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1.
A programmable microcomputer-based sonar echo processor has been developed and field tested to process echo data in real time. The device was designed for use in fisheries acoustics and to analyze echoes from the sea floor. The instrument simultaneously performs the functions "echo integration" and "echo peak detection' on the sonar signal. The "echo integration" circuitry measures the relative acoustic energy of the echo while the "echo peak detection' electronics measure the probability density function (PDF) of the peak of the echo envelope. Each process is gated so the echoes may be processed in many short time intervals. In fisheries applications, estimates can be made of fish density (fish per unit volume), average backscattering cross section, and a combination of fish size and behavior. When using the device to analyze bottom echoes, it is possible to measure both the returned energy from the bottom sediment interfaces and the microrelief characteristics. The durability, flexibility, computer link, and floppy-disk data-storage features of the system are discussed. Data are presented of the processed echoes from biological organisms and the ocean bottom from a recent research cruise on the Atlantic Ocean near Cape Hatteras, NC. The biological results illustrated the organisms to be clearly divided into two separate spatial distributions-an observation not obvious from a standard echogram which was simultaneously used. The results from the bottom showed both 1) the difference in sub-bottom structure between two locations and 2) changes in microrelief of the water-bottom interface between another pair of locations.  相似文献   

2.
The ultrasonic signals of dolphins show as “interference noise” on an echo‐sounder record. Some records obtained from Delphinus delphis in Hauraki Gulf, New Zealand, suggest that these emissions were being used for echo‐ranging, a phenomenon well established by previous work. Possible uses of such records in studying dolphin behaviour are explained.  相似文献   

3.
Active sonar detection in shallow water using the Page test   总被引：1，自引：0，他引：1  
The use of active sonar in shallow water results in received echoes that may be considerably spread in time compared to the resolution of the transmitted waveform. The duration and structure of the spreading and the time of occurrence of the received echo are unknown without accurate knowledge of the environment and a priori information on the location and reflection properties of the target. A sequential detector based on the Page test is proposed for the detection of time-spread active sonar echoes. The detector also provides estimates of the starting and stopping times of the received echo. This signal segmentation is crucial to allow further processing such as more accurate range and bearing localization, depth localization, or classification. The detector is designed to exploit the time spreading of the received echo and is tuned as a function of range to the expected signal-to-noise ratio (SNR) as determined by the transmitted signal power, transmission loss, approximate target strength, and the estimated noise background level. The theoretical false alarm and detection performance of the proposed detector, the standard Page test, and the conventional thresholded matched filter detector are compared as a function of range, echo duration, SNR, and the mismatch between the actual and assumed SNR. The proposed detector and the standard Page test are seen to perform better than the conventional thresholded matched filter detector as soon as the received echo is minimally spread in time. The use of the proposed detector and the standard Page test in active sonar is illustrated with reverberation data containing target-like echoes from geological features, where it was seen that the proposed detector was able to suppress reverberation generated false alarms that were detected by the standard Page test  相似文献   

4.
It has long been known that the statistical properties of acoustic echoes from individual fish can have non-Rayleigh characteristics. The statistical properties of echoes from zooplankton are generally less understood. In this study, echoes from individual fish and zooplankton from a series of laboratory measurements from the past decade are investigated. In the experiments, acoustic echoes from various individual organisms were measured over a wide range of frequencies and orientations, typically in 1/spl deg/-3/spl deg/ increments. In the analysis in this paper, the echoes from most of those measurements are grouped according to ranges of orientation, which correspond to typical orientation distributions of these organisms in the natural ocean environment. This grouping provides a distribution of echo values for each range of orientation. This approach, in essence, emulates a field experiment whereby distributions of echoes would be recorded for different distributions of orientations of the organisms. For both the fish and zooplankton data, there are conditions under which the echoes are strongly non-Rayleigh distributed. In some cases, the distribution is quantitatively connected to the physics of the scattering process while, in other cases, the connection is described qualitatively. Exploitation of the animal-specific statistics for classification purposes is suggested.  相似文献   

