Bearing Estimation Accuracy Research Articles

The Accuracy of Bearing Estimates of Wideband Signals Produced by Marine Animals

The problem of estimating bearings of impulsive wideband acoustic signals produced by vocalizing animals and received by a compact array of synchronized sensors is addressed. The accuracy provided by the maximum-likelihood (ML), the beamformer (BF), and the time-difference-of-arrival (TDOA) based estimators is evaluated by simulations and in situ tests and compared with the Cramér-Rao bounds. Test results demonstrated that the ML estimator and BF provided similar bearing estimation accuracy for all types of signals. They are more accurate than the TDOA-based estimator for mid- and low-frequency impulsive signals. The accuracy of the TDOA-based estimates comes close to the ML- and BF-based estimates when the signal bandwidth increases. TDOA-based estimators outperformed the BFs and the ML algorithms when estimating the bearings of clicks. The empirical standard deviations provided by the ML/BF and TDOA-based estimators were 0.2° ...3° and 2°...70° for mid- and low-frequency impulsive signals and 5.0° and 0.6° for clicks, respectively.

Using a Stationary Compact Array of Acoustic Sensors to Estimate the Motion Parameters of Sources

Compact arrays of acoustic sensors can provide bearing measurements of detected sounds. An important application for compact arrays is estimating the motion parameters of sources. This work considers the problem of bearings-only estimating of the positions and heading angles of vessels in the presence of bearing and speed measurement errors. Statistical simulations are used to evaluate the dependence of bearing estimation accuracy on the duration of the observation interval and the variance of speed errors. Plots of range and heading estimation errors obtained for 171 vessel passes with known positions are presented. Test results demonstrate that the accuracy of the estimating range depends strongly on speed error variance.

Direction of arrival estimation using virtual array search

This study explores the application of the advanced array interpolation technique for direction of arrival estimation. It uses an array of Global Positioning System (GPS) sonobuoys, as a method for enhancing the bearing estimation accuracy, improving target tracking capabilities. Currently, the bearing estimation of underwater targets using sonobuoys is based on fusion of bearings, obtained through individual element processing. This preserves the advantage of having a widely spread field of sonobuoys to detect underwater targets. However, the low levels of signal-to-noise ratio (SNR) jeopardise the bearing estimation accuracy. This can be improved using array processing of a directional frequency analysis and recording (DIFAR) sonobuoy field. The environmental conditions and deployment strategies impose limitations on the array processing of a DIFAR sonobuoy field. These factors mainly cause the array of sonobuoys to be a non-uniform sparse array. Advanced array interpolation is proposed to mitigate the current processing limitations degrading the system performance. This method is tested using acoustic level simulation. Simulation results show that the proposed method improves the processing of non-uniform sparse arrays based on the SNR and the inter-element distances of the array.

Bearing estimation for a distributed source: modeling, inherent accuracy limitations and algorithms

The problem of using sensor array measurements to estimate the bearing of a radiating surrounded by local scatterers is considered. The concept of partial coherence is introduced to account for temporal as well as spatial correlation effects often encountered in a Rayleigh fading-type propagation channel formed between a and sensor array elements. A simple parametric model for temporal channel correlation is presented, yielding an overall spatio-temporal channel model that is more realistic than formerly proposed models (which assume either full or zero temporal channel correlation). Thus, previously proposed source models for bearing estimation problems are generalized to a parametric spatio-temporal model for what is called partially coherently distributed (PCD) sources. A study of the associated Cramer-Rao Bound (CRB) is undertaken for a simple but illustrative problem formulation. The inherent limitations in bearing estimation accuracy for this spatio-temporal problem are seen to lie between the cases of zero and full temporal correlation, becoming more severe as temporal channel correlation increases. In addition, the associated maximum likelihood estimators for bearing are proposed, and their performance is compared with that predicted by the CRB.

Performance comparison of the Wagstaff–Berrou and maximum entropy method beamformers

The performances of the maximum entropy method (MEM) and Wagstaff–Berrou broadband (WB2) high-resolution spatial processing techniques are compared with each other and with the conventional fast Fourier transform (FFT) beamformer. The comparisons are based on the analysis of three sets of measurements acquired at sea during two different environmental acoustics field exercises. Chosen for comparison are the effects of signal-to-noise ratio (SNR) on beamwidth and the effect of the number of array elements on the bearing estimation accuracy and beamwidth of the spatial processors. Results from these data indicate that both of the high-resolution methods yield smaller beamwidths than the conventional FFT processor, and that the high-resolution beamwidths show little dependence on SNR for values greater than 8 dB at the hydrophone input. Also, MEM beamwidths are generally slightly smaller than WB2 beamwidths and show less dependence on aperture. Measured MEM beamwidths show the same general trend as theoretical calculations for sensitivity to SNR, and the average arrival angles of all three beamformers show the same general dependence on the aperture.

Range and Bearing Estimation in Passive Sonar

Passive sonar systems are used for estimating the range and bearing of signal sources, such as ships or submarines. In this study, the Cramer-Rao bounds on estimation errors are used as measures of the accuracy of the estimates. The bounds show how parameters such as observation time, signal bandwidth, signal-to-noise ratio, and array geometry can be chosen to obtain maximum accuracy. When the array geometry satisfies certain conditions, the bound for range estimate is shown to be independent of the actual source bearing and the bound for bearing estimate independent of both the range and bearing of the source. It is also shown that the same conditions on array geometry ensure that the range or bearing estimation accuracy is not degraded when tne other pammeter is not known.