Improved retracking algorithm for oceanic altimeter waveforms

Over the deep oceans without land/ice interference, the waveforms created by the return altimeter pulse generally follow the ocean model of Brown, and the corresponding range can be properly determined using the result from an onboard tracker. In the case of complex altimeter waveforms corrupted due to variety of reasons, the processor on the satellite cannot properly determine the center of the leading edge, and range observations can be in error. As an efficacious method to improve the precision of those altimeter observations with complex waveforms, waveform retracking is required to reprocess the original returning pulse. Based on basic altimeter theory and the geometric feature of altimeter waveforms, we developed a new altimeter waveform retracker, which is valid for all altimeter waveforms once there a reasonable returning signal exists. The performances of the existing Beta-5 retracker, threshold retracker, improved threshold retracker, and the new retracker are assessed in the experimental regions (China Seas and its adjacent regions), and the improvements in the accuracy of sea surface height are investigated by the difference between retracked altimeter observations and referenced geoid. The comparisons denote that the new algorithm gives a best performance both in the open ocean and coastal regions. Also, the new retracker presents a uniform performance in the whole test region. Besides, there is a significant improvement in the short-wavelength precision and the spatial resolution of sea surface height after retracking process.     

海南近海Envisat测高波形重构海面高质量评价

以海南近海(14~20°N,108~120°E)为研究区域,采用四种波形重构算法(Ocean1算法,阈值(Threshold)算法,重心偏移(OCOG)算法和Beta-5参数算法)对Envisat高度计RA2第20周期八条轨迹的测高波形数据重新进行计算,并对波形重构后的海面高(SSH)精度进行评价.结果表明:波形重构算法能显著提高测高海面高数据质量,且重构后海面高的空间分辨率有较大改善.其中Threshold 50%算法的重构精度最高,Ocean1算法的精度也较好.Threshold 50%算法的结果最为稳定,比其他三种算法更适合于海南近海的测高波形重构.     

Jason-2 卫星波形重定技术在研究贝加尔湖水位中的应用

利用Jason-2测高卫星2008—2013年的Waveform数据,以贝加尔湖为例,研究卫星测高数据编辑标准、地球物理改正方法及波形重定方法;利用波形重定后的数据计算贝加尔湖年水位异常时间序列与季度水位异常时间序列,分析得到贝加尔湖水位的季节性变化规律;利用组合模型预测贝加尔湖2013年10月的水位,并与测高所得水位进行了比较。研究结果表明,利用波形重构技术可提高对贝加尔湖水位测量精度,对其水位变化研究具有一定的可行性。     

SARAL测高卫星近海域波形重定新方法

利用AVISO提供的SARAL卫星浙江近海海域周年的WAVEFORM数据,通过对卫星波形分析,提出一种新的波形重定方法,该方法在顾及波形物理机制的基础上,根据各波形的特征进行重定。通过对重定前后的波形数据进行粗差剔除、共线平均和对比分析,结果表明:当纬度为27°左右时,未进行波形重定数据求得的平均海面高为10.770 m、标准差为4.515 m,而进行波形重定后数据求得的平均海面高为12.601 m、标准差为1.263 9 m;当纬度为30°左右时,未进行波形重定数据求得的平均海面高为12.236 m、标准差为1.877 m,而进行波形重定后数据求得的平均海面高为12.503 m、标准差为0.419 m。通过对波形重定前后卫星测高数据与验潮站数据对比,得到未进行波形重定的卫星测高数据与验潮站数据差值平均值为0.275 m、标准差为0.273 m,进行波形重定后卫星测高数据与验潮站数据差值平均值为0.046 m、标准差为0.049 m。研究结果显示利用本文提出的方法能显著提高卫星测高数据的精度与质量。     

高度计资料提取内潮信号的方法

为探索高度计资料提取内潮海表面信号更简便有效的方法,利用1992-2002年共10a的TOPEX/Poseidon(T/P)卫星高度计数据进行处理分析。首先,将10a高度计资料的调和分析结果与历史数据进行比较,验证调和分析方法的可靠性。在此基础上,采用2种不同的多项式拟合方法提取夏威夷海区M2内潮的海表面信号:一种是对振幅A、迟角G分别进行沿轨多项式拟合,另一种是对Acos G、Asin G分别进行沿轨多项式拟合。2种方法的结果对比表明,后者的拟合结果优于前者,且11次多项式拟合的结果最优。     