5.
An outstanding problem in fisheries acoustics is the depth dependence of scattering characteristics of swimbladder-bearing fish, and the effects of pressure on the target strength of physoclistous fish remain unresolved. In situ echoes from deepwater snappers were obtained with a sonar transducer mounted on a manned submersible next to a low-light video camera, permitting simultaneous echo recording and identification of species, fish size and orientation. The sonar system, consisting of a transducer, single board computer, hard disk, and analog-to-digital converter, used a 80 μs, broadband signal (bandwidth 35 kHz, center frequency 120 kHz). The observed relationship between fish length and in situ target strength shows no difference from the relationship measured at the surface. No differences in the species-specific temporal echo characteristics were observed between surface and in situ measures. This indicates that the size and shape of the snappers’ swimbladders are maintained both at the surface and at depths of up to 250 m. Information obtained through controlled backscatter measurements of tethered, anesthetized fish at the surface can be applied to free-swimming fish at depth. This is the first published account of the use of a manned submersible to measure in situ scattering from identified, individual animals with known orientations. The distinct advantage of this technique compared with other in situ techniques is the ability to observe the target fish, obtaining accurate species, size, and orientation information.  相似文献   

6.
A “Pingerprobe” is a system of echo sounding in which the sound source is placed near bottom to improve resolution by restricting the area investigated. It is demonstrated that a commercially available 12-kHz “pinger” with a synchronized shipboard receiver is useful not only in the monitoring of the positioning of a bottom or near-bottom instrument package (such as a corer) but also in making observations on the acoustic nature of the sea floor. In rough terrain the Pingerprobe has measured stratified sediments in some places where the PDR (Precision Depth Recorder) cannot. Observations on proximal abyssal plains indicate that the prolonged echo character common to these areas may result from small-scale roughness or inhomogeneity. When a suspended instrument is sent to the bottom in rough terrain, or in areas of intermittent subbottom reflections, use of a Pingerprobe improves information about the conditions at the point of contact and permits selection of the desired topographic setting.  相似文献   

7.
车昊函  邢磊  蔺玉曌 《海洋科学》2023,47(11):121-131
目前常规海洋测绘手段主要包括电子海图、单波束、多波束、侧扫声呐等,这些方法的单独使用会存在诸如数据样本稀疏、施工成本昂贵、难以获取确切深度等局限之处。基于超声波回声原理的科研鱼探仪广泛用于渔业资源调查与评估中,是渔业领域的主要统计手段,具有数据体量大、来源丰富、采集成本低的特点。超声回波数据在刻画鱼群数量、方位的同时,携带有海底地形与海水温盐结构信息,可以作为常规海洋测绘方法的补充。特别是数据解编后得到的高精度水体数据,可以用于海洋地球物理等研究,故针对科研鱼探仪数据的解编工作亟待进行。本文针对科研鱼探仪(SIMRAD EK80)的采集数据进行解编处理,并基于对道头信息的分析,实现对数据文件的重新分类,提取与海洋地球物理领域相关的位置、样点能量值等数据信息进行分析研究,旨在丰富海洋地球物理研究数据来源,为常规海洋探测工作提供借鉴,提升数据利用效能。  相似文献   

8.
Details of all known data on New Zealand snapper tagging operations to 1963 are presented and briefly analysed. Nearly 8,000 fish have been tagged, with 43 (0.5%) returned. Fishing methods have included beach‐seining, trawling, and hand‐lining; tags used have been “pig‐rings”, operculum strap tags, or Petersen discs attached by two different methods. The greatest number of returns were from line‐caught fish with Petersen discs attached through the body by nylon thread. Of the 43 fish recaptured, 33 were taken less than six miles from their tagging site, and seven had moved between 10 and 260 miles (no recapture site was given for three fish. Days at liberty ranged from one to 1,127, with a mean of 164. There were insufficient growth data for analysis.  相似文献   

9.
Scales from 17 body areas of juvenile snapper, Chrysophyrs auratus (Forster), were examined to determine scale growth characteristics, with the aim of denning the most suitable body site for routine scale‐sampling. Least‐square regressions of fish length on scale measurement from 0+ fish were calculated for several body areas, and back‐calculations were made to fish length at first annulus (L1) from a sample of 1+ fish, using both the “uncorrected” and “corrected” formulae.

The overall fish/scale relationship is curvilinear, but high correlation coefficients show that fish/scale regressions from 0+ snapper may be taken as essentially linear. Such regressions give hypothetical fish lengths at scale formation of 8–23 mm. Mid‐body scales form at 10–14 mm, caudal scales earlier, head scales later.

