Radiosondage exploration

The radiosondage exploration is a process of weather measurements in situ. A whole of sensors measuring the relevant data integrated inside a case of a few hundred grams it radiosonde - rises in the atmosphere thanks to a latex balloon. The rise lasts in general between one and two hours and makes it possible to trace a vertical profile of the measured data - a cut of the atmosphere. Most of the time, the surveys are known as PTU-wind type, because one measures the donnéees P (Pression), T (Température), U (moisture), as well as parameter FF (force of the wind) and DD (direction of the wind). Sometimes specific sensors are associated (measurement of stratospheric ozone, for example).

History: pioneers

The first aerological surveys with an aim of including/understanding the nature and the structure of the atmosphere were carried out in second half of the 19th century by means of Cerf-volant S equipped with recorders with temperature and pressure (generally of the covered lampblack drums). However the kite showed its limits well quickly, by imposing the presence of a cable connected on the ground it to control, at the same time heavy and malcommode; moreover it did not allow measurements high-altitude and could not be used by too weak wind or too extremely. They are Gustave Hermite and Georges Besancon which, the first as of 1892, used a free balloon equipped with a recorder of temperature and pressure. Released of the constraints weighing on the kite, the balloon rises freely in the atmosphere as high as the resistance of its envelope allows him. The balloon falls down then on the ground and one can recover the recordings. In 1898, Leon Teisserenc de Bort organizes at the Dynamic Observatory of Meteorology of Trappes the beginnings of the systematic exploration of the upper atmosphere. He discovers that from some Altitude, varying at the same time according to the Saison and the geographical position, the temperature ceases dropping when one rises: it is the discovery of the Tropopause and the Stratosphère which he announces in 1902 with the Academy of Science. After some tests starting from 1927, Pierre Idrac and Robert Bureau associate with the Capteur S a small lamp broadcasting transmitter which retransmet on the ground in real-time measured values. The first flight of a balloon probes retransmettant by radio the temperature measurement is accomplished on January 17th, 1929. The recovery of the data is not dependant any more on a random recovery of the wreck of the balloon. It is the birth of the radiosondage exploration.

Devices of measurement

The basic elements of a modern Radiosonde are:

the power supply (which must support without failing a temperature variation going of +20°C, on the ground, -50°C, the altitude of the Tropopause)
the broadcasting transmitter (subjected to the same constraints)
a device of Radionavigation - or failing this a transponder or reflectors radar (essential to measure displacements of the balloon probes and to extract the force and the direction from it from the wind)
a pressure pick-up (absent on certain models of probes having other systems of measurement of altitude)
a temperature gauge and a sensor of moisture.

Process of measurement

The balloon is inflated in order to have a climbing speed from approximately 5 m/S. The probe takes measurements at approximately every ten seconds, which roughly speaking results in a sampling of the profile of the atmosphere all the 50 Mètre S, ground until the altitude of bursting of the balloon. The latter in general lies between 20.000 and 30.000 Mr.

Importance of the radiosondage exploration in weather forecasting

Models of numerical Forecast of time (NWP: Numerical Weather Prediction in English) solve the whole of the differential equations of the physics of the atmosphere thanks to very powerful computers. The radiosondage explorations make it possible to provide the initial data to the models and are thus an essential link of the chain of prediction. However, the cost high as men and material of the vast world network of radiosondage exploration led to its re-examination recently.

The throws of balloons thus were largely automated since the years 1990 and certain stations were closed with the profit of other sensors such measurements by the airliners and satellite S weather. However, the radiosondage explorations have as favors to be effectuables whatever the time and always at the same places whereas the other methods are not also robust: the data of planes cover only zones and limited altitudes, the satellite data are able to be extrapolated only in the layer above the clouds.

See too

External bonds

Site of consultation of the world radiosondage explorations of the University of Wyoming

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