基于混合密度网络的NSCAT散射计海面风场反演

以NSCAT散射计数据为例,介绍了一种神经网络反演海面风场的方法.风速的反演是基于多层感知器网络;多解风向的反演是基于多层感知器网络和混合密度模型组合而成的混合密度网络,其中的核函数采用高斯函数的形式.通过与欧洲中期天气预报模式风场和现场浮标数据对比,证明了该神经网络反演海面风场的有效性.     

我国首台天基微波散射计测量海面风场的应用研究

介绍了微波散射计测量海面风场的原理和反演算法,并将此算法应用于我国首台天基微波散射计.获得了我国自主资料的第一幅海面风场图.     

一种温度相关的HY-2A散射计地球物理模型函数

利用散射计测量海面后向散射系数, 并通过地球物理模型函数(geophysical model function, GMF)反演得到海面风场。目前散射计风场反演所采用的GMF一般只考虑雷达极化方式、雷达入射角、风速和相对风向对海面后向散射系数的影响, 而相关研究表明海表温度(sea surface temperature, SST)对Ku波段散射计风场反演具有不可忽略的影响。文章利用海洋二号A卫星散射计(Haiyang-2A Scatterometer, HY2A-SCAT)后向散射系数观测值、欧洲中期天气预报中心(European Center for Medium-Range Weather Forecasts, ECMWF )再分析风矢量和SST数据, 采用人工神经网络方法, 建立起一种SST相关的GMF (TNGMF)。对TNGMF进行分析后发现, 海面后向散射系数随着SST的增加而增加, 并且其增加幅度与雷达极化方式、风速有关。为了对比, 文章使用相同数据集和相同方法建立了不包含SST的GMF (NGMF), 将美国国家航天航空局散射计-2 (National Aeronautics and Space Administration Scatterometer-2, NSCAT2) GMF、TNGMF和NGMF分别用于HY2A-SCAT风场反演实验。试验结果表明, 采用NSCAT2 GMF、NGMF反演得到的风速在低温时系统性偏小, 在高温时系统性偏大; 而TNGMF可较好地纠正SST对风速偏差均值的影响, 从而提高反演风场质量。     

星载微波散射计海面风场与海洋环境噪声的相关特性分析

根据海洋环境噪声机理及风关噪声已有的研究成果,提出利用星载微波散射计反演的海面风场数据进行海洋环境噪声分析,并对HY-2A和ASCAT数据与噪声谱级的相关性进行了对比分析。选取南海海域作为研究区,利用潜标测量系统获取的噪声数据和多源散射计风场数据开展了相关实验,并采用NCEP海面风场数据进行对比分析。结果表明,ASCAT数据与噪声的相关性优于HY-2A,散射计数据优于NCEP数据,散射计风场更适合海洋环境噪声的分析研究。该研究内容拓展了微波散射计风场数据的应用领域,并为海洋环境噪声研究提供了更好的技术手段。     

星载微波散射计两种体制的比较

星载微波散射计可以提供全球、全天候、高精度、高分辨率和短周期的海面风场数据。根据雷达天线足印的形状,雷达散射计主要包括扇形波束体制与笔形波束体制两种形式。概述了两种体制微波散射计在设计结构及后期数据处理算法中的优缺点,并对两种不同体制散射计的系统仿真数据进行比较。分析结果表明:对于小型卫星平台,Ku波段的旋转扫描扇形波束散射计比笔形波束圆锥扫描散射计具有更优的风场反演性能。     

HY-2B卫星散射计海面风场产品质量分析 *

星载微波散射计是获取全球海面风场信息的主要手段, HY-2B卫星散射计的成功发射为全球海面风场数据获取的持续性提供了重要保障。本文利用欧洲中期天气预报中心(European Center for Medium-Range Weather Forecasts, ECMWF)再分析风场数据、热带大气海洋观测计划(Tropical Atmosphere Ocean Array, TAO)和美国国家数据浮标中心(National Data Buoy Center, NDBC)浮标获取的海面风矢量实测数据, 对HY-2B散射计海面风场数据产品的质量进行统计分析。分析表明, HY-2B风场与ECMWF再分析风场对比, 在4~24m·s^-1风速区间内, 风速和风向均方根误差(root mean square error, RMSE)分别为1.58m·s^-1和15.34°; 与位于开阔海域的TAO浮标数据对比, 风速、风向RMSE分别为1.03m·s^-1和14.98°, 可见HY-2B风场能较好地满足业务化应用的精度要求(风速优于2m·s^-1, 风向优于20°)。与主要位于近海海域的NDBC浮标对比, HY-2B风场的风速、风向RMSE分别为1.60m·s^-1和19.14°, 说明HY-2B散射计同时具备了对近海海域风场的良好观测能力。本文还发现HY-2B风场质量会随风速、地面交轨位置等变化, 为用户更好地使用HY-2B风场产品提供参考。     

星载全极化微波散射计仿真与海面风场反演研究

通过建立全极化微波散射计系统仿真模型,探索全极化微波散射计的风场反演方法;通过对比不同仪器测量精度下全极化和同极化微波散射计风场反演结果,分析评价全极化微波散射计系统反演海面风场的性能.全极化微波散射计通过增加测量信息来减少模糊解出现的概率,进一步提升风场反演精度.结果表明全极化微波散射计相比同极化微波散射计具有更好的风场反演性能,对于风向结果的改善较为明显:在仿真实验中,全极化仿真反演的风速误差结果优于同极化10°以上,证明了全极化微波散射计能够提升风场反演性能.该仿真结果对我国后续海洋卫星的研发具有一定的借鉴作用.     

