Acoustic Coherence Imaging Through the Atmosphere

114 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2000.The imaging of acoustic "scenes" through the atmosphere is a subject with little treatment in the literature. This thesis strives to set the state of the art in this field by presenting imaging methods and their performance in the turbulent atmosphere. Both narrowband interferometry and wideband techniques that can be solved using tomographic methods are presented. An extensive series of field experiments was conducted in which multiple sensor arrays of microphones recorded the signals received from loudspeaker sources outdoors under varying atmospheric conditions. Besides providing data for characterizing the imaging performance under different conditions, the field data also allowed for measurements to be made that characterize the atmosphere itself. Methods for enhancing image quality are discussed. It is shown that the popular self-calibration family of reconstruction methods from the radio astronomy community are not applicable to the acoustic imaging case. A new method, based on estimating the intensity distribution jointly with atmospheric distortion model parameters using multiple short integration period measurements, is derived. Theoretical performance bounds in the form of the Cramer-Rao lower bound are derived, and the method is applied to both synthetic and field data. The performance of this method is encouraging.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD