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Release Date 9 July 2021
Anemoment LLC
Inside each TriSonica Mini sensor a high-speed processor running custom
software applies principles of math and physics to extract atmospheric data from the
tiny changes in how quickly soundwaves travel along paths between pairs of
transducers.* By sending and detecting sound waves along multiple acoustic paths
(TriSonica products use 4 acoustic paths intersecting the three spatial axes), three-
dimensional information about atmospheric conditions at the site of the sensor can
be obtained.
Our custom software results from decades of experience in sonic
anemometry software design (including creation of the software currently featured
in Applied Technologies, Inc. products). Our software also reflects years of testing
and refinement for the unique geometry of the TriSonica Mini sensor through fluid
dynamic modeling, digital signal processing, and wind-tunnel based shadow-
correction verification.
This software enables the sensor to identify precisely how long it takes for
sound to pass between two transducers. As a result, the only calibration
measurement of importance is knowing the
exact distance of the acoustic paths
between the pairs of transducers.
Before leaving our facility, each TriSonica Mini undergoes calibration to
identify that exact distance for each acoustic path. We do this by locking down the
TriSonica Mini in a zero-airflow chamber fitted with an independent temperature and
humidity sensor. After an appropriate time for the chamber conditions to settle, the
calibration routine of our software runs the math and physics equations backwards,
in a sense, to calculate the exact distance between pairs of transducers, down to the
micron level. These results are stored in the TriSonica Mini sensor’s memory to
supply the known distance from which time-of-flight changes are detected. Packed in
the box with each TriSonica Mini sensor you will find a certification that the sensor
passed this power-up and calibration testing, and the distance values were stored.
The TriSonica Mini sensor is resilient, functioning well under many adverse
conditions. However, if your sensor has been knocked about, or was skewed during
attachment to your custom mounting device, the distance between pairs of
transducers may have changed slightly. If you believe this has been the case, you can
re-calibrate your sensor in the field using the Calibrate command. You will need to
create a zero-air condition around your sensor, and to enter in the temperature and
humidity values for your location. This will allow your sensor to find the precise
lengths of the acoustic paths for improved data accuracy.
*For a brief and elegant explanation of the math and physics of sonic anemometry, see Section II of “A Martian
Acoustic Anemometer”, D. Banfield,
et al
., T
HE
J
OURNAL OF THE
A
COUSTICAL
S
OCIETY OF
A
MERICA
140, 1420-1428
https://doi.org/10.1121/1.4960737
. The truly curious may enjoy Dr. J. Chandran Kaimal’s history of the
science, in “Advances in Meteorology and the Evolution of Sonic Anemometry”, available at
https://www.apptech.com/wp-content/uploads/2016/08/Evolution-of-Sonic-Anemometry.pdf
Let’s talk Calibration – It’s all in the Math and Physics
