Advanced array techniques for unattended ground sensor applications

Sensor arrays offer opportunities to beamform, and time-frequency analyses offer additional insights to the wavefield data. Data collected while monitoring three different sources with unattended ground sensors in a 16-element, small-aperture: (similar to 5 meters) geophone array are used as examples of model-based seismic signal processing on actual geophone array data. The three sources monitored were: (Source 01). A frequency-modulated chirp of an electromechanical shaker mounted on the Boar of an underground bunker. Three 60-second time-windows corresponding to (a) 50 Hz to 55 Hz sweep, (b) 60 Hz to 70 Hz sweep, and (c) SO Hz to 90 Hz sweep. (Source 02). A single transient impact of a hammer striking the Roar of the bunker. Twenty seconds of data (with the transient event approximately mid-point in the time window. (Source 11). Tile transient event of a diesel generator turning an, including a few seconds before the ''turn-on time'' and a few seconds after the generator reaches ''steady-state conditions''. The high-frequency seismic array was positioned at the surface of the ground at a distance of 150 meters (North) of the underground bunker. Four Y-shaped subarrays (each with 2-meter apertures) in a Y-shaped patient (with a 6-meter aperture) using a total of 16 3-component, high-frequency geophones were deployed. These 48 channels of seismic data were recorded at 6000 and 12000 samples per second on 16-bit data loggers. Representative examples of the data and analyses illustrate the results of this experiment.