卫星重力场恢复中海潮负荷效应的改正

本文详细介绍了海潮负荷效应对卫星重力测量影响的基本理论,并采用不同分辨率的FES2004、TPXO7.2和GOT00全球海潮模型计算了海潮负荷对卫星重力结果前60阶的影响;并用各个模型之间的差异作为海潮模型精度的估计量,计算了海潮模型误差对卫星重力结果的影响,与GRACE恢复的重力场精度的比较说明:海潮负荷效应主要影响卫星重力观测结果的低阶系数,35阶以下的影响都超过了目前重力场恢复精度;尽管由于卫星测高技术的发展,全球海潮模型的分辨率及精度均得到很大提高,但目前的全球海潮模型用于GRACE重力场恢复的前12阶的改正还是不够精确.受近海地区特殊海岸线及复杂海底地形的影响,整体精度仍得不到提高,利用高精度高分辨率的中国近海模型对不同分辨率全球海潮模型进行局部精化,进一步提高了全球海潮模型的整体精度,同时改善了卫星重力场恢复中的海潮负荷改正效果.     

基于半解析法有效和快速估计GRACE全球重力场的精度

首先基于半解析法建立了新的GRACE卫星K波段测量系统星间测速、GPS接收机轨道位置和加速度计非保守力误差联合影响累计大地水准面的误差模型;其次,基于各关键载荷精度指标的匹配关系,论证了误差模型的可靠性;最后,基于美国喷气动力实验室（JPL）公布的2006年的GRACE Level 1B实测误差数据,有效和快速地估计了120阶全球重力场的精度,在120阶处累计大地水准面的精度为18.368 cm,其结果和德国地学研究中心（GFZ）公布的EIGEN-GRACE02S全球重力场模型符合较好. 本文的研究为将来国际卫星重力测量计划（如GRACE Follow-On, 360阶）中高阶全球重力场模型精度的有效和快速估计提供了理论基础和计算保证.     

GRACE/GOCE扩展重力场模型确定我国1985高程基准重力位的精度分析

高精度高程基准重力位的确定往往依赖于高精度全球重力场模型,其对全球和区域高程基准的高精度统一非常关键,GRACE、GOCE卫星重力计划极大地提高了全球重力场模型中长波的精度.本文首先对GRACE/GOCE卫星重力场模型的内符合和外符合精度进行讨论分析,结果说明卫星重力模型的截断误差影响可达到分米级水平,在确定高程基准重力位时该影响不可忽略.利用EGM2008模型扩展GRACE/GOCE卫星重力场模型至2190阶,可有效减弱卫星重力模型的截断误差影响,但不同模型扩展时的最优拼接阶次不同,其中DIR-1、DIR-5模型对应的最优拼接阶次分别为180阶和220阶,以GPS水准数据检验,扩展模型在中国区域的精度均优于18cm.最后,基于最优拼接阶次获得的扩展重力场模型对我国1985高程基准重力位进行了估计,DIR-5和TIM-5模型对应数值分别为62636853.47m~2·s~(-2)和62636853.49m~2·s~(-2),精度均为1.51m~2·s~(-2);发现在中国区域模型大地水准面与GPS/水准数据的差值存在微弱的系统性倾斜,东西向倾斜约为9cm,南北向倾斜约为1.4cm,考虑倾斜改正后基于DIR-5和TIM-5模型估计我国1985高程基准重力位的精度提高了0.16m~2·s~(-2).     

卫星重力梯度恢复地球重力场的频谱分析

根据仪器功率谱密度和重力位系数阶方差的定义,本文建立了卫星重力梯度测量噪声功率谱密度与重力场模型的误差阶方差的直接对应关系,并基于此讨论了重力梯度测量精度、卫星轨道高度以及运行时间对地球重力场恢复精度的影响.相比于传统的基于最小二乘法评估卫星载荷噪声对地球重力场恢复精度的影响而言,本文提出的方法简单、直接,有助于快速设计和确定卫星重力测量计划的有关参数.     

Spectral analysis for recovering the Earth's gravity potential by satellite gravity gradients

根据仪器功率谱密度和重力位系数阶方差的定义,本文建立了卫星重力梯度测量噪声功率谱密度与重力场模型的误差阶方差的直接对应关系,并基于此讨论了重力梯度测量精度、卫星轨道高度以及运行时间对地球重力场恢复精度的影响.相比于传统的基于最小二乘法评估卫星载荷噪声对地球重力场恢复精度的影响而言,本文提出的方法简单、直接,有助于快速设计和确定卫星重力测量计划的有关参数.     

