A new model to estimate significant wave heights with ERS-1/2 scatterometer data

A new model is proposed to estimate the significant wave heights with ERS-1/2 scatterometer data. The results show that the relationship between wave parameters and radar backscattering cross section is similar to that between wind and the radar backscattering cross section. Therefore, the relationship between significant wave height and the radar backscattering cross section is established with a neural network algorithm, which is, if the average wave period is ≤7s, the root mean square of significant wave...     

Calculation of significant wave height using the linear mean square estimation method

Significant wave height is an important criterion in designing coastal and offshore structures. Based on the orthogonality principle, the linear mean square estimation method is applied to calculate significant wave height in this paper. Twenty-eight-year time series of wave data collected from three ocean buoys near San Francisco along the California coast are analyzed. It is proved theoretically that the computation error will be reduced by using as many measured data as possible for the calculation of significant wave height. Measured significant wave height at one buoy location is compared with the calculated value based on the data from two other adjacent buoys. The results indicate that the linear mean square estimation method can be well applied to the calculation and prediction of significant wave height in coastal regions.     

Analysis on monthly-averaged distribution of sea surface wind and wave over the seas southeast of Asia using ERS-2 scatterometer data

The wind system over the seas southeast of Asia (SSEA) plays an important role in China's climate variation. In this paper, ERS scatterometer winds covering the period from January 2000 to December 2000 and the area of 2-41 °N, 105- 130°E were analyzed with a distance-weighting interpolation method and the monthly mean distribution of the sea surface wind speed were given. The seasonal characteristics of winds in the SSEA were analyzed. Based on WAVEWATCH Ⅲ model, distribution of significant wave height was calculated.     

Wave Height Estimation from SAR Imagery

This paper presents a method developed for estimating wave height from synthetic aperture radar (SAR) imagery without prior assumption of noise distribution. It is based on two-dimenslonal ocean wave spectra retrieved from fully calibrated SAR images. Wen‘s spectrum was used as first-guess wave spectrum in the retrieval process. Comparison of the estimated wave height obtained by this method from two ERS-1 SAR subimages dated 23 July 1994 with in-situ measurements showed that the method works well.     

Ocean wave diffraction in near-shore regions observed by Synthetic Aperture Radar

Observation and analysis of ocean wave diffraction in near-shore and near-island region was performed with Synthetic Aperture Radar (SAR) data, using an optimized retrieval method named parameterized first-guess spectrum retrieval method. The results retrieved from ERS-SAR and ENVISAT-ASAR images showed that, in the region sheltered by land jut, the energy of long waves is reduced by 10%-20% and that the propagation direction of long waves is changed due to the effect of topography. In the shadow zone behind the island, ocean wave can propagate along the seashore instead of perpendicular to the coastline, as shown by SAR images.     

Distribution of the nonlinear random ocean wave period

Because of the intrinsic difficulty in determining distributions for wave periods, previous studies on wave period distribution models have not taken nonlinearity into account and have not performed well in terms of describing and statistically analyzing the probability density distribution of ocean waves. In this study, a statistical model of random waves is developed using Stokes wave theory of water wave dynamics. In addition, a new nonlinear probability distribution function for the wave period is presented with the parameters of spectral density width and nonlinear wave steepness, which is more reasonable as a physical mechanism. The magnitude of wave steepness determines the intensity of the nonlinear effect, while the spectral width only changes the energy distribution. The wave steepness is found to be an important parameter in terms of not only dynamics but also statistics. The value of wave steepness reflects the degree that the wave period distribution skews from the Cauchy distribution, and it also describes the variation in the distribution function, which resembles that of the wave surface elevation distribution and wave height distribution. We found that the distribution curves skew leftward and upward as the wave steepness increases. The wave period observations for the SZFII-1 buoy, made off the coast of Weihai (37°27.6′ N, 122°15.1′ E), China, are used to verify the new distribution. The coefficient of the correlation between the new distribution and the buoy data at different spectral widths (ν=0.3−0.5) is within the range of 0.968 6 to 0.991 7. In addition, the Longuet-Higgins (1975) and Sun (1988) distributions and the new distribution presented in this work are compared. The validations and comparisons indicate that the new nonlinear probability density distribution fits the buoy measurements better than the Longuet-Higgins and Sun distributions do. We believe that adoption of the new wave period distribution would improve traditional statistical wave theory.     

