Maximum effective aperture size for source direction estimates in a complex terrain
Mark L. Moran, D. Keith Wilson, Roy J. Greenfield · The Journal of the Acoustical Society of America · 2004
Source resolution and clutter suppression from ground sensor arrays scales directly with sensor array aperture. However, boundary layer complexities can disrupt acoustic and seismic wavefronts at a variety of spatial scales. Hence, usage of an array dimension that is larger than these wavefront distortions can lead to degraded resolution and poor clutter suppression. Using experimental data, we demonstrate the maximum effective aperture for determining a line of bearing to a light moving ground vehicle. Our data were collected in mountainous terrain with open fields, dense forests, and steep hills. We deployed a field of 36 seismic sensors (geophones) and 36 high quality microphones. These sensors were distributed in triangular subclusters within a larger equilateral triangle that was roughly 100 m on each side. Our microphone separations were as small as 10 cm, with common separations of 1, 5, 10, and 25 m. Our seismic subclusters had common separations of approximately 5, 15, and 30 m. We apply a high resolution 2-D maximum-likelihood (ML) wavenumber estimation method to analyze array gain characteristics at multiple aperture sizes. Our results show large angular and range dependencies that correlate strongly with terrain complexity and disruptions of line-of-sight with a moving vehicle.