A comparison of the main methods for estimating probabilities of extreme still water levels

Sea-level return periods are estimated at 18 sites around the English Channel using: (i) the annual maxima method; (ii) the r-largest method; (iii) the joint probability method; and (iv) the revised joint probability method. Tests are undertaken to determine how sensitive these four methods are to three factors which may significantly influence the results; (a) the treatment of the long-term trends in extreme sea level; (b) the relative magnitudes of the tidal and non-tidal components of sea level; and (c) the frequency, length and completeness of the available data. Results show that unless sea-level records with lengths of at least 50 years are used, the way in which the long-term trends is handled in the different methods can lead to significant differences in the estimated return levels. The direct methods (i.e. methods i and ii) underestimate the long (> 20 years) period return levels when the astronomical tidal variations of sea level (relative to a mean of zero) are about twice that of the non-tidal variations. The performance of each of the four methods is assessed using prediction errors (the difference between the return periods of the observed maximum level at each site and the corresponding data range). Finally, return periods, estimated using the four methods, are compared with estimates from the spatial revised joint probability method along the UK south coast and are found to be significantly larger at most sites along this coast, due to the comparatively short records originally used to calibrate the model in this area. The revised joint probability method is found to have the lowest prediction errors at most sites analysed and this method is recommended for application wherever possible. However, no method can compensate for poor data.     

Modelling of complex coastal environments: Some considerations for best practise

The numerical modelling of large-scale sediment transport and coastal morphology frequently requires significant model reduction and optimisation in order to achieve expedient conclusions. This study provides a detailed sensitivity analysis of various model ‘reduction’ techniques using the Bristol Channel, western U.K. as a case study. The work elucidates a number of the best practises for employment of state-of-the-art systems to complex coastal regions.     

不同气候情景下中国滨海城市海岸极值水位重现期预估

气候变化背景下,海平面上升叠加台风—风暴潮、天文大潮等产生的海岸极值水位事件趋多增强,对我国滨海城市社会经济可持发展构成了严重威胁。为认识未来我国滨海城市海岸极值水位危害性（强度和频率）的变化,本文首先采用第五次国际耦合模式比较计划（CMIP5）数据,分析了不同气候情景下（RCP2.6, 4.5, 8.5,简称为RCPs）下,未来不同年代（2030年、2050年和2100年）我国滨海城市沿岸海平面变化幅度;其次,基于沿海验潮站的历史观测资料和文献数据,分析了未来热带气旋强度变化对海岸极值水位的影响;最后,利用皮尔逊Ⅲ型（P-Ⅲ）水文概率曲线方法,预估了不同气候（RCPs）情景下未来不同年代（2030年、2050年和2100年）我国9个滨海城市海岸极值水位重现期的变化。结果表明：（1）在不同气候情景下,我国滨海城市沿海平均海平面均呈现上升趋势,其中,到21世纪末,长三角地区沿海海平面上升幅度最大,上升速度比全国平均高出约30%;（2）热带气旋的强度与台风—风暴潮的增水幅度存在正相关关系。预计到21世纪末,热带气旋的整体强度很可能将增强,热带气旋引发的台风—风暴潮的增水幅度较当前很可能有明显提高。（3）未来我国滨海城市沿海极值水位将有显著增高的趋势,当前极值水位的重现期将明显缩短。到21世纪末,我国滨海城市当前百年一遇的极值水位,重现期几乎都将缩短至20年一遇以下,其中,大连、青岛、上海和厦门等城市海岸极值水位重现期很可能缩短为（或低于）1年一遇。本文虽在一定程度上反映了不同气候情景下海岸洪水危害性的变化,但对于未来热带气旋的变化及其影响的研究尚有待进一步深入。     

Estimating hypocentral uncertainties for marine microearthquake surveys: A comparison of the generalized inverse and grid search methods

For microearthquake surveys conducted with small networks in regions where the seismic velocity structure has large vertical gradients, the formal errors accompanying hypocentral solutions obtained by a generalized inverse method may be misleading since they do not incorporate the effects of nonlinearity in travel times. An alternative method for estimating uncertainties involves calculating travel time residuals over a regular grid and using the F statistic to contour confidence volumes. We present a statistical expression for the latter confidence limits that is applicable when an independent estimate of arrival time errors is available from observations accumulated for a number of earthquakes. Synthetic experiments comparing the results of the grid search and generalized inverse methods show that in cases where solutions are obtained either without S wave information or for epicenters which lie well outside the network, the effects of nonlinearity on the shape of the confidence regions may be significant. However, for the well-observed events both methods yield comparable confidence volumes in good agreement with the distribution of hypocenters obtained from repeated locations incorporating random errors. The generalized inverse method has the advantage that it requires fewer calculations, so the examination of systematic errors in hypocentral parameters produced by uncertainties in the seismic velocity structure can be studied in a more computationally efficient manner. Except in the cases of poorly resolved earthquakes, the effects of nonlinearity on uncertainties in hypocentral parameters can be observed by the application of the F statistic to the variation of the generalized inverse travel time residuals with focal depth.     

