Optical sensors have become more prominent in atmospheric measurement systems, with LiDAR instruments deployed on a variety of earth-bound, air-borne, and space-based platforms. In recent years, the interest in the human exploration of Mars has created a substantial push towards reliable and compact sensing elements for Mars exploration missions, particularly during a spacecraft’s entry, descent, and landing stages. Real-time sensors able to reliably measure the craft’s speed relative to the surrounding atmosphere during these stages are thus of great interest. In this dissertation, a proof-of-concept for an optical microfabricated sensor, which leverages the whispering-gallery-mode (WGM) and Doppler shift principles, is developed to measure wind speed from atmospheric particles through light scattering. WGM micro-resonators could replace Fabry–Perot interferometers and other optical frequency discriminators often employed in remote sensing applications, thereby significantly reducing the size and weight of the measurement system. The capabilities of the presented sensor concept are first studied under the aerosol scattering regime, and the measurement resolution of the WGM resonators is assessed. An optical system is developed, and velocity measurements near the exit of a seeded air jet nozzle are carried out to validate the velocity measurement capabilities from aerosol streams.
The feasibility of employing WGM resonators for molecular scattering-based measurements of atmospheric properties is also investigated. A modified mathematical model for coherent and spontaneous scattering is implemented in the performance analyses of the resonators for different altitudes of Earth and Mars atmospheres. Spectral profiles generated from the model are compared to those in the literature under similar conditions. An analysis for photon count under various atmospheric conditions and altitudes is also carried out. The analyses indicate that WGM resonator-based spectral instruments may be viable as part of future compact and lightweight atmospheric sensors.
M. Volkan Otugen
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Salameh, Elie Ramon, "Optical Microresonator-Based Flow-Speed Sensor" (2022). Mechanical Engineering Research Theses and Dissertations. 45.