| 摘要 |
A novel system for remote detection and imaging of underwater objects is presented. In accordance with the present invention, a laser is used to generate short pulses of light with pulse widths on the order of nanoseconds. The laser light is expanded by optics and projected down toward the surface of the water and to an object. Intensified CCD (charge coupled device) cameras (preferably two) are electronically shuttered after a time delay corresponding to the round trip propagation time and from to the object. This timing eliminates light scattered by the water from in front of and behind the object. As a result, the veiling luminance of the water is greatly attenuated and faint target signatures can be seen. The resulting gated images (displayed on a CRT) have sufficient spatial resolution to classify and/or identify the object. The imaging lidar system of the present invention takes advantage of the fact that all opaque targets will cast a shadow. The exposure of the two cameras in the system are timed such that one camera gives an image of the object against the backscattered light from the water while the other camera gives an image of the shadow of the object against the backscattered light. These two images are then subtracted to improve the detectability of the object.
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