Mean sea surface heights of the South and East China Seas from ocean circulation model and geodetic leveling

The mean sea surface heights (sea surface topography) of the South China, East China, Yellow and Bohai Seas are derived from an ocean general circulation model and surface air pressure. The circulation model covers the global oceans, with fine grid (1/6°) covering the East Asian marginal seas and coarse grid (3°) covering the rest part of the global oceans. The result shows that the China 1985 National Altitude Datum is 24.7 cm above the mean sea surface height of the world oceans. The mean sea surface in the coastal ocean adjacent to China is higher in the south than in the north. Intercomparison of the model results with the geodetic leveling measurements at 28 coastal tidal stations shows a standard deviation of 4.8 cm and a fitting coefficient of 95.3%. After correction through linear regression, the standard deviation is reduced to 4.5 cm. This indicates that the accuracy of model results is sufficient for practical application. Based on the model results, the mean sea surface heights for the study area with a resolution of 1/6 degree are given. This result also links the mean sea levels at islands with those on the mainland coast and gives the mean sea surface heights at tidal stations in the Taiwan Island, the Dongsha Islands, the Xisha Islands and the Nansha Islands relative to the China 1985 National Altitude Datum.     

Low-frequency sea level variation and its correlation with climate events in the Pacific

Global mean sea level(GMSL) has not only significant secular trend and seasonal variations,but also inter-annual and decadal variations.This paper reconstructs the time series of GMSL variations between 1948 and 2007 by combining satellite altimeter measurements and tide gauge observations.Based on the time series,the acceleration of GMSL rise in the second half of 20th century is estimated to be 0.010±0.009 mm/a 2,and multi-scale low frequency sea level oscillations including decadal variations are detected,and the high-rate of GMSL rise during 1993-2003 is locate in the ascending phase of low frequency oscillation.Then,using the reconstructed GMSL time series after removing the secular trend from satellite altimetry and tide gauges measurements,it shows that low frequency signal of sea level variation has strong correlations with the index of El Ni o/Southern Oscillation(ENSO) and Pacific Decadal Oscillation(PDO).But in several time periods,they have large difference due to effects of both high frequency occurrence of El Ni o and La Ni a phenomenon and short term switch of PDO events.     

山东沿海海洋监测浮标网的构建

针对山东沿海独特的地理位置,构建了浮标监测网,按照远海、近海、近岸三个层次,分布在山东沿海从近岸到60海里的范围内,主要测量气象要素、水文要素以及水质生态等参数。设计的浮标监测网布局合理,能够有效的监测海洋污染、赤潮和水质情况,监视风暴潮和台风的发展和走向趋势。     

基于JASON-1高度计的海况偏差校正参数模型

基于JASON-1高度计研究海况偏差校正参数模型。采用交叉点处测量值差分的方法消除高度计中除海况偏差之外的噪声信号。基于泰勒展开构造以有效波高、风速为变量的32种海况偏差参数模型,利用线性回归的方法得到各模型的参数估计值,并对其进行评价、筛选得到最优模型。通过将该模型的海况偏差校正值与JASON-1的地球物理数据集(GDR)数据相对比,进一步验证该参数模型的有效性。结果表明:该参数模型有效,可以用于JASON-1高度计的海况偏差校正。     

星载激光测高仪海面回波的仿真与分析

星载激光测高仪发射的1 064 nm波长激光被波动海洋表面反射,系统接收的时间波形与瞬时海面波浪分布相关。而海面波浪又直接受海面风速影响,因此可以通过观测激光测高仪回波变化监测不同风速下海态变化。本文依据激光雷达方程,利用蒙特卡洛法模拟不同风速下的海面波浪分布,通过光线追击建立海面回波波形仿真器;以地球科学激光测高系统(geo-science laser altimeter system,GLAS)参数为输入,仿真得到不同风速下的海面回波:发现当海面风速在3~10 m/s之间时,回波呈单峰高斯波形,与GLAS发布的实际回波相符;且回波脉宽,以及有效能量反射率(即有效回波能量与发射能量之比)与实测参数误差小于10%。进一步分析可知,回波特征参数与海面风速之间存在显著关联,为利用激光测高仪大规模精确反演海洋表面风速奠定了基础。     

