244. RADIO WAVE PROPAGATION EXPERIMENTS 
NUMBER OF POINTS 140 
AVERAGE DIFFERENCE +0.10 
MEDIAN +0.1 
MODE -0.! 
o 0.30 CG 
DRY BULB TEMPERATURE 
DIFFERENCE DISTRIBUTION 
TEMPERATURE IN DEGREES C 
FREQUENCY OF OCCURRENCE 
VAPOR PRESSURE 
FROM TO DIFFERENCE DISTRIBUTION 
—1.8—1.7 Bs 
1.6 1.5 Bey 
— 1.4 -1,3 
—1.2 —t! 
— 1.0 -0.9 
—0.8 -0.7 
—0.6 —0.5 
—0.4 -0.3 
—0.2 —0.! 
° 
+ 0.1 +0.2 
+0,3 +0.4 
+0.5 +0.6 
+0.7 +0.8 
+0.9 +1.0 
+1. +12 
+1.3 +1.4 
+15 +1.6 
+ 1.7 +1.8 
NUMBER OF POINTS 140 
AVERAGE DIFFERENCE +0.06 
MEDIAN —0.1 
MODE —0.4 
o = 0.98 MILLIBARS 
MILLIBARS 
FREQUENCY OF OCCURRENCE 
DIFFERENCE EQUALS MIT PSYCHROGRAPH LESS WSC WIRED SONDE IN DEGREES CENTIGRADE 
AND MILLIBARS OF VAPOR PRESSURE 
Ticure 9. Instrument comparison. MIT psychrograph and WSC wired sonde on Aircraft L-4. 
the effects of weather) 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 over land are not suffi- 
ciently accurate for operation uses. Further study of 
the over-land forecasting problem is indicated. 
4. For maximum operational employment 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 
site, and supplementary airborne soundings are re- 
quired. : 
5. Psychrometer equipment MI-313/AM mounted 
on a slow, single-engined aircraft is suitable for low- 
level airborne soundings for propagation forecasting 
work. 
APPLICATION OF FORECASTING 
TECHNIQUES AND CLIMATOLOGY‘ 
MAtTErtaAL Coverep 
Radio-Meteorology. Since most of the basic infor- 
mation which has been obtained by various research 
‘By A. T. Waterman, Jr., and C. Harrison Dwight, Colum- 
bia University Wave Propagation Group. 
groups and in military and naval operations involving 
radar is familiar to the reader or is adequately covered 
in other reports,*” the essential points with reference 
to the effect of meteorological factors have been ex- 
tracted and are here presented in condensed form. The 
primary emphasis is on the phenomena associated with 
nonstandard propagation, i.e., on the conditions under 
which radar ranges are unusually large or unusually 
small. Related elements—temperature, humidity, the 
variation of each of these with height, M curves, 
ducts, ete.—are defined, and the role they play in the 
effectiveness of radar performance is discussed briefly. 
Specific Relationships between Meteorological Hle- 
ments and Radar Performance. Of the several investi- 
gations carried out on this subject, mostly in connce- 
tion with the prediction of trapping effects and consc- 
quently of radar ranges, one which has met with as 
much success as any and is fairly similar in essence 
to some of the others is presented here. It was devel- 
oped in a study of the modification that air undergoes 
in passing over water and is designed to predict the 
formation and subsequent structure of surface ducts 
which are formed along coast lines and over oceanic 
areas. 
From observations of the representative surface 
temperature and humidity of the air, the sea tempera- 
ture, and the wind direction and velocity, this method 
indicates whether a surface duct is to be expected and 
the height to which it is likely to extend. Practical 
