A method of extending towed array measurements that provides an aperture greater than that of the physical array is presented. Such a technique can be used by matched-field estimators to obtain information about the range and depth of a source and in other towed array applications requiring a very large aperture. The approach is to combine coherently the acoustic signals arriving at a moving array of hydrophones by making proper compensation through a factor that corrects for considerable fluctuations in phase irregularities in the tow path of the physical array as well as fluctuations in amplitude experienced during the coherent integration time. In this manner, the finite aperture of the physical array is exploited in a process that synthesizes the extended aperture of the method. The concept is based on an algorithm that we call an ‘‘overlap correlator,’’ which provides the phase correction factor by correlating overlapping space samples of the acoustic signal received at successive moments by the moving towed array. This is in contrast to the standard, passive synthetic aperture technique, which requires either highly accurate a priori knowledge of the source frequency or a maneuver in order to obtain a wavenumber or bearing estimate. The algorithm has been tested on numerical data generated by the SACLANT Undersea Research Centre’s normal mode model SNAP. The effects of space and time coherence of the signal and the random and systematic errors on the extended towed array measurements are examined and used to derive guidelines for experimental applications of this algorithm.

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Due to recent technical advancements of three-dimensional ultrasound imaging systems, applications of this imaging modality have been expanding from the fetal imaging to cardiac- and abdominal-diagnosis. Among all internal organs, diagnosing the kidney has a paramount importance for rapid bedside treatment of trauma and kidney stone patients using ultrasound images. Although three-dimensional ultrasound provides higher level of structural information of kidneys, manual kidney diagnosis using three-dimensional ultrasound images requires a highly trained medical staff, due to the extensive visual complexity which three-dimensional images contain. Therefore, computer aided automated kidney diagnosis becomes very essential. Due to the challenging problems of ultrasound images, such as speckle noise and inhomogeneous intensity profile, kidney segmentation in three-dimensional ultrasound images has not been sufficiently investigated by researchers. In this paper, we first propose a new automated kidney detection approach using three-dimensional Morison's pouch ultrasound images. Then, we proposed a shape-based method to segment the detected kidneys. A preprocessing step is utilized to overcome the ultrasound challenges. Based on a set of 14 ultrasound volumes, we have evaluated the detection rate of our proposed kidney detection approach which is 92.86%. For kidney segmentation, we compared our proposed method with an existing approach, and the performed statistical analysis strongly validates the superiority of our proposed method with p = 0.000032.

Automated segmentation of kidneys in three-dimensional (3-D) abdominal ultrasound volumes is a task of paramount importance in automated diagnosis of abdominal trauma. However, ultrasound speckle noise, low-contrast boundaries, partial kidney occlusion, and probe misalignment restrict the utility of the solution, especially when it is used in emergency rooms and Focused Assessment with Sonography Trauma applications. This paper introduces a systematic and cost-effective method capable of detecting and segmenting the kidney's shape in acquired 3-D ultrasound volumes, using off-line training datasets. This paper offers a new shape model representation, called the complex-valued implicit shape model, to generate a 3-D kidney shape model by combining prior knowledge of training shapes and anatomical knowledge. We apply shape-to-volume registration, based on a new similarity metric, to detect the kidney shape by fitting the 3-D shape model on 3-D ultrasound volumes. Upon kidney detection, the fitted shape model is used to initialize and evolve a new level-set function, called complex-valued rational level-set with shape prior, to segment the kidney's shape. Experimentation using both simulated and actual ultrasound volumes indicate that the proposed solution provides a better performance over the state-of-the-art volumetric ultrasound segmentation methods.

This paper examines the limits of the angular resolution capability of a moving towed array (MTA) by finding the Cramer–Rao lower bounds (CRLB) and provides algorithms that extend the physical aperture of an MTA. The model that is considered for the CRLB estimates assumes that an N-hydrophone towed array is moving at a known constant speed and that in the received signal unknowns are all the parameters for two sources. The estimated CRLBs for this model indicated that an N-hydrophone MTA provides very high angular resolution when the duration T of the received signal is very long. This ability of the moving array to resolve two closely spaced sources is related to the fact that the physical aperture has been extended by the distance traveled by the array during the T seconds of the observation period. Computer-simulation examples using a maximum-likelihood estimator and an extended towed array algorithm to find the bearing of sources are presented. The results of these simulations agree with the CRLB if the signal-to-noise ratio (SNR) is higher than 0 dB at the hydrophone level, which suggests that both of the above techniques are efficient estimators. Real-data applications using the extended towed-array algorithm were successful, and the physical aperture of a 32-hydrophone MTA was extended to an equivalent of a 512-hydrophone fully populated array during 185 s of observation period. These results have also indicated that the performance of the above algorithm is very robust, since it extends the physical aperture of an array by more than one order of magnitude for the case of a very low signal-to-noise ratio (SNR) broadband signal and for a pure tone, even though the source had a speed of 3.6 kn along its bearing.