Simulations for performance evaluations of a family of fluctuation-based processors.
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A family of processors developed at NRL [R. A. Wagstaff, ‘‘The WISPR Filter: A method for exploiting fluctuations to achieve improved sonar signal processor performance,’’ (submitted to J. Acoust. Soc. Am.)] have been shown in data analyses to yield gains in signal-to-noise ratios, and detect weak signals buried in noise. These processors take advantage of the notion that signals from submerged sources (especially those which undergo relatively fewer interactions with the surface) are relatively steady though they may be weak, but ambient noise has greater fluctuations. Simulations using synthetic data have been done to verify the validity of the above premises, and to assess the performance of the family of filters collectively called ‘‘WISPR’’ under several environments. The simulations are also compared with analyses of experimental data. The results of the simulations and the experimental analyses will be discussed. [Work supported by ONR.]Keywords:
SIGNAL (programming language)
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Sonar operation in coastal waters is challenging due to high false alarm rates and strongly varying sonar conditions. Optimal choices for sonar design and pulse characteristics depend strongly on target location and velocity, as well as the present environment. Given a description of the target and environment, acoustical models may estimate sonar performance for different sonar parameters. Updating sonar parameters to best meet shifting sonar conditions impose an unnecessary workload on operators and must be automated for unmanned systems. We suggest an optimization approach that takes into account both a variable environment and a random target. An acoustic ray trace model is run in all directions for a large number of different environment, target, and sonar realisations. Target parameters such as Doppler and aspect are modelled, and optimal sonar parameters are determined. The method is demonstrated for a littoral test case, where both the sonar design and its pulse parameters are optimized. The design takes into account whether the sonar is towed or hull-mounted, and its frequency. The pulse parameters include pulse length and pulse repetition time. The method can easily be extended to other sonar parameters, but the main intent here is to demonstrate the approach.
Synthetic aperture sonar
False alarm
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Most investigators emphasize the importance of detecting the reflected signal from the defect to determine if the pipe wall has any damage and to predict the damage location. However, often the small signal from the defect is hidden behind the other arriving wave modes and signal noise. To overcome the difficulties associated with the identification of the small defect signal in the time history plots, in this paper the time history is analyzed well after the arrival of the first defect signal, and after different wave modes have propagated multiple times through the pipe. It is shown that the defective pipe can be clearly identified by analyzing these late arriving diffuse ultrasonic signals. Multiple reflections and scattering of the propagating wave modes by the defect and pipe ends do not hamper the defect detection capability; on the contrary, it apparently stabilizes the signal and makes it easier to distinguish the defective pipe from the defect-free pipe. This paper also highlights difficulties associated with the interpretation of the recorded time histories due to mode conversion by the defect. The design of electro-magnetic acoustic transducers used to generate and receive the guided waves in the pipe is briefly described in the paper.
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Electromagnetic acoustic transducer
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Fluctuations of signals and noise are commonplace in sonar and have profound effects on the detectability of sonar targets. In this paper, "transition curves", giving probability of detection vs "signal excess", are derived for three theoretical fluctuation models and their use in making sonar performance predictions by means of the sonar equations is described. Some detection results from fleet exercises are presented. They seem to show that the handy and oft-assumed log-normal fluctuation model, with a σ of 6 to 8 dB, provides as good a fit as any to the sparse and scattered field data.
Synthetic aperture sonar
SIGNAL (programming language)
Sonar signal processing
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Sonar sequences were introduced by Golomb and Taylor in 1982. We introduce the concept of extended sonar sequences, which is similar to that of sonar sequences except that blank columns are permitted. Several constructions for extended sonar sequences are offered here. Some of these are close to constructions for ordinary sonar sequences, but they provide improvements to the list of best sonar sequences with up to 100 symbols.
