RADAR PROPAGATION FORECASTING 



117 



NUMBER OF POINTS 140 



AVERAGE DIFFERENCE +0.10 

 MEDIAN -1-0. 1 



MODE -0.1 



CT 0.30 C 



FROM TO 



- 1.8 -1.7 

 -I .6 -1.5 



- 1.4 -1.3 



- 1.2 —I.I 



- 1.0 -0.9 

 -0.8 -0.7 

 -0.6 -0.5 



- 0.4 -0.3 

 -0.2 -0.1 





 + 0.1 +0.2 

 + 0.3 +0.4 

 +-0.5 +0.6 

 + 0.7 +0.8 

 + 0.9 +1.0 

 + I.I +1.2 

 + 1.3 +1.4 

 + 1.5 + 1.6 

 + 1 .7 + 1.8 



FREQUENCY OF OCCURRENCE 



VAPOR PRESSURE 

 DIFFERENCE DISTRIBUTION 



NUMBER OF POINTS 140 

 AVERAGE DIFFERENCE +0.06 

 MEDIAN —0.1 



MODE -0.4 



a = 0.98 MILLIBARS 



I 



1 



!^ . ■■■..-..■.■ ' ■. ■ ' ■■ ' ■ ' I ' 



I 



JL 



t^^t^ttiiitititititititi 



20 



' FREQUENCY OF OCCURRENCE 



DIFFERENCE EQUALS MIT PSYCHROGRAPH LESS WSC WIRED SONDE IN DEGREES CENTIGRADE 

 AND MILLIBARS OF VAPOR PRESSURE 



FitiuiiE 9. Instrument conijiarison. MIT psychrogrupli ;ind WSC wired sonde on Aircraft L-4. 



The AA^SC wired sonde was mounted on the strut 

 of the L-4: some 5 ft away from the cabin of the 

 plane. The comparison data follow: 



Dry bulb 



Number of pairs of readings: 



Average difference; 



67% of the points agree to within 



Vapor pressure 



Number of pairs of readings: 



Average difference: 



67% of the points agree to within 



140 



+ 0.10 C 



0.30 C 



140 



+ 0.06 mb 



0.98 mb 



The differences in moisture readings are rather 

 larger than desirable. 



The sling psychrometer ML-24A was tested sim- 

 ilarly but was considered unsuitable because of lack of 

 protection from radiation. 



Of the ground-based sounding equipment used dur- 

 ing the program, the MIT psychrograph consistently 

 gave excellent results. The AVSC wired sonde is capable 

 of good results, but several mechanical difSeulties 

 render it unsuitable for field use by the services in its 



present form. It is exjiected that these difficulties will 

 be ironed out in a revision of the wired sonde. 



The following statements are the personal opinions 

 of the authors and do not represent the official opinion 

 of the Army Air Forces Board. 



1. There is a military need for a proi^agation fore- 

 casting service. If a radar set is to be used most efB- 

 cienth', its full capabilities and limitations (including 

 the effects of weatlier) must be known. 



2. Propagation forecasts over water using the 

 method described in reference 3 are sufficiently 

 accurate for operational purposes. It is recommended 

 that further experimental study of long over-water 

 propagation and vertical coverage be carried on. 



3. Propagation forecasts o\'er land are not suffi- 

 ciently accurate for operation uses. Further study of 

 tlie over-land forecasting jiroblem is indicated. 



4. For maximum operational empiloyment of the 

 forecasts, the forecaster should be located at the radar 

 site. Communication with a class A weather station, 

 a ground-based low-level sounding station at the radar 



