The effect of ground sensor and UAV flight path geometry on the tomographic reconstruction of a weakly sheared daytime convective planetary boundary layer
Date
2015
Authors
Finn, A.
Rogers, K.
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Journal article
Citation
Journal of the Acoustical Society of America, 2015; 137(4):2387-2387
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Abstract
A time-frequency signal analysis of the sound of a propeller-driven unmanned aerial vehicle (UAV) shows that its acoustic signature comprises a set of strong narrow band tones superimposed onto a broadband random component. If such a UAV overflies an array of microphones, the projected and observed Doppler shifts in frequency of these narrow band tones may be compared and converted into effective sound speed values: 2- and 3D spatially varying atmospheric temperature and wind velocity fields may then be estimated using tomography. The technique has practical application in a number of research fields, including boundary layer meteorology, land/sea surface-atmosphere interactions, theories of turbulence, and wave propagation through a turbulent atmosphere. In this paper we examine the influence of UAV flight path and ground sensor geometry on the feasibility and usefulness of UAV-based atmospheric tomography. Realistic conditions for a weakly sheared daytime convective atmospheric boundary layer are synthesised through use of massively parallel large eddy simulation code that utilises pseudo-spectral differencing in horizontal planes and solves an elliptic pressure equation. Particular attention is paid to the accuracy with which the surface layer (lowest 50m of atmosphere) may be reconstructed using UAV-based acoustic tomography as this region typically experiences the greatest spatio-temporal variation in temperature and wind speed; and arrangements of UAV flight path and sensor geometry do not permit ray paths to intersect without the UAV flying very low and disturbing the atmosphere. The influence of meteorological observations obtained onboard the UAV and by ground sensors is also examined.