INSTRUMENTS AND TECHNIQUES FOR METEOROLOGICAL MEASUREMENTS 
By MICHAEL FERENCE, Jr. 
Evans Signal Laboratory, Signal Corps Engineering Laboratories 
INTRODUCTION 
During the past several years a number of authors 
[15, 19, 24] have adequately and critically discussed 
meteorological equipment commonly employed for 
weather observations. The purpose of this article, there- 
fore, is to examine the more recent equipment and 
techniques and focus attention on the degree of relia- 
bility of this equipment. Three things will become ap- 
parent from this discussion: first, that the major effort 
during recent years has been devoted to improving 
upper-atmosphere sounding systems; second, that elec- 
tronic techniques are playing an ever-increasing and 
important role in equipment design; and third, that 
with the manyfold increase in information now possi- 
ble for weather centrals an urgent need exists for a 
more efficient utilization of data transmission and pres- 
entation systems. 
The pattern that will be followed in this article is 
to present a functional description of equipment or 
technique, followed by a more detailed examination of 
the major components of the equipment, with the view 
of analyzing errors and presenting an over-all evalua- 
tion of the system. In an article of this length it will 
not be possible to present all the data employed in the 
evaluation, but an effort will be made to supplement 
the discussion with appropriate references to the liter- 
ature. No mention will be made of aerographs, sferics 
equipment, and radar storm-detection equipment, since 
they are described elsewhere in this Compendium. 
RADIOSONDE-RADIOWIND SYSTEMS 
General Description. Within the past ten years more 
time and effort have probably been expended on the 
development of radiosonde-radiowind systems than on 
any other single meteorological system. Many systems 
have been proposed and several have been successfully 
developed and put into operational use [12, 20, 27, 32]. 
However, the major portion of the present survey will 
be devoted to the latest equipment development, and 
in particular to the redesigned radiosonde-radiowind 
system just being introduced in this country. The 
design features of this system are such as to lend them- 
selves to mass-production techniques. 
A complete radiosonde-radiowind system consists 
of a number of major components—flight equipment, 
including the meteorological sensing elements, radio 
transmitter, and balloon; a ground direction finder 
for precise angle measurements; and ground recorders 
or data-presentation equipment. As constituted at pres- 
ent, the system will yield information on temperature, 
1. Consult articles by A. C. Bemis, M. G. H. Ligda, R. 
Wexler, and R. C. Wanta. 
relative humidity, pressure, and the magnitude and 
direction of the wind. 
One of the earliest successful radiosonde-radiowind 
systems (placed in widespread use during World War 
II) is the now familiar Radio Set SCR-658. This set, 
operating at 400 megacycles per second (me sec), 
and now being used by the United States Weather 
Bureau and the United States military services, repre- 
sented the best design compromise between the availa- 
bility of mexpensive and efficient radio-frequency os- 
cillators for radiosonde use and the requirement of a 
narrow antenna pattern. However, it became evident 
that two sources of error were present in this system: 
(1) the very broad antenna pattern which limited wind 
determination to within 15 degrees of the horizon, and 
(2) the presence of the human link in the tracking sys- 
tem. Both sources of error have been considerably 
reduced in the design of the new radiowind system 
operating at 1680 me sec and incorporating auto- 
matic tracking features. To take advantage of the 
increased accuracy possible in wind determination, the 
sensing elements of the radiosonde have also been 
improved. A brief, qualitative description will be given 
here of the over-all operation of the system, followed 
by a more detailed analysis. The block diagram of 
Fig. 1 will aid in this description. 
The flight equipment of this redesigned radiosonde 
is basically that first introduced by Diamond and 
Hinman [10]. Resistance changes of the temperature 
and humidity elements control the audio modulation 
frequency (10-190 cps) of a blocking oscillator which 
in turn deletes 65-microsecond segments from the 
1680-me radio-frequency carrier at the audio rate. This 
modified 1680-me carrier is transmitted to the ground 
and received by a parabolic antenna of the automatic 
direction finder which thus tracks the airborne trans- 
mitter (see Fig. 2). The received signal, suitably modi- 
fied by the direction finder, is then divided into two 
parts—one used as an error signal for tracking purposes 
and the other (containing the meteorological message) 
fed to a recorder. A record is also made of the azimuth 
and elevation angles of the direction finder at pre- 
scribed time intervals. From these basic data, tempera- 
ture, pressure, relative humidity, and wind velocity as 
a function of altitude may be computed. In order to 
analyze the errors present in this new radiosonde- 
radiowind system it is necessary to discuss its major 
components in some detail. 
Radiosonde Flight Equipment. A typical radiosonde 
now in general field use by the Weather Service of the 
United States Air Force is illustrated in Fig. 3. This 
instrument consists of a meteorological modulator, a 
radiosonde transmitter, and batteries. The modulator 
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