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1.
This study presents a river invertebrate and classification system (RIVPACS) type bioassessment methodology for the Manawatu‐Wanganui region of New Zealand. Aquatic macroinvertebrates and related physico‐chemical data were collected at 127 sites, with minimal human impacts (reference sites) in 2000. The reference sites were classified into five groups based on their macroinvertebrate data using TWINSPAN. These biotic groupings were then applied to their corresponding physico‐chemical data and discriminant functions were obtained to assign sites into the biotic groups using the physico‐chemical data. The discriminant functions correctly allocated 72% of the sites to the correct classification group using a jack‐knife validation. The probabilities from the discriminant functions were used to predict macroinvertebrate assemblages and these were compared with observed macroinvertebrate assemblages. The model was then used to assess the health of 29 test sites with known impacts. All test sites were assessed as impacted based on the 10th percentile of the reference data. To evaluate the temporal reliability of the model, data available for 11 sites sampled in 1997 and 2000 were run through the model. The results of this comparison showed little variation in O/E ratios over time and the two sites classed as impacted in 1997 were also classed as impacted in 2000. 相似文献
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The dynamics of daily weather types according to Schüepp's classification in the Alpine region is investigated by means of seasonal Markov chain models. A logit model is employed for the transition probabilities of the Markov chain. The parameters follow from a maximum likelihood estimation. A 1st‐ and a 2nd‐order Markov chain model are compared and found to yield very similar results. Model predictions are compared with counted frequencies of seasonally‐averaged joint probabilities for the occurrence of weather types at subsequent days, monthly‐averaged probabilities of a change of the weather type from one to the next day, and daily averages of the probabilities of occurrence of the different weather types. All these predictions coincide with the observations within the statistical limits. The only large deviations occur in the tails of the lengths distributions of uninterrupted episodes of the two most frequent weather types. 相似文献
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Sarah E. Zedler Guido Kanschat Robert Korty Ibrahim Hoteit 《Journal of Oceanography》2012,68(2):227-241
We seek to determine if a small number of measurements of upper ocean temperature and currents can be used to make estimates
of the drag coefficient that have a smaller range of uncertainty than previously found. We adopt a numerical approach using
forward models of the ocean’s response to a tropical cyclone, whereby the probability density function of drag coefficient
values as a function of wind speed that results from adding realistic levels of noise to the simulated ocean response variables
is sought. Allowing the drag coefficient two parameters of freedom, namely the values at 35 and at 45 m/s, we found that the
uncertainty in the optimal value is about 20% for levels of instrument noise up to 1 K for a misfit function based on temperature,
or 1.0 m/s for a misfit function based on 15 m velocity components. This is within tolerable limits considering the spread
of measurement-based drag coefficient estimates. The results are robust for several different instrument arrays; the noise
levels do not decrease by much for arrays with more than 40 sensors when the sensor positions are random. Our results suggest
that for an ideal case, having a small number of sensors (20–40) in a data assimilation problem would provide sufficient accuracy
in the estimated drag coefficient. 相似文献
4.
Over the past five decades, several approaches for estimating probabilities of extreme still water levels have been developed. Currently, different methods are applied not only on transnational, but also on national scales, resulting in a heterogeneous level of protection. Applying different statistical methods can yield significantly different estimates of return water levels, but even the use of the same technique can produce large discrepancies, because there is subjective parameter choice at several steps in the model setup. In this paper, we compare probabilities of extreme still water levels estimated using the main direct methods (i.e. the block maxima method and the peaks over threshold method) considering a wide range of strategies to create extreme value dataset and a range of different model setups. We primarily use tide gauge records from the German Bight but also consider data from sites around the UK and Australia for comparison. The focus is on testing the influence of the following three main factors, which can affect the estimates of extreme value statistics: (1) detrending the original data sets; (2) building samples of extreme values from the original data sets; and (3) the record lengths of the original data sets. We find that using different detrending techniques biases the results from extreme value statistics. Hence, we recommend using a 1-year moving average of high waters (or hourly records if these are available) to correct the original data sets for seasonal and long-term sea level changes. Our results highlight that the peaks over threshold method yields more reliable and more stable (i.e. using short records leads to the same results as when using long records) estimates of probabilities of extreme still water levels than the block maxima method. In analysing a variety of threshold selection methods we find that using the 99.7th percentile water level leads to the most stable return water level estimates along the German Bight. This is also valid for the international stations considered. Finally, to provide guidance for coastal engineers and operators, we recommend the peaks over threshold method and define an objective approach for setting up the model. If this is applied routinely around a country, it will help overcome the problem of heterogeneous levels of protection resulting from different methods and varying model setups. 相似文献
5.
