The relationship between beamwidth, aperture, and frequency is 



= ^ 

 "^1/2 " fD 



where 



D = antenna aperture diameter, m 



f = radiometer operating frequency, GHz. 



A reasonable estimate for the projected area of a 



o 3 2 



100-ft vessel viewed at an angle of incidence of 55 is 2 X 10 ft . We 



assume that approximately 507o of this area will be effective radiometrically 



3 2 

 as a target cooler than the ocean, which gives 1 x 10 ft of effective 



radiometric area for our nominal fishing vessel. An airborne sensor 



with an antenna aperture diameter of 1 m would be capable of detecting 



4 

 our assumed vessel to a maximum range of 1.1 X 10 ft when operating 



at the assumed frequency of 35 GHz. If the side-to-side scan angle is 



3 

 110°, then the maximum platform altitude is 6,2 X 10 ft. 



With the platform height and side-to-side scan 



angle specified, one can calculate the ratio of the antenna temperature 



contrast, AT , caused by viewing the ship to the minimum detectable 



temperature difference that can be discerned with the radiometer system. 



The minimum detectable temperature difference, AT . , is 



min 



T + T. 

 rec A 



^T . = /-: 



mm J Bt 



where 



T = receiver temperature, K 

 rec 



T = antenna temperature, K 



63 



