Interferometric Direction Finding by a Vector-Scalar Receiver

A method for interferometric direction finding of a broadband sound source in an oceanic waveguide by a single vector-scalar receiver is presented. The method is based on the double Fourier transform of the interference pattern formed during motion. The efficiencies of the proposed direction finding method and the method based on measuring the delay times of signals arriving at spaced scalar receivers are compared based on the natural experiment results. The noise immunity of the interferometric direction finding method is considered.     

Experimental study of the directional characteristics of a vector-scalar array

We analyze the spatial spectra of a vector-scalar array when the signals are processed using methods with different resolution. The method of presenting the signals used in the research allowed us to apply the previously developed method of detecting and estimating the parameters of signal sources obtained in the calculation of the theoretical characteristics of detecting the signal sources and realization of the algorithms of signal processing. We compared the resolution of vector-scalar and scalar arrays with the same aperture. The experiments were carried out in stationary conditions and in the towing regime. During the towing regime, the accuracy of determination of the source location was controlled using the GPS receivers. It was shown experimentally that the signal to noise ratio at the output of the receiving array is three times greater if the vector-scalar array is used rather than the scalar one. The level of the lateral background appeared to be three times smaller during operation with the vector-scalar array than with the scalar one even in the towing regime. The results of measurements are confirmed by theoretical calculations.     

Vector-scalar noise fields formed by an excited sea surface

Vector-scalar noise fields in a waveguide were studied using computer simulation. A stochastic model of dynamic acoustic noise was used in the calculations. Noise field parameters on a single vector-scalar module and spatial correlation functions on vector-scalar arrays in a homogeneous waveguide were analyzed. Calculations were performed for vertically and horizontally located arrays. It was shown that the vector-scalar noise field characteristics depend on the bottom parameters and the state of the ocean surface due to the wind force. The calculation results can be used to predict the characteristics of detection and direction finding of signal sources for vector-scalar arrays working in a waveguide against the background of sea noise.     

Methods for studying water characteristics and the spatial orientation of vector-scalar module

The results of natural studies of the methods for simultaneous measurements of the speed of sound in water and water temperature, as well as the depth, true bearing, and orientation of vector-scalar antenna in three-dimensional space, are reported. The tests were performed in the towing mode using a portable multifunctional complex, including hydrophysical, orientation, and direction finding units. The complex is recommended to be included in the composition of stationary or towed scalar or vector-scalar antennas.     

Interferometric method for estimating the velocity of a noise sound source and the distance to it in shallow water using a vector-scalar receiver

An experiment on estimating the velocity of a noise source and the distance to it using a single vector-scalar receiver has been performed on shallow-water Pacific shelf. Expressions for the components of the vector-scalar receiver field are derived. The source parameters are reconstructed using the interferometric method. The noise immunity of the method is analyzed for different acoustic field components and their combinations. The sensitivity of the method with respect to changes in the bottom parameters is considered.     

Comparison of unidirectional signal reception in a waveguide with linear vector-scalar and combined antennas

Experimentally measured spatial responses of linear scalar, vector-scalar, and combined antennas have been analyzed. A combined antenna consists of an extended scalar antenna and one or several vector-scalar modules. It is shown that a combined antenna, which multiplicatively processes signals (just like a vector-scalar antenna), suppresses reflection lobes and provides unidirectional reception (in comparison with a scalar antenna). At the same time, the side field level decreases, thus increasing noise immunity.     

Resolving Power of the Interferometric Method of Source Localization

Results of a computer simulation of the resolution of three noise sources with different intensities against the background of isotropic noise in an oceanic waveguide are presented. A comparative analysis of the error in determining their coordinates (bearing, radial velocity, distance, depth) is performed. A computational experiment is implemented based on the interferometric method of source localization using vector-scalar receivers.     

Experimental research of the interference and phase structure of the power flux from a local source in shallow water

The paper studies the interference structure of low-frequency tonal and wideband signals in shallow water, received by four-component vector-scalar modules. The spatial amplitudes and phase characteristics of the scalar field are analyzed, as well as three components of the vibration velocity vector and the power flux vector. A relationship is established between the zone of interference maxima and minima and the phase gradient in the horizontal and vertical plane, the change in direction of the vertical and horizontal components of the vibration velocity vector, and the change in the depression angle of the power flux vector in the horizontal plane.     

