Determination of the spatial distribution of atmospheric fluxes by using a UAV
Abstract
It is well known that the composition of the planet's atmosphere is changing at an unprecedented rate. Tremendous and well-documented amounts of man-made carbon are being released into the atmosphere, but is not clear where that extra carbon is going and how it interacts with the environment. The influence of human activities on the carbon cycle is of particular concern to scientists and policymakers. To clarify this important issue, in-situ measurements must be taken to improve our understanding of the mechanism that drives the exchange of CO2 within the atmosphere, which is dominated by turbulence. As such, there is great interest in the measurement of CO2 concentration and CO2 flux within the atmosphere. A wide variety of platforms, in both mobile and fixed configurations, are being used to study closely the flux of CO2 within the atmosphere's boundary layer. Most of these platforms tend to be expensive and complex to operate. Recent developments of technologies such as microelectromechanical devices, GPS, and batteries have enabled the use of unmanned aerial vehicles as a viable method for performing atmospheric studies. Parallel to the studies of carbon exchange, field measurements of buoyancy flux are valuable. This variable helps to understand the mechanisms of turbulence production. It can be assessed with the use of a sonic anemometer, which has the ability of measuring wind speed fluctuations, alongside with virtual temperature. This has motivated the creation of an instrumented UAV the measurement of in situ variables such as CO2 flux, virtual temperature, wind speed, and turbulence. An unmanned aerial system, nicknamed UAV Esperanza, was designed, constructed and tested with the purpose of measuring turbulent flux. The novelty of this system was the incorporation of an onboard sonic anemometer, an inexpensive inertial measurement unit/GPS navigation system, and a relatively low-cost gas analyzer. Field experiments demonstrated the capability of the system to resolve vertical profiles of average wind speed, virtual potential temperature, turbulent kinetic energy, CO2 concentration, and turbulent fluxes of buoyancy and CO2. The UAV system has the ability to obtain average CO2 flux values comparable to existing manned aircraft-based systems. Moreover, this is accomplished with a fraction of the operational costs of manned airplanes. Error analysis of different scenarios demonstrated that the developed UAV system is appropriate for measuring plumes of power plants, daytime fluxes of crops, and forests. However, limitations of the onboard gas analyzer, range, and endurance of the aircraft render the system unsuitable for spectrum analysis
Degree
Ph.D.
Advisors
Sullivan, Purdue University.
Subject Area
Aerospace engineering
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