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This paper studies passive problems where the receiver extracts from the source radiated signature information concerning the parameters defining the relative source/receiver geometry. A model encompassing the fundamental global and local characteristics for passive positioning and navigation is presented. It considers narrow-band signals, imposes linear constraints on the geometry, and exhibits explicitly the symmetry between the space and time aspects. The analysis concentrates on questions of global geometry identifiability, emphasizing the passive global range acquisition. The maximum-likelihood processor is analyzed by studying the ambiguity structure associated with inhomogeneous passive narrowband tracking. Bounds on the global and local mean-square error performance are studied and tested via Monte Carlo simulations. By considering two limiting geometries, a distant and a close observer, simple approximate expressions for the mean-square errors are presented and compared to the exact bounds. Herein the study is restricted to stationary geometries where the source is located by an extended array (spatial diversity). Subsequent papers generalize the study to moving sources (temporal diversity) and to coupled geometries. 相似文献
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Mikhalevsky P.N. Gavrilov A.N. Baggeroer A.B. 《Oceanic Engineering, IEEE Journal of》1999,24(2):183-201
In April 1994, coherent acoustic transmissions were propagated across the entire Arctic basin for the first time. This experiment, known as the Transarctic Acoustic Propagation Experiment (TAP), was designed to determine the feasibility of using these signals to monitor changes in Arctic Ocean temperature and changes in sea ice thickness and concentration. CW and maximal length sequences (MLS) were transmitted from the source camp located north of the Svalbard Archipelago 1000 km to a vertical line array in the Lincoln Sea and 2600 km to a two-dimensional horizontal array and a vertical array in the Beaufort Sea. TAP demonstrated that the 19.6-Hz 195-dB (251-W) signals propagated with both sufficiently low loss and high phase stability to support the coherent pulse compression processing of the MLS and the phase detection of the CW signals. These yield time delay measurements an order of magnitude better than what is required to detect the estimated 80-ms/year changes in travel time caused by interannual and longer term changes in Arctic Ocean temperature. The TAP data provided propagation loss measurements to compare with the models to be used for correlating modal scattering losses with sea ice properties for ice monitoring. The travel times measured in TAP indicated a warming of the Atlantic layer in the Arctic of close to 0.4°C, which has been confirmed by direct measurement from icebreakers and submarines, demonstrating the utility of acoustic thermometry in the Arctic. The unique advantages of acoustic thermometry in the Arctic and the importance of climate monitoring in the Arctic are discussed. A four-year program, Arctic Climate Observations using Underwater Sound is underway to carry out the first installations of sources and receivers in the Arctic Ocean 相似文献
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We consider the problem of estimating structure (interface reflection coefficient values) from noisy reflection observations of a discrete, layered, lossless waveguide; this is a special case of the general acoustic reflection inverse problem. Our approach is to develop a statistical lower bound, the Cramer-Rao bound, on estimator performance. We demonstrate, by computing the bound for the one- and two-reflector cases, that the bound is not merely theoretical but also provides, through its parametric behavior, physical insight into the estimation problem. In addition, we present two estimator structures for this problem, a statistically optimal estimator, (maximum-likelihood), and a suboptimal estimator (based on the special character of the medium's response), and compare their performance. We perform Monte Carlo tests to verify that, for high signal-to-noise ratios, estimator performance is predicted by the Cramer-Rao bound. Moreover, we find that in these regions the ad hoc estimator performs comparably to the maximum likelihood. 相似文献
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Sequential decoding of long-constraint convolutional codes is shown to be a feasible technique for digital data telemetry over realistic marine acoustic channels. A computational bound for sequential decoding over a fading dispersive channel is derived for hardlimiting and quantizing decoders. The results indicate that a minimum of 8 dB of bit SNR (signal-to-noise ratio) is required for sequential decoder operation. Simulations indicate that 14-dB bit SNR results in simple and feasible implementations. Diversity methods for coded transmissions over Rayleigh fading channels are examined. The optimal diversity level for minimum error probability of uncoded systems and the diversity level of minimizing the sequential decoder computational load are derived and shown to be different, with the latter requiring a higher order of diversity. Performance differences between fixed-diversity and optimal-diversity systems are presented 相似文献