34 TECHNICAL SURVEY 
experiments. The path is 27 miles long with receivers 
mounted on a tower at several altitudes. The trans- 
mitters operate on the S and X bands and are 
pulsed. In addition, radar measurements are being 
undertaken by means of corner reflectors that are 
spaced at regular intervals along. a path 45 miles 
long. It may be expected: that valuable results will 
soon be received on the completion of these experi- 
ments. 
EXPERIMENTS IN 
THE SOUTHWESTERN UNITED STATES 
The Navy Radio and Sound Laboratory at San 
Diego has performed a considerable number of 
propagation experiments which have substantially 
aided our understanding of the phenomena of guided 
propagation. Moreover the meteorological conditions 
During the winter of 1942 to 1943, a series of 
measurements were made on the intensities of arti- 
ficial fixed echoes of a 700-mc radar located near 
San Diego,!?°138 and these were compared with 
measured temperature and humidity gradients in 
the lower atmosphere. A pronounced correlation 
between excessive echo ranges and nonstandard 
M gradients at once appeared. The quantitative 
aspects of these correlations will not be discussed 
here since they are very similar to others of this 
type already reported. 
Another set of observations where the receiver 
was located in a plane is shown in Figure 12.3 The 
receiving antenna was a Yagi, mounted in the nose 
of the plane, records being made when the plane was 
flying over the ocean toward the transmitter which 
was a 500-me radar. Figure~12 represents the results 
of flights at various altitudes on two different days, 
the maxima of the signal strength curves corres- 
ra 
ud 
2 : , 
SAN DIEGO RAYSONDE 2) 
a BASE OF TEMPERATURE INVERSION 8 e}SAREDIEGORG AY SOND oo? 
= 08 DO OU gd Ole 2 % 0% 0 °F © 
a 0°,50%, 0 G50 + °s ex) Bi) 
2 Orie 00% ° 00° ic O,e ote 
= Oo 9 a ° e °°? eo 8 
i C) ° e le 0 
a (0) o) so *. 
, DB ABOVE FREE SPACE 
10 15 
SEPTEMBER 
20- 25 30 5 
OCTOBER 
Ficure 13. Signal strength over 80-mile path, San Diego to San Pedro, correlated with height of temperature inversion. 
found in this part of the United States are rather 
unique; and, while they are not, perhaps, reproduced 
at many other places of the earth, they are so clear- 
cut and regular as to facilitate greatly experimental _ 
investigations and their interpretations. | 
The meteorological conditions at San Diego during 
most of the year are characterized by the presence 
of a high-pressure area and high-level subsidence. 
In more concrete terms, there is a surface stratum 
of comparatively cool and moist air on top of which 
there is a layer of very dry, warm air. The transition 
between the two strata is as sharp as can be found 
anywhere, and the transitional layer is often no more 
than a few hundred feet thick. The height of the 
transition layer above the ground is usually between 
1,000 and 3,000 ft and sometimes as much as 4,000 ft. 
ponding to the “lobes” of the transmitter pattern. 
On one of these days a duct was present as shown’ 
in the inset where M is plotted against height. The 
dot-and-dash straight line in this diagram represents 
the condition dh/dM = constant. The most con- 
spicious feature of Figure 12 is the difference between 
the signal distribution in the absence and presence of 
a duct at 500 ft, the lowest level measured, whereas 
the intensities agree fairly well at the higher levels. 
This behavior is in full agreement with the general 
predictions of propagation theory. Nevertheless, the 
detailed interpretation Jed to a slightly different 
result from that expected, as was brought out by 
subsequent experimental investigations. 
In 1944 a one-way transmission path was operated 
between San Pedro and San Diego, an over-water 
