Tests of Spatial and Temporal Parameters in a Sea Mine Detection Technique Basedon Seismic Exploration Methods

摘要

This is a project to demonstrate the feasibility of transferring a successfultechnology from seismic exploration for oil and gas to the problem of imaging the shallow seabed-10-20m-and small scatterers-7.5cm radius. In this first study, we demonstrate that we have adapted our current code to this imaging problem and we provide tests of our choice of spatial and temporal parameters. Our simple example places a single scatterer at a water/sediment interface. Synthetic data is generated for a survey in which a towed array of receivers collects data from a series of impulsive sources, set off at regular intervals. The parameters we use are a source bandwidth of 20-80Khz, sources set off at 5m intervals, a 10m receiver array with receivers spaced every 4cm along the array. The sample rate in time is .005msec. Fourteen shots are set off, so that the transverse coverage of the subsurface extends over 80m. We then show that even a modest decrease of the bandwidth, or spatial or temporal sampling rate degrades the image. It should be noted that the sampling criteria we demonstrate here are not peculiar to our imaging method; they apply to any method whose objective is to resolve the boundaries of a target of this size. We then provide a simple example of simultaneous velocity analysis and target detection. In this method, we find a 'best fit' of velocity and target location from the travel time records of two surveys of the previous type carried out along parallel lines. This is an admittedly primitive example that is only suggestive of more sophisticated methods of the type listed in the references.