RADIOSONDES -- An Upper Air Probe
The radiosonde is a balloon-borne instrument platform with radio transmitting capabilities. It is lighter than air balloon. Originally named a radio-meteorograph, the instrument is now referred to as a radiosonde, a name apparently derived by H. Hergesell from a combination of the words "radio" for the onboard radio transmitter and "sonde", which is messenger from old English.
It is released from a location in which characteristics of the troposphere are desired to know. It slowly makes its way up through the atmosphere vertically while communicating atmospheric conditions and weather back to the ground through its radio communication link.
There are several advantages to using radiosondes to measure water vapour in the atmosphere. First is that it can be placed anywhere. Scientists can go to almost any location and release a radiosonde and accumulate desired data. Also, little processing of the data is needed. True humidity, temperature, pressure, and any other data can be obtained without lengthy processing and manipulating of the data. Finally, since radiosondes have been around for a long time, they are very reliable and their results have been proven to be dependable and accurate. Unfortunately, there are several drawbacks to the use of radiosondes. Because of the fundamental nature of balloons, the equipment can only be used once and then lost. This makes the use of radiosondes very cost inefficient. Also, in many cases, radiosondes are not as useful as other methods. There is a delay in the reception of data, because you physically have to be in the location where data is wanted, then release the radiosonde, wait until it reaches the desired altitude, then acquire the desired atmospheric data. If data is needed for prediction of bad weather, or rapidly changing weather, this method is not useful. Finally there is a severe limit on the physical space that one can measure using a radiosonde. Once released, data are abundant for the space in that area. This completely eliminates the possibility of making maps of significant area with this technique.
The radiosonde contains instruments capable of making direct in-situ measurements of air temperature, humidity and pressure with height, typically to altitudes of approximately 30 km. A radio transmitter located within the instrument package transmits these observed data immediately to the ground station. The ascent of a radiosonde provides an indirect measure of the wind speed and direction at various levels throughout the troposphere. Ground based radio direction finding antenna equipment track the motion of the radiosonde during its ascent through the air. The recorded elevation and azimuth information are converted to wind speed and direction at various levels by triangulation techniques.
A rawinsonde (or radio wind sonde) is a radiosonde package with an attached radar reflector that permits radio-direction finding equipment to determine the wind direction and wind speed at various altitudes during the ascent of the package.