考虑海平面上升影响的极值水位计算

本研究基于非平稳序列极值理论,定量分析极端水位事件年超越概率受海平面上升的影响;以工程设计使用年限内极端水位发生概率作为控制条件,构建考虑海平面上升的极值水位计算方法;结合平均海平面的长期变化过程,推算海平面上升下的极值水位。基于全球10个验潮站历史水位观测资料,验证历史平均海平面长期变化与高、低水位耿贝尔分布位置参数变化的一致性以及构建方法的合理性。结合政府间气候变化专门委员会对海平面上升的预测,推算和对比分析不同海平面上升情景下的极值水位,并评估相应极值水位在当前极值分布中的重现期。     

A comparison of methods for calculating the motion of a semi-submersible

The 17th ITTC Ocean Engineering Committee undertook the comparison of methods for calculating semi-submersible wave motion, and 34 programs from 28 different organizations participated in the project. The summary of the results are reported in the Technical Report of the 17th ITTC (ITTC, 1984).In this paper, the details of the project are described. Namely, almost all the calculation results of the 34 programs are shown and examined from the viewpoints of the validity of the program itself and of the correlation between the differences in the various calculation methods and the differences in the calculation results. The calculation results are also compared with the experiments, the details of which are also illustrated.     

深水中极限波峰下速度场快速算法

基于五阶斯托克斯规则波理论,提出了一种快速求解深水极限波峰下速度场的数学模型.研究中,按照上跨零点和下跨零点的方法由计算或实测的极限波浪波面时间历程确定包含极限波峰的相邻两个周期的平均值为五阶斯托克斯规则波的波浪周期,然后根据极限波峰反推确定波浪入射波幅.通过与已有的数值结果和实验数据对比,验证了所建立的数值模型可以快速准确的计算出极限波峰下的速度场,相比其他模型,更适合于工程应用.     

A comparison of four methods for bubble size and void fractionmeasurements

We compare the performance of four different bubble-sensing techniques in a range of environment from the surf zone to the open ocean: a remote sensing method using high-frequency backscatter, two in situ methods using an acoustical resonator and a pulse propagation sensor, and a bulk method using electrical conductivity. Comparisons between the techniques show general consistency within the appropriate operational bubble density ranges, although spatial variability in bubble clouds introduces substantial variance. Each technique has its strengths and limitations. Our acoustical resonator is suitable for bubble concentrations with air fractions greater than approximately 10 ^-9 and the pulse propagation sonar for air fractions from 10 ^-6; the upper limit for both is constrained by attenuation and the validity of the Foldy scattering approximation. Both sensors can be implemented to encompass a wide frequency range with high resolution, corresponding to resonant bubble radii of 10~1200 μm. For air fractions higher than ~5×10^-4, bulk measurement using electrical conductivity provides a measure of air fraction. Sufficient overlap in operational air-fraction range exists between in situ acoustical techniques and conductivity measurement to permit comparison and demonstrate consistency in the measurement. Single- and multi-frequency backscatter sonars may be used for low air fractions (<1×10^-5) and provide a continuous vertical profile from a deployment beneath the active surface zone, but are subject to masking by dense bubble clouds and are unable to resolve high air fractions close to the surface. This study suggests that the best approach is to use a combination of sensors to probe the bubble field     

A field comparison of two methods for the determination of copper complexation: Bacterial bioassay and fixed-potential amperometry

Complexation of copper added to seawater was determined by bacterial bioassay and fixedpotential amperometry. Consistent results were obtained by these two fundamentally different methods. The results of this study support the validity of both techniques and the field applicability of fixed-potential amperometry.The intercomparison studies were performed on samples collected at the N.Y.C. sewage sludge dumpsite and in relatively unpolluted coastal waters. In this limited study, the calculated free cupric ion concentrations at ambient total copper concentrations were similar at both sites.     