Estimating the acoustic characteristics of surface layers of the sea bottom using four-component vector-scalar receivers

It is shown that scalar, horizontal, and vertical vector receivers efficiently split modes of different numbers, which makes it possible to analyze the mode structure and estimate the characteristics of surface layers of a shallow sea bottom. To analyze the mode structure of propagating pulses from a towed pneumatic source, Winger transform was applied, with which seven modes were isolated by vertical vector receivers, whereas the scalar receivers and horizontal vector receivers isolated only three modes. It is established that the use of four-component vector-scalar receivers makes it possible to increase the accuracy in estimating the parameters of a layered bottom model.     

Extended discrete-ordinate method considering full polarization state

This paper presents an extension to the standard discrete-ordinate method (DOM) to consider generalized sources including: beam sources which can be placed at any (vertical) position and illuminate in any direction, thermal emission from the atmosphere and angularly distributed sources which illuminate from a surface as continuous functions of zenith and azimuth angles. As special cases, the thermal emission from the surface and deep space can be implemented as angularly distributed sources. Analytical-particular solutions for all source types are derived using the infinite medium Green's function. Radiation field zenith angle interpolation using source function integration is developed for all source types. The development considers the full state of polarization, including the sources (as applicable) and the (BRDF) surface, but the development can be reduced easily to scalar problems and is ready to be implemented in a single set of code for both scalar and vector radiative transfer computation.     

Effects Due to a Scalar Coupling on the Particle-Antiparticle Production in the Duffin-Kemmer-Petiau Theory

The Duffin-Kemmer-Petiau formalism with vector and scalar potentials is used to point out a few misconceptions diffused in the literature. It is explicitly shown that the scalar coupling makes the DKP formalism not equivalent to the Klein-Gordon formalism or to the Proca formalism, and that the spin-1 sector of the DKP theory looks formally like the spin-0 sector. With proper boundary conditions, scattering of massive bosons in an arbitrary mixed vector-scalar square step potential is explored in a simple way and effects due to the scalar coupling on the particle-antiparticle production and localization of bosons are analyzed in some detail.     

An Interferometric Method for Detecting a Moving Sound Source with a Vector-Scalar Receiver

The paper discusses the conditions imposed on the spectrum of an emitted signal for which the interferometric method of detecting a moving sound source in shallow water is applicable for vector-scalar receivers. It is shown that a normalized spectrogram representing a two-dimensional Fourier transform of the interferometric pattern is identical for all four acoustic field components and combinations thereof. Results of a field experiment in which a vector-scalar receiver was applied are presented. The interference immunity of the method is considered for different field components in the case of isotropic interference.     

Localization of a sound source in a noisy environment by hyperbolic curves in quefrency domain

Time Difference of Arrivals (TDOAs) of sound waves between microphones have to do with source localization. How well a sound source can be localized depends on how precisely the TDOAs are estimated. Although many ways to estimate TDOA have been proposed, noise always prevents us from finding exact time differences more or less in practice. Cross correlation has been the most prevalent way to estimate time difference, and various cross correlations robust to noise have also been developed. Nevertheless, much remains to be done for exact TDOA estimation under noisy environments. A novel way to show time delays in quefrency domain by removing noise has been proposed, which is called Minimum Variance Cepstrum (MVC). In particular, it is practically desirable to visualize source position with as few number of sensors as possible. Once TDOAs are obtained precisely, it is enough to show the source position in a 2-D plane using hyperbolic curves with only three sensors. In this work, the MVC is adopted to accurately estimate TDOAs under noise, and a way to localize an acoustic source by intersecting hyperbolic curves using the TDOAs between three microphones is proposed. Numerical simulations on TDOA estimation and source localization with white Gaussian noise demonstrated that the proposed method worked well under the noisy environment, and we compared the results with those of other old but well-established cross correlation estimators. In addition, experiments to detect a leaking point on a pipe successfully showed where the leak sound was generated.     

Estimation of all model parameters of chaotic systems from discrete scalar time series measurements

A strategy for estimating all parameters of chaotic systems using discretely sampled data of a measured scalar output is developed and tested. The effect of measurement noise on the asymptotic synchronization error is studied. The robustness of the method in the presence of noise and its ability to track changes in operating parameters of an experimental system is also demonstrated.     

