Profilor of winds

A Profileur of winds is a type of Radar assembled vertically used in Météorologie to measure the direction and the speed of the winds. Such an apparatus is often provided with a CLOSE-CROPPED ( R adio- has coustic S ounding S ystem), a system of survey radio-acoustics of the atmosphere, to estimate the Température in low the Troposphère.

Principle of operation

A profilor of winds is a radar Doppler with very high resolution (typically 100 to 200 m with the vertical and less than 100 m to horizontal) pointing vertically. He notes the variation of the index of refraction of the air according to the theory of the diffusion of Bragg (Loi of Bragg). This variation is due to turbulences of the air moving by the variation of its density. When the index changes at a distance which corresponds to half the wavelength of the radar used, there is a constructive return between the waves returning of the successive zones of variation.

This distance from variation is typically about a few centimetres with a few meters with the result that one will use a wavelength of this order of magnitude. It is the same spectrum as for the weather radars and thus one also follows with the profileurs, of the targets such as the rain, snow, the insects, the birds and even sometimes the planes. It is thus necessary to filter these targets of the desired signal to be able to estimate the true air volume displacement.

To measure the horizontal wind, the radar is directed in two orthogonal directions one of the other with a certain angle of the zenith. For example, one analyzes the Doppler change of the echoes emitted by the radar in northern direction with 30 degrees of the vertical and then towards the east to find the components speed in these directions. Then, one finds the air velocity according to the vertical while pointing towards the zenith. One combines the three components thus found in the equation of mass continuity to obtain the total wind and thus his horizontal component.

Incidentally, one obtains the reflectivity of the hydrometeors at high resolution and their falling speed. That gives an additional detail to that of any close weather radar. Indeed, this last has less of resolution but covers a very great area and does not see the vertical component speeds of the particles, since it probes horizontally.

The profileurs of winds operate in a broad range wavelengths. The layer between the ground, where the friction slows down the air volume displacement, and the height where the latter becomes negligible is called the planetary boundary layer (CLP). It is about less than 3 kilometers in general. In this layer, the gradients of temperature and moisture are large and require a low wavelength. The profileurs UHF (30 to 40 cm) are thus used for this study. They are compact and can be moved easily: they are often used for data acquisition campaigns.

Profileurs VHF (1 to 10 m) are sensitive to variations in temperatures varying at longer distances, therefore above the boundary layer. They will be used for the survey of the atmosphere from 2 to 16 km above the ground. According to the wavelength, their dimensions vary. More the wavelength is large plus the antenna will be it (a wavelength of one meter requires an antenna of 10 X 10 m, one from 6 to 10 m is equivalent to the dimension of a football field) with the same resolution.

In France, the services of Weather France are authorized by the ANFR to use the following wavebands for the radars profileurs of wind: 45,00 to 68,00 MHz; 900,00 to 1 400,00 MHz and 35,20 to 36,00 GHz. There exist also some radars profileurs of wind in the band of the 72 MHz in agreement with EDF (the services of intervention of EDF use band 72,5250 to 73,1125 MHz for their radiocommunications).

See too

References

Angevine, W.M., A.W. Grimsdell, L.M. Hartten and A.C. Delany 1998. The Flatland boundary to bush-hammer experiments . Bull. Land-mark. Meteor. Plowshare, 79,419-31.
Ecklund, W.L., D.A. Casing, & B.B. Balsley, HAS UHF wind to profile for the boundary to bush-hammer: brief description and initial results , J. Atmos.Oceanic.Tech., 5,432-441, 1988.
Mailhot J., J.W.Strapp, J.I. MacPherson, R. Benoit, N.R. Donaldson, F. Froude, Mr. Benjamin, I. Zawadski, and R.R. Roger, 1998: The Montreal-96 Experiment one Regional Mixing and Ozone (MERMOZ): Year overview and nap preliminary results . Bull. Land-mark. Meteor. Plowshare, 79, 433-442.
Rogers, R.R., S.A. Cohn, W.L. Ecklund, J.S. Wilson, and D.A. Casing, Experience from one year off operating has boundary-to bush-hammer to profile in the center off has broad city , Ann. Geophysicae, 12,529-540, 1994.

External bonds

Profileur of the McGill University, Montreal, Canada
Network of profileurs of the NOAA
Profileurs of winds of France on the site of [[Blaise-Pascal university] of Clermont-Ferrand] the
Network of profileurs of Europe by [[Met Office]]

Random links: