Ultrasonic anemometers enable measurements of multiple physical quantities with only one device. As fully heated sensor model option, they can be employed worldwide even in most harsh environments.
For decades, cup anemometers have been the dominating sensor for measuring wind speed and wind vanes have been the main sensor for measuring wind direction. Selecting a First Class cup anemometer like from Adolf Thies, Windspeed Ltd. (trading as Vector Instruments) or WindSensor, ensure the base for measuring reliable, bankable results.
In the world of meteorology and in particular for wind measurements, ultrasonic anemometers get an increasingly important role. These instruments can measure wind speed and wind direction through ultrasonic waves. In addition, 3D ultrasonic anemometers can measure acoustic virtual temperature, turbulence intensity and about 70 more variables that allows users to substitute several other sensors in an economic, effective and accurate way. And the best is: since there are no rotating parts like cup anemometers or wind vanes, these sensors virtually have no wear and tear and are a maintenance free solution to study 3D wind fields.
For areas with perma-frost or hard winters (arctic or alpine conditions), ultra-sonic anemometers can be equipped with an ample heating feature, that also supplies the sending and receiving caps in order to operate under all conditions as heated sensor with no wear and tear.
Required for wind speed
One of the two main functions of an anemometer is to know how specific is the wind speed at a specific location and time. This meteorological equipment is necessary to be able making according calculations on the weather forecast, resp. the wind forecast. Also, the wind speed that’s thrown from the anemometers is necessary for air and water navigation bodies, hence these devices often can be found at airports, harbors or alpine stations.
Covering a wide operational range and a huge variety of physical variables that can be measured, ultrasonic anemometers have emerged as an affordable option for precisely spot numerous requirements from different disciplines.
Determine the wind direction
The other important subject in wind vanes is their ability to determine and measure wind direction. It’s not just a matter of knowing how many degrees of variation a wind vane is capable of picking up, but of understanding its precision and the dead band around the north gap. Using an 3D ultrasonic anemometer avoids potential problems and increases the wind direction measurement precision and resolution with no wear and tear.
Determine the turbulence intensity, vertical wind speed and virtual temperature
A superior feature 3D ultrasonic anemometers provide, is the possibility to assess turbulence intensity, vertical wind speed and virtual temperature at a high precision and resolution.
Why is it an ultrasonic measurement?
Ultrasonic anemometers have one main feature: they measure the speed of time by aid of ultrasonic waves.
The process is simple: ultrasonic sensors have two sensors (resp. a sensor pairs) at different points. The signal is emitted from a starting point (emitter) to an arrival point (microphone), and it measures the phase shift by time.
Hence it measures the time and calculates the difference between the two results to obtain the speed and directions. That’s ultrasonic measurement.
Vertical wind speed
Some ultrasonic anemometers calculate two or even three magnitudes of speeds: horizontal and vertical wind speed and even lateral wind speed respectively wind direction. Horizontal wind speed is one of the most common form measured by up anemometers. 3D ultrasonic anemometers stand out, measuring also lateral and vertical wind speed and wind flux, in order to precisely derive quantities as wind direction and turbulence intensity.
Turbulence Intensity
For all wind turbines, it is necessary to calculate the turbulence intensity, which allows them to define their useful life and design parameters. The turbulence intensity is nothing more than the standard deviation between an average wind speed and the speed at a specific moment. If you’re interested in maximum quality, it's important that one considers the turbulence intensity of the wind measurement campaign.
3D ultrasonic anemometers measure the wind directions in all three dimensions. Since this measurement principle includes vertical wind speeds and lateral wind speeds, respectively vectors and hence wind directions, the turbulence intensity can be assessed in three dimensions.
Importance of heated sensors
The world has many places with hostile temperatures. That is why the best ultrasonic anemometers have heated sensors and other components to ensure the availability of measurement readiness at any moment, because they don't freeze. In this way, ultrasonic heated sensors allow the operation with no wear and tear nearly at all times and in all places.
What about the wind vane & cup anemometers? Are No Wear and Tear?
The main defect for many cup anemometers is the wear of their parts, which causes them to lose precision and accuracy, visible as trends intrinsic data time series. Depending on meteorological factors, these instruments are heavily exposed to long-term degradation and damage. A rotating principle is the best-known part of many anemometers and wind vanes, but it’s not present at ultrasonic anemometers, which or the same reason don’t underlie no wear and tear. This is because ultrasonic anemometers instruments make their measurements through sonic wave signals and not through mechanical movement.
Of course, common cup anemometers and conventional wind vanes can be maintained and the bearings can be replaced. That not even is expensive. However, the logistics to dismantle the device, sending it to an authorized service partner like ProfEC Ventus and later on attaching it again to the measurement mast structure bears quite some time, logistics and hence also financial resources occupied.
The ultrasonic anemometers are more expensive during procurement, but cheaper during operation.
In the practice the best compromise found is to have a measurement mast equipped with several First Class cup anemometers and First Class wind vanes, but to have also employed at least one ultra-sonic anemometer in parallel, having a particular added value referring to the measurement of virtual temperature, vertical wind speed and hence 3D turbulence intensity.
