RADAR PROI'AGATION FORECASTING 



113 



Figure 4A. Class 3 pattern, SCR-271, Crystal River. 

 Coast line well painted in. 



Figure 4B. Typical Class 4 pattern, SCR-271, Crystal 

 River 



As it was impracticable to establish a permauent 

 target in the Gulf of Mexico beyond the radar hori- 

 zon, the existence of superrefraction was generally 

 assumed when there was extended appearance of 

 coast-line clutter. It is realized that such an effect 

 may not be representative of open water conditions 

 because of the possibility of local sea breezes giving 



rise to the necessary teiupeiature and moisture gradi- 

 ents for trapping. However, on this basis, 18 out of 

 20 forecasts correctly verified the presence or absence 

 of extended coast-line clutter to within 1 to 2 hours 

 of the total duration. With extended echoes existing 

 during 55 per cent of the test days over the coastline, 

 this accuracy is considerably greater than could be 

 arrived at by any purely statistical procedure. It 

 should be stated here that these forecasts proved to 

 be particularly valuable to the radar personnel, since 

 certain engineering tests in i:>rogress on the radars 

 made an accurate evaluation of the effects of super- 

 refraction on the radar set performance necessary 

 during the calibration flights. 



As an additional check on the existence of super- 

 refraction over water, forecasts were made of the 

 ranges for S-band radars and A-^HF communication 

 on low-level coverage flights into the Gulf. Of a total 

 of ten flights, six were made during periods of ex- 

 tended coast-line return, three of which were cor- 

 rectly forecast as giving superrefraction on S-band 

 radar and two as giving increased ranges on VHF 

 communication. Although this is not so accurate as 

 the forecast of surface effects, a large error may have 

 been introduced by the fact that the forecasted duet 

 heights were of the same order of magnitude as the 

 lowest levels attained by the plane in its flight over 

 the Gulf. All the over-water flights showed normal 

 horizon ranges at 1,000- to 3,000-ft levels on the re- 

 turn legs. 



In another attempt to determine the vertical cov- 

 erage patterns resulting from low-level nonstandard 

 propagation, several free balloon flights were made. 

 Standard weather service reflectors were attached to 

 the balloons, which were released from Army crash 

 boats at distances of 20 and 60 miles from the coast. 

 Possibly because of lack of radar effieiency, only the 

 balloons released at 20 miles were picked up by the 

 coastal radar. Although no nonstandard conditions 

 were observed during the releases, the method seems 

 suitable for making vertical coverage measurements. 



Eadar and weather data for the period January 1 

 to March 15 were tabulated and analyzed during the 

 month of March. The primary data consisted of S- 

 band radar reports from Winter Garden and Lees- 

 burg and low-level soundings from Leesburg, sup- 

 plemented by the synoptic charts and radiosonde ob- 

 servations supplied by the 26th Weather Eegion. 



The analysis resulted not in a system of forecasting 

 such as that developed for over-water use but rather 



