Millimeter-wave polarimetric radar sensor for detection of power lines in strong clutter background.

摘要

Collision avoidance is a concern of all types of aircraft, requiring the detection and identification of hazardous terrain or obstacles. Collision avoidance is even more demanding for helicopters, as their unique capabilities result in extensive operations at low-altitude, near to terrain and other hazardous obstacles. High voltage power transmission lines and their supporting structures are one of the major hazard for low flying helicopters due to their low observability. A reliable and all-weather collision warning system can rectify this problem and a number of approaches have been proposed including optical and infrared sensors. These systems have a number of limitations due to atmospheric attenuation. None of the other approaches proposed so far have proceeded preceded beyond the demonstration phase.; In this thesis, a reliable all-weather collision warning system which is based on a millimeter-wave polarimetric radar is proposed. This system will alert the pilots of power lines in the direction of the flight path even in strong clutter background. Polarimetric radar backscatter measurements on a variety of power line samples were performed to characterize the radar backscatter of power lines. Using the polarimetric backscatter features of power lines, a power line detection algorithm in a strong clutter background is proposed and the feasibility is tested under laboratory conditions. Prediction of polarimetric radar backscatter of power lines is essential in the development of the proposed collision avoidance radar and a high frequency analytical technique based on iterative physical optic (PO) is developed and the validity is tested. The detection algorithm is based on the coherence between co-polarized and cross-polarized components of radar backscatter from targets. The analytical expression for the false alarm, probability of detection, and number of samples are formulated and the performance of the algorithm for mapping power lines embedded in clutter were demonstrated using 35 GHz SAR images. Performance of a real aperture imaging radar system and modified detection algorithm is demonstrated for a number of simulated traffic scenes. Finally a radar simulator is developed to test the idea and scenarios related to detection of power lines using a radar mounted on a moving helicopter.