Ocean wave parameters retrieved directly from compact polarimetric SAR data

We aim to directly invert wave parameters by using the data of a compact polarimetric synthetic aperture radar(CP SAR)and validate the effectiveness of ocean wave parameter retrieval from the circular transmit/linear receive mode andπ/4 compact polarimetric mode.Relevant data from the RADARSAT-2 fully polarimetric SAR on the C-band were used to obtain the compact polarimetric SAR images,and a polarimetric SAR wave retrieval algorithm was used to verify the sea surface wave measurements.Using the data and algorithm,there is no need to estimate complex hydrodynamic modulation transfer functions,even at large radar incidence angles.First,the radar backscattering cross-sections and backscattering cross-section of the radar linearly polarized with any polarization orientation angle were calculated in the two compact polarimetric SAR modes.Then,the wave slopes along the azimuth direction and the range direction were calculated directly using CP SAR data.Finally,we obtained the slope spectrum of the wave from the estimated wave slopes along azimuth and range directions.The wave parameters extracted from the synthetic wave slope spectrum were compared with those obtained from buoy observations of the National Data Buoy Center,verifying a suitable agreement.

An empirical method for joint inversion of wave and wind parameters based on SAR and wave spectrometer data

Synthetic aperture radar(SAR)and wave spectrometers,crucial in microwave remote sensing,play an essential role in monitoring sea surface wind and wave conditions.However,they face inherent limitations in observing sea surface phenomena.SAR systems,for instance,are hindered by an azimuth cut-off phenomenon in sea surface wind field observation.Wave spectrometers,while unaffected by the azimuth cutoff phenomenon,struggle with low azimuth resolution,impacting the capture of detailed wave and wind field data.This study utilizes SAR and surface wave investigation and monitoring(SWIM)data to initially extract key feature parameters,which are then prioritized using the extreme gradient boosting(XGBoost)algorithm.The research further addresses feature collinearity through a combined analysis of feature importance and correlation,leading to the development of an inversion model for wave and wind parameters based on XGBoost.A comparative analysis of this model with ERA5 reanalysis and buoy data for of significant wave height,mean wave period,wind direction,and wind speed reveals root mean square errors of 0.212 m,0.525 s,27.446°,and 1.092 m/s,compared to 0.314 m,0.888 s,27.698°,and 1.315 m/s from buoy data,respectively.These results demonstrate the model’s effective retrieval of wave and wind parameters.Finally,the model,incorporating altimeter and scatterometer data,is evaluated against SAR/SWIM single and dual payload inversion methods across different wind speeds.This comparison highlights the model’s superior inversion accuracy over other methods.

Internal wave parameter inversion based on Empirical Mode Decomposition

Wind, the result of earth rotation and other processes,inaugurate the phenomenon of oceanic internal waves（OIWs）, including driving turbulence, affecting nutrient and biomass distribution, and resuspending sediment. Therefore, a good understanding to OIWs＇ characters becomes a vital component to enhance its monitoring and utilization. The parameter inversion was conducted in the article for the OIW based on the empirical mode decomposition（EMD） method. The experimental data, the advanced synthetic aperture radar（ASAR） image, was captured in Dongsha Islands surrounding area on July 22, 2011. Considering the formation mechanism of internal waves, two important issues in the EMD method-the curve fitting and end effects-were studied. After comparing different algorithms, the cubic spline interpolation（CSI） was used for curve fitting and the boundary full-wave（BFW） method was applied to inhibit the end effects. Used this inversion method, the internal wave signal was extracted from the ASAR image, the distance of the internal wave between peak and trough was calculated, and the half-width of soliton was obtained as well. In addition, the inversion result is consistent with the previous experimental findings, which indicates the effectiveness of our algorithm.

Parameterization of Longwave Optical Properties for Water Clouds

Based on relationships between cloud microphysical and optical properties, three different parameterization schemes for narrow and broad band optical properties in longwave region for water clouds have been presented. The effects of different parameterization schemes and different number of broad bands used on cloud radiative properties have been investigated. The effect of scattering role of cloud drops on longwave radiation fluxes and cooling rates in cloudy atmospheres has also been analyzed.

SOLVING THE VELOCITY PARAMETER OF THE 2-D WAVE INVERSE PROBLEMS WITH THE INTEGRATION-CHARACTERISTIC METHOD

For the 2-D wave inverse problems introduced from geophysical exploration, in this paper, the author presents integration-characteristic method to solve the velocity parameter, and then applies it to common shotpoint model data, in noise-free case. The accuracy is quite good.