HPLC analysis of algal pigments: a comparison exercise among laboratories and recommendations for improved analytical performance

Pure individual and mixed pigment standards were distributed among Joint Global Ocean Flux Study (JGOFS) pigment analysts to estimate the variability of their spectrophotometric and chromatographic systems. To monitor the integrity of the pigments during the comparison exercise, chlorophyll and carotenoid standards were archived and periodically analyzed by high-performance liquid chromatography (HPLC). Pigment standards stored in the dark under nitrogen at − 20 °C were found to be stable for periods of at least one year. Results from three separate intercalibration exercises document a better agreement for spectrophotometric analyses than for HPLC. For the spectrophotometric comparisons, 90% of the pigments analyzed by participant laboratories were within ± 6% of the mean “consensus” values. By contrast, 65 and 85% of the laboratories agreed to within ± 10 and ± 20%, respectively, when chromatographic analyses were compared. Chlorophyll absorption measurements obtained with a diode array-type spectrophotometer were 6–9% lower than those obtained with monochromator-type spectrophotometers. These underestimates probably result from chlorophyll fluorescence contamination associated with the optical configuration of the diode array spectrophotometer. It was also determined that HPLC methods which are not capable of separating monovinyl chlorophyll a from divinyl chlorophyll a can produce 15–25% overestimates of total chlorophyll a concentration in Prochlorococcus-dominated oceanic waters. A simple dichromatic approach is described for eliminating this variable source of error caused by co-elution of these structurally-related pigments. The use of internal standards and periodic calibration checks with external standards is highly recommended for improving analytical performance.     

深水极端波浪非线性几何特征试验分析

为了解极端波浪非线性特征,明确波群在演化过程中的水动力学特性,针对一系列高斯波群进行了深水物理试验分析。试验结果显示,增加波陡或波群宽度,均可使波面偏度Sk发生明显变化,尤其当波浪发生破碎后,在破碎区域内,波面偏度变化范围剧烈增大,说明该偏度极大值可能作为判断破碎的一个指标。波陡和波群宽度对波面不对称度影响程度不同:当波陡或波群宽度增加后,波峰不对称度所受影响最大,波峰前端波谷不对称度次之,波峰后端波谷不对称度所受影响最小,但仍不可忽略。在波浪演化过程中,幅值谱出现不同程度频带下移,波浪破碎后,会出现永久频带下移;当调制不稳定发生时,随着调制不稳定指数增加,频带下移量呈现快速增长趋势。     

A comparison of two methods for determining copper partitioning in oxidized sediments

Model estimations of the proportion of Cu in oxidized sediments associated with extractable organic materials show some agreement with the proportion of Cu extracted from those sediments with ammonium hydroxide. Data were from 17 estuaries of widely differing sediment chemistry. The modelling and extraction methods agreed best where concentrations of organic materials were either in very high concentrations, relative to other sediment components, or in very low concentrations. In the range of component concentrations where the model predicted Cu should be distributed among a variety of components, agreement between the methods was poor. Both approaches indicated that Cu was predominantly partitioned to organic materials in some sediments, and predominantly partitioned to other components (most probably iron oxides and manganese oxides) in other sediments, and that these differences were related to the relative abundances of the specific components in the sediment. Although the results of the two methods of estimating Cu partitioning to organics correlated significantly among 24 stations from the 17 estuaries, the variability in the relationship suggested refinement of parameter values and verification of some important assumptions were essential to the further development of a reasonable model.     

A preliminary methods comparison for measurement of dissolved organic nitrogen in seawater

Routine determination of dissolved organic nitrogen (DON) is performed in numerous laboratories around the world using one of three families of methods: UV oxidation (UV), persulfate oxidation (PO), or high temperature combustion (HTC). Essentially all routine methods measure total dissolved nitrogen (TDN) and calculate DON by subtracting the dissolved inorganic nitrogen (DIN). While there is currently no strong suggestion that any of these methods is inadequate, there are continuing suspicions of slight inaccuracy by UV methods.This is a report of a broad community methods comparison where 29 sets (7 UV, 13 PO, and 9 HTC) of TDN analyses were performed on five samples with varying TDN and DIN concentrations. Analyses were done in a “blind” procedure with results sent to the first author. With editing out one set of extreme outliers (representing 5 out of 145 ampoules analyzed), the community comparability for analyzing the TDN samples was in the 8–28% range (coefficient of variation representing one standard deviation for the five individual samples by 28 analyses). When DIN concentrations were subtracted uniformly (single DIN value for each sample), the comparability was obviously worse (19–46% cv). This comparison represents a larger and more diverse set of analyses, but the overall comparability is only marginally better than that of the Seattle workshop of a decade ago. Grouping methods, little difference was seen other than inconclusive evidence that the UV methods gave TDN values for several of the samples higher than HTC methods. Since there was much scatter for each of the groups of methods and for all analyses when grouped, it is thought that more uniformity in procedures is probably needed. An important unplanned observation is that variability in DIN analyses (used in determining the final analyte in most UV and PO methods) is essentially as large as the variability in the TDN analyses.This exercise should not be viewed as a qualification exercise for the analysts, but should instead be considered a broad preliminary test of the comparison of the families of methods being used in various laboratories around the world. Based on many independent analyses here, none of the routinely used methods appears to be grossly inaccurate, thus, most routine TDN analyses being reported in the literature are apparently accurate. However, it is not reassuring that the ability of the international community to determine DON in deep oceanic waters continues to be poor. It is suggested that as an outgrowth of this paper, analysts using UV and PO methods experiment and look more carefully at the completeness of DIN conversion to the final analyte and also at the accuracy of their analysis of the final analyte. HTC methods appear to be relatively easy and convenient and have potential for routine adoption. Several of the authors of this paper are currently working together on an interlaboratory comparison on HTC methodology.     

