Unmanned aerial platform for atmospheric flux measurements

Oscar D Garibaldi, Purdue University

Abstract

There is a great concern about the influence of the humankind on the cycle of CO2 and its impact on the global climate change. This has motivated a worldwide effort to study the budgets of CO2, which requires field measurements of flux that is dominated by atmospheric turbulence. The study of atmospheric flux requires three-dimensional wind measurements, and one way to do this is by using airborne platforms equipped with sensors like pressure probes, hotwires, etc. Another way is to use a sonic anemometer aboard an inexpensive unmanned aerial vehicle, which is an unexplored technique that has the advantage of gathering data at very low altitudes where manned missions are extremely dangerous. In addition, the application of sonic anemometers has several other advantages, which are robustness, long-term calibration, and lack of moving parts. Together with other sensors like airborne gas analyzers, thermometers etc, it is possible to conduct the atmospheric flux measurement by using unmanned aerial vehicles. A combination of the unmanned aerial vehicle with a sonic anemometer as a technique to measure atmospheric turbulence has been evaluated. To do this, the performance of the sonic anemometer has been analyzed and compared to other existing anemometry techniques, such as hotwires and pressure probes. The unmanned aerial vehicle carrying the sonic anemometer and inertial navigation, global positioning sensors and data acquisition devices has been developed. The entire system has been evaluated by flying at a set altitude same as a nearby ground station. Comparison of the flight test data with the ground station measurements revealed that the airborne system was capable of measuring the mean wind speed. However, the measured vertical turbulence intensity was larger than that measured by the ground station. For this reason, a computational fluid dynamic model of the airplane was developed using a low order panel code. This simulation showed that the aerodynamic disturbances of the aircraft were one of the possible causes of the discrepancy. An error analysis of the complete system has been performed and an overall accuracy of ± 0.11 m/s has been determined. It has been found that the measurement errors of inertial navigation sensors, compared to the error introduced by the remaining instrumentation, had the largest impact on the accuracy.

Degree

M.S.E.

Advisors

Sullivan, Purdue University.

Subject Area

Aerospace engineering

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