Radiosonde housing

A housing for electrical components and equipment sent aloft with a weather balloon to measure atmospheric parameters comprises a light-weight polystyrene case that serves as a shipping container and flight package. The housing also includes an air duct and a humidity sensor in the duct. Means in the duct minimize the reflection of sunlight onto the sensor to maintain at ambient temperature the air which flows over a humidity sensor.

BACKGROUND OF THE INVENTION 
The invention relates to a radiosonde housing. 
One known method of measuring atmospheric parameters such as temperature, 
humidity, and pressure at various altitudes has been the use of a 
miniature radio transmitter and sensing instruments carried aloft by, for 
example, an unmanned balloon for transmitting data signals back to earth 
stations. This transmitter, with accompanying sensing instruments, is 
generically known as a radiosonde. Current designs employ analog circuitry 
contained in a relatively large and heavy container. Furthermore, the 
battery and humidity element necessary for the operation of the radiosonde 
have been shipped in cans external to the radiosonde, a factor which 
increases both the shipping weight and volume. 
The ambient humidity in a radiosonde is sensed by a humidity sensor which 
is exposed to the ambient air. However, if the humidity sensor is heated 
by being exposed to the sunlight, it may well produce erroneous 
indications of humidity. Ducts employed in the sensor radiosondes were 
mechanically complex and costly, and introduced an undesirable error in 
humidity readings by warming the air within the ducts. In addition, these 
prior art ducts consisted of several individually molded plastic pieces 
which required assembly. 
It is an object of the invention to reduce the shipping weight and volume 
of a radiosonde. 
It is another object of the invention to provide a sturdy, shock absorbent, 
light weight and inexpensive housing for the flight package which contains 
the radiosonde. 
A still further object of the invention is to provide a radiosone housing 
which functions as a direct sunlight screen in which the housing 
integrally forms a duct which allows an adequate air flow across a 
humidity element while also maintaining the air at, approximately, ambient 
temperature. 
SUMMARY OF THE INVENTION 
The present invention provides a light-weight housing formed, for example, 
from expanded polystyrene beads. This housing serves as a light-weight 
shipping package which may contain the battery, humidity element, antennas 
and other eletronic sensing and transmitting equipment. This shipping 
package also serves as the flight housing for the radiosonde and again has 
the advantage of being light in weight, sturdy, shock absorbent, and 
inexpensive. Such factors are particularly important in systems such as 
radiosondes which must be carried aloft by a balloon and which must also 
be able to withstand severe wind turbulance. Moreover, since a free fall 
back to earth after balloon burst destroys a radiosonde after only one 
use, it is highly desirable to keep the housing cost to a minimum by using 
inexpensive polystyrene or similar material. 
To accurately record humidity, the sensing element in the radiosonde of the 
invention is shielded from the sun to prevent warming of the element. Thus 
it is necessary for the humidity sensing element to be placed within a 
duct so as to be shielded from the sun. The duct is integrally formed 
within the radiosonde housing, reduces heating of air to a minimum 
previously unachieved and improves humidity sensor transient response time 
.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the embodiment of the invention depicted in FIG. 1, a radiosonde 
housing, generally indicated as 10, is shown in its shipping 
configuration. The navigational and telementry antennas 11, battery 12 and 
sensors including a humidity sensing element 13 placed in a shipping 
container 34 are all packed within the housing for shipment. To seal out 
moisture, the humidity sensing element 13 and its shipping container 34 
may also be sealed in a foil packet. 
In FIG. 2, the radiosonde housing 10 is shown divided along lines a-b into 
a top 21 and bottom 20 so as to show an outer two-piece shell revealing a 
hollow interior, which contains the components such as the main printed 
circuit board 14, transmitter 15, battery 12, thermistor sensor 16, 
humidity sensing element 13, and a pressure sensor 17. The housing 10 also 
has formed therein an air duct 18, which is described in greater detail in 
a later part of the specification. 
In use, the radiosonde housing 10 is shipped to a user in the form depicted 
in FIG. 1. The user then removes packing restraints such as tapes and 
bands to release antennas 11, the battery 12 and the humidity sensor 
container 34. The humidity sensor 13, upon removal from the protective 
shipping container 34, is positioned in duct 18 through aperture 30 and 
supported by clips 24 and connected electrically by clips 24 to the main 
printed circuit board 14. Battery 12 is connected electrically to circuits 
14 and 15. The battery may either be an alkaline type, ready for immediate 
use, or a water-activated unit employing a magnesium cuprous chloride 
chemical system. The antennas 11, and thermistor 16, are pulled outside of 
the housing. Finally, the housing 10 is attached to a weather balloon and 
is carried aloft. The flight configuration of the radiosonde is shown in 
FIG. 3. It will thus be appreciated that the housing is used both as the 
shipping package for the radiosonde and also as the housing for the 
radiosonde when the latter is sent aloft. 
