incidence the components K v and AY of the reflection complex (A„+./AV) 

 are given by: 



T r ( €r 2 + er) cos 2 — (c 2 +d 2 ) 



AV = 



(e r 2 +er) cos 2 0+(c 2 +d 2 )+2(e r c--e^) cosfl 



— 2(e r d-\-eic) cos0 

 (e r 2 +6i 2 ) cos 2 0+(c 2 +rf 2 )+2(e r c-e J d) cos0 



in which the symbols have the same significance as in the equations 

 above. It can be seen from these equations that the reflection coefficient 

 tends to unity as the angle of incidence approaches 90°, and is zero for 

 all angles of incidence for a body having zero conductivity and unity di- 

 electric constant. The results of these computations are shown in figure 

 40. A number of conclusions can be drawn from this figure: 



1. The reflection coefficient of ice is three times less than that of sea 

 w r ater. This fact helps explain the results of relative power measurements 

 shown in figure 39. 



2. In both cases of polarization, the reflection coefficient is less for 

 vertical than for horizontal polarization for all angles of incidence. 



3. S- and X-band behave the same on both ice and sea water for all 

 practical purposes. Field experiments in 1946 [3~\ confirm the fact that 

 ice is not frequency sensitive ; however, because the reflection from drop- 

 lets contributes appreciably to the sea echo, there is some measured [5] 

 frequency dependence of the radar cross section per unit area for sea 

 echoes. 



4. The Brewster angle for pure ice is 60°13'. An examination of the 

 vertical polarization curves reveals that although, theoretically, less sea 

 return would be observed using vertically polarized radiation, the reduced 

 ice reflection coefficient is the limiting factor. It appears that the mariner 

 using vertically polarized radar is at a disadvantage during calm or slight 

 sea conditions. A limited number of qualitative measurements using 

 vertical polarization for the detection of growlers in sea return during the 

 1946 studies [2~] gave negative results. 



EVALUATION OF ANTICLUTTER CIRCUITS 



Genera/ 



The masking effect of sea return and weather has long been of concern 

 to radar manufacturers and mariners. The program for the field work of 

 this investigation was designed to place most of the emphasis on an 

 evaluation of the effectiveness of commonly used anticlutter devices in 

 the discrimination of small ice targets from sea clutter. Two types of 

 devices most common to commercial marine radars were evaluated on 

 different sized targets during various stages of the sea. The observations 

 were documented by PPI photographs, cognizance of set performance, 



89 



