ANALYSIS OF A NONLINEAR FREQUENCY DIVERSE CLUTTER SUPPRESSION ALGORITHM

The target signal is often received in the presence of coherent noise resulting from a large number of complex and randomly distributed scatterers known as clutter, whose echoes can suppress or mask the actual target echo. This is a fundamental limitation which exists in all imaging and detection applications and cannot be removed by conventional techniques, such as time averaging. This paper examines a non-linear signal processing algorithm (polarity thresholding) used in conjunction with a frequency diversity technique (split-spectrum processing), which decorrelates clutter. Since the target echo exhibits significantly smaller amplitude variations with frequency compared to clutter, the polarity thresholding algorithm can achieve flaw enhancement by setting the output to zero at time instants where phase reversal occurs. Theoretical derivations are provided to determine the signal to noise ratio enhancement capabilities of the algorithm. Ultrasonic data obtained from large grained stainless-steel samples with flat-bottom holes are used to verify the theoretical results and demonstrate the grain echo suppression capability of the algorithm in imaging applications. © 1990.