The problem of associating data with targets in a cluttered multi-target environment is discussed and applied to passive sonar tracking. The probabilistic data association (PDA) method, which is based on computing the posterior probability of each candidate measurement found in a validation gate, assumes that only one real target is present and all other measurements are Poisson-distributed clutter. In this paper, a new theoretical result is presented: the joint probabilistic data association (JPDA) algorithm, in which joint posterior association probabilities are computed for multiple targets (or multiple discrete interfering sources) in Poisson clutter. The algorithm is applied to a passive sonar tracking problem with multiple sensors and targets, in which a target is not fully observable from a single sensor. Targets are modeled with four geographic states, two or more acoustic states, and realistic (i.e., low) probabilities of detection at each sample time. A simulation result is presented for two heavily interfering targets illustrating the dramatic tracking improvements obtained by estimating the targets' states using joint association probabilities. 相似文献
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热液喷口附近的羽状流中存在明显的化学及浊度异常,通过探测这些异常可判断是否存在热液喷口及确定喷口的具体位置。本文研制了一款可用于探测热液喷口的多通道化学传感器,该传感器具有体积小、精度高的特点,且可在4000米深海中进行工作。该化学传感器共配备五个全固态电极,一个为参比电极,其余四个为离子选择性电极,并且可根据所测量的化学离子进行更换。本文基于该化学传感器共进行了两组实验。在第一组浅海试验中,化学传感器集成了pH,Eh,CO32-和SO42-电极,在浅海海域中测量对应化学量,结果表明该化学传感器可在实际应用中获得高精度、稳定的测量数据。第二组实验为深海热液探测,装配了pH,Eh,CO32-和H2S电极的化学传感器在西南印度洋中脊区域的29次测线中投入使用,共获得有效数据27组。通过对测量所得到的化学量进行分析,本文提出了一种确定热液喷口的化学异常探测方法,若某时间段内Eh和H2S的电势降低,而pH和CO32-的电势上升则可判定存在化学异常。利用该方法对27组有效数据进行分析,共发现5个潜在的热液喷口。实验结果表明,该化学传感器可有效地探测由热液引起的化学异常,适用于实际热液探测中。 相似文献
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The formation of acoustic images in real-time requires an enormous computational burden. To reduce this demand the use of sparse arrays for beamforming is mandated. The design of these arrays for adequate mainlobe width and low sidelobe level is a difficult nonlinear optimization problem. A new approach to the joint optimization of sensor placement and shading weights is discussed. Based on the concept of importance sampling an optimization method is presented and some examples given to illustrate its effectiveness. 相似文献
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基于多参数化学传感器的海底热液探测方法研究 总被引：1，自引：0，他引：1
基于热液及其羽状流的化学异常提出了一种海底热液的化学式探测方法。根据自行开发的Eh.Ag/Ag2S和pH三种化学电极,设计了多参数化学传感器系统。通过海试证明多参数化学传感器可灵敏地检测出由热液异常引起的化学量变化,并在长达半年的多次使用中表现出其稳定性好、寿命长的特点。在东太平洋中脊(EPR)赤道区域和西南印度洋中脊(SWIR)的60条测线中,获得有效测线55条,其中在29条测线上发现明显或可能的热液异常。研究表明,应用多参数化学传感器探测进行海底热液化学异常,是一种有效的方法。 相似文献
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为解决多传感器水下目标纯方位跟踪中的传感器测量衰减问题,建立水下目标静态多传感器纯方位跟踪模型,将传感器测量衰减建模为统计特性已知的随机变量,基于融合中心接收到的各水声传感器的原始测量值,设计了一种集中式状态估计器结构,利用最小方差方法推导出最优的集中式目标状态估计增益。通过算例仿真可以得出,所提出的算法能够在水声传感器不做机动的前提下跟踪目标,弥补了单个水声传感器观测性不足的缺点,对比传统的集中式Kalman估计器,具有更高的精度,能够有效解决传感器测量衰减问题。 相似文献
12.