Wetland hydrologic application of satellite altimetry-A case study in the Poyang Lake watershed

Hydrologic variation affects many functions of wetlands.Rapidly and accurately measuring hydrologic dynamics in a wetland watershed has become a fundamental need for estimating functional changes of wetlands.The satellite altimeters have become good data sources that can complement the measurements of gauge stations.As a case project applied in the Poyang Lake watershed,this study has developed a technical approach that integrates the altimeter measurements with the in situ water level data.The derived water surface heights with Envisat RA-2 data are compared with the daily observations of in situ water levels.The average absolute observation difference between the "altimeter station" and its nearest gauge station is 0.307 m,which is comparable to the average differences among the gauge stations.The results suggest that the derived water surface heights from the altimeter data have a good accuracy,which can be used along with the in situ observations as supplements to fill the ungauged area in Poyang Lake wetlands.     

利用星载雷达高度计确定海面动力高度的一种新方案

运用共轭变分同化的方法，就如何把卫星高度计资料同化到中尺度分辨率的大洋环流数值模式中去进行了研究。提出了直接利用距平资料来反演平均的海面动力高度的变化同化方案，并验证了可行性，为利用卫星资料进行海洋动力环境研究提供了新途径。     

相似路径台风风暴潮过程对比

基于MIKE 21模型和Holland台风风场模型,构建了1909号利奇马和0509号麦莎2次相似路径台风期间的风场和气压场,并模拟了相应的风暴潮过程。结果表明：台风中心附近增水变化显著,浙江东北部海域在台风登陆期间的增水更大;受台风强度影响,台风利奇马期间增水高值区更大,部分海域2次台风期间最大增水差值接近1.0 m;潮致欧拉余流速度较大值主要分布在100 m水深以浅的海域,量值超过20 cm/s,江苏沿海、台湾东北部海域存在欧拉余环流;台风利奇马期间近海斯托克斯余流值普遍小于麦莎期间;斯托克斯余流项对台风期间长江口、浙闽等近海浅水区短期物质输运过程起一定主导作用。用EMD方法和Hillbert变换分析了典型站点风暴潮位的特征,发现站点IMF1模态和天文潮位较吻合;水深和IMF3模态的最大功率谱密度呈现出较高的相关性,并且随着水深的增加,IMF3模态的最大功率谱密度逐步变大。     

模式识别在波形分析中的应用

根据波形自动分析的需要,将典型波形进行傅立叶变换,所得数据形成波形模式,继而形成典型波形空间,然后利用空间模式识别方法,把测试波形模式与典型波形空间中的模式进行比较,按离差度给出测试波形与典型波形的匹配程度,从而确定测试波形类型。文中还讨论了加权法模式识别在测试波形出现噪声时的应用。最后用实际应用中的波形数据进行了分析验证,结果表明空间模式识别方法的波形分析中具有良好性能。     

涠洲岛附近海域一次红海束毛藻赤潮生消过程分析

红海束毛藻（Trichodesmium erythraeum）属蓝藻门、颤藻科、束毛藻属。2004年6月28日至7月1日涠洲岛附近海域发生了一次小规模的红海束毛藻赤潮，这已是该海域近3年内的第3次红海束毛藻赤潮。赤潮生物的最高密度为7．0×10^8cell／L。在赤潮发生前涠洲岛附近海域海水中的营养盐含量变化较大，海水硅酸盐和磷酸盐含量逐月降低，赤潮发生前1天硅酸盐和磷酸盐降至最低。赤潮发生前海水温度持续升高。赤潮发生区与未发生赤潮海区相比，赤潮发生区在赤潮发生前硅酸盐含量更低，基本检不出；赤潮发生区磷酸盐含量降低，但是较对照区含量高。在赤潮形成期间，赤潮发生区硅藻数量明显的降低。本次赤潮发生与海水的富营养化无关，是一次非富营养化引发的赤潮，赤潮的发生导致海区的COD升高。     

