【作者】 杨元德；

【导师】 鄂栋臣； 黄金维； 晁定波；

【作者基本信息】 武汉大学 ， 大地测量学与测量工程， 2010， 博士

【摘要】 受南极地理位置、自然环境和观测手段的限制,长期以来对南极的认识不足,而南极与全球气候和生态环境等一系列重大问题密切相关,因此增强对南极的认识和了解十分重要。海洋重力异常是南极海域的基础数据,高精度高分辨率的南极海域海洋重力异常有助于提高对该海域地球内部构造和海洋资源勘探等方面的认识,也是确定大地水准面的基础数据,而卫星测高是获取大范围高分辨率海洋重力异常的唯一手段。海面高是卫星测高应用的基本物理量,卫星测高在开阔海域的回波信号符合Brown模型,其测距和海面高精度较高,直接采用GDR数据反演的海洋重力异常精度较高。而受多种因素的影响,非开阔海域(尤其是南极海域)的海面高精度偏低,限制了测高在这些区域的应用,也导致南极海域测高海洋重力异常精度偏低。为获得高精度高分辨率南极海域海洋重力异常,必须得到南极海域高精度的垂线偏差,通常采用的手段包括波形重定、改正量选取、对海面高和垂线偏差的数据处理等。本文从波形理论出发,系统提出了波形分类的概念,总结了不同类型反射面的波形重定算法并提出了子波形阈值法,探讨了不同反射面波形重定算法的选取,详细讨论了不同数据处理阶段海面高的数据处理方法,给出了垂线偏差数据处理方法,反演得到了南极海域高分辨率的测高海洋重力异常,与船测重力比较,结果表明南极海域整体统计结果的精度约7mGal;与国际最新的测高模型比较,表明本文得到的模型整体精度接近、部分区域超过了国际最新模型精度。以高精度的船测重力为控制点,与测高海洋重力异常进行数据融合,得到了高精度高分辨率南极海域海洋重力异常。本文具体研究成果及贡献包括以下几方面：1.子波形阈值法与最佳波形重定算法的确定研究出了子波形阈值法,以提取卫星测高回波波形中精度较高的有效子波形,进而提高测高的测距精度。南极海域存在不同的反射面,而不同反射面需采用不同波形重定算法,为确定不同反射面的最佳波形重定算法和反演得到高精度南极海域海洋重力异常,提出了与垂线偏差精度密切相关的参数选取最佳波形重定算法。在南极海域实验区,对子波形阈值法、β-5和阈值法进行了比较,结果表明子波形阈值法的结果优于其他两算法。子波形阈值法对Geosat/GM漫射波形、ERS-1/GM漫射波形和镜面波形的改善率分别达到38%、78.8%和90%。2.测高海面高的数据处理深入研究了测高海面高的数据处理问题,为了提高海面高精度,将移去恢复过程应用于其数据处理阶段,分析不同数据处理阶段海面高残差的特点,提出了高斯滤波、海面高均值平移法和调整的样条多项式进行数据处理,获得了2Hz高精度的海面高。研究发现沿轨迹海面高有时存在着海面高平移现象,分析指出该现象主要由测高数据、测高改正量或回波信号质量太差由波形重定引起。3.最佳反演组合的确定深入探讨了不同垂线偏差输入、参考重力场和反演算法等不同反演组合对测高海洋重力异常精度的影响,研究发现,相对于360阶EGM08,以2160阶EGM08作为参考重力场的统计结果精度改善率达30%；逆Verning-Meinsz算法和最小二乘配置法反演结果精度相当,但前者计算时间仅为后者的40%；以所有测高卫星垂线偏差反演的重力异常精度更高。4.南极海域测高海洋重力异常反演与精度评估反演和评估了南极海域的测高海洋重力异常精度,以最佳反演组合,分区域反演了2′×2′南极海域测高海洋重力异常模型,将该模型和国际最新模型Sandwell and Smith与DNSC08,采用船测重力对南极海域海洋重力异常精度进行评估,结果表明测高重力与船测重力的重力异常余差的统计结果精度约3.2～11.2mGal;本文模型精度总体达到、部分海域甚至超过了国际最新模型,如areal区域,本文模型精度优于Sandwell and Smith模型约2.2 mGal,优于DNSC08模型约1.1 mGal。5.船测重力与测高重力的数据融合以高精度的船测重力为控制点,详细讨论了船测重力与测高重力的数据融合,为消除船测重力采样率的影响,对船测重力重采样,对最小二乘配置法和Draping算法进行比较,结果表明Draping算法在结果精度和计算效率等方面优于最小二乘配置法。采用Draping算法得到了2′×2′南极海域新的海洋重力异常。6.回波信号波形分类及测高在海冰的应用系统探讨和提出了回波信号波形分类的概念、识别流程和适用性分析,并采用简单指标进行波形分类,其结果可用于特定反射面监测和不同反射面波形重定算法等研究。在波形分类的基础上,详细探讨了卫星测高用于监测海冰密集度和海冰空间分布,并给出了测高测高获取海冰厚度的原理。利用遥感资料验证和检核,研究发现利用卫星测高可获取不同时间段的海冰密集度,其结果高于遥感结果。测高用于海冰空间分布不仅有效,且能分辨漂浮的海冰。更多还原