Synthetic aperture sonar
Golomb coding
Sequence (biology)
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Since World War II, the standard metrics for sonar system performance have been Figure-of-Merit and detection range if a specific environment was considered. Detection range can be computed many times for objects of varied depths to yield a similar metric - the depth coverage map. Although satisfactory for general comparisons of simple sonar systems, these metrics fail to account for essential features of sophisticated systems. A more comprehensive measure of sonar system performance is the containment region. For our purposes, containment region is the region in which objects can be detected based on environmental factors and sonar system characteristics. Sonar system characteristics include detailed signal processing, reradiation characteristics, and searcher and object trajectories. A computer model has been developed which accounts for all these characteristics and additionally allows for the imposition of fixed physical boundaries and avoidance tactics. Although different in detail the model is based on principles previously developed by Sudha Reese. The resulting pictures of containment area present an enlightening view of sonar system performance and provide a basis for evaluating current and future systems.
Containment (computer programming)
Synthetic aperture sonar
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본 연구는 센스리더를 사용한 Sonar의 접근성 평가 결과를 바탕으로, 시각장애인이 NCS의 컴퓨터음악제작 직무를 수행할 수 있는 지를 확인하고, 부가적인 접근방안과 개선사항을 제안하기 위한 목적이 있다. 본 연구는 NCS의 [미디프로덕션]과 [오디오프로덕션]의 수행준거와 능력단위요소를 기준으로 단위작업과 상세작업을 도출하고, 시각장애인이 상세작업을 수행하기 위해 센스리더를 사용한 Sonar 접근성을 평가하고, 그 결과를 통하여 단위작업과 능력단위요소의 수행 가능성이 평가되었다.
연구결과, 센스리더 사용자가 Sonar를 사용하여 NCS의 컴퓨터음악제작 직무를 수행할 수는 있으나, 일부 기능의 접근성 결여로 완성도 있는 음악제작은 어려운 것으로 나타났다. 접근이 가장 어려웠던 기능은 플러그인 형태로 제공되는 가상악기와 가상이펙터로 나타났다. 이 결과를 바탕으로 시각장애인의 NCS 컴퓨터음악제작 직무수행을 위해 필요한 개선방안이 제안되었다.
Synthetic aperture sonar
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Sonar operational range is an important tactics and technique parameter for sonar system.It is a variable number because of many factors affecting in the actual using, so it brings more complex in the test.Being analyzing the influencing factors for sonar operational range, this paper summarizes the traditional test.Joint of simulation and sea test for sonar operational range is discussed on the base of analyzing the localization of traditional method and the demand of sonar developing and using. Factors analyzing of affecting sonar operational rangeSonar operational range is an important tactics and technique parameter for sonar system.As the sonar's working environment is a complicated underwater acoustic environment, the actual sonar operational range is a synthetical index which depends on the performance of sonar system, environment of the underwater acoustic propagation and target characteristics.Sonar equation is a useful tool in designing the sonar system.It is usually used to analyze and attest the performance of sonar system.It forms an organic structure of hydrophone, underwater sound channel, noise, reverberation, detection and signal designing.Active and passive sonar equation is as follows, Active sonar equation (Reverberation Limited),
Synthetic aperture sonar
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Synthetic aperture sonar
Sonar signal processing
SIGNAL (programming language)
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The steps which a sonar operator goes through in finally calling "target" while using a trainable beam passive sonar in the aural mode are described. Three distinct processes are identified: (a) single observation, (b) multiple sequential observation, and (c) multiple sweep. Using these concepts and data from two-alternative forced-choice psychoacoustic experiments, one can calculate a transition curve for realistic sonar operator performance. These calculations are compared with transition curves obtained from sonar performances on a more realistic sonar mock-up. The significance of the paper is in the detailed description of the aural process and in the method for calculating aural detection performance.
Synthetic aperture sonar
Mode (computer interface)
Operator (biology)
Psychoacoustics
Sonar signal processing
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Based on the detection theory of ASW helicopter'dipping sonar and its characteristic,a scatter model for searching submarine is built on the condition of the known submarine initial location and the unknown course and speed of submarine,and then deduces dipping sonar's searching efficiency formula,and build searching efficiency model of dipping sonar by round or square searching shapes according to the regular scatter pattern of the submarine. Simulation analyzes the searching efficiency by using dipping sonar on the condition of the known submarine initial location and the unknown course and speed of submarine is based on Monte Carlo Method. It proves that the results of searching probability is almost the same to the searching algorithm through the tests of dipping sonar in different times,which gets the result that it is effective to the use of searching efficiency model and also analyzes the influence of the varieties of searching range of dipping sonar versus searching efficiency.
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