Wave-Dependence of Friction Velocity, Roughness Length, and Drag Coefficient over Coastal and Open Water Surfaces by Using Three Databases

The parameterization of friction velocity, roughness length, and the drag coefficient over coastal zones and open water surfaces enables us to better understand the physical processes of air-water interaction. In context of measurements from the Humidity Exchange over the Sea Main Experiment （HEXMAX）, we recently proposed wave-parameter dependent approaches to sea surface friction velocity and the aerodynamic roughness by using the dimensional analysis method. To extend the application of these approaches to a range of natural surface conditions, the present study is to assess this approach by using both coastal shallow （RASEX） and open water surface measurements （Lake Ontario and Grand Banks ERS-1 SAR） where wind speeds were greater than 6.44 m s-1. Friction velocities, the surface aerodynamic roughness, and the neutral drag coefficient estimated by these approaches under moderate wind conditions were compared with the measurements mentioned above. Results showed that the coefficients in these approaches for coastal shallow water surface differ from those for open water surfaces, and that the aerodynamic roughness length in terms of wave age or significant wave height should be treated differently for coastal shallow and open water surfaces.

Study on the growth of wind wave frequency spectra generated by cold waves in the northern East China Sea

The growth of frequency spectra and spectral parameters of wind waves generated by cold waves, a kind of severe weather system, in the northern East China Sea is studied in this paper. Based on a third-generation wave action model(the Simulating WAves Nearshore model), simulations were developed to analyze the spatiotemporal characteristics of wind waves and to output spectral data. It is shown that the cold wave-induced spectra can be well described by the modified Joint North Sea Wave Project spectral form. The growth of wave spectra is comprehensively reflected by the evolution of the three characteristic parameters: peak frequency, spectral peak and wave energy. Besides, the approximations of dependences between spectral parameters and the three types of universal induced factors are obtained with the least squares method and compared systematically. Fetch and peak frequency turn out to be suitable parameters to describe the spectral parameters, while the dependences on the inverse wave age vary in different sea areas. In general, the derived relationships improve on results from previous studies for better practical application of the wind wave frequency spectrum in the northern East China Sea.

基于UG/WAVE的蒸压釜参数化设计

以蒸压釜为研究对象,运用UG/WAVE和PTS模块,并结合UG软件的表达式功能,建立了公称直径2000mm蒸压釜的参数化模型,首先详细介绍了实现蒸压釜参数化设计所运用到的模块与功能,提出了具体实现蒸压釜参数化设计的方法步骤,然后以釜体法兰为例,详细阐述了参数化的过程,最终实现了蒸压釜参数化设计系统与参数化模型人机交互界面的开发,很大程度地缩小了蒸压釜的研发所需时间。此参数化设计方法有着一定的实用性,在对其它机械类产品进行参数化设计时,可以借鉴此方法。

基于UG/WAVE的产品参数化建模技术

在分析了参数化建模设计思想的基础上,进一步分析了UG软件的WAVE参数化设计功能,以及如何实现参数化设计理念——自顶向下装配设计及网络并行工程等概念,并通过推进器的外壳设计说明UG/WAVE的产品参数化建模实现过程,为实现利用UG软件进行产品快速开发提供了技术支持。

Wave effects on the retrieved wind field from the advanced scatterometer(ASCAT)

To improve retrieval accuracy, this paper studies wave effects on retrieved wind field from a scatterometer. First, the advanced scatterometer （ASCAT） data and buoy data of the National Data Buoy Center （NDBC） are collocated. Buoy wind speed is converted into neutral wind at 10 m height. Then, ASCAT data are com- pared with the buoy data for the wind speed and direction. Subsequently, the errors between the ASCAT and the buoy wind as a function of each wave parameter are used to analyze the wave effects. Wave param- eters include dominant wave period （dpd）, significant wave height （swh）, average wave period （apd） and the angle between the dominant wave direction （dwd） and the wind direction. Collocated data are divided into sub-datasets according to the different intervals of each wave parameter. A root mean square error （RMSE） for the wind speed and a mean absolute error （MAE） for the wind direction are calculated from the sub-datasets, which are considered as the function of wave parameters. Finally, optimal wave conditions on wind retrieved from the ASCAT are determined based on the error analyses. The results show the ocean wave parameters have correlative relationships with the RMSE of the retrieved wind speed and the MAE of the retrieved wind direction. The optimal wave conditions are presented in terms of dpd, swh, apd and angle.

