is a diagrammatic illustration showing the variation in radar propagation 

 conditions with air How trajectory. Under conditions of moist warm air 

 blowing over warm water (fig. 33A) little change is expected in the air 

 mass and more-or-less standard conditions prevail. However, as this 

 moist warm air moves over cold water surfaces as the Labrador Current 

 or shipping lanes during early spring (fig. 33B), the air loses heat and 

 moisture in the lower levels, and as the moisture loss predominates the 

 index of refraction increases with height for the first few hundreds of 

 feet and radar waves bend upward more rapidly than normal. This re- 

 sults in subnormal microwave propagation and reduced radar ranges as 

 illustrated by the ray path "B". Unfortunately, this condition pre- 

 dominates in the ice areas during the early spring and summer months. 

 Close under the Newfoundland coast, dry cold air blowing over the cold 

 water surface will result in increased moisture in the lower levels and a 

 condition of superrefraction or "ducting" (fig. 33C). Under these circum- 

 stances and those resulting from this cold relatively dry air from the 

 north blowing over the warm water surface of the south (fig. 33D), a 

 large portion of the energy of the radar pulse is confined to a narrow 

 region in the lower atmosphere resulting in extended ranges. This phe- 

 nomena of superrefraction is a common occurrence at sea and ranges are 

 extended 3 to 5 times. Unfortunately, this supernormal condition usually 

 exists during clear days when extended radar ranges are not required. 

 An analysis of the weather observations taken while the iceberg maximum 

 range observations were being made indicates that average and better- 

 than-average ranges might be expected on clear days, and that below- 

 average ranges are to be expected on foggy days which is in conformance 

 with theory. 



Quantitative Measurements 



To assess the magnitude of decreased ranges due to the subnormal 

 propagation conditions which might be found on the Grand Banks area 

 it would be necessary to make serial measurements of the vertical distri- 

 bution of temperature and humidity over an extended period of time. 

 From these observations ray diagrams or coverage charts might be 

 constructed and an estimate made of the reduction or increase in the 

 expected range. A more practical approach would be to treat the problem 

 statistically using the routine data of sea temperature, air temperature. 

 humidity, and wind speed as proposed by Anderson and Gossard [17] 

 and others. To gain confidence in any of the quantitative radar data it 

 was necessary to make as many weather observations as practical in the 

 Grand Hanks area. Where possible a sounding was made with the captive 

 Wiresonde instrument which accurately measures temperature and hu- 

 midity at any desired altitude interval. Measurements from the surface 

 to above 300 feet were made at frequent intervals depending on the ex- 

 pected gradient. As a result it was possible to obtain excellent information 

 on the propagation conditions during 30 percent of the radar tests. 



76 



