北斗反射信号软件接收机的设计与实现

通过对GNSS(global navigation satellite system)反射信号软件接收机和硬件接收机进行对比分析,提出北斗反射信号软件接收机的结构及模块,包括接收直射和反射信号的天线、四通道射频前端、采样量化变换器和数据处理工作站。设计实现北斗导航卫星反射信号处理软件的实现方法及软件整体流程,给出捕获及跟踪两大主要模块的详细流程及处理方法。进行海面测高的岸基实验,通过与实际海面高度的对比验证了软件接收机系统的实用性。     

基于文氏方向谱的海浪仿真技术研究

研究不同成长状态下的海浪真实性优化问题,海浪方向谱不仅与风速风向有关,还与风浪的成长状态息息相关.为获取海面波高数据,不仅要求正确地反映风速风向的影响,还应能够真实地反映海浪成长状态的变化.为解决上述问题,提出了一种采用能正确反映海浪成长状态的文氏方向谱来作为靶谱的三维海浪仿真方法,利用海洋谱能量散布随角频率以及不同风浪成长状态变化的具体特性,根据频率等分以及能量等分的采样原则,分别对多种成长状态下的海浪进行了数值仿真.仿真结果表明,新方法能够正确地反映海浪成长状态的变化以及风速风向因子的影响,仿真的海面波高数据与实际海况相符.     

基于GPU的海浪特效实时渲染

对于海浪特效的模拟能有效增强海洋场景仿真的真实感,模拟的实时性也是海洋场景仿真系统的重要需求之一.为了实现基于GPU的海浪特效实时渲染,以PM海浪谱为基础进行了研究,从而生成海浪高度场,并结合视相关反投影方法生成海浪网格,采用硬件着色器进行基于物理光照模型的实时光照处理,生成了具有较强真实感的海面效果,较好地满足了时渲染场景实时性和真实感的要求,达到了实时视景仿真系统中对海洋模块的实时仿真要求.     

基于现场观测数据的卫星雷达高度计海面风速和有效波高真实性检验方法研究

卫星遥感产品定量化应用前需通过真实性检验。卫星雷达高度计可观测海面风速大小和有效波高等海洋动力环境参数,而对其进行真实性检验存在不同的时空匹配方法。使用3种不同的时空匹配方法,利用美国国家浮标数据中心(NDBC)现场观测数据对2011年的Jason2海面风速和有效波高产品进行了检验。Jason2海面风速大小和有效波高的均方根误差分别为1.28 m/s和0.28 m,同时结果表明:采用卫星高度计海面风速大小(有效波高)和同步的现场观测数据在一定时间(1 h)和空间(50 km)限制条件下进行对比检验,可以得到合理的高度计海面风速大小和有效波高精度评价结果。 Jason2卫星高度计海面风速大小和有效波高的精度与探测海域有关,其精度在墨西哥湾与西大西洋海域相对较高。     

基于GNSS-R的反演海面风速技术的研究

对利用全球导航定位系统的海洋反射信号(GNSS-R)反演海面风速的方法进行了研究。GNSS-R技术作为一种新型的、低成本的海洋微波遥感测风技术,与其他测风技术相辅相成,弥补了某些测风手段的不足。文中还讨论了散射信号相关功率模型中的散射截面、多普勒区、等延时区、天线覆盖区四部分函数的定义和性质。使用Elfouhaily海浪谱模型,数值模拟了机载高度下散射信号相关功率的理论波形,在此基础上,又结合机载高度下获得的实测数据反演得到海面风速,反演得到的风速的均值与试验时浮标数据所对应的风速的均值比较相差1.4 m/s,误差在可接受的范围内,反演得到的风速与浮标数据相一致。     

基于海浪谱的实时海洋场景仿真

研究海洋场景中海浪等视景的实现,是计算机在图形学中的具体应用.风浪是海洋表面最主要的一种波浪,从海洋学已有的统计观测结果出发,利用海浪频谱与方向谱的相关公式,对开阔海面深水域由风引起的海浪进行定量分析.利用粒子系统对雨、雪、云等自然现象进行仿真,实现了对海洋场景的实时显示.在VC平台上用OpenGL开放图形库实现了所述海洋场景的仿真.实践证明,提出的方法在实时性与真实感方面均取得了不错的效果.     

