【作者】 杨乐；

【导师】 潘德炉； 林明森； 李振华；

【作者基本信息】 南京理工大学 ， 模式识别与智能系统， 2009， 博士

【摘要】 雷达高度计作为一种主动式星下点测量微波遥感器,可以测量卫星到海面距离、海面有效波高和后向散射系数,由这些数据可进一步分析或反演瞬时海面高度、海面风浪场、平均海平面、海洋重力场和潮波系统等。本文围绕高度计目前仍存在的两方面问题展开研究:由于陆地回波的影响,高度计在近海区域测量数据大面积不可用;高度计在热带气旋、台风和飓风等恶劣的海况条件下测量数据受降雨等多种因数的影响。论文的主要工作包括:(1)分析了JASON1和ENVISAT两颗高度计的大量回波波形,给出了这些波形数据在中国海及毗邻海区受影响的范围及原因,以及近海测高数据存在的问题。(2)利用JASON1高度计在远海的测量波形,通过已业务化使用的海洋拟合算法反演了高度计测量的海面基本参数:海面高度、有效波高。在近海,研究和实现了目前已有的多种波形重构算法:Beta5/9算法、OCOG算法、Ice-2算法和阈值算法,并采用三种方法对这些算法在近海使用的优劣进行了分析:高度计升降轨交叉点的海面高度异常值(SLA)比较、高度计反演海面高度(SSH)与验潮站实测水位的比较、以及高度计反演有效波高(SWH)与验潮站和浮标的实测有效波高比较。在此基础上,提出了适用于我国近海的基于波形分类和子波形的波形重构算法,并进行了相关的验证。在一定程度上解决了高度计在近海测量的回波波形反演的问题,提高了高度计在近岸海洋测量数据的数量和质量。(3)在台风等高海况发生时,基于一个大气-白沫-海水的三层模型和电磁波散射理论,分析了降雨和海面白沫对双频高度计及大气校正辐射计测量的影响,发现在高海况下,不能忽略海面白沫的影响。由此,在已有的只考虑降雨校正算法的基础上,提出了辅助大气校正辐射计的测量数据,同时校正降雨和白沫的算法。利用JASON1高度计对台风珊珊的双频测量数据,反演得到台风可靠的风速、有效波高,风圈大小,以及降雨量和海面白沫覆盖率的信息。综上所述,本论文对中国近海及其邻近海域的高度计海洋遥感信息反演和应用的关键技术进行了深入研究,包括高度计遥感信息的反演,特别是在近海的波形重构技术,以及高海况下遥感反演技术,拓展了高度计数据的应用范围。作为对高度计研究的扩展,本文还对一种新的传感器—海浪波谱仪进行了研究。波谱仪是通过在高度计的基础上,增加五条非星下点的波束,360度扫描实现海面波浪谱的测量。本文对波谱仪的测浪原理进行了分析,并与雷达高度计、真实孔径雷达和合成孔径雷达进行了比较,在此基础上,实现了波谱仪测量波浪谱的仿真和反演。更多还原

【Abstract】 Radar altimeter is an active microwave sensor, which measured the instantaneous range between the satellite and sea surface, SWH (Significant Wave Height) and radar cross section of the ocean surface at the nadir point of satellite. The instantaneous SSH (Sea Surface Height), ocean surface wind and wave field, mean sea level, ocean gravitational field, tidal system, etc. can be derived, which are widely used by oceanography community. There are two limiting factors of altimetry, one is that most coastal altimetry data are flagged as useless; the another is that altimetry data under extreme weather events such as tropical cyclones, typhoons and hurricanes are affected by various factors associated with high sea states, such as atmospheric rains and ocean surface foams. The object of this thesis is to solve those two problems. Main achievements are as following:(1) Based on evaluation of large amount of coastal return waveform of JASON1 and ENVISAT altimeter, the problems and affected distances of altimetry waveform at China and adjacent coastal areas are presented.(2) The raw SSH and SWH are derived from JASON1 waveform measurements by using the standard Ocean retracking algorithm at open ocean, which are consist with JASON1 GDR products. Four specialized retrackers: Beta5/9, OCOG (Offset Centre of Gravity), Ice-2, and Threshold retracking algorithms are employed at coastal sea. In order to quantitative compare retracker, the bias, root mean square and standard deviation of the SLA(Sea Level Anomaly) difference between the ascending and descending passes at the crossovers are calculated; the SSH derived from five retracking algorithms are compared with in-situ gauge station measurements; the SWH derived from five retracking algorithms are compared with in-situ gauge station and buoy measurements. Based those studies, we proposed the retracking strategy based on waveform classification and sub-waveform extraction for coastal altimetry. The corresponding validations are given.(3) Using a simplified stratified foam model and scattering theory of electromagnetic wave, the attenuation effect of foam is investigated, which should not be neglected under high sea state. We proposed an iterative method to correct both rain and sea foam effects aided by the liquid water content measurements from Jason Microwave Radiometer. Therefore, the accurate wave height, wind speed, rain rate, and the additional foam coverage from dual frequency altimeter measurement in typhoon can be obtained considering both effects of rain and sea foam. In summary, the waveform retracking algorithm and correction method proposed in this these are helpful to solve the problems of coastal altimeter waveform processing and altimeter data under high sea state, respectively. The quantity and quality of satellite altimetry data are improved.The Wave Spectrometer is new sensor, which employs five non-nadir beams with beam scanning in azimuth (0-360°) in addition to nadir beam of altimeter. The principle of Wave Spectrometer to measure wave spectrum at small incidence is analysis and compared to the real aperture radar and Synthetic Aperture Radar. The simulation and retrieval of Wave Spectrometer are performed based on the non-linearity of the relation between image spectrum and wave spectrum.更多还原