In this paper a finite array of hinged flap-type wave energy converters are modelled using a mathematical approach. These are illustrative of the Oyster device of Aquamarine Power Ltd.1 A novel semi-analytic solution method is presented for a set of boundary-value problems involving the scattering and radiation of waves by thin barriers used to model the device hydrodynamics. The approach makes use of the geometry to apply Fourier transforms, deriving non-singular integral equations in terms of the jumps in pressure across the flaps. These are then solved numerically using a highly efficient Galerkin expansion method. The focus of the results is on optimisation. We suggest optimal parameters for a single device, identifying flap length as crucial to device performance. This optimisation is then carried through to arrays with optimal arrangements and spacings being determined for a model sea state. Here, the lateral displacement of the devices emerges as a critical factor in optimal array configuration. 相似文献
13.
This paper examines the effectiveness of horizontal line arrays (HLAs) for matched-field inversion (MFI) by quantifying geoacoustic information content for a variety of experiment and array factors, including array length and number of sensors, source range and bearing, source-frequency content, and signal-to-noise ratio (SNR). Emphasis is on bottom-moored arrays, while towed arrays are also considered, and a comparison with vertical line array (VLA) performance is made. The geoacoustic information content is quantified in terms of marginal posterior probability distributions (PPDs) for model parameters estimated using a fast Gibbs sampler approach to Bayesian inversion. This produces an absolute, quantitative estimate of the geoacoustic parameter uncertainties which can be directly compared for various experiment and array factors. 相似文献
14.
G. A. Moiseev 《Physical Oceanography》1993,4(3):183-192
The idea of the weak variability of the fields is introduced, which means that when they are recorded by some measuring instrument (MI), the output signal obtains increments of the order of one/several quanta of sensitivity at the discreteness interval. At small scales (microstructure), this field is described in terms of random discrete values which reflect the properties of both the field measured and the MI. Theoretical relationships which define the probabilities of increments at the compound intervals in terms of the probabilities of increments at the sampling intervals, are derived for the case of independent random increments at the sampling intervals of discreteness. The validity of this model is illustrated by respective computations using data of microstructure measurements of the temperature profile in the main thermocline in the Sargasso Sea.Translated by Mikhail M. Trufanov. 相似文献
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The measurement and analysis of turbulent boundary layer wall pressure fluctuations using a wavenumber filter of sensors provide quantitative knowledge of turbulence physics. In addition, the sources of flow-induced noise and vibration for towed SONAR arrays can be determined. An axisymmetric turbulent boundary layer can have significantly different features than those of a comparable flat-plate boundary layer. Here, a detailed comparison of the distribution of wall pressure energy in both wavenumber and frequency between flat-plate and thick axisymmetric boundary layers is presented. The background theory of wavenumber-frequency spectra and state-of-the-art models for flat-plate boundary layers are discussed. The widely used model of Chase (1987), valid for flat-plate boundary layers over a wide range of Reynolds numbers, is used and combined with a sensor response function to allow the effects of spatial averaging to be considered. It is demonstrated that when measured boundary layer parameters for the axisymmetric case are used in the Chase flat-plate model, the results accurately predict the axisymmetric boundary layer wall pressure measurements. 相似文献
17.
This paper reports empirical data on short-period internal waves in the Black Sea and Aegean frontal zones, collected through the use of distributed temperature sensor arrays. Peculiar features of the behaviour and propagation of the internal waves in these zones are shown. It is shown that the wavefield is anisotropic and reduction of the wave lengths diminishes during the climb up a sloping pycnocline. The energy level of the spectra of internal wave oscillations in the frontal zones of non-tidal seas was found to be lower than that relating to oceanic frontal zones.Translated by Vladimir A. Puchkin. 相似文献
18.
