Abstract: In the ultrasonic anemometer, ultrasonic emitting probes (E1-E4) and receiving probes (R1-R4) are mounted to define at least three different paths for propagation of ultrasonic signals in the air, and means (20) are provided for measuring the ultrasonic signal propagation time along the different paths and for calculating the direction and the speed of the wind based upon these measurements. The emitting and receiving probes are low frequency probes, the emitting probes producing a predetermined wave train type signal of frequency between 10 and 200 kHz; and the measuring and calculating means include means for measuring propagation time by correlation between the emitted and received signals.

Abstract: A measuring rod carrying a plurality of temperature sensors distributed over its height is placed in such a way that at least its lower part is embedded in the product of which the height is to be measured. Signals produced by the sensors and representing the temperatures in the locations of the various sensors on the rod are picked up and the variation in time of the picked-up signals is monitored in order to identify the lowest situated sensor which delivers a signal of which the variation is higher than a predetermined threshold.