RADAR PROPAGATION FORECASTING 



111 



Leesburg sounding site, the SCK-5S-± at Winter Gar- 

 den, and the P-band SCE-371 at Crystal Elver dur- 

 ing their operating hours. The Tarpon Springs pro- 

 gram employed a medium early warning and an SCE- 

 615 radar, both on S band, located on the Gulf coast, 

 and the Crystal Elver SCE-271 and Winter Garden 

 SCE-58J:. The sounding station was located within 

 a half mile of the Tarpon Springs radar site. During 

 the entire program sea surface temperatures were 

 measured several times weekly at either the Cedar 

 Keys or Anclote Crash Boat bases out to a distance 

 of about 20 miles at 2- to 4-mile intervals. 



Low-level soundings were made during the entire 

 project primarily as an aid in interpreting radar per- 

 formance and in determining representative air values 

 and secondarily in an attempt to evaluate the opera- 

 tional suitability of the available sounding equip- 

 ment. Eesults of the latter portion of the work will 

 be presented later in this report. Ground-based sound- 

 ings were made by means of various combinations of 

 350- and 700-g balloons, 7-ft Seyfang kites, and a 

 small barrage balloon. 



The sounding stations were originally located so 

 as to be as representative as possible of interior and 

 coastal areas, although it was found later that, with- 

 out the additional mobility of airborne measurements, 

 individual ground-based soundings were likely to be 

 too strongly influenced by local topographic effects to 

 be completely reliable. Because of clearance require- 

 ments, the ground-based soundings were restricted to 

 600 ft, although it was determined that 1,000 ft would 

 be a mrich safer limit, with occasional measurements 

 up to 3,000 ft considered desirable. Soundings were 

 taken before dawn at 1000 Eastern War Time, after 

 sunset, and at 2300 EWT to obtain sufficient data on 

 the effects of radiation and other meteorological phe- 

 nomena. As far as specific sounding procedures are 

 concerned, both the small balloons and kites gave 

 satisfactory results, although for most of the wind 

 speeds encountered in this area the 7-ft kite was too 

 small for efficient operation. No limiting surface wind 

 speed can be given as a dividing line between kite and 

 balloon operation, since it has been found that occa- 

 sionally even in surface calms strong velocity gradi- 

 ents exist immediately above the surface layer. Al- 

 though it is realized that a barrage balloon is not a 

 standard item of equipment for sounding measure- 

 ments, it is unreservedly recommended and whenever 

 available should be used for simplicity and relia- 

 bility of sounding procedure. 



The method employed in this project for the 

 radar verification of superrefraction was to record 

 plan position indicator [PPI] scope appearance of 

 ground clutter return. The oscilloscope screen was 

 assumed segmented into eight 45° sectors, and the 

 maximum range on a ground target in each sector was 

 noted hourly during periods of operation. In an at- 

 tempt at correlating the radar performance with the 

 existing meteorological conditions, a classification 

 system was devised in which each distinguishable 

 propagation condition was assigned a single number.. 

 After collecting observations for some time from each 

 unit the data were examined, and an average of the 

 normal pattern was chosen as the standard, or class 

 1, type of propagation. Averages of reported increased 

 ranges in various sectors were calculated, while the 

 azimuthal variations due to shadow effects of sur- 

 rounding terrain, coast line and obstructions were 

 considered. The consistency with which various in- 

 creased range averages were attained determined the 

 number of classes of propagation assumed for each 

 unit. On the assumption that the meteorologist could 

 forecast and correlate i¥-curve types corresponding 

 with four types of propagation, four such propaga- 

 tion classes were chosen for the S-band V beam and 

 the P-band SCE-271 at Crystal Eiver. Figures 3 and 

 4 show the four classes of propagation as defined for 

 tlie SCE-271 at Crystal Eiver. Tlie class 4 picture 

 definitely shows the Florida coast-line detail painted 

 in. Observations from most of the other units, how- 

 ever, were classed only as 1 (standard) and 2 (non- 

 standard) propagation because of the radar shadows 

 of certain topographical features near their sites. Due 

 possibly to the peninsular situation of Florida, it was 

 impracticable to forecast accurately four different 

 classes of propagation, but forecasting on a basis of 

 two classes, standard and nonstandard, can and 

 should be done. 



During the first part of the over-land program an 

 attempt was made to forecast the specific M curves 

 as shown by the Leesburg and New Port Eichey 

 sounding stations and to correlate these curves with 

 the two to four propagation classes outlined for each 

 radar unit. However, because of the wide variation 

 of surface terrain (sand, swamps, lakes, forests) in 

 this general area, no single sounding was necessarily 

 representative of the entire air mass, since subsid- 

 ence and radiation effects almost certainly varied con- 

 siderably over the different kinds of terrain surround- 

 ing the sounding locations. On this basis, then, rather 