This paper describes an architecture for a compact real-time time-delay sonar beamformer. The design is based on a time-domain interpolation concept, and includes shading, interpolation, and time-delay functions for up to 64 sensor data inputs. A one card per beam configuration has been achieved. The digital interpolation technique used improves the effective sampling rate by a factor of 128. The beamformer design features 16-bit arithmetic precision, up to approximately a 5-kHz sampling rate for each of the 64 sensor input channels, and adaptability to any type of array, e.g., linear, circular, or arrays with nonequal interelement spacings. A 31-beam beamformer system, performing more than 620-million arithmetic operations a second, is discussed. 相似文献
19.
Dushaw B.D. Howe B.M. Mercer J.A. Spindel R.C. Baggeroer A.B. Menemenlis D. Wunsch C. Birdsall T.G. Metzger K. Clark C. Colosi J.A. Comuelle B.D. Dzieciuch M. Munk W. Worcester P.F. Costa D. Forbes A.M.G. 《Oceanic Engineering, IEEE Journal of》1999,24(2):202-214
Acoustic signals transmitted from the ATOC source on Pioneer Seamount off the coast of California have been received at various sites around the Pacific Basin since January 1996. We describe data obtained using bottom-mounted receivers, including US Navy Sound Surveillance System arrays, at ranges up to 5 Mm from the Pioneer Seamount source. Stable identifiable ray arrivals are observed in several cases, but some receiving arrays are not well suited to detecting the direct ray arrivals. At 5-Mm range, travel-time variations at tidal frequencies (about 50 ms peak to peak) agree well with predicted values, providing verification of the acoustic measurements as well as the tidal model. On the longest and northernmost acoustic paths, the time series of resolved ray travel times show an annual cycle peak-to-peak variation of about 1 s and other fluctuations caused by natural oceanic variability. An annual cycle is not evident in travel times from shorter acoustic paths in the eastern Pacific, though only one realization of the annual cycle is available. The low-pass-filtered travel times are estimated to an accuracy of about 10 ms. This travel-time uncertainty corresponds to errors in range- and depth-averaged temperature of only a few millidegrees, while the annual peak-to-peak variation in temperature averaged horizontally over the acoustic path and vertically over the upper 1 km of ocean is up to 0.5°C 相似文献
20.
Coral reefs are one of the most diverse ecosystems on Earth. They are currently exposed to increasing levels of anthropogenic perturbations. Several recent reviews point to the lack of good indicators for these perturbations especially to monitor their effects on fish populations or fish assemblages. The SW lagoon of New Caledonia is an ideal location to test indicator species in this context as contrasting sites are present within a small geographical range. This study analysed fish from four sites, one with heavy industrial pollution, another dominated by domestic waste, a third with historic mining activities, and the fourth as a control. The butterfly fish, Chaetodon speculum, was chosen to determine C. speculum's potential as an indicator species due to its link to coral, its sedentary behaviour and its wide geographical distribution. The size distribution, growth rate, age distribution and whole otolith composition were analysed at each site. Age and mean growth rate were analysed from daily increments of the otoliths. The concentrations of eight elements (Li, Mg, Co, Ni, Cu, Rb, Sr, and Ba) were measured by ICP-MS in the otoliths of a subset of individuals. The sites under anthropogenic impact were distinct from the control site by fish size frequencies, age distributions, and the chemical content of their otoliths. The chemical elements Mg, Co, Ni, Cu, and Rb showed differences amongst sites. Fish belonging to the sites furthest from Nouméa could be discriminated in nearly 80% of samples or 60% of the cases when otolith weight or fish age respectively were taken into account. Ni concentrations of the otoliths were also higher in the bays where water concentrations of this element were known to be higher, but these differences were no longer significant once corrected for otolith weight. These results should be mitigated by the fact that: (1) despite significant differences between sites in age distribution and size frequencies there were no differences in growth rates or body condition; (2) differences in age or size were not correlated to perturbation levels; and (3) discrimination between sites based on chemical levels in the otoliths, even though significant, was not sufficient to identify the origin of the fish at a level useful for screening tests. The hypothesis that environmental differences between sites would be reflected in the otolith chemical composition is therefore not fully supported by our results. 相似文献