基于遗传算法的微波散射计海面风矢量反演研究

针对目前传统反演方法存在的不足和限制,引入遗传算法用于风矢量反演中的目标函数优化.以SeaWinds散射计为例,根据其模型函数和模糊解的基本特征,设计并实现了一套可用于该散射计的海面风矢量反演算法,并利用SeaWinds散射计部分L2A实测数据对该反演算法进行了验证.实验结果表明,通过多代遗传操作,算法能够收敛于几个局部极值点,从而证明该算法能够有效解决数值风矢量的优化搜索问题.     

基于HY-2 卫星观测分析南海风浪关系

海面有效波高(H1/3)是表征海浪的重要参数,随着卫星遥感技术的发展,雷达高度计已成为获取海面有效波高的重要手段,但也只能对卫星星下点轨迹处进行有效观测,远无法满足大范围应用的需求.本研究结合2013年10月HY-2雷达高度计观测的海面有效波高和微波散射计观测的海面风场资料,分别对高、低风速下风浪数据进行拟合,建立了适用于0~40 m/s风速范围内的南海海域风浪关系模型,经模型比对和结果验证,结果表明,基于HY-2卫星数据分析建立的南海海域风浪关系模型是可信的,特别是低风速的风浪模型与实测数据建立的风浪模型具有很好的一致性;根据建立的风浪关系模型,从卫星散射计大面观测的海面风场出发,能推算出风浪条件下海面有效波高的大面信息,数据覆盖远高于卫星高度计的星下点观测,能为分析和预报海浪、风暴潮灾害提供大范围的海面有效波高信息.     

星载SAR对雨团催生海面风场的观测研究

雨团或对流雨是热带与亚热带地区的主要降雨形式,较易被高分辨率星载合成孔径雷达（SAR）探测到。SAR图像上的雨团足印是由大气中雨滴的散射与吸收、下沉气流等共同导致形成的。本文以RADARSAT-2卫星100 m分辨率的SAR图像上雨团引起的海面风场及其结构反演与解译作为实例进行分析。使用CMOD4地球物理模式函数,分别以NCEP再分析数据、欧洲MetOp-A卫星先进散射计（ASCAT）和中国HY-2卫星微波散射计的风向为外部风向,进行了SAR图像的海面风场反演。反演的海面风速相对于NCEP、ASCAT和HY-2的均方根误差（RMSE）分别为1.48 m/s,1.64 m/s和2.14 m/s。SAR图像上一侧明亮另一侧昏暗的圆形信号图斑被解译为雨团携带的下沉气流对海面风场（海面粗糙度）的改变所致。平行于海面背景风场其通过雨团圆形足印中心的剖面上的风速变化可拟合为正弦或余弦曲线,其拟合线性相关系数均不低于0.80。背景风场的风速大小、雨团引起的风速大小以及雨团足印的直径可利用拟合曲线获得,雨团足印的直径大小一般为数千米或数十千米,本文的8例个例解译与分析均验证了该结论。     

Neural network wind retrieval from ERS-1/2 scatterometer data

1IntroductionSatellite observations of the ocean,includingobservation of sea surface wind fields,have tendedto be a perfect technology.Scatterometer is a prima-ry remote sensing sensor,which can get the globalscale information of wind.Other means of remot…     

Global air-sea surface carbon-dioxide transfer velocity and flux estimated using ERS-2 data and a new parametric formula

Using data from the European remote sensing scatterometer（ERS-2） from July 1997 to August 1998,global distributions of the air-sea CO₂ transfer velocity and flux are retrieved.A new model of the air-sea CO₂ transfer velocity with surface wind speed and wave steepness is proposed.The wave steepness（5） is retrieved using a neural network（NN） model from ERS-2 scatterometer data,while the wind speed is directly derived by the ERS-2 scatterometer.The new model agrees well with the formulations based on the wind speed and the variation in the wind speed dependent relationships presented in many previous studies can be explained by this proposed relation with variation in wave steepness effect.Seasonally global maps of gas transfer velocity and llux are shown on the basis of the new model and the seasonal variations of the transfer velocity and llux during the 1 a period.The global mean gas transfer velocity is 30 cm/h after area-weighting and Schmidt number correction and its accuracy remains calculation with in situ data.The highest transfer velocity occurs around 60°N and 60°S,while the lowest on the equator.The total air to sea CO₂ llux（calculated by carbon） in that year is 1.77 Pg.The strongest source of CO₂ is in the equatorial east Pacific Ocean, while the strongest sink is in the 68°N.Full exploration of the uncertainty of this estimate awaits further data.An effectual method is provided to calculate the effect of waves on the determination of air-sea CO₂ transfer velocity and fluxes with ERS-2 scatterometer data.     