利用星载SAR图像检测海洋锋的方法

海洋锋区剪切流、辐聚流与海洋表面波之间存在相互作用,将这种相互作用处理为对海浪谱的扰动,来分析其对海浪谱密度和谱梯度的影响;根据两尺度模型,分析了海面小尺度波(厘米级)和大尺度波(海浪)与雷达后向散射系数的关系,从而说明了海洋锋的SAR成像原理。在海面SAR图像中,海洋锋的尺度比海浪的尺度大2~3个数量级,可以通过二维空间谱分析,将海浪信息的主要部分滤除,再利用数字图像处理技术提取海洋锋的特征信息,由此形成了一套用海面SAR图像提取海洋锋特征参数的信息处理方法。     

我国近海海洋现象的星载SAR观测

利用ＳＩＲ－Ｃ／Ｘ－ＳＡＲ，ＥＲＳ－１和ＪＥＲＳ－１的ＳＡＲ图像观测中国近海洋现象。分析结果表明：ＳＡＲ图像揭示了海浪，内波，浅海水下地形，海面油膜，表层流场，河口羽流和海面船只等现象，Ｘ－ＳＡＲ观测到了南海东沙群岛附近海区的海浪和内波。在中等海面风速和强潮流的条件下，登州浅滩等浅海水下地菜特征在ＥＲＳ－１ＳＡＲ图像上清晰可辨，从ＳＡＲ海面油膜获得了山东北部海区的表面流场结构并与海流图作了比较，二     

新型海洋摆动发电系统设计

海浪能摆动发电是实现海洋浮体续能的有效方式,利用海浪运动规律和周期摆动特点,提出一种新型海洋波浪能悬锤摆动发电系统,基于海浪波动规律以及运动和能量传递特性,建立了发电系统的数学模型,设计优化方案;采用Rouge-Kut-ta方法对数学模型进行时域仿真,并开展原理样机试验进行对比分析验证.研究结果表明:试验结果与仿真结果一致性好;系统输出的电压和功率具有周期性,且频率等于海浪频率.研究成果可作为海洋波浪能有效利用和摆动发电系统优化设计的理论依据.     

基于MATLAB/SIMULINK的海面回波模拟器仿真与分析

星载雷达高度计是一种重要的对海洋进行精确测量的主动式微波遥感器。因为高度计能够有效地测量卫星到海面的高度、海面有效波高和海面后向散射系数,它在海洋大地水准面研究和海洋应用研究的诸多方面得到了广泛的应用。海面回波模拟器能够接收和处理高度计信号,产生海面回波波谱来调制高度计信号,最后精确延时后发射回高度计,是在地面对高度计进行测试和定标的一种有效手段。由于功能的全面性,回波模拟器是一个复杂度不亚于高度计本身的系统,因此,对回波模拟器的分析和仿真对于指导它的设计、确定它的精度以及定标的效果有着重要意义。介绍了回波模拟器的结构,分析了海面回波波谱的产生原理并设计了回波模拟器的SIMULINK仿真模型,给出并分析了仿真结果。     

Global structure of extreme wind and wave climate derived from TOPEX altimeter data

Sea surface wind speed and significant wave height (SWH) are two basic parameters, in addition to sea surface height, which can be inferred from satellite altimeter measurements. Traditionally, altimeter-derived wind and wave data are less extensively used compared to sea surface height, as they are sometimes considered as by-products of satellite altimetry (in contrast to, for example, the dedicated scatterometer missions for marine wind observations). However, it is clear that altimeter-based wind and wave data have the unique advantage of being concurrent and collocated with each other. Using eight years (1993–2000) of TOPEX altimeter data with unprecedented accuracy and continuity, the 10-, 50- and 100-year return values of global wind speed and SWH are derived, their characteristics are discussed in relation to wind climatology and wind variability. Validations against in situ observations indicate that the uncertainties of altimeter-derived extreme winds and waves are at the levels of 10% and 5%, respectively. These results suggest that satellite altimeter data, with present quality and duration, can be very useful in many aspects of coastal engineering and marine technology such as design of offshore facilities, ship routing, and preparation of other sea-going activities.     