雷州半岛东部近岸海域潮流特征分析

为进一步研究雷州半岛东部近岸海域的潮流分布规律,采用准调和分析的方法,对2012年8—9月雷州半岛东部海域海洋观测获取的潮流数据进行分析,探讨该海域的潮流性质、实测潮流统计特征、潮流运动形式、最大可能潮流流速和余流的分布特征。研究结果表明:雷州半岛东部海域为不规则全日潮流,涨潮段流速大于落潮段流速,最大流速基本都出现在表层。近岸浅水测站涨、落潮流平均流向基本沿海岸线方向,呈往复流,深水测站基本呈旋转流,区域性变化显著。潮流的可能最大流速出现在C9测站的表层,余流主要受风况、地形因素影响,强度较小,一般在10 cm/s以下。本研究结果可为雷州半岛东部海域的数值模型验证和工程应用研究提供重要参考。     

基于DPSS的高噪声条件下混合LFM波形提取方法设计

 随着电磁对抗与反对抗技术的不断发展,低截获概率信号应用越来越广泛。传统的信号提取方法对低截获信号波形的提取已经无法满足用户使用需求。基于椭球基序列（discrete prolate spheroidal sequence,DPSS）构建时间窗函数对混合线性调频信号（multiple linear frequency modulation）进行分析,提出了恒门限判定概率捕获信号方法,并采用自适应二值化以及改进的霍夫变换（Hough transform）等图形处理算法完成信号波形的提取。仿真表明,本方法比短时傅里叶变换算法（short-time Fourier transform）具有更为优秀的噪声控制,同时在低信噪比下仍能准确提取波形。     

气候变化影响下2050年广东沿海地区风暴潮风险评估

 随着气候变化的影响,广东沿海地区台风风暴潮灾害时空分布逐渐发生变化。本文根据近30年来广东沿海地区18个验潮站的风暴潮资料以及近60年来西北太平洋热带气旋资料,结合前人对西北太平洋热带气旋与海表温度关系研究以及对珠江三角洲地区海平面上升趋势的预测研究,利用ArcGIS空间分析技术,对2050年广东省沿海地区风暴潮淹没范围进行了预测,并对不同区域风暴潮的危险性进行了分析评价。从社会经济、土地利用、生态环境、滨海构造物和承灾能力5个方面构建风暴潮承灾体脆弱性评估体系,完善了广东省沿海地区风暴潮脆弱性指标预测模型,通过该模型对2050年该地区风暴潮脆弱性进行了评估。在未来气候变化影响下风暴潮灾害危险性评价和脆弱性评估的基础上,对2050年广东沿海地区风暴潮灾害风险进行了综合评估,绘制了该地区风暴潮灾害风险评价图。     

Comment on “Low-frequency sea level variation and its correlation with climate events in the Pacific”

The tide gauge results exhibit strong multi-decadal oscillations with detected periodicities up to a quasi-60 years. This translates in the requirement of at least 60-70 years of continuously recorded data without any quality issue and the use of a procedure appropriate for time series with periodic components to infer the acceleration trend. This is not what is done in many recent papers where the oscillating behaviour is neglected and short or incomplete records arbitrarily extended or reconstructed are used to infer wrong accelerating trends. All the tide gauges of enough length and quality show the sea levels are oscillating with important multi-decadal periodicities but absolutely not positively accelerating. The satellite radar altimeter reconstruction of the global mean sea level only available since 1993 shows despite the many uncertainties of a still imperfect procedure a not positively accelerating behaviour. The presence of acceleration in the reconstructed or extended data sets and the lack of acceleration in all the individual tide gauge measurements of enough quality and length certainly deserve further discussion. This is a comment to a previously published original paper made on the basis of other previously published results and not a new original paper.     

广西铁山港海域环境容量及排污口位置优选研究

用交替方向隐式法（ADI法）模拟铁山港海域COD潮扩散,计算铁山港海域COD环境容量。铁山港海域内,石头埠至老鸦以北海域环境容量小,而肋至三合以北海域环境容量大。说明港内海域允许容纳的污染物要比港外的少。石头埠至北暮近海两槽区,水深流强,水交换能力较强,是排污口的良好位置。