 20 GHz and accuracy is estimated at 10%. 



Radiometers have also found wide application in 

 the mapping of sea ice through persistent cloud cover from both airborne 

 and satellite platforms. The ice is a much better emitter of microwave 

 (emissivity 0.95 for first-year ice and 0.8 for multiyear ice) than the 

 ocean, thus appearing warmer than the surrounding sea. In addition to 

 the ice surveillance capability, the ability to differentiate fresh 

 ice from multiyear ice allows the ice boundaries to be detected and is 

 useful for ship navigation. 



Airborne or satellite-borne radiometer systems 

 have also been very useful in mapping weather fronts and measuring 

 rainfall. ■"^'^^ The brightness temperature measured by the downward- looking 

 radiometer increases with rainfall rate. A rainfall rate of 13 mm/hr 

 produces an increase in apparent microwave brightness temperature of 

 100°K at 19,4 GHz according to Allison. ■■•* 



Two additional areas of application of microwave 

 radiometers that have received considerable attention are detection of 

 oil spills and missile terminal guidance. Airborne radiometric measure- 

 ments of oil spills have been made at several frequencies with limited 

 success. Microwave radiometers have been frequently suggested for use 

 in missile terminal guidance systems using map-matching techniques. 

 Technology developed in the latter area is primarily concerned with con- 

 tinental terrain and will have limited impact on support of the 200-nmi 

 zone. 



In summary, existing technology in microwave 

 radiometry is more than adequate for the detection of fishing vessels 



57 



