An image processing approach for aircraft flight parameter estimation using the acoustical Lloyd's mirror effect

A time-frequency analysis of the output of an acoustic sensor located above the ground during the transit of an aircraft shows an interference (or fringe) pattern on the time-frequency plane. This interference pattern, referred to as the Lloyd's mirror effect, is caused by the temporal variations of the constructive/destructive interference frequencies of the direct and ground-reflected aircraft sound fields at the sensor. A model has been developed to describe the temporal variations of the destructive-interference frequencies for an aircraft in level flight over a hard ground. This paper describes two methods to estimate the aircraft flight parameters based on this model. In both methods, the time-frequency distribution of the sensor output is treated as an image. This image is pre-processed to enhance the destructive-interference pattern and then the flight parameters are extracted from the resultant image by optimising a cost function. The effectiveness of the methods is verified using real acoustic data.