重力潮汐改正

高精度重力测量迫切要求提高重力潮汐改正的精度,本文应用现有的我国重力潮汐观测成果和海潮重力负荷改正计算结果,提出一组重力潮汐改正的实用计算公式。并且根据计算误差要求小于±1μGal的条件下,将我国划分为四个区,与合适的计算式相对应。此外,对近年来国外学者所提出的理论重力潮汐改正计算公式进行了评述,尤其对过去不曾注意的潮汐永久项（M₀S₀波）在潮汐改正中的影响进行了较详细的讨论。最后还对目前海潮负荷改正的精度提出了一些看法。     

用东海和南海潮汐资料修正全球海潮模型对中国及邻区重力场负荷计算的影响

利用11个全球海潮模型和中国东海及南海近海潮汐资料,计算了海潮负荷对中国及邻区重力场的影响,进而讨论了用近海潮汐资料修正全球海潮模型对负荷结果的影响. 结果表明, 用近海潮汐资料修正全球海潮模型对沿海地区的负荷计算影响较大, 因此在计算海潮负荷对沿海台站的影响时, 必须顾及近海潮汐效应. 计算M2波海潮负荷时, 选择CSR4.0, FES02, GOT00, NAO99和ORI96海潮模型, 则对于内陆大部分台站负荷的近海效应在0.1times;10-8m/s2量级; 而计算O1波时, 如选择AG95或CSR3.0模型, 则在0.05times;10-8m/s2量级. 这说明模型中的各个潮波在我国沿海的准确性并不是一致的, 因此模型的选择是比较复杂的.      

中国大陆精密重力潮汐改正模型

利用理论和实验重力固体潮模型,充分考虑全球海潮和中国近海潮汐的负荷效应,建立了中国大陆的精密重力潮汐改正模型.结果表明,采用不同的固体潮模型会对重力潮汐结果产生相对变化幅度小于0.06％的差异;在沿海地区海潮负荷的影响约为整个潮汐的4％,而中部地区约为1％,其中中国近海潮汐模型的影响约占整个海潮负荷的10%,内插或外推潮波的负荷约占海潮负荷的3％.通过比较实测的重力数据表明,本文给出的重力潮汐改正模型的精度远远优于0.5×10^-8 m·s^-2,说明了本文构建的模型的实用性,可为中国大陆高精度重力测量提供有效参考和精密的改正模型.     

联合星载GPS和KBRR星间测速数据反演GRACE时变重力场模型

高精度GRACE卫星时变重力场反演一直是卫星重力测量中的难题.为了恢复高精度的时变地球重力场模型,本文联合GRACE卫星的星载GPS和KBR星间测速观测数据,在对GRACE卫星进行精密定轨的同时,解算出60阶月平均地球重力场模型.通过对GRACE卫星的定轨精度、星载GPS相位和KBR星间测速数据的拟合残差以及时变地球重力场模型解算精度等分析,表明:(1)与美国宇航局喷气推进实验室(JPL)发布的约化动力学精密轨道相比,本文确定GRACE卫星轨道三维位置误差小于5 cm.(2)星载GPS相位数据拟合残差为5~8 mm,KBR星间测速数据拟合残差为0.18~0.30μm·s~(-1).(3)解算的月平均重力场模型与美国德克萨斯大学空间研究中心(CSR)、德国地学研究中心(GFZ)和JPL发布的RL05模型精度接近,时变信号在全球范围内具有很好的空间分布一致性.通过计算亚马逊流域和长江流域的水储量变化,本文与上述三个机构的计算结果无明显差异,且相关系数均达0.9以上.可见,本文建立的卫星轨道与重力场同解算法具有反演高精度GRACE时变重力场能力,为我国卫星重力场反演提供了重要的技术支持.     