Adaptive window-length detection of underwater transients using wavelets

This paper describes a detection method that adapts to unknown characteristics of the underlying transient signal, such as location, length, and time-frequency content. It applies a set of embedded detectors tuned to a number of signal partitions. The detectors are based on the wavelet theory, whereby two different techniques are examined, one using local Fourier transform and the other using discrete wavelet transform. The detection statistics are computed so as to enable prewhitening of unknown colored noise and to allow for a constant false-alarm rate detection. An adapted segmentation of the signal is next obtained with a goal of finding the largest detection statistics within each segment of the partition. The detectors are tested using several underwater acoustic transient signals buried in ambient sea noise.     

Joint spectrum of photon pairs measured by coincidence Fourier spectroscopy

We propose and demonstrate a method for measuring the joint spectrum of photon pairs via Fourier spectroscopy. The biphoton spectral intensity is computed from a two-dimensional interferogram of coincidence counts. The method has been implemented for a type-I downconversion source using a pair of common-path Mach-Zehnder interferometers based on Soleil compensators. The experimental results agree well with calculated frequency correlations that take into account the effects of coupling into single-mode fibers. The Fourier method is advantageous over scanning spectrometry when detectors exhibit high dark count rates leading to dominant additive noise.     

Improved passive acoustic band-limited energy detection for cetaceans

Acoustic detection of cetaceans is challenged by the variability of calls and the presence of variable background noise. One detection method is to start with frequency band-limited signal and noise estimates, and apply a likelihood ratio test (LRT). These detectors suffer from false alarms when broadband signals overlap the band of interest, triggering detection. Some detectors only consider previous samples, causing further false alarms. The authors propose a method of reducing false alarms by defining a guard band that is not expected to contain energy from the species of interest. A second LRT is performed by testing the ratio of the signal estimate in the signal band with the signal estimate of the guard band. This method is shown to reduce false alarms with a small reduction in detection performance. A detection method is also presented that can be optimized for high processing efficiency, while improving false-alarm rejection from signals that are longer in duration than the signal of interest. Performance is demonstrated on real cetacean recordings and ocean noise. The detection algorithm is implemented in PAMGUARD, an open source Java application designed for passive acoustic monitoring (PAM) of cetaceans.     

阵列探测器对斜入射激光的功率测量不确定度

为了对斜入射情况下的激光功率进行准确测量,采用了对阵列探测器的功率响应度依角度进行修正的方法。推导了依赖于光源位置、阵列探测器位置和阵列探测器姿态角的激光光线方向余弦和入射角的数学表达式,推导了光线方向余弦和入射角的测量不确定度表达式以及阵列探测器功率修正因子的不确定度表达式,并根据功率表达式进一步推导了功率测量不确定度表达式。由此建立了斜入射情况下激光功率阵列探测器测量方法及功率测量不确定度评定的一套较完整的方法。以典型参数为例,计算了斜入射下阵列探测器测量激光功率的不确定度,结果表明采用修正方法可显著减小激光功率测量不确定度。     

Analysis of noise barrier overlap gaps

Sound propagation through the gap produced by two parallel vertical barriers with overlapped ends is formulated for traffic noise sources. The analysis identifies both source and receiver regions according to the mechanisms that influence noise propagation in the vicinity of an overlap gap. A method to account for the contributions from the various source regions for a given receiver location is described. The derived method can be implemented using various equations for sound propagation. The results of using equations approved by the United States Federal Highway Administration for traffic noise propagation are given. Uncalibrated predictions are compared with field measurements for up to 30 receiver positions from each of four overlap gaps. The relative importance of contributions from reflected rays to the noise levels at receiver positions is given. The analysis confirms the initial hypothesis that a commonly used strategy of overlapping barriers by an amount equal to two or three times the overlap width is useful for controlling line-of-sight propagation but ignores the substantial effect of reflections.     

Complex response function of magnetic resonance spectrometers

A vectorial analysis of magnetic resonance spectrometers, based on traveling wave resonators and including the reference arm and the automatic control of frequency, has been developed. The proposed model, valid also for stationary wave resonators, gives the response function of the spectrometer for any working condition, including scalar detectors with arbitrary response law and arbitrary excitation frequency. The purely dispersive and purely absorptive linear responses are discussed in detail for different scalar detectors. The developed approach allows for optimizing the performances of the spectrometer and for obtaining the intrinsic lineshape of the sample in a very broad range of working conditions. More complex setups can be modeled following the proposed scheme.