Sea surface wind speed and sea state retrievals from dual-frequency altimeter and its preliminary application in global view of wind-sea and swell distributions

Altimeter radar backscatter intensity, in terms of the normalized radar cross section (NRCS), is known to be modulated by surface wind forcing and the state of wind-sea development. Based on a data set of collocated altimeters (including Topex/Poseidon, Jason-1 and Jason-2) and in situ measurements, different responses to various wind speeds and wave ages (i.e. the state of wind-sea development) were illustrated for altimeter dual-frequency NRCSs (K_u-band at 13.6 Hz and C band at 5.4 Hz), which can facilitate the retrieval of wind speed and wave age parameters. A statistical parametric algorithm was developed to retrieve the two dynamic parameters from the altimeter dual-frequency NRCSs using the neutral network method. The wind-sea significant wave height (SWH) was estimated from wind speed and wave age parameters, which partitions the swell SWH from the altimeter SWH measurement. All newly derived parameters were well validated by comparison against in situ buoy measurements. A preliminary application of the method in examining the swell or wind-sea contributions to global waves was performed; it was found the swell dominance in an open ocean, and the wind-sea dominance in marginal and semi-enclosed seas. The methods would benefit other applications such as studies of air–sea interactions, validation of wave model, determination of swell decay rate and studies of wave climate.     

基于海浪谱的Gerstner波浪模拟

本文从海洋学现有的观测和研究成果出发，结合海浪的Gerstner模型，提出一种风力作用下的基于海浪谱的三维Gerstner海浪模型。首先，通过分析Gerstner模型各个参数的随机性，利用海浪谱和方向谱相关公式，获得固定风速下模型各随机参数值，建立固定风速下的海浪模型；然后，在此基础上进一步构造了基于海浪谱的风力模型，模拟了风力作用下的海浪；最后，采用基于视点的网格拓扑结构，实现了海浪的实时绘制。实验结果表明，该模型不仅能更真实地模拟海浪，还具有较好的交互性。     

High-resolution satellite measurements of coastal wind field and sea state

Methods to derive wind speed and sea state by simple empirical models from synthetic aperture radar (SAR) data are presented and applied for use in high-resolution numerical modelling for coastal applications. The new radar satellite, TerraSAR-X (TS-X), images the surface of the sea with a high resolution up to 1 m. Therefore, not only wind information and integrated sea state parameters but also individual ocean waves with wavelengths down to 30 m are detectable. Two-dimensional information on the ocean surface retrieved using TS-X data is validated for different oceanographic applications: derivation of finely resolved wind fields (XMOD algorithm) and integrated sea state parameters (XWAVE algorithm). Both algorithms are capable of taking into account fine-scale effects in coastal areas. Wind and sea state information retrieved from SAR data are applied as the input for a wave numerical spectral model (wind forcing and boundary condition) running at a fine spatial horizontal resolution of 100 m. Results are compared to collocated buoy measurements. Studies are carried out for varying wind speeds and comparisons against wave height, simulated using original TS-X-derived wind data, showing the sensitivity of waves to local wind variation and thus the importance of local wind effects on wave behaviour in coastal areas. Examples for the German Bight (North Sea) are shown. The TS-X satellite scenes render well-developed ocean wave patterns of developed swell at the sea surface. Refraction of individual long swell waves at a water depth shallower than about 70 m, caused by the influence of underwater topography in coastal areas, is imaged on the radar scenes. A technique is developed for tracking wave rays depending on changes in swell wavelength and direction. We estimate the wave energy flux along wave tracks from deep water to the coastline based on SAR information: wave height and wavelength are derived from TS-X data.     

An analytical algorithm with a wave age factor for altimeter wind speed retrieval

Based on the specular reflection theory of electromagnetic waves at rough sea surface and the wind wave spectrum model with a wave age factor, the sea surface wind speeds are retrieved from the normalized radar backscatter cross‐section (NRCS) measured by TOPEX/Poseidon (T/P) Ku‐band altimeter using the mean square slope (MSS) calculated from the spectrum models of the wind waves and the gravity‐capillary waves. A relationship between wave age and non‐dimensional wave height is applied to compute the wave age factor using the significant wave height (SWH) and wind speeds obtained from buoy or altimeter simultaneously. The study indicates that the wave age factor has a significant impact on the retrieval of altimeter wind speed. Compared with the operational algorithm for retrieving altimeter wind speed, the wind speed retrieved from the new analytical algorithm based on the wind wave spectrum model with the wave age factor, proposed in this study, can match the buoy measurements better. The effects of the wave age factor on altimeter wind speed retrieval are also shown quantitatively through a series of experiments and measurements. The comparison with the operational algorithm indicates that both the bias and root mean square error (RMSE) between wind speeds retrieved by the proposed analytical algorithm and those observed by the buoy decrease significantly. In the Gulf of Mexico, with the new analytical algorithm, more accurate altimeter wind speeds are retrieved.     