利用解析法有效快速估计将来GRACE Follow-On地球重力场的精度

本文首次利用解析法有效快速估计了将来GRACE（Gravity Recovery and Climate Experiment） Follow-On地球重力场的精度. 第一,基于功率谱原理分别建立了新的GRACE Follow-On卫星激光干涉星间测量系统星间速度、GPS接收机轨道位置和轨道速度以及加速度计非保守力误差影响累计大地水准面的单独和联合解析误差模型. 第二,利用提出的GRACE卫星关键载荷匹配精度指标和美国喷气推进实验室（JPL）公布的GRACE Level 1B实测精度指标的一致性,以及估计的GRACE累计大地水准面精度和德国波兹坦地学研究中心（GFZ）公布的EIGEN-GRACE02S地球重力场模型实测精度的符合性,验证了本文建立的解析误差模型是可靠的. 第三,论证了GRACE Follow-On卫星不同关键载荷匹配精度指标和轨道高度对地球重力场精度的影响. 在360阶处,利用轨道高度250 km、星间距离50 km、星间速度误差1×10^-9m/s、轨道位置误差3×10^-5m、轨道速度误差3×10^-8m/s和非保守力误差3×10^-13m/s²,基于联合解析误差模型估计累计大地水准面的精度为1.231×10^-1 m. 本文的研究不仅为当前GRACE和将来GRACE Follow-On地球重力场精度的有效快速确定提供了理论基础和计算保证,同时对国际将来GRAIL（Gravity Recovery and Interior Laboratory）月球卫星重力测量计划的成功实施具有重要的参考意义.     

海潮误差对GRACE时变重力场解算的影响研究

海潮误差是GRACE时变重力场反演中重要的误差源,目前发布的海潮模型中主要包含振幅较大的主潮波分量模型,在时变重力场反演中次潮波的影响也是不可忽略的,因此,GRACE时变重力场反演中的海潮误差主要包括受限于海潮模型误差和次潮波影响.本文利用轨道模拟方法检测了短周期潮波的混频周期以及次潮波对ΔC20,ΔC30的时序特征,并进一步通过轨道模拟结果分析了海潮误差对时变重力场反演的影响,然后通过实测数据解算分析了海潮误差对当前GRACE时变重力场解算的影响,研究发现:(1)利用轨道模拟能够有效地检测短周期潮波的混频周期;(2)时变重力场解算过程中,次潮波的影响大于海潮模型误差的影响;(3)海潮模型误差以及次潮波影响是当前GRACE没有达到基准精度的重要因素之一.     

Accuracy assessment of ocean tide loading computations for precise geodetic observations

The increasing resolution of ground based gravity measurements (e.g. by superconducting gravimeters) as well as satellite based gravity field studies allows to study very small signals, globally as well as local. On the other hand, this requires the correction of such signals to uncover others. To study the Earth’s deep interior and the on-going dynamic processes requires the correction of disturbing signals, and one of these signals is related to ocean tidal loading. Although new ocean tide models are being derived from current satellite missions, there are still uncertainties.In this paper we present an intercomparison ocean tide models to test their fit to world-wide observations. Therefore, three TOPEX/POSEIDON (T/P) satellite derived models (CSR3.0, FES95.2 and TPXO.2) beside the classical SCHW80 model were selected for an accuracy assessment study. The selected models have been subjected to an intercomparison test, tide gauge validation test and comparison to 59 tidal gravity stations.The intercomparison test shows a good agreement between the T/P-based models for the open ocean and remarkable disagreement between the selected models in the coastal regions indicating that such models are still problematic in these regions. The tide gauge validation shows that the T/P derived models fit tide gauges better than SCHW80, with a better fit for the semidiurnal constituents than for the diurnal constituents. Comparing the gravimetric ocean-tide loading computed from the selected models with the residuals from a set of 59 tidal gravity stations shows that there is an improvement of the T/P derived models with respect to the Schwiderski model, especially in M2. However, this improvement is not as significant as the result of the comparison with the pelagic data. The procedure developed for the comparison of T/P derived models with SCHW80 is presented. The results provide not only information and improvement with regard to SCHW80, but also information about the properties of the new models. It is intended to continue this work applying the very recent models to see how they perform compared to this study.With this study we provide boundary conditions for the improvement of new ocean-tide models in order to benefit from the gravity measurements now possible regarding the evaluation of Earth structures and dynamic processes.     

Influence of the modified global ocean tide model with local tides of East and South China Seas on load gravity in China and its neighbor area

Introduction With the development of science and technology, the accuracy of gravity measurement is im-proved. The gravity observation with FG5 gravimeter has reached accuracy of μ magnitude. And the high accurate superconducting gravimeter can detect the tiny signal of 10?2 μ magnitude in frequency domain. With the high-accuracy gravity observation on Earth′s surface, the Earth′s tidal parameters can be determined precisely. And the observations can also be used to invert the struc-ture…     

