INSTRUMENTS AND TECHNIQUES FOR METEOROLOGICAL MEASUREMENTS 
power and receiver sensitivity it should be possible to 
detect and locate clouds and cloud layers. These studies 
were based on the concept that the microwaves are 
scattered by water droplets of radii between 10 and 
30 microns. 
These results were strikingly verified with an experi- 
mental radar set designed to operate on a wave length 
in the one-centimeter region. The equipment was de- 
signed so that the radar beam was directed vertically 
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JULY 23,1948 
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structure of a cloud resolved by the equipment. At 
the bottom of the photograph is a record of a thunder- 
storm of 23 July 1948. This cumulonimbus built up to 
approximately 45,000 ft before it gave rise to an in- 
tense rainfall. The white vertical lines are due to instru- 
mental difficulties of detuning. The very deep hole to 
the right of the white lines is probably due to excessive 
attenuation by the rain. An example of a recording 
showing two distinct cloud decks is illustrated in Fig. 
TORRE APRIL 28,1948 — 
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Fre. 8.—Typical cross section of cloud structures taken with an experimental radar cloud-base and cloud-top indicator. Recordings 
were made at the Evans Signal Laboratory, Belmar, N. J. (Courtesy, Signal Corps Engineering Laboratories.) 
and the returned cloud echoes were presented on a 
standard “A” type cathode-ray tube. According to 
Gould [16], clouds were detected to heights in excess of 
45,000 ft. It has also been possible to locate clouds 
through several thousand feet of light rain. However, 
the minimum altitude that can be detected is about 
800 ft, this limitation being due to the length of the 
pulse and the finite recovery time of the radar receiver. 
In order to obtain continuous records of the cloud 
tops and bases, a conventional-type facsimile recorder 
has been modified to record the cloud echoes. The 
recording device gives a plot of altitude of the cloud 
versus time. In this way a good cross section of the 
clouds that go by overhead is obtained. 
Figure 8 is a typical record made with this radar 
set. At the top of the photograph is shown the fine 
9. The development of the radar cloud-base and cloud- 
top indicator represents one of the most significant 
advances in meteorological instrumentation of the past 
fifteen years. 
GENERAL TRENDS 
During the past ten years many new and clever 
experimental techniques have been developed and made 
available for the solution of meteorological problems. 
For example, a few of the more obvious advances the 
last decade has seen are (1) the introduction of radar 
capable of radiating megawatts of electromagnetic peak 
power and detecting micro-microwatts of scattered 
power, (2) basic advances in electro-mechanical systems, 
(8) basic advances in sensitive infrared devices, (4) 
development of versatile and rapid analogue and digital 