The housing 10 can be fabricated from any light-weight, sturdy and 
inexpensive material having good insulating properties, and may be 
advantageously made of expanded polystyrene beads. The housing 10 is 
compact, easy to use and is durable enough for flight. 
One problem with measuring humidity in prior art radiosondes is the error 
caused when the air whose humidity is to be measured is warmed by both the 
sun and the radiosonde itself. This problem can be illustrated by 
considering the relationship between relative humidity ["RH"] and the 
saturated water vapor pressure. Relative humidity is determined by the 
equation RH=W/WS where W equals the weight of water in a given volume and 
WS equals the weight of water when the same volume is saturated. If the 
ambient temperature of the air entering the duct is changed by a small 
amount, the weight of water for saturation is changed resulting in an 
error in the relative humidity measurement. FIG. 5 shows the humidity 
measurement error in percent for 1.degree. C. air temperature change 
verses ambient temperature. 
One known method of lessening the warming of air has been the use of a duct 
in which the humidity sensor is positioned. However, the ducts in prior 
radiosondes still warm the ambient air to a point resulting in appreciable 
error in humidity measurement. The air duct 18 of the radiosonde of the 
present invention reduces the humidity measurement error to almost 
one-half of that obtained in the prior art arrangements. As shown in FIG. 
6, wherein plot 40 represents the results obtained with a prior art NWS 
duct and plot 41 represents the plot obtained with the present invention, 
the temperature error due to loading above 600 millibars is about one half 
for the present invention than that exhibited by the prior art duct. 
To this end, in contrast to the prior art duct which consisted of several 
individually molded plastic pieces which also required assembly, the duct 
18, according to one aspect of the invention, is molded into the two 
halves 20 and 21 of the radiosonde housing 10 and does not require 
separate molding or assembly, which further reduces material and labor 
cost. 
The duct 18, as shown in FIG. 4, is molded within the polystyrene housing 
into a venturi form. The venturi formed duct 18 increases the flow of 
external air over the humidity sensor 13 mounted within the duct while 
shielding the sensor 13 from direct solar radiation. Internal surfaces 27 
and 28 of the interior wall of duct 18 are blackened to prevent solar 
radiation reflection onto humidity sensor 13, whereas nonblackened 
surfaces 32 and 33 remain a light color, such as white, to reflect solar 
radiation and minimize warming of the interior wall of duct 18 and thus 
minimize warming of the ambient air adjacent the interior wall. As the 
housing rises aloft, air is forced into the inlet port 23 of duct 18 and 
is guided so as to flow across humidity sensor 13, which is longitudinally 
positioned in the center of the narrowest point of air passage in duct 18 
and is maintained in this position by a pair of laterally offset clips 24. 
The offset clips 24 allow easy external insertion of the humidity sensor 
13 through aperture 30 and enable the humidity element 13 to be held 
orthogonally to the printed circuit board 14. Air leaves duct 18 through 
outlet port 29. The venturi configuration of duct 18 tapers toward outlet 
port 29, and sensor 13 is preferably positioned nearer to outlet port 29. 
Another improvement resulting from the design of duct 18 is air flow and 
transient response of the humidity sensor 13. In one set of wind tunnel 
tests performed on the radiosonde of the invention at an ascent rate of 
one meter per second, the humidity sensor 13 was placed in a duct designed 
according to the present invention, and in another set of tests the same 
humidity sensor 13 was placed in a prior art design employed by the U.S. 
National Weather Service ["NWS"]. The results of these tests indicate that 
the transient response time for the duct according to the present 
invention is equal or faster than that obtained with the prior art duct. A 
summary of the tests results is as follows: 
______________________________________ 
Conditions: 20.degree. C. 
1 meter/sec aspiration 
30% RH to saturation 
Average of 10 repeated cycles 
Transient Response: 
DUCT 
Present Invention 
NWS 
Time in Seconds 
67% of Final Reading 
0.5 0.7 
95% of Final Reading 
1.2 1.8 
______________________________________ 
The shape of the housing, other than the duct configuration hereinabove 
described, is illustrative only and it is to be understood that the use of 
a polystyrene material for construction of the housing is only one 
preferred embodiment. It will be further understood that whereas the 
invention has been herein disclosed with respect to one embodiment 
thereof, these and other variations may be made without departing from the 
spirit and scope of the invention.