Back‐calculated L1 values from each area were compared with the mean for the whole body. Using the uncorrected formula there is a general trend for them to be lower than the mean at the head and higher at the tail, while the mid‐body region shows minimum variation from the mean. These variations are caused at least partly by differences in time of scale formation. The corrected formula gives smaller L1 variations and a mean back‐calculated L1almost identical to an observed L1 from independent length frequency data.

The observed variations in scale structure and growth suggest that the “pectoral area”, bounded by the lateral line and the ventral edge of the pectoral fin, is the most suitable site for scale sampling.  相似文献   

10.
Fish sonars have long been used to survey and monitor migratory salmon in rivers and at sea. However, research has been lacking in the development of algorithms to extract fish tracks from data collected in a riverine or oceanic environment. Current fish trackers, based on a pulse-to-pulse tracking method, only work well under ideal conditions when targets are well separated and the signal-to-noise ratio is high. Fisheries biologists often have to identify fish traces visually from raw echograms. This approach is both labor-intensive and time-consuming, limiting the usefulness of hydroacoustic techniques for fisheries management. This paper presents a fish-tracking algorithm which sorts randomly distributed echoes into coherent fish traces. Fish counts obtained with the algorithm compare well with visual counts at two quite different sites in the Fraser River watershed. The key features of the algorithm are: (1) the linking mechanisms among sequential fish echoes are range-dependent; (2) the growth echo for a developing track depends not only on its space-time relation with the previous track echo (the pulse-to-pulse statistics) but also on its relation to the entire track being constructed; (3) there are a total of only five echo-association criteria in the algorithm; (4) the simplicity of the algorithm structure provides a convenient platform for implementing specific and sophisticated tracking criteria to meet specific needs; and (5) the user can fully control the performance of the algorithm by choosing values for the 11 well-defined tracking parameters  相似文献   

11.
基于LabVIEW的深水网箱鱼群监测系统的信号处理   总被引：1，自引：0，他引：1  
深水网箱鱼群活动状态的实时监测是开展深水网箱渔业资源可持续发展中急需解决的关键技术。文中介绍了深水网箱鱼群监测系统中基于LabVIEW的数据信号处理方法。该方法采用软件编程技术取代传统的硬件电路设计,实现了深水网箱鱼群监测系统的时间增益补偿、信号相关处理、图像处理和鱼群量估计等功能,海上现场实验证明系统具有较高的抗噪声和混响干扰能力,鱼群回波图像显示简洁、海上操作方便,采用鱼群回波能量积分方法能较好地估计鱼群量大小。  相似文献   

12.
A computer code that simulates multibeam echo‐sounding over realistic (three‐dimensional) bathymetry was used to compare available sounding systems. Two‐dimensional modeling dealt with the resolution of seafloor bathymetry and with the effect of postprocessing algorithms for some typical multibeam systems. The 2‐D bathymetric inputs were idealized bottom features. Three‐dimensional modeling dealt with the gross character of the seafloor, as detected by echo‐sounding systems. The 3‐D bathymetric inputs were realizations of terrain generated by a stochastic model of seafloor roughness. Three‐dimensional modeling indicated that the sounding system may slightly shift the location of peaks within the beam footprint. In addition, the simulated measurements were more sensitive to low‐wavenumber features (i.e., large‐scale roughness) than to high‐wavenumber features (i.e., small‐scale roughness). Resolution gradually decreased with increasing distance from centerline, due to the increasing footprint size of beams at increasing angular distance from the vertical. Lineated terrain was also smoothed by simulated echo‐sounding; lineations may indeed remain undetected if sounding system parameters are not properly selected. Inversion of the simulated measurements indicated that echo‐sounding measurements are dependent not only on the characteristics of the sounding system itself, but on other factors such as the character of the roughness and the orientation of the survey relative to the strike of lineations. The modeling technique provides a way to quantify the system response of a multibeam echo‐sounding system. This work resulted in recommendations as to the most appropriate system for an application in an area of rough bathymetry, and it led to the establishment of criteria for comparing multibeam systems in future applications.  相似文献   

