An overview of applied research in passive sonar signal processing estimation techniques for naval systems is presented. The naval problem that motivates time delay estimation is the source state estimation problem. A discussion of this problem in terms of estimating the position and velocity of a moving acoustic source is presented. Optimum bearing and range estimators are presented for the planar problem and related to the optimum time delay vector estimator. Suboptimum realizations are considered together with the effects of source motion and receiver positional uncertainty.

Time delay estimation for passive sonar signal processing

An approach to controlling the two-way pattern (ie, the product of the transmitting and receiving antenna patterns) for a distributed digital subarray antenna (DDSA) is presented Collectively combining periodic widely separated subarrays results in grating lobes (GLs), and they are unwanted because of the ambiguities that accompany them The approach to GL control presented here involves a combination of conventional suppression methods on the transmitting side and in the digital beamforming on the receiving side, filling the gaps between the subarrays with “virtual” elements, thus forming a contiguous array Individually, the transmitting and receiving antenna patterns may not have adequate performance, but it is demonstrated that if designed to complement each other, the two-way pattern can achieve ultralow sidelobe performance The effects of receiving element signal-to-noise ratio (SNR) and errors in calibration are also addressed

Two-Way Pattern Grating Lobe Control for Distributed Digital Subarray Antennas

A receiving array processing method is presented that synthesizes the antenna response of a contiguous array from the outputs of physically separated arrays of subarrays. It involves filling the gaps between the subarrays with “virtual” elements, thus forming a contiguous array. Therefore, the synthesized pattern has no grating lobes, and amplitude tapering for sidelobe control can be applied. The contiguous array's response can be duplicated in a number of directions limited by the total number of elements. The directions of interest would normally be those of the desired signals (main beam) and interference or clutter (low sidelobes). The directions of arrival of the signals of interest must first be determined before synthesizing the contiguous array response. The modified matrix pencil method has been extended to handle the problem of multiple subarrays for both single and multiple snapshots. The performance of the synthesis method is examined as a function of signal-to-noise ratio (SNR) per element and various array parameters .

Grating Lobe Suppression for Distributed Digital Subarrays Using Virtual Filling

Three methods of nonlinear processing for direction finding

: In Part I, non-coherent detection of narrowband signals in Gaussian- Gaussian mixture noise is considered. The forms of the optimum detectors are found and evaluated for single and multiple observations. These detectors are sensitive to information on the signal and noise parameters. Also evaluated are several suboptimum detectors which perform well under certain conditions without requiring knowledge of signal and noise parameters. In Part II, a new technique for detecting signals using arrays of sensors is investigated, based on the principles of canonical correlation. The theoretical results indicate that for a sufficient number of sensors, multiple, spatially separate signals, at the same frequency can be individually detected without knowledge of sensor position or using conventional beamforming. If sensor positions are known the algorithm supplies the direction of the signal arrivals. The limited numerical results show that a few sensors can automatically steer on and detect a single signal, but are incapable of resolving multiple signals successfully. Keywords: Non- Gaussian noise; Detection; Probability; Correlation; Beamforming.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA160931&Location=U2&doc=GetTRDoc.pdf

Ocean Surveillance Detection Studies. Part 1. Detection in Gaussian Mixture Noise. Part 2. An Investigation of Canonical Correlation as an Automatic Detection and Beamforming Technique

: Investigation is made of a 'multiplicative' receiver array to determine its capability as signal detector and bearing estimator. The same analyses are made of the conventional square-law array for comparison purposes. The probability density functions for the filter outputs of array models are obtained for these arrays for the input signals consisting of monochromatic signals and narrowband additive Gaussian noise. The number of sensor elements, SNR, source bearing, and interelement noise correlation, are treated as parameters of the distribution, and their influences are displayed graphically. Based on these probability density functions for the square-law and multiplicative array processors, the authors then examine their performances as signal detectors and bearing estimators.

Leonard E Miller

Papers

Capabilities of Multiplicative Array Processors as Signal Detector and Bearing Estimator