The study described in this thesis aims to assess the effects of wind-generated noise on potential infrasound measurements on future Mars missions. Infrasonic sensing on Mars is being considered as a means to probe the long-scale atmospheric dynamics, thermal balance, and also to infer bolide impact statistics. In this study, a preliminary framework for predicting the principal wind noise mechanisms to the signal detected by a sensor placed inside a hemispherical porous dome on the Martian surface is developed. The method involves calculating the pressure power density spectra in the infrasonic range generated by turbulent interactions and filtered by dome shaped filters of varying porosities. Knowing the overall noise power spectrum will allow it to be subtracted from raw signals of interest and aid in the development of infrasound sensors for the Martian environment. In order to make these power spectral predictions, the study utilizes the Martian Climate Database (MCD) global circulation model, developed by Laboratoire de Meteorologie Dynamique in Paris, France. Velocity profiles are generated and used in semi empirical functions generated by von Kármán along with equations for describing the physical turbulent interactions. With these, turbulent interactions in the free atmosphere above the Martian surface are described. For interactions of turbulence with the porous filter, semi-empirical formulations are adapted to the Martian parameters generated by the MCD and plotted alongside contributions in the free atmosphere outside and inside the dome to obtain the total wind noise contribution from turbulence. In conclusion, the plots of power spectral densities versus frequency are analyzed to determine what porosity filter would provide the best wind-noise suppression when measured at the center the dome. The study shows that 55% (0.02 to 5 Hz) and 80% (6 to 20 Hz) porosities prove to be the better of the five porosities tested.
|Commitee:||Petculescu, Gabriela, Sidorovskaia, Natalia|
|School:||University of Louisiana at Lafayette|
|School Location:||United States -- Louisiana|
|Source:||MAI 56/05M(E), Masters Abstracts International|
|Subjects:||Physics, Atmospheric sciences, Acoustics|
|Keywords:||Boundary, Layer, Mars, Noise, Turbulence, Wind|
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