13.
Survival and reproductive rates in fish are often a function of body size. Consequently, spatial‐ and sex‐specific variation in somatic growth rates can have important consequences for population growth and resilience. We used otolith‐based approaches to estimate geographic‐ and sex‐specific growth rates of yellow‐eyed mullet (Aldrichetta forsteri) collected from 14 estuaries and harbours around New Zealand. Aldrichetta forsteri is an abundant and dominant component of New Zealand's estuarine fish fauna. We extracted otoliths from 511 fish, validated daily and annual increments, and prepared transverse thin sections of otoliths to determine age. “Size‐at‐age” relationships were estimated using both linear‐ and non‐linear (von Bertalanffy) growth models, and model performance was evaluated using Akaike's Information Criterion. Because growth rates of sampled fish were best approximated by linear functions, we used ANCOVA to test the null hypothesis that growth rates of A. forsteri were homogeneous between sexes and among geographic locations around New Zealand. Our analyses suggest heterogeneous growth rates between sexes and among locations. Interestingly, relative growth rates between sexes appeared to vary across separate latitudinal gradients for North Island and South Island. Within each island (but not across islands), female A. forsteri generally grew faster than males at the lowest latitudes; relative growth rates of females declined progressively below males with increasing latitude.  相似文献   

14.
The effects of no‐take marine reserve (NTMR) protection and changes in benthic habitat on fusiliers (family Caesionidae) were investigated at four small Philippine offshore islands on time scales of 10–31 years. Fusiliers are highly mobile, schooling, medium‐sized planktivorous fish that generally feed “off‐reef.” For these reasons, and given the small size of the NTMRs (3.6–37.5 ha) in this study, it was predicted that fusilier density would be unlikely to show clear effects of NTMR protection, or to respond to changes in benthic habitat. In contrast to predictions, clear NTMR effects were observed on fusilier density at three of the four NTMRs, with durations of protection from 14 to 31 years. Furthermore, the study provided strong evidence that benthic variables, specifically cover of live hard coral and dead substratum, affect the density of fusiliers. This effect of benthic habitat on density was highlighted by several major environmental disturbances that caused shifts in the benthic habitat from live hard coral to dead substratum. For two of the three most abundant species of fusiliers individually, and for all three of them combined (Pterocaesio pisang + Caesio caerulaurea + Pterocaesio digramma/tessellata), as live hard coral cover decreased, fish density decreased. It is hypothesized that these “off‐reef” daytime feeders may have such a strong association with live hard coral cover because they use this habitat as nocturnal sleeping sites. Multivariate analyses indicated that, across all sites and times sampled, cover of live hard coral and dead substratum accounted for 38% of the variation in fish assemblage structure. These results are important as there are very few reports in the published literature of strong effects of NTMR protection or changes in benthic habitat on the density and assemblage structure of fusiliers.  相似文献   

15.
A geographic fishery research database system (GFRDBS), called ECHOBASE, for storing and management of data on pelagic fish resources from acoustic surveys and catch samples, combined with environmental data in a geographic context, has been developed. The system constitutes a portable and inexpensive yet powerful tool for fishery research and environmental monitoring and provides on‐board data processing and mapping capabilities.

Data are acquired from an echosounder, echo signal processor, environmental profiler (CTD probe), and Global Positioning System (GPS) receiver. The electronic digitized maps (based on C‐MAP public format files) provide active on‐screen nautical charts.

The basic GFRDBS platform is a portable PC 486 machine, which is used as an on‐board data acquisition and processing tool running under MS Windows 3.1 operating environment. The system is designed around the Borland's PARADOX package, which provides a relational database for managing acoustic, catch, and environmental data. The ECHOBASE programs were written in Borland C ++ language as a Windows application.  相似文献   

16.
Acoustic echoes obtained during high-resolution shallow marine seismic surveys contain information about the statistical nature of the sedimentary bottom and its spatial variability. Use of a broad-band seismic source and an appropriately chosen data acquisition window makes the acoustic responses particularly amenable to quantitive analysis. The work reported utilizes experimental frequency-domain spatial coherence functions of along-track acoustic echoes as empirical metrics of bottom character, and by virtue of their correlation with known sediment types, as objective bases for remote sediment classification. Theoretical relationships between parameters describing sediment surface topographies and echo coherence are derived for the case of dominant water-sediment interface acoustic scattering. The diverse experimental data base was acquired from the Grand Banks of Newfoundland using a 1- to 10-kHz Huntec DTS system. Bottom photographs, cores, and grab samples combined with expert geological synthesis provide qualitative and quantitative control.  相似文献   

