Compact 3D Ultrasonic Anemometers & Weather Sensors for Drones, UAVs & GCS

Ultrasonic Anemometers for Air Flow Measurement

By Mike Ball / 30 Dec 2021

Anemoment has released the following article detailing how ultrasonic anemometers are used in the measurement and characterization of air flow. Anemoment’s compact 3D anemometer, the TriSonica Mini is ideal for UAVs (unmanned aerial vehicles) undertaking a wide range of applications such as environmental monitoring, precision agriculture and wind profiling.

Measuring air flow is nothing new. It has been done for decades using a variety of techniques. On one hand are the very simple but still effective techniques like tufts or smoke, which gives users a sense of what the flow does, but not much more than that. On the other hand, you have high-complexity, high-cost techniques like particle image velocimetry (PIV) or the scanning approaches where probes are deployed on a traversing system. A numerical approach, where you simulate flows with your computer, always leaves one wondering if the result is close enough to reality. Especially challenging are low-speed applications like HVAC room ventilation or passenger comfort in cars and trains, where most traditional methods are not applicable and the boundary conditions for a simulation are difficult to determine.

streamwise gmbh of Männedorf, Switzerland has developed a novel approach for intuitive and fast capturing flows, even in low-speed applications below 1 m/s.

“Our strategy is quite revolutionary,” says Andrin Landolt, Ph.D., Sensor Expert and partner at streamwise. “We give users access to flow topology in real time through a scan and paint approach based on a hand-held probe and optical tracking. With our solution, ProCap (from probe capturing), you use your probe to paint your volume of interest and see the air flow immediately. We wanted to provide a tool that is very intuitive to use and can be setup for use in minutes, not hours or days. Our goal is to lower the hurdles of flow measurement for the engineers.” (Figure 1)

Figure 1: Ceiling (left) and wall outlet (right) showing the airstream entering a 3-4°C below room temperature and drop due to the higher density.

Additional Applications for Low-Speed Flow Measurements

An example of where streamwise solutions have been successfully deployed is in measuring air flow in clean room environments. The investigation focused on the flow topology around ventilation outlets in the ceiling. The resulting images captured within minutes visually illustrated the air distribution required to create the required condition for a clean room.

“The beauty of our approach is that you visually see and understand during the measurement what is actually happening,” Landolt says. “In the past, researchers would spend hours capturing data and then go back to their office and do the post processing, only to discover that they were actually measuring in the wrong location. That is the entire point to our technology. You immediately see what you are measuring. That immediate feedback is extremely valuable in a multitude of ways and overall saves tons of time.”

Best-in-Class Strategy

ProCap (Figure 2) is built upon the expertise of streamwise’s founders, Dr. Andrin Landolt and Dr. Benjamin Rembold. Dr. Landolt specializes in experimental fluid dynamics and sensors, while Dr. Rembold brings a wealth of knowledge and experience in theoretical modelling and code development for computational fluid dynamics (CFD). They strive to take the best of these worlds and create an intuitive user experience for flow measurements.

Figure 2: ProCap, leveraging a 3D ultrasonic anemometer from Anemoment, measures velocity and air temperature simultaneously.

“What we provide is essentially a software solution,” Landolt emphasizes. “What probe you’re using doesn’t matter much to us from a technical point of view. If you have a probe that measures fast and accurate enough, we can use it with our program. We take best-in-class available products and integrate them into our system rather than trying to develop things on our own.”

A Quick Introduction to Sonic Flow Probes

Ultrasonic anemometers are based on time of flight (TOF) measurements between opposite ultrasonic transducers. Without flow, the TOF is equal for both directions. If a flow is present, the signal travelling against the flow (upstream) is delayed while the signal downstream travels faster. From the time difference between up and downstream TOF the velocity component pointing in the direction of the signal path can be calculated. Multiple transducer pairs allow to measure more than one velocity component.

“Our introduction to ultrasonic anemometers came back in 2017 or 2018,” said Landolt. “Up to that point we used pressure-based flow sensors only. Pressure based methods have this quadratic behavior between pressure and velocity, which makes them ineffective at low speeds. Naturally, we were looking for a technology that could fill the gap between zero and one meter per second flow speed, which can’t be covered with pressure-based sensors. Of course, one of the obvious choices is ultrasonic anemometers but in general they are very bulky and extremely expensive. One sensor we tested weighed nearly five kilos and was half a meter in length. It worked well, but it was just too big for our applications.”

In searching for a smaller, equally capable sonic anemometer, Landolt stumbled upon Anemoment’s website and subsequently reached out to them. Landolt explains, “It became clear to me when I contacted Anemoment that I was dealing with someone (Stephen Osborn, Anemoment’s CTO) that is really into their product with their whole heart and that they truly understand how it works.”

“We immediately had great success using the TriSonica Mini 3D sonic sensor from Anemoment,” states Landolt. “The TriSonica Mini uses two pairs of transducers with four possible paths and can measure all three components of the flow as required for our application. I think it’s a fantastic product. It’s very robust. It’s small, lightweight, and it gives us the output we need. There may be one or two other products on the market comparable in size, but they are like 10-times the price. And for our customers, that is too expensive for something that you have in your hand and wave around and you might bang into stuff.”

streamwise Becomes an Anemoment Authorized Integrator

As a result of the success streamwise has achieved with the TriSonica Mini, the company recently expanded their relationship becoming an Authorized Integrator for Anemoment’s growing family of sonic anemometers.

Anemoment will release in Q1 of 2022 its newest sonic anemometer, the TriSonica Sphere. The TriSonica Sphere’s patent-pending spherical design (Figure 3) dramatically reduces the effects of wind shadowing and increases the accuracy of vertical wind measurements. In addition to its open architecture, it features sampling rates (up to 100 Hz), making it a highly anticipated product release.

Figure 3: TriSonica Sphere’s patent-pending spherical implementation.

“We each have our area of expertise,” Landolt underscores. “Anemoment on the sensor side and streamwise on the software and application side. Together we represent cutting-edge technology that provides the customer with an exceptional product. As I stated before, our approach to take the real-time data stream from the probe and its position at the same time and combine this with real time visualization software, is completely unique. It’s the only system that’s out there that can do that.”

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Posted by Mike Ball Mike Ball is our resident technical editor here at Unmanned Systems Technology. Combining his passion for teaching, advanced engineering and all things unmanned, Mike keeps a watchful eye over everything related to the unmanned technical sector. With over 10 years’ experience in the unmanned field and a degree in engineering, Mike’s been heading up our technical team here for the last 8 years. Connect & Contact