Reduction of Sidelobe and Speckle Artifacts in Microwave Imaging: The CLEAN Technique

摘要

Large random thinned arrays provide high angular resolution microwave images. These images are plagued with artifacts caused by high sidelobes. Specifically, these artifacts are false targets and target break-up or speckle. The CLEAN algorithm was introduced in radio astronomy in the last decade to reduce the sidelobe-induced artifacts. CLEAN is extended to the coherent radiation field and the theory placed on a quantitative basis. A condition is derived which, when satisfied, guarantees that all proper targets will be preserved in the cleaned image and all false targets discarded. An algorithm involving moving thresholds is derived to extract the target coordinates. It is shown that targets much weaker than the sidelobe level can be detected and displayed without the hazard of artifacts. It is further shown that the target dynamic range and the image contrast can be increased by up to twice the signal-to-noise ratio (SNR) per element. Reprints. (RH)