Comparison and analysis of Envisat ASAR ocean wave spectra with buoy data in the northern Pacific Ocean

The validation and assessment of Envisat advanced synthetic aperture radar (ASAR) ocean wave spectra products are important to their application in ocean wave numerical predictions. Six-year ASAR wave spectra data are compared with one-dimensional (1D) wave spectra of 55 co-located moored buoy observations in the northern Pacific Ocean. The ASAR wave spectra data are firstly quality control filtered and spatio-temporal matched with buoy data. The comparisons are then performed in terms of 1D wave spectra, significant wave height (SWH) and mean wave period (MWP) in different spatio-temporal offsets respectively. SWH comparison results show the evident dependence of SWH biases on wind speed and the ASAR SWH saturation effect. The ASAR wave spectra tend to underestimate SWH at high wind speeds and overestimate SWH at low wind speeds. MWP comparison results show that MWP has a systematic bias and therefore it should be bias-modified before used. The comparisons of 1D wave spectra show that both wave spectra agree better at low frequencies than at high frequencies, which indicates the ASAR data cannot resolve the high frequency waves.

基于UG/WAVE的柴油机缸盖参数化设计

本文根据企业近年来对缸盖、气缸体等复杂零部件快速设计的需求,以缸盖为例介绍了这类复杂零部件快速设计的一般要求和方法。然后利用UG/WAVE技术对某柴油机缸盖进行了自顶向下的参数化设计,缩短了缸盖的改型和研发周期,提高了产品的市场竞争力。

基于UG/WAVE的大型矿用挖掘机铲斗参数化设计

基于UG/WAVE装配技术和PTS模块,建立了大型矿用挖掘机铲斗的参数化模型,实现了无代码的可重用系统的编制,大大缩短了挖掘机铲斗的变型和设计周期。铲斗的设计方法为机械产品的可重用设计提供了一种新思路,具有一定的实用性。

UG NX/WAVE在FA702并纱机设计中的应用

介绍了FA702并纱机的结构和特点,对UG NX/WAVE技术的主要内容及其技术内涵进行了简要的阐述,并以FA702并纱机数字化样机设计为例,介绍了如何利用WAVE技术实现产品模型设计过程中的参数化设计方法。

Wind Wave Characteristics and Engineering Environment of the South China Sea

Wave simulation was conducted for the period 1976 to 2005 in the South China Sea （SCS） using the wave model, WAVEWATCH-III. Wave characteristics and engineering environment were studied in the region. The wind input data are from the objective reanalysis wind datasets, which assimilate meteorological data from several sources. Comparisons of significant wave heights between simulation and TOPEX/Poseidon altimeter and buoy data show a good agreement in general. By statistical analysis, the wave characteristics, such as significant wave heights, dominant wave directions, and their seasonal variations, were discussed. The largest significant wave heights are found in winter and the smallest in spring. The annual mean dominant wave direction is northeast （NE） along the southwest （SW）-NE axis, east northeast in the northwest （NW） part of SCS, and north northeast in the southeast （SE） part of SCS. The joint distributions of wave heights and wave periods （directions） were studied. The results show a single peak pattern for joint significant wave heights and periods, and a double peak pattern for joint significant wave heights and mean directions. Furthermore, the main wave extreme parameters and directional extreme values, particularly for the 100-year return period, were also investigated. The main extreme values of significant wave heights are larger in the northern part of SCS than in the south- ern part, with the maximum value occurring to the southeast of Hainan Island. The direction of large directional extreme Hs values is focus in E in the northem and middle sea areas of SCS, while the direction of those is focus in N in the southeast sea areas of SCS.

On the parameterization of drag coefficient over sea surface

Six parameterization schemes of roughness or drag coefficient are evaluated on the basis of the data from six experiments. They present great consistency with measurement when friction velocity u＊〈0.5 m/s （ap- proximately corresponding to 10 m wind speed U10〈 12 m/s） and large deviation from measurement when u＊≥0.5 m/s （approximately U10 ≥ 12 m/s）. In order to improve the deviation, a new parameterization of drag coefficient is derived on the basis of the similarity theory, Charnock relationship and Toba 3/2 power law. Wave steepness and wind-sea Reynolds number are considered in the new parameterization. Then it is test- ed on the basis of the measurements and shows significant improvement when u＊≥0.5 m/s. Its standard errors are much smaller than the ones of the other six parameterizations. However, the new parameteriza- tion still needs more tests especially for high winds.

An evaluation of input/dissipation terms in WAVEWATCH Ⅲ using in situ and satellite significant wave height data in the South China Sea

A WAVEWATCH III version 3.14（WW3） wave model is used to evaluate input/dissipation source term packages WAM3, WAM4 and TC96 considering the effect of atmospheric instability. The comparisons of a significant wave height acquired from the model with different packages have been performed based on wave observation radar and HY-2 altimetry significant wave height data through five experiments in the South China Sea domain spanning latitudes of 0°–35°N and longitudes of 100°–135°E. The sensitivity of the wind speed correction parameter in the TC96 package also has been analyzed. From the results, the model is unable to dissipate the wave energy efficiently during a swell propagation with either source packages. It is found that TC96 formulation with the ＂effective wind speed＂ strategy performs better than WAM3 and WAM4 formulations. The wind speed correction parameter in the TC96 source package is very sensitive and needs to be calibrated and selected before the WW3 model can be applied to a specific region.