17.
An active sonar is described that adaptively changes its location and configuration in response to the echoes it observes in order to locate an object, position it at a known location, and identify it using features extracted from the echoes. The sonar consists of a center transmitter flanked by two receivers that can rotate and is positioned at the end of a robot arm that has five degree-of-freedom mobility. The sonar operates in air using Polaroid transducers that are resonant at 60 kHz with a nominal wavelength equal to 6 mm. The emitted pulse has a short duration with a useful bandwidth extending from 20 to 130 kHz. Using binaural information, the transmitter rotates to position an echo-producing object on its axis to maximize the acoustic intensity incident on the nearest echo-producing feature. The receivers rotate to maximize the echo amplitude and bandwidth. These optimizations are useful for differentiating objects. The system recognizes a collection of ball bearings, machine washers, and rubber O-rings of different sizes ranging from 0.45 to 2.54 cm, some differing by less than 1 mm in diameter. Learning is accomplished by extracting vectors of 32 echo envelope values acquired during a scan in elevation and forming a data base. Recognition is accomplished by comparing a single observed echo vector with the data base to find the least squared error match. A bent-wire paper clip illustrates the recognition of an asymmetric pose-dependent object  相似文献   

18.
The method of acoustic backscattering measurement from different parts of fish using the focus array of transducer developed recently is described in this paper. The results of the measurements of several kinds of flsh are given in this paper, indicating that the backscattering from fish is closely relative to the anatomy of fish. Its application in forming backscattering model of fish and that in using this model to obtain the information of fish kinds by the echoes from fish sonar are discussed.  相似文献   

19.
Distinctly different water masses are to be found near the sea surface within 40 km of the coast off Otago Peninsula, south‐eastern New Zealand (45° 50’ S, 170° 45’ E). Although the hydrological regime is complex in this area, the three water masses have a stable relationship to one another: neritic water close to shore, then modified Subtropical Water, and Subantarctic Water off shore. Quantitative zooplankton samples from the upper 150 m were taken from a four‐station, 50‐km latitudinal transect at monthly intervals over 15 months, October 1966‐December 1967. Data were analysed by group‐average sorting methods into a hierarchical classification of 37 components, identified to species where practicable. Each species group was clearly associated with particular stations and from this hydrological affinities were deduced. The classification recognised a primary division between “neritic” and “oceanic” groups of zooplankton, each of which contained further subdivisions. “Neritic” zooplankton contained “coastal” and “shelf” subgroups; “oceanic” plankton contained “transitional” and “subantarctic” subgroups. Zooplankton from Otago waters had hydrological affinities which were consistent with their wider distributions. Presence of subtropical zooplankton in Otago waters helps to resolve confusing differences between various interpretations of surface circulation in the southern Tasman Sea.  相似文献   

20.
Functional groups have become an important tool for characterizing communities of marine and estuarine environments. Their use also holds promise for a better understanding of the temporal dynamics of phytoplankton. This study aimed to evaluate the contributions of phytoplankton size fractions and functional groups characterizing short‐term variation throughout tidal cycles and between dry and rainy seasons in a tropical estuarine system. Camamu Bay is an oligotrophic estuarine system that is under strong influence from tropical shelf waters and is characterized by high salinity and low concentrations of dissolved nutrients. Surface‐water samples were collected at nine sampling sites distributed among the three hydrodynamic regions of the bay, and at a mooring, at 3‐hr intervals during tidal cycles (12 hr each) in both the rainy and the dry season. Although the abundances of the phytoplankton fractions (pico‐, nano‐, and micro‐) were higher in the rainy season and during periods of higher tide, they were not significantly higher. The phytoplankton community in the bay comprises three functional groups: GI = “colonial” (i.e., chain‐forming diatoms and filamentous cyanobacteria); GII = “GALD >40” (i.e., pennate and centric diatoms with MDL >40 µm), and GIII = “flagellates” (i.e., species with motility via flagella). Nanoflagellates were the most abundant form in the bay, while chain‐forming diatoms, in particular, contributed to the microphytoplankton fraction during both the rainy and dry seasons. Functional groups, as defined by cluster analysis, reflected ecological strategies compatible with the high hydrodynamics of Camamu Bay, which is characterized by processes of tidal‐forced intense mixing, mainly during periods of spring tides. The phytoplankton of the bay was found to possess a series of attributes (functional traits) that endow them with some resistance to sinking. Functional diversity indexes (FEve, FDiv, and FDis) indicated a stable community without significant short‐term variation due to low variability in the environmental conditions of the system during the study period.  相似文献   

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