INSTRUMENTS AND TECHNIQUES FOR METEOROLOGICAL MEASUREMENTS 
altitude performance comparable to the daytime per- 
formance of the neoprené balloons has been attained. 
A curious variation of the average bursting height of 
the natural rubber balloons with the seasons has re- 
cently been noted. During the summer and autumn 
about 55 per cent of the balloons reached altitudes of 
about 90,000 ft. During the winter and spring, only 
8 per cent reached this altitude. Whether or not this 
variation in balloon performance can be attributed to 
the seasonal variation in ozone remains to be deter- 
mined. 
Ascensional Rates. One important way of improving 
the over-all performance of the present radiosonde- 
radiowind system is to increase the ascensional rate of 
the balloons to about 2000 ft min. With values of 
this order, very favorable elevation angles can be at- 
taimed for wind determination. This objective should 
be attained without sacrificing the bursting altitude of 
the balloon and without using an excessive amount of 
hydrogen. This latter consideration is of practical im- 
portance. To date, the use of rubber balloons to attain 
high ascensional rates has not been entirely successful. 
However, the use of balloons made of polyethylene 
material 0.0015 in. thick, and designed to conform to 
an optimum aerodynamic shape, has given rather in- 
teresting results. Teardrop balloons, 22 ft long and 
544 ft maximum width, have attained stable rates of 
climb in excess of 2000 ft min up to altitudes of 
45,000 ft. 
Im studies of the ascensional rates of the 2000-¢ 
balloons for varying free lifts Sharenow [29] has found 
that the ascensional rates of spherical rubber balloons 
do not continue to increase with increasing free lift. 
The optimum free lift for the 2000-¢ balloon is roughly 
5000 g, providing the maximum average ascensional 
rate and a high bursting altitude. Greater free lifts 
reduce the average rate of ascent and also the bursting 
altitude. In analyzing the reasons for these effects, 
Sharenow concludes that the back pressure of the bal- 
loon controls in part the initial ascensional rate of a 
given balloon and thus the over-all average rate. 
According to Vaisala [24, p. 151], the back pressure 
of a balloon of thickness d and unstretched radius 79 is 
given by 
Ap = ne P(n), (3) 
where P(n) is characteristic of the material and n = 
r/ro, with r the radius at any time during inflation. 
In order to improve Ap appreciably, it appears necessary 
to change the characteristics of the material, since the 
thickness d and unstretched radius 7) are reasonably 
fixed by pay-load and altitude requirements. Sharenow 
suggests investigating the effect of cure on back pres- 
sure. 
Summary. These basic problems in balloon develop- 
ment are in need of solution: (1) substantial increase 
im ascensional rates of balloons without impairing other 
desirable performance characteristics, (2) design of a 
balloon to reach heights of about 150,000 ft economi- 
cally and with a high degree of reliability and, (3) im- 
1215 
provement of the nighttime performance of the syn- 
thetic balloon. 
PARACHUTE RADIOSONDES 
Introduction. The parachute radiosonde was designed 
to be launched from a weather-reconnaissance plane, 
operating at a maximum altitude of 30,000 ft and with 
a maximum speed of 300 mph. The basic data of 
temperature, pressure, and relative humidity, obtained 
from the flight level to the earth’s surface, are trans- 
mitted in Morse code signals back to the plane. The 
equipment consists of the telemetering device, sensing 
elements, transmitter, and parachute assembly. 
Telemetering System. One of the early requirements 
of this type of radiosonde that greatly influenced its 
design was that the telemetered data must be received 
in the plane with the minimum amount of recording 
equipment. A very simple telemetering system using 
phonograph-type disks was suggested by J. M. Brady 
and developed into a practical parachute radiosonde 
by Brailsford [5]. In the present system, a vinylite 
disk with 200 grooves is used. Each groove in turn is 
engraved with a unique set of Morse code letters, so 
that the exact position of a set of pickup arms can be 
determined from the code letters. The three pickup 
arms, arranged around the circumference of the disk 
at about 90-degree intervals, are mechanically linked 
to an aneroid capsule, a bimetal, and a hair hygrometer. 
As the sensing elements respond to changing mete- 
orological conditions, their respective pickup arms 
sweep across the disk. 
Only an 85-degree sector of the disk contains the 
coded information. As the disk rotates, this sector comes 
into contact with each stylus of the pickup arm suc- 
cessively, so that the transmitted signal will consist of 
three code groups representing pressure, temperature, 
and humidity, followed by a pause. In order that each 
pickup arm can move freely in accordance with atmos- 
pheric changes, the 85-degree sector is raised about 
0.62 in. above the rest of the disk. By this device, all 
arms are free except the one transmitting a signal. 
The over-all sensitivity of the coding system is de- 
pendent on the number of grooves and the range of 
the sensing elements. For this instrument, the pressure 
sensitivity is 5 mb per groove width, the temperature 
sensitivity is 0.8C per groove, and the relative-humid- 
ity sensitivity is 2 per cent per groove. The self-starting 
unidirectional motor drives the disk at a rate of 12 
rpm, so that with a descent rate of 1200 ft min, the 
atmosphere is sampled once every 100 ft. 
Temperature. In designing the various components 
of the radiosonde, it is important to bear in mind the 
transient shock of 20g to which the instrument is sub- 
jected at release. This is particularly true of the sens- 
ing elements. The bimetal used for temperature meas- 
urements is in the form of an elliptical spring, with 
the inner surface of each leaf as the high-expansion 
side. With this construction it is possible to use quite 
thin materials for low temperature lags and at the 
same time retain a reasonably stiff structure. In addi- 
tion, it turns out that the element possesses linear 