A satellite-derived climatology of global ocean winds

An interactive Climatology of Global Ocean Winds (COGOW) is presented based on 5 years (August 1999-July 2004) of QuikSCAT satellite measurements of wind speed and direction 10 m above the sea surface. This climatology provides the first high spatial resolution, observationally based, online atlas of ocean winds. Users can retrieve climatological wind maps and wind statistics, both in tabular and graphical form, from the COGOW web-based atlas. The global coverage of these data provides highly accurate information about the wind statistics in regions of the world ocean that are sparsely sampled by ships and buoys. A case study of the recovery of the vessel Ehime Maru off the Hawaiian Island of Oahu is presented to demonstrate the usage and value of COGOW. Evidence of air-sea interactions, one of many wind phenomena visible within COGOW, is discussed to further familiarize users with COGOW. Finally, the utility of COGOW with regard to various operational and research communities is summarized.     

基于SWIM、SCAT联合观测小卫星的总体设计要点

海洋对全球气候、气象、环境和经济发挥着重要作用,因此,有必要对其进行监测、研究及预测发生在海洋内部和海洋表面的运动过程。海面风场信息、海面波浪谱信息能够体现并反演海洋气象、海洋动力学特性、海洋资源、海洋污染情况、海洋经济性和海岸环境。波谱仪(SWIM,Surface Wind Investigation and Monitoring)和微波散射计(SCAT,Scatterometer )可以用于获取海面波浪谱信息和海面风场信息。首先对这两套载荷系统进行了介绍,并简要对基于这类主动微波遥感载荷配置的卫星设计进行了任务分析,最后给出了基于波谱仪、微波散射计联合使用在小卫星平台应用背景下卫星系统级设计的几个主要方面进行了研究和分析。     

基于残差U型卷积网络的海面风速多步时空预测

准确的海面风速预测是保证远洋船舶航行安全和节能减排的重要条件.针对远洋航行领域的海面风速预测存在空间特征难以解析和多步预测精度偏低两个问题,设计一种改进的多步时空预测方法.在多步预测方面,使用超前时刻策略使单个模型学习并区分不同的预测时刻,并将海面风向作为外生变量,将月份、日期和时刻作为协变量,与历史风速数据结合以扩展样本空间.在空间特征方面,利用编码器-解码器结构的残差U型卷积神经网络,对多层级空间信息进行提取和解析,并将超前时刻特征同时输入编码器和解码器,强化深层特征解析为对应预测时刻的效果.在全球原油运输路线上进行的12小时预测实验表明,所提出方法较其他6种预测方法具有更低的预测误差.     

Dependence of mean square slope on wave state and its application in altimeter wind speed retrieval

Mean square slope (MSS) of sea surface is a parameter describing the sea surface roughness and plays a key role in understanding the sea surface dynamics. Although MSS is influenced by many factors such as wind speed and sea surface waves, it has been traditionally parameterized by wind speed only. In this study, the surface wave impact on MSS is investigated using a collocated data set of altimeter and buoy measurements. It is found that the MSS detected by Ku-band altimeter is closely related to the wind wave components and increases with the degree of wind wave development; however, it is almost independent of the swell. The wave effect on MSS is mainly ascribed to the contribution of longer waves rather than shorter waves. An analytical spectral MSS model is proposed, and it is shown that the MSS calculated from the model agrees well with the altimeter-measured MSS when the pseudo-wave age is adjusted to the wave age corresponding to wind waves. This model is applied to derive wind speeds from altimeter data including the normalized radar cross section and the significant wave height of sea surface waves. With the collocated data set, it is shown that this new algorithm performs better than previous empirical algorithms.