Role of metal-organic complexes in the marine environment: A comparison of the copper and ligand titration methods

The differences in quality of the conditional stability constants deduced from ligand titration and metal titration methods are theoretically examined. The ecological role of the metal-organic complexes in seawater was considered on the basis of the concept of the metal buffering capacity index which is calculated from the conditional stability constant and the organic ligand concentration. The results of theoretical examination of the effect of metal contamination on the uptake of metals by phytoplankton indicate that the ecological significance of metal-organic complexes is essentially in the metal-buffering action. This means that the activities of free metal ions are maintained at a native constant level against relatively small perturbations by the addition or uptake of metals in the marine environment.     

Surface gravity waves from direct numerical simulations of the Euler equations: A comparison with second-order theory

When the wave spectrum is sufficiently narrow-banded and the wave steepness is sufficiently high, the modulational instability can take place and waves can be higher than expected from second-order wave theory. In order to investigate these effects on the statistical distribution of long-crested, deep water waves, direct numerical simulations of the Euler equations have been performed. Results show that, for a typical design spectral shape, both the upper and lower tails of the probability density function for the surface elevation significantly deviate from the commonly used second-order wave theory. In this respect, the crest elevation is observed to increase up to 18% at low probability levels. It would furthermore be expected that wave troughs become shallower due to nonlinear effects. Nonetheless, the numerical simulations show that the trough depressions tend to be deeper than in second-order theory.     

Application of Monte-Carlo statistical experiments in design of ocean engineering——Estimating the parameters, models and probabilities

Recently, some results have been acquired with the Monte- Carlo statistical experiments in the design of ocean en gineering. The results show that Monte-Carlo statistical experiments can be widely used in estimating the parameters of wave statistical distributions, checking the probability model of the long- term wave extreme value distribution under a typhoon condition and calculating the failure probability of the ocean platforms.     

Steepness and asymmetry of extreme waves and the highest waves in deep water

Traditional wave steepness s=H/L does not define steep asymmetric waves in a random sea uniquey. Three additional parameters characterising single zero-downcross waves in a time series are crest front steepness, vertical asymmetry factor and horizontal asymmetry factor. Results for steepness and asymmetry from zero-downcross analysis of wave data obtained from full scale measurements in deep water on the Norwegian continental shelf in 58 time series are presented. The analysis demonstrates clearly the asymmetry of both “extreme waves” and the highest waves. The period and height of the highest waves are also given together with their correlation to spectral parameters. The measured maximum wave heights are also compared with predicted values of maximum wave heights showing good agreement.     

A comparison of non-hydrolytic methods for extracting amino acids and proteins from coastal marine sediments

Advances in analytical techniques now allow for the potential analysis of intact peptides and proteins isolated from marine sediments. However, there is no established technique for the extraction of macromolecular materials from marine sediments. Six different methods for extracting the amino acid component from coastal marine sediments were compared to the standard hot acid hydrolysis technique for their percent recovery and amino acid composition. The standard hot acid hydrolysis on dried, whole sediments released the greatest concentration of total amino acids (PS-THAA; 3.52 mg gdwt^− 1 ± 10% (SMD)), yet this only accounted for 22% of the total nitrogen in Puget Sound sediments (Washington, USA). Repeated hydrolysis of the same samples did not improve the recovery of nitrogen by more than an additional 10%. Base extraction (0.5 N NaOH) was the second best method for recovering amino acid nitrogen, releasing 60% of the Puget Sound total hydrolyzable amino acids (PS-THAA) (corresponding to 13% of the total sedimentary nitrogen), and has the advantage that it does not rely on peptide hydrolysis to free the nitrogenous component from the sediment matrix. The amino acid distribution of the 0.5 N NaOH extract was not significantly different than the initial THAA. Other non-hydrolyzing methods released lower yields of amino acids (Triton X-100 ≥ hot water > 50 mM NH₄HCO₃ > HF), but might prove to be of use to investigators interested in specific fractions of sedimentary organic nitrogen because these four methods had distinctly different amino acid compositions (enrichments in basic amino acids and depletions in acidic amino acids). Treatments with HF both before and after traditional hydrolysis and/or extractions with base did not release any more of the sedimentary nitrogen. Our results are consistent with the hypothesis that a large fraction of the sedimentary nitrogen (TN) is protected within an organic matrix.