Energy and blast performance of beryllium in a model thermobaric composition in comparison with aluminum and magnesium

A direct comparison is made between the effectiveness of Al,Mg,and Be powders as additional fuels in model thermobaric compositions containing 20%fuel,20%ammonium perchlorate,and 60%RDX(1,3,5-Trinitro-1,3,5-triazacyclohexane)passivated with wax.Experimentally determined calorimetric measurements of the heat of detonation,along with the overpressure histories in an explosion chamber filled with nitrogen,were used to determine the quasi-static pressure(QSP)under anaerobic conditions.Overpressure measurements were also performed in a semi-closed bunker,and all blast wave parameters generated after the detonation of 500 g charges of the tested explosives were determined.Detonation calorimetry results,QSP values,and blast wave parameters(pressure amplitude,specific and total impulses)clearly indicate that Be is much more effective as an additional fuel than either Al or Mg in both anaerobic post-detonation reactions as well as the subsequent aerobic combustion.The heat of detonation of the RDXwax/AP/Be explosive mixture is over 40%and 50%higher than that of the mixture containing aluminum and magnesium instead of beryllium,respectively.Moreover,the TNT equivalent of the Be-containing composition due to the overpressure in the nitrogen-filled explosion chamber is 1.66,while the equivalent calculated using an air shock wave-specific impulse at a distance of 2.5 m is equal to 1.69.The high values of these parameters confirm the high reactivity of beryllium in both the anaerobic and aerobic stages of the thermobaric explosion.

非静力地形重力波参数化方案对气候模式大气环流模拟的影响

本文通过在中国气象局BCC-AGCM3-MR(middle-atmosphere version of Beijing Climate Center Atmospheric General Circulation Model version 3)数值模式中引入非静力地形重力波参数化方案,研究非静力效应对次网格地形重力波垂直动量传输及大气环流的影响.本研究开展了两组次网格地形重力波参数化方案试验,分别采用原有的静力地形重力波参数化方案以及考虑非静力效应的新方案.结果表明,在南半球冬季,新方案相比原方案在南极地区将更多的地形重力波动量通量上传至平流层高层,产生更强的地形重力波拖曳.地形重力波拖曳经向梯度的增强导致更强的绝热下沉增温,从而减弱南极极涡的冷偏差和西风偏差.此外,南半球中高纬地区的行星Rossby波上传也增强,同样有利于极涡西风偏差的减少.在两者共同作用下,有效缓解了模式中的南极极涡破碎延迟问题.在北半球冬季,新方案对大尺度环流的整体影响并不显著,但是能够显著改善青藏高原复杂地形区的东风偏差.

尺度适应重力波拖曳方案在高分辨率数值预报中的应用研究

随着数值模式分辨率越来越高,在复杂地形区域仅考虑高层重力波拖曳作用和地形阻塞作用具有局限性,WRFv4.3模式中新型重力波拖曳方案在原有大尺度重力波拖曳和地形阻塞作用基础上新加入了边界层小尺度重力波拖曳作用,且对湍流地形拖曳作用增加了描述,从而可以达到尺度适应。为了验证新的重力波拖曳方案的效果,本文基于华北区域3 km对流可分辨模式开展了2021年冬季重力波拖曳参数化方案应用试验,对比分析了三组试验方案:不开启重力波拖曳、原有的仅考虑大尺度重力波拖曳和阻塞作用的方案以及新型的尺度适应方案的模拟结果。试验结果表明:原有重力波拖曳方案仅考虑重力波拖曳和大尺度地形阻塞,在3 km模式中对复杂地形附近整层风场影响较大,但是正效果有限;新型尺度适应重力波拖曳方案在3 km分辨率模式中大尺度重力波拖曳和阻塞拖曳作用为0,仅由边界层内小尺度重力波拖曳和湍流地形拖曳起作用,能够达到尺度适应效果;由于高层重力波拖曳为0,开启新型重力波拖曳会降低低空尤其是边界层内风场预报正偏差,对高空风场无影响;对模拟区域的统计检验结果表明,新型重力波拖曳方案可以有效减少地形复杂区域近地面风场预报的误差,但对温度等其它要素的改善有限。