Truth About SoDar

ASC has a long history in the field of Sonic Detection and Ranging (SoDAR) dating back to the 1970s. During this time, we have obtained experience and knowledge that is unsurpassed in the industry, so much so that our CEO even wrote his doctorate on the topic over 30 years ago and has been in the field ever since. Because of this wealth of knowledge, we would like to dispel common misconceptions through a FAQ (frequently asked questions) about SoDAR. These questions are not specifically tied to ASC SoDARs, but tied to the principals behind SoDAR.

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FAQ

I was at a conference where someone mentioned overcoming the humidity problem with SoDAR. Is it true that humidity hurts SoDAR data recovery?

No, definitely not. This is a common question. Humidity actually helps all SoDARs recover data. SoDARs use reflections from atmospheric turbulence to obtain their return signal. The less the atmosphere absorbs the sound the stronger the reflection. Sound absorption decreases as air density increases. Humidity increases air density. So, humidity increases atmospheric density and therefore enhances the return signal, not hurts it regardless of the system.

Do SoDARs work in the rain?

To our knowledge, all SoDARs operate (or work) in the rain. The real question is what type of data is recovered during a rain event. During light rain or mist, there typically is little to no impact on the data. The issue lies when moderate to heavy rain occurs. This downward force causes a change in the frequency being received by all SoDAR systems. The result is an exaggerated downward velocity and high wind speed results. Many companies offer a method to sense rain so the information can be flagged and then removed. This is similar process to removing icing events on a meteorological tower.

Are SoDARs as accurate as anemometers?

Another popular question, this topic is widely debated. In actuality, this is comparing apples to oranges. Anemometers measure a single point in space. Cup anemometers do not take into account vertical velocities. SoDAR on the other hand is a volumetric measurement. In comparisons where the volumetric measurement and the point measurement are expected to be the same, many SoDARs have demonstrated excellent correlations.