诱发成瘾性戒毒疗效测评系统中自动血压检测的设计

针对戒毒疗效测评系统中吸毒患者血压检测的特殊需求,设计了自动血压采集电路和软件算法,实现对吸毒患者人体血压的波动检测。基于示波法原理,使用单片机电路控制气泵和气阀实现对血压袖带的阶梯充放气,通过气压传感器检测袖带内的气压波动得到脉搏波,软件通过阈值处理异常波动,根据脉搏波峰值的波动获取收缩压与舒张压。临床实验结果显示,吸毒患者先后观看风景和吸毒场景视频,诱发成瘾性戒毒疗效测评系统连续监测其血压,观看不同场景时血压变化明显。同时,轻微的身体和肢体活动不影响检测数据。该血压检测功能模块很好实现了检测功能,有较强抗干扰能力,测量数据可以作为戒毒疗效测评系统的参数指标。     

Wave steepness retrieved from scatterometer data in a genetic algorithm

Wave steepness is an important characteristic of a high sea state, and is widely applied on wave propagations at ports, ships, offshore platforms, and CO2 circulation in the ocean. Obtaining wave steepness is a difficult task that depends heavily on theoretical research on wavelength distribution and direct observations. Development of remote-sensing techniques provides new opportunities to study wave steepness. At present, two formulas are proposed to estimate wave steepness from QuikSCAT and ERS-1/2 scatterometer data. We found that wave steepness retrieving is not affected by radar band, and polarization method, and that relationship of wave steepness with radar backscattering cross section is similar to that with wind. Therefore, we adopted and modified a genetic algorithm for relating wave steepness with radar backscattering cross section. Results show that the root-mean-square error of the wave steepness retrieved is 0.005 in two cases from ERS-1/2 scatterometer data and from QuikSCAT scatterometer data.     

Long-term variation of storm surge-associated waves in the Bohai Sea

When investigating the long-term variation of wave characteristics as associated with storm surges in the Bohai Sea, the Simulating Waves Nearshore(SWAN) model and ADvanced CIRCulation(ADCIRC) model were coupled to simulate 32 storm surges between 1985 and 2014. This simulation was validated by reproducing three actual wave processes, showing that the simulated significant wave height(SWH) and mean wave period agreed well with the actual measurements. In addition, the long-term variations in SWH, patterns in SWH extremes along the Bohai Sea coast, the 100-year return period SWH extreme distribution, and waves conditional probability distribution were calculated and analyzed. We find that the trend of SWH extremes in most of the coastal stations was negative, among which the largest trend was-0.03 m/a in the western part of Liaodong Bay. From the 100-year return period of the SWH distribution calculated in the Gumbel method, we find that the SWH extremes associated with storm surges decreased gradually from the center of the Bohai Sea to the coast. In addition, the joint probability of wave and surge for the entire Bohai Sea in 100-year return period was determined by the Gumbel logistic method. We therefore, assuming a minimum surge of one meter across the entire Bohai Sea, obtained the spatial SWH distribution. The conclusions of this study are significant for offshore and coastal engineering design.     

A background error covariance model of significant wave height employing Monte Carlo simulation

The quality of background error statistics is one of the key components for successful assimilation of observations in a numerical model.The background error covariance(BEC) of ocean waves is generally estimated under an assumption that it is stationary over a period of time and uniform over a domain.However,error statistics are in fact functions of the physical processes governing the meteorological situation and vary with the wave condition.In this paper,we simulated the BEC of the significant wave height(SWH) employing Monte Carlo methods.An interesting result is that the BEC varies consistently with the mean wave direction(MWD).In the model domain,the BEC of the SWH decreases significantly when the MWD changes abruptly.A new BEC model of the SWH based on the correlation between the BEC and MWD was then developed.A case study of regional data assimilation was performed,where the SWH observations of buoy 22001 were used to assess the SWH hindcast.The results show that the new BEC model benefits wave prediction and allows reasonable approximations of anisotropy and inhomogeneous errors.     

