Method and apparatus for three dimensional range resolving imaging

Abstract

A three dimensional range resolving imaging sensor is presented. The sensor comprises a transmitter for generating a light pulse which passes through beam homogenizer and a pair of Fresnel-Risley prisms. This pulse is then directed through an environmental window towards an object enveloped in a backscattering medium. A portion of the light pulse is reflected back towards the sensor. However, prior to detecting the return light pulse, a detector array is internally calibrated by exposure to a calibration pulse. This detector array preferably comprises a two-dimensional photo multiplier tube (PMT) array. A corresponding array of light tapers is disposed before the PMT array to increase the fill factor of the PMTs. Gain and offset corrections are made for each PMT from this exposure. The return pulse passes through the environmental window and impinges a pair of Fresnel-Risley scanner plates. These plates introduce a fixed angular deviation which is dependent on the orientation of the plates. This pulse then passes through a spectral bandpass filter and onto a collection mirror. The collected return pulse is then directed to the PMT array. The output of the PMT array comprises a plurality of electrical signals. These signals are conditioned and then processed by an image processor. The image processor provides a visual display which is available to an operator. Also, the image processor may perform automated target recognition and alert the operator when a target is detected.