Polarization ratiometry object detection system and method

Abstract

A method and system for detecting objects having preferential polarization plane reflection characteristics. The method includes the steps of: (a) transmitting from a first given location, a first plane-polarized electromagnetic wave that is oriented in a predetermined reference plane; (b) transmitting from the first given location a second electromagnetic wave having the same frequency and intensity as the first wave and not being oriented in the predetermined reference plane: (c) receiving at a second given location, reflections of the first transmitted wave to provide a first received signal; (d) receiving at the second given location, reflections of the second transmitted wave to provide a second received signal; and (e) comparing the first received signal to the second received signal for detecting an object that preferentially reflects the transmitted radiation in a distinct plane so as to distinguish such object from other objects not having such characteristics. Movement of the detected object is detected by detecting a change in the results of such comparison. The first and second transmitted waves are shifted in phase to be in phase with each other, with the degree of such phase shift being varied periodically to avoid consistent multipath wave cancellations and reinforcements. The first and second waves are transmitted by a carrier signal at the frequency of the first and second waves. The carrier signal is modulated for transmission by a modulation signal having a lower modulation frequency. The received signals are mixed with the unmodulated carrier signal to provide the received signals at the modulation frequency.