Parameterized first-guess spectrum method for retrieving directional spectrum of swell-dominated waves and huge waves from SAR images

A method to retrieve ocean wave spectra from SAR images, named Parameterized First-guess Spectrum Method (PFSM), was proposed after interpretation of the theory to ocean wave imaging and analysis of the drawbacks of the retrieving model generally used. In this method, with additional information and satellite parameters, the separating wave-number is first calculated to determine the maximum wave-number beyond which the linear relation can be used. The separating wave-number can be calculated using the additional information on wind velocity and parameters of SAR satellite. And then the SAR spectrum can be divided into SAR spectrum of wind wave and of swell according to the result of separating wave-number. The portion of SAR spectrum generated by wind wave, is used to search for the most suitable parameters of ocean wind wave spectrum, including propagation direction of ocean wave, phase speed of dominating wave and the angle spreading coefficient. The swell spectrum is acquired by directly inversing the linear relation of ocean wave spectrum to SAR spectrum given the portion of SAR spectrum generated by swell. We used the proposed method to retrieve the ocean wave spectrum from ERS-SAR data from the South China Sea and compared the result with altimeter data. The agreement indicates that the PFSM is reliable.     

Joint occurrence period of wind speed and wave height based on both service term and risk probability

Return periods calculated for different environmental conditions are key parameters for ocean platform design.Many codes for offshore structure design give no consideration about the correlativity among multi-loads and over-estimate design values.This frequently leads to not only higher investment but also distortion of structural reliability analysis.The definition of design return period in existing codes and industry criteria in China are summarized.Then joint return periods of different ocean environmental parameters are determined from the view of service term and danger risk.Based on a bivariate equivalent maximum entropy distribution,joint design parameters are estimated for the concomitant wave height and wind speed at a site in the Bohai Sea.The calculated results show that even if the return period of each environmental factor,such as wave height or wind speed,is small,their combinations can lead to larger joint return periods.Proper design criteria for joint return period associated with concomitant environmental conditions will reduce structural size and lead to lower investment of ocean platforms for the exploitation of marginal oil field.     

THE WAVE GROUPING EFFECT ON WAVE FORCES ON A VERTICAL BREAKWATER

Linear wave theory and Longuet-Higgins and Steward's (1964) group-induced second-order longweve (GSLW) theory ware used in this study on the grouping effect on wave forces acting on a verticalbreakwater. The calculated variance of total wave pressure on the vertical breakwater was closer tothe measured value if the wave grouping effect was considered.     

Analysis of the global swell distributions using ECMWF Re-analyses wind wave data

The existence of three well-defined tongue-shaped zones of swell dominance, termed as ‘swell pools’, in the Pacific, the Atlantic and the Indian Oceans, was reported by Chen et al. (2002) using satellite data. In this paper, the ECMWF Re-analyses wind wave data, including wind speed, significant wave height, averaged wave period and direction, are applied to verify the existence of these swell pools. The swell indices calculated from wave height, wave age and correlation coefficient are used to identify swell events. The wave age swell index can be more appropriately related to physical processes compared to the other two swell indices. Based on the ECMWF data the swell pools in the Pacific and the Atlantic Oceans are confirmed, but the expected swell pool in the Indian Ocean is not pronounced. The seasonal variations of global and hemispherical swell indices are investigated, and the argument that swells in the pools seemed to originate mostly from the winter hemisphere is supported by the seasonal variation of the averaged wave direction. The northward bending of the swell pools in the Pacific and the Atlantic Oceans in summer is not revealed by the ECMWF data. The swell pool in the Indian Ocean and the summer northward bending of the swell pools in the Pacific and the Atlantic Oceans need to be further verified by other datasets.     

STATISTICAL PROPERTIES OF WAVE GROUPS DESCRIBED BY GROUP-INDUCED LONG WAVES

A new method using group-induced second-order long waves (GSLW) to describe wave groups is presented in this paper on the basis of the GSLW theory by Longuet- Higgins and Steward (1964) . In the method , the parabolic relationship between GSLW and the wave envelope is first deduced , and then the distribution function of GSLW amplitude is derived . Thus, the formulae in terms of the moments of GSLW and short wave spectra for the average time duration and the mean length of runs of wave heights exceeding a certain level can be derived . A new groupiness factor equivalent to half the mean wave number in wave groups is defined by taking into account the widths of spectra of GSLW and short waves . Compared with theoretical results of others , ours are closer to measured wave data .     

