1216 
response characteristics over the temperature range 
of +40C to —70C. The temperature lag constant of 
the radiosonde is about 15 sec. The over-all probable 
error in temperature measurement of this instrument 
is £1.5C. 
Pressure. The aneroid pressure-cell will operate over 
a pressure range of from 200 to 1060 mb. The probable 
error In pressure measurement is --5 mb. 
Humidity. The humidity measurements are subject 
to the inherent limitations of hair hygrometers. Un- 
fortunately, in most operations the hair is exposed 
very quickly to low temperatures, with the result that 
the lag constant becomes prohibitively high. Under 
these conditions the humidity indication can only be 
considered as qualitative. 
Transmitter. The radio transmitter used in this equip- 
ment is a one-tube standard contmuous-wave crystal- 
controlled oscillator, operating at specific frequencies 
in the range of from 2 to 12 me sect. The oscillator is 
interrupted by a keying relay actuated by the vibrat- 
ing styli of the pickup arms. The radio frequency output 
is about 14 watt, ample for the operational range of 
the airplanes. The transmitting link introduces no ap- 
preciable errors in the meteorological message. 
Parachute. The parachute assembly contains a 5-ft 
nylon parachute with a 135-ft load line. The trans- 
mitting antenna is woven into the load line. In addi- 
tion, the parachute is provided with a time-delay re- 
lease mechanism to delay the opening of the parachute 
from 3 to 5 sec. The over-all dimensions of the ‘“‘para- 
chute radiosonde,” including parachute and batteries, 
are about 10 in. by 6 in. by 19 in., and it weighs ap- 
proximately nine pounds. 
General Remarks. The equipment described above 
represents a first attempt to design a parachute radio- 
sonde to meet rather severe operating conditions. In 
spite of the fact that the humidity response is disap- 
pointing, as it is In most equipment, the radiosonde 
does give reliable and meaningful data on temperature 
and pressure. In addition, the simplicity of data trans- 
mission and reception has much to commend it. To 
improve the humidity response, the use of the lithium 
chloride strip, or better still the new carbon element, 
appears as a possibility. The new white-coated thermis- 
tors would improve the temperature measurements. 
However, use of these electrical elements would neces- 
sitate either an electrical-mechanical adapter kit, a 
very undesirable solution, or a complete redesign of 
the telemetering system. There are many elegant tele- 
metering schemes available today and possibly a suit- 
able one can be adapted for this use. 
WIRE SONDES 
Introduction. The wire sonde is a specialized piece 
of meteorological equipment designed to provide tem- 
perature and humidity data from the ground to a 
height of approximately 1000 ft for micrometeorological 
purposes and, more particularly, for microwave-propa- 
gation studies. The typical system includes sensing 
elements for temperature and relative humidity, ground 
recording devices, and captive-balloon equipment. Al- 
METEOROLOGICAL INSTRUMENTS 
though several systems [1, 2, 28] have been developed 
and are in use at present, basically they have much in 
common and differ only in details. The typical system 
that will be described and used to illustrate sources 
of error is one that was developed for the Signal Corps. 
Airborne Unit. The airborne unit consists of the 
sensing elements, radiation shields, blower, and bat- 
teries; the entire unit weighing approximately 34 lb. 
Temperatures are measured by means of a small ceramic 
bead, similar to that employed in the standard radio- 
sondes. Relative humidity is measured in two different 
ways, depending on the ambient temperature. For 
temperatures above freezing, the wet-bulb tempera- 
tures are read. A thermistor bead identical to that used 
for dry-bulb measurements is covered with a light 
cloth wick immersed in a well of water. For tempera- 
tures below freezing, the lithium chloride electrolytic 
element, previously described, is used. Proper ventila- 
tion for these elements is supplied by a small blower, 
powered by a six-volt cuprous chloride-magnesium 
water-activated battery. 
Recording Unit. The recording device consists essen- 
tially of a Wheatstone bridge with the balancing dials 
calibrated to read either the temperature directly or, 
by throwing a switch, the wet-bulb temperature or — 
relative humidity. The resistance network of the bridge 
is compensated for the resistance of the cable leads. 
In operation, the bridge is electrically connected to the 
thermistors through a nylon-encased three-conductor 
cable, 2000 ft long and weighing about 4.5 Ib. 
Balloon. To maintain the airborne unit at a reason- 
ably constant height during observations, a kite-type 
balloon called the ‘‘kytoon’” is used. The kytoon is 
streamlined and combines the aerodynamic properties 
of a balloon and a kite. The balloon is approximately 
61% ft long and 39 in. in diameter. During a strong 
wind, the kytoon lifts like a kite and is not driven 
downward as easily as a captive spherical balloon. 
Under average conditions the kytoon has a lift of about 
three pounds. Calculation of the height of the balloon 
is made by measuring the length of cable payed out 
and the angle of the cable leaving the reel. Difficulties 
in computation arise if a variable wind is present. 
Accuracy of Measurements. With the proper ex- 
posure and ventilation of the elements, temperature 
may be measured with a probable error of about +0.1C 
over the temperature range of from +40C to —40C. 
The wet-bulb reading can be made with a probable 
error of +0.2C for temperatures above 0C. The lithium 
chloride strip will yield values of relative humidity to 
within -+-2 per cent for temperatures to —10C and for 
humidity ranges of 15-96 per cent. Below this tempera- 
ture, the element rapidly becomes sluggish and its 
accuracy will strongly depend on the rate of humidity 
change as indicated earlier in this survey. 
General Comments. As stated above, many varia- 
tions have been suggested for wire-sonde equipment. 
Investigators at the Naval Electronics Laboratory [1] 
2. The kytoon is manufactured by the Dewey and Almy 
Chemical Co., Cambridge, Mass. 
