The uSonic-3 Multipath

Characteristics and usefulness of an innovative ultrasonic anemometer


Patrizia Favaron

12/7/20222 min read

Recently, Metek GmbH has released a new member of the uSonic-3 3D ultrasonic anemometer family: the Multipath model.

The major difference between the Multipath and all other models of uSonic-3 family is the latter are three-path only. In a three-paths ultrasonic anemometer the six ultrasonic heads are arranged so that they face exactly along three measurement directions not belonging to the same plane. Each measurement direction head couple is polled in a fixed sequence. The along-path wind components are then combined trigonometrically, and restituted according to a Cartesian monometric reference aligned to the sensor North arrow.

But, what happens if one of the paths gets obstructed? This may happen, for example during heavy rain. And as sound pulses are ultrasonic minimal diffraction and "passing around" occurs: the pulse is strongly attenuated and gets lost.

The uSonic-3 anemometers mitigate this issue by employing an oversampling strategy: each measurement path is polled six times in a rapid sequence, and each poll result is plausibility checked; plausible poll results are then combined in the average we all know as "raw data". The ratio of valid to total measurements is then used to define a quality score, which is transmitted to the sensor' data stream. This helps to reduce the effect of temporary obstructions, but does not eradicate the issue.

And this is just one - the most important. There is another, however: whatever the sensor geometry, in presence of non-zero wind (that is always on this planet) there will always be one measurement path downwind of it. This is not that good, as ultrasonic anemometers are also turbulence sensors: the downwind path will "see" some friction induced turbulence which is due to the sensor itself, and not to Mother Nature. In Metek anemometers this is overcome in part by a tiny correction made by firmware, derived from extensive wind tunnel experiments. But surely it would be better if this effect, as small as it is, would be not present at all.

Enters the uSonic-3 Multipath.

Now, each transmitted pulse is received and processed simultaneously by 3 receiving heads. Once again, emission alternates from head #1 to #2 (not shown) to #3, then back to #1 cyclically. The two figures here show emission from above, but the process is repeated using the bottom heads.

The end result is than now 9 measurement paths are present. From their processing, the firmware known where mean wind was blowing from, and gives users the option to not consider downwind paths (there still remain many more than the usual 3).

In addition: nine paths are many. This is even more evident if you consider that three of them are sampled simultaneously: the probability an obstruction intercepts them all is really small, resulting just because of this fact negligible in many applications.

So: the uSonic-3 Multipath is an ideal completion of the uSonic family with ideal uses in eddy covariance fluxes measurement, high-data-dependability in industrial surveillance stations, scientific research, and more generally whenever data count individually.

If you need some information about, you may send an enquiry to Servizi Territorio srl at (from Italy), or directly to Metek GmbH.