【Abstract】 Due to the limitations of poor geographical conditions and a lack of in-situ observations, knowledge about Antarctic Oceans (AOs) has not been explored well for a long time. However, these ocean areas are closely connected to global climate and ecological environment. Thus, it is important to improve our knowledge over these areas.Gravity anomaly (GA) is one of the basic physical quantities over the oceans. Highly accurate GA can help to improve the knowledge of internal structure and marine resources exploration, and satellite altimeter is the currently best approach to obtain the data over the oceans.Sea surface height (SSH) is the basic parameter derived from satellite altimeter. Normally, in the open ocean, it is relatively precise as the altimeter radar return follow ocean model of Brown, making it possible to derive precise gravity anomalies. However, the accuracy of SSH is often degraded due to a variety of factors, and may lead to false results in the resulting GAs. In order to improve the determination of GAs, SSH needs to be ameliorated by waveform retracking, updated altimeter corrections and data processing.This thesis introduces the ocean waveform model of Brown with a detailed waveform classification. It develops a new algorithm, called sub-waveform threshold, and presents an optimal waveform retracker. Next this thesis discusses data processing of SSH at different stages and deflection of the vertical (DOV), and derives 2’×2’ gridded GAs over AOs. The quality of the derived gravity anomalies is evaluated by comparison with ship gravity data, resulting in a RMS agreement of about 7 mGal over AOs. This result is close to or even better than those of the DNSC08 and Sandwell and Smith gravity models. Finally this thesis discusses data fusing using altimeter-only and ship gravity value, and derives a new GA model around AOs.The major findings of thesis are summarized below:1. Sub-waveform threshold and the optimal waveform retracker selection This thesis presents a sub-waveform threshold retracker to determine sub-waveform with good sample waveforms, and improve the accuracy of gravity anomalies. A criteria parameter, which is correlated with quality of DOV, is present to determine the optimal retracker for the gravity anomaly derivation. The performances of P-5, threshold and sub-waveform threshold are assessed over waters around AOs. The sub-waveform threshold outperforms the other two. Use of the sub-waveform threshold leads to the improvement percentage of about 38%,78.8% and 90%, for Geosat/GM, diffuse and specular waveforms of ERS-1/GM over AOs, respectively.2. Data processing of altimeter SSHIn order to improve the accuracy of high-frequency SSH, the standard remove-restore procedure is firstly used at the stage of SSH processing. Different data processing methods, such as Guassian filter, average-moving of SSH and a modified spline polynomial function of Maus’ (Maus et al,1998), are used at the corresponding stages, and a re-sampling 2-Hz SSHs are derived. Along some tracks, there exists large SSH jumps caused by the errors in altimeter data, incorrect corrections or bad waveforms.3. The optimal strategy determination for gravitySeveral factors, such as reference gravity field and the methods of gravity determination and deflection of the vertical, may affect the quality of satellite-only gravity anomalies. Altimeter-only gravity anomalies on a 2’×2’grid are derived based on several strategies. The altimeter-derived gravity anomalies are compared with ship gravity to determine the optimal strategy for gravity. The standard deviation of the differences between altimeter-derived gravity and ship gravity improves 30% as the 2160 degree of EGM08 the reference gravity field, compared to that of 360 degree. The accuracy of inverse Verning-Meinsz is close to that of least-square collocation, while the computation time of the former is just 40% of that of the latter.4. Marine gravity anomaly derivation over AOFollowing optimal strategy for gravity, gravity anomalies over sub-regions of Antarctic Oceans are derived from altimeter data on a 2’×2’ grid. The gravity anomaly grids from this thesis (current model), DNSC08 model and Sandwell and Smith, are compared with ship gravity. The standard deviation of the differences between altimeter-derived gravity and ship gravity are about 3.2～11.2 mGal over AOs. The accuracy of current model is close to those of the other two, and better over several oceans. Over AOs, the current model improves by 2.2 mGal and 1.1 mGal compared to Sandwell and Smith model and DNSC08 model, respectively.5. Data fusing of ship and altimeter-only gravityTaken high-accuracy ship gravity as the control points, two methods of combining ship and altimeter-only gravity have been experimented over coastal waters around Taiwan. One is least square collocation and the other is Draping. Draping outperforms the LSC in the accuracy and efficiency and is used to get the marine gravity anomalies over AOs on a 2’×2’ grid, which improves over the altimeter-only gravity and ship-only gravity anomaly grids.6. Waveform classification and altimeter application in sea iceReturned waveforms of altimeter depend largely on the property of the reflecting surface. This thesis presents methods of waveform identification and classification. An altimeter application on sea ice concentration (SIC) and sea ice distribution (SIS) is investigated, with an introduction to the principle of sea ice depth determination. The altimeter-derived SIC is compared with that of remote sensing, and the former shows a higher concentration of sea ice in the studied area. Altimeter data can not only be used to derive SIC and SIS, but also identify floating sea ice.更多还原