Evaluation of NSCAT-2 Wind Vectors by Using Statistical Distributions of Wind Speeds and Directions

In order to validate wind vectors derived from the NASA scatterometer (NSCAT), statistical distributions of wind speeds and directions retrieved by the NSCAT-2 geophysical model function have been investigated by comparison with wind data retrieved by the other model functions such as SASS-2 and NSCAT-1 and those derived from the wind analyses of the European Centre for Medium Range Weather Forecasts (ECMWF). The histogram of the NSCAT-2 wind speeds has a similar shape to those of the ECMWF and NSCAT-1 winds, but is slightly shifted toward higher wind speed to adjust negative bias which has been found in the NSCAT-1 winds by previous buoy comparison studies. Variations of the standard deviation of the NSCAT-2 wind speeds with incidence angle are greater than those of the ECMWF and NSCAT-1 winds. The frequency distribution of wind directions relative to spacecraft flight direction has been calculated to assess the self-consistency of the wind directions. It was found that the NSCAT-2 wind vectors exhibit systematic directional preference relative to antenna beams. This artificial directivity is considered to be caused by imperfections in the antenna beam balancing and the geophysical model function. The skill of the ambiguity removal procedure is discussed as a function of wind speed and incidence angle, and is found to be improved compared to the NSCAT-1 winds, especially at high incidence angles. It is concluded that systematic errors in wind directions might be increased by modifications from NSCAT-1 to NSCAT-2, though the wind speed bias is removed and the ambiguity removal skill is improved.     

Construction of surface wind stress fields with high temporal resolution using ERS-1 scatterometer data

Wind stress fields with high temporal resolution over the North Pacific have been constructured by using ERS-1 scatterometer data. A simple objective analysis, a successive correction method, was used to construct the fields. Several necessary parameters used in the method are examined by a simulation based on the climatological data. The meridional decorrelation scale of the wind stress depends strongly on the season, while the zonal decorrelation scale is highly stable. We determined the decorrelation scale depending on the location and the time and applied to the successive correction method. The monthly mean field constructed by averaging the daily mean data is free from an aliasing error, which is a serious problem if a simple monthly averaging is applied. The daily wind stress data obtained in the present study represent small time- and spatial-scale variation and large amplitudes compared with data interpolated from simple monthly mean data. The satellite-derived data are also compared with in situ data obtained by meteorological buoys. The satellite wind speeds are lower than in situ wind speeds for every buoy. This underestimation is not due to the present objective analysis, but due to the original data, the ERS-1 Scatterometer Value-Added Product.     

Validation of gridded data set of global surface wind/wind-stress vector field

Gridded data of global surface wind/wind-stress vectors, called J-OFURO v2, were obtained from satellite scatterometer (QuikSCAT/SeaWinds) data for the decade from August 1999 to July 2009. The data were validated by comparing with (1) in situ measurements from moored buoy observations, (2) a data product from the same scatterometer using a different gridding procedure (IFREMER), and (3) data products based on numerical models (NCEP-1 and NCEP-2). The results on averaging all buoy data revealed lower mean differences, lower root-mean-square (RMS) differences, and higher correlations for the wind/wind-stress components for the J-OFURO v2 product than the other data products. The statistical values calculated for each buoy station showed tendencies of decreasing reliability with increasing latitude in the mid-latitude region, while the reliabilities in the equatorial areas were low. We performed intercomparisons between the J-OFURO v2 data and the other data sets to clarify discrepancies among different wind products in open ocean regions with few moored buoys. We determined that the meridional wind components from the NCEP products exhibited poleward deviations compared to data from the J-OFURO v2 product. Relatively high mean differences, high RMS differences, and low correlations were found in the equatorial ocean for the NCEP products. Striped features were spatially correlated with buoy locations in the equatorial Pacific, which suggested that the reliability of the NCEP products was governed by buoy locations in this region.     

用圆中数滤波器排除卫星散射计风场反演中的风向模糊

由卫星散射计测量得到的归一化雷达截面积σ^0值以及这些σ^0值关联海面风速风向的经验模型函数可以反演海面的风矢量。但是对应一分辨面元上测量的σ^0值并不是唯一的风矢量解与之对应,选择一个风矢量解来表示真风矢量的处理过程就叫模糊排除或称消去伪解。本文引入一种圆中数滤波技术,在由模拟的ERS－1散射计数数据反演风场中,不附加任何其他信息的情况下,圆中数滤波器改进风向模糊排除方法,很好地重现模拟的海面真风矢量。     

Spatio-temporal variability in sea surface wind stress near and off the east coast of Korea

Sea surface wind stress variabilities near and off the east coast of Korea, are examined using 7 kinds of wind datasets from measurements at 2 coastal (land) stations and 2 ocean buoys,satellite scatterometer (QuikSCAT), and global reanalyzed products (ECMWF,NOGAPS,and NCEP/NCAR). Temporal variabilities are analyzed at 3 frequency bands; synoptic (2-20 d), intra-seasonal (20-90 d),and seasonal (>90 d).Synoptic and intra-seasonal