EES 
INSTRUMENTS AND TECHNIQUES FOR METEOROLOGICAL MEASUREMENTS 
use the lithium chloride strip for humidity over the 
entire temperature range. At the National Bureau of 
Standards [28] a wire sonde has been completed that 
will give accurate heights through the use of a sensitive 
pressure-altimeter in the airborne unit. This latter de- 
velopment will ease the serious problem of height de- 
termination. Practically all of the systems in use today 
will yield useful information within the lag-constant 
limits of a few seconds. 
AUTOMATIC WEATHER STATIONS 
Introduction. Although the need for automatic 
weather stations has been recognized by meteorologists 
for a good many years, it has not been until rather 
recently that developments in radio communications, 
telemetric techniques, and power units have advanced 
sufficiently to insure a practical system. In general, a 
system can be considered practical if it can operate 
unattended for at least three months and preferably 
six months under a variety of climatic conditions and 
furthermore be reasonably transportable. 
Several successful automatic weather stations have 
been designed to meet particular needs [7, 25]. How- 
ever, for general use in isolated regions where standard 
meteorological data at the surface are required, two 
systems have been developed sufficiently to warrant 
discussion here. One system uses the telemetric tech- 
nique, now extensively employed in the audio-modu- 
lated-frequency radiosonde [9]. The other is based on 
the “comb” principle of coding, originally suggested 
by the work of Moltchanoff [27]. The audio-modulated 
system has recently been described in some detail 
by Wood [85]. The present discussion will be centered 
around the code-type station which will be used to 
illustrate the accuracy of the data obtained from un- 
attended stations and the problems peculiar to this 
type of research. 
Code-Type Automatic Weather Station. The essen- 
tial components of any unattended station are pro- 
gramming and coding devices, sensing elements, power 
supply, and communications equipment. Most systems 
differ in the coding device employed. 
In the present system, measures of temperature, 
pressure, relative humidity, precipitation, wind speed 
and direction, and light from the sky are transmitted 
via a two-letter Morse code. In order to accomplish 
this coding, each indicating element has been so de- 
signed that changes in meteorological conditions are 
translated into angular positions of an arm. To measure 
the angular position of the arms, use is made of the 
“comb” principle. The freely moving arm ranges over 
a series of contacts insulated from each other and ar- 
yanged in the are of a circle. Two sets of combs in 
juxtaposition are utilized, one containing 100 narrow 
contact pins, and the other containing 10 contacts 
sufficiently wide for each to subtend 10 of the narrow 
pins. Associated with each wide contact, therefore, are 
the 10 narrow contacts, so that a total scale of 100 
unique units is provided by the combs. During the 
measurement of temperature, for example, a depressor 
bar is actuated and forces the freely moving tempera- 
1217 
ture arm into the teeth of the comb, necessarily touch- 
ing one wide contact, say, number 30, and one of the 
narrow contacts associated with it, say number 6. 
The number “36” then represents a measure of tempera- 
ture in arbitrary units. At the instant the arm touches 
the contacts, an electrical circuit through the depressor 
bar is closed, so that keying of the transmitter with the 
two-letter Morse code, characteristic of “36,” is made 
possible. 
Programming of the station is controlled by a marine 
chronometer, electrically wound. About two minutes 
before transmission time the clock turns on the power 
through a series of relays. While the gasoline engine 
used to power the station is warming up, various other 
electrical devices, such as radio tubes, are placed in 
operational readiness. At the end of two minutes a 
series of motor-driven cams for switching the sensing 
elements into the keying circuit are started. During 
the time the depressor bar keeps the arm of a sensor 
element in the teeth of the comb, coded signals at the 
rate of 12 per min are transmitted. The total trans- 
mission time required for the meteorological message 
and station identification is about two minutes. The 
station transmits once every three hours. The received 
signal may be taken down by a trained radio operator 
or fed into a tape recorder of standard design. 
The power required to operate this station is supplied 
by a gasoline-engine-driven generator having a capac- 
ity of about 714 kilowatts. The engine employs a four- 
cylinder four-cycle liquid-cooled system. The liquid 
that circulates through the engine is part of a 30-gallon 
heat-ballast tank required to maintain the temperature 
of the weather station at about 40F. For operations in 
cold regions, about one gallon of gasoline is consumed 
each day. 
Conventional radio-transmitting equipment has been 
adapted for this use. However, since the transmitting 
ranges may vary between 100 and 1000 miles and since 
transmitting conditions vary with location and season, 
the selection of appropriate radio gear has been on an 
individual station basis. It is expected that 75- and 
500-watt transmitters, covering the frequency range of 
from 2 to 20 me sec“, will provide satisfactory ranges 
for most applications. Provisions are available in the 
programming unit for converting automatically to ap- 
propriate daytime or nighttime frequencies in order 
to obtain optimum results. 
Measurements of temperature, pressure, relative hu- 
midity, winds, and precipitation are made with stand- 
ard weather-station equipment, slightly modified for 
the coding device. A Bourdon-tube measuring element 
is employed for the measurement of ambient tempera- 
ture. The element itself is exposed in a standard instru- 
ment shelter. Two sets of combs in series are used to 
cover the temperature range of from +110F to —60F. 
The probable error of the temperature measurement is 
about +1F. 
The pressure unit is a sensitive one-cell aneroid 
barometer whose indicating arm travels through 720 
degrees for a pressure range of from 1050 to 700 mb. 
For this pressure range, three sets of combs are 