A study on the Antarctic circumpolar wave mode-A coexistence system of standing and traveling wave

The Antarctic circumpolar wave （ACW） has become a focus of the air-sea coupled Southern Ocean study since 1996, when it was discovered as an air-sea coupled interannual signal propagating eastward in the region of the Antarctic Circumpolar Current （ACC）. In order to analyze the mechanism of discontinuity along the latitudinal propagation, a new idea that ACW is a system with a traveling wave in the Southern Pacific and Atlantic Ocean and with a concurrent standing wave in the southern Indian Ocean is proposed in this paper. Based on the ideal wave principle, the average wave parameters of ACW is achieved using a non-linear approximation method, by which we find that the standing part and the traveling part possess similar radius frequency, proving their belonging to an integral system. We also give the latitudinal distribution of wave speed with which we could tell the reason for steady propagation during the same period. The spatial distribution of the propagation reveals complex process with variant spatial and temporal scales--The ENSO scale oscillation greatly impacts on the traveling process, while the result at the south of Australia indicates little connection between the Indian Ocean and the Pacific, which may be blocked by the vibration at the west of the Pacific. The advective effect of ACC on the propagation process should be examined clearly through dynamical method.     

������ˮλ���봨������Ӧ�����Ӧ

???λ????????????????????????????????峱????????????????????λ???????????????????λ??????????·?????????????????????????????????M2???????????????λ?????????????????????????????????????????λ?????????????Ms8.0????????????????????????????沨??????????沨???????????λ????????????????????λ??????????????????????????????????????????????????????沨?????????????????λ???????????1??????????     

A new modulation transfer function for ocean wave spectra retrieval from X-band marine radar imagery

When imaging ocean surface waves by X-band marine radar,the radar backscatter from the sea surface is modulated by the long surface gravity waves. The modulation transfer function(MTF) comprises tilt,hydrodynamic,and shadowing modulations. A conventional linear MTF was derived using HH-polarized radar observations under conditions of deep water. In this study,we propose a new quadratic polynomial MTF based on VV-polarized radar measurements taken from heterogeneous nearshore wave fields. This new MTF is obtained using a radar-observed image spectrum and in situ buoy-measured wave frequency spectrum. We validate the MTF by comparing peak and mean wave periods retrieved from X-band marine radar image sequences with those measured by the buoy. It is shown that the retrieval accuracies of peak and mean wave periods of the new MTF are better than the conventional MTF. The results also show that the bias and root mean square errors of the peak and mean wave periods of the new MTF are 0.05 and 0.88 s,and 0.32 and 0.53 s,respectively,while those of the conventional MTF are 0.61 and 0.98 s,and 1.39 and 1.48 s,respectively. Moreover,it is also shown that the retrieval results are insensitive to the coefficients in the proposed MTF.     

近岸带波浪传播过程中波性质的统计对比分析

通过对粤东后江湾近岸带垂岸方向上4个测站,同步观测到的波浪数据进行频域统计分析,初步探讨分析了波浪近岸传播过程中波浪统计性质的变化规律。结果表明:碎波带内波的频谱多峰特征显著,峰频两侧均存在着显著能量峰值,峰频能量发生转移;波浪经过破碎后,约束长波能量被释放出来;波浪向岸过程中谱宽度(ε)变大,同时谱尖度(Qp)减小,显著波陡(Ss)增大,峰值周期(Tp)增大,平均周期(Tm02)减小。     

2022-01-15汤加火山喷发的地震学震级测定北大核心CSCD

利用山东地震台网70个宽频带测震台站记录的2022-01-15南太平洋汤加海底火山喷发原始地震波形数据,从时间域和频率域分析火山喷发地震波的记录特征;通过对20 s优势周期面波进行研究,测算该次火山喷发的地震学震级与地震波辐射能量。研究表明,该次汤加火山喷发的面波震级为M_(S)5.674、能量震级为M_(e)5.704,与GFZ测定震级基本一致,比USGS测定震级小0.126。本次汤加火山爆炸指数(VEI)为5级,但本文测定的地震波辐射能量为8.155×10^(12)J,可见火山喷发以地震波辐射方式释放的能量较少,绝大部分能量以超过1000 km/h的冲击波形式穿过大气层迅速释放到空中,这种能量的快速释放会抑制深部应力的挤压与拉伸。