Ocean tides from satellite altimetry and GRACE

Satellite altimetry and GRACE observations carry both the signature of ocean tides and have in general complementary potential to resolve tidal constituents. It is therefore straightforward to perform a combined estimation of a global ocean tide model based on these two data sources. The present paper develops and applies a three step procedure for generating such a combined ocean tide model. First, the processing of multi-mission altimetry data is described along with the harmonic analysis applied to derive initially a pure empirical ocean tide model. Then the capability of GRACE to sense particular tidal constituents is elaborated and an approach to estimate tidal constituents from GRACE is outlined. In a third step a combination strategy with optimal stochastic data treatment is developed and applied to the altimetry-only tide model EOT08a and four years of GRACE observations, leading to the combined model EOT08ag. The differential contributions of GRACE to EOT08ag remain small and are mainly concentrated to the Arctic Ocean, an area with little or poor altimetry data. In comparison with other tide models, EOT08ag is validated by K-band range residuals, the impact on gravity field modelling and on precise orbit determination and by variance reduction of crossover differences. None of these comparison exhibits a significant improvement over the altimetry-only tide model except for a few areas above 60°N. Overall the improvements of the combination remain small and appear to stay below the current GRACE baseline accuracy.     

Feasibility study on application of satellite formations for eliminating the influence from aliasing error of ocean tide model

Currently,aliasing error of temporal signal model becomes the main factor constraining the accuracy of temporal gravity field.In provision of three types of satellite formations,i.e.,GRACE-type,Pendulum-type and n-s-Cartwheel-type,which are suitable for gravity mission and composed of observation in different directions,here we design two cases and conduct a simulation experiment on the feasibility to apply satellite formations for eliminating the influence from the aliasing error of ocean tide models.The result of our experiment shows that,when the aliasing error is disregarded,n-s-Cartwheel formation can provide the best conditions for gravity field determination,which,compared with GRACE-type,can improve the accuracy by 43%.When aliasing error of the ocean tide model acts as the main source of error,the satellite formation applied in dynamic method for gravity field inversion cannot eliminate aliasing or improve the accuracy of gravity field.And due to its higher sensitivity to the high-degree variation of gravity field,the Cartwheel-type formation,which includes the radial observation,can result in the gravity field containing more high-frequency signals for the ocean tide model error,and lead to a dramatically larger error.     

联合多代卫星测高和多源重力数据的局部大地水准面精化方法

本文研究了基于泊松小波径向基函数融合多代卫星测高及多源重力数据精化大地水准面模型的方法.分别以沿轨垂线偏差和大地水准面高高差作为卫星测高观测量,研究了使用不同类型测高数据对于大地水准面建模精度的影响.针对全球潮汐模型在浅水区域及部分开阔海域精度较低的问题,引入局部潮汐模型研究了不同潮汐模型对于大地水准面的影响.数值分析表明:相比于使用沿轨垂线偏差作为测高观测量,基于沿轨大地水准面高高差解算得到的大地水准面模型的精度更高,特别是在海域区域,其精度提高了2.3cm.由于使用沿轨大地水准面高高差作为测高观测量削弱了潮汐模型长波误差的影响,采用不同潮汐模型对大地水准面解算的影响较小.总体而言,船载重力及测高观测数据在海洋重力场的确定中呈现互补性关系,联合两类重力场观测量可以提高局部重力场的建模精度.     

武汉台重力潮汐长期观测结果

采用武汉台超导重力仪(SG C032)14年多的长期连续观测资料,研究了固体地球对二阶和三阶引潮力的响应特征,精密测定了重力潮汐参数,系统研究了最新的固体潮模型和海潮模型在中国大陆的有效性.采用最新的8个全球海潮模型计算了海潮负荷效应,从武汉台SG C032的观测中成功分离出63个2阶潮汐波群和15个3阶潮汐波群信号,3阶潮波涵盖了周日、半日和1/3日三个频段.重力潮汐观测的精度非常高,标准偏差达到1.116 nm·s^-2,系统反映了非流体静力平衡、非弹性地球对2阶和3阶引潮力的响应特征.结果表明,现有的武汉国际重力潮汐基准在半日频段非常精确,但在周日频段存在比较明显的偏差,需要进一步精化.对于中国大陆的大地测量观测,固体潮可以采用Dehant等考虑地球内部介质非弹性和非流体静力平衡建立的固体潮理论模型或Xu 等基于全球SG观测建立的重力潮汐全球实验模型作为参考和改正模型,海潮负荷效应应该采用Nao99作为改正模型.     

Accuracy assessment of ocean tide loading computations for precise geodetic observations

The increasing resolution of ground based gravity measurements (e.g. by superconducting gravimeters) as well as satellite based gravity field studies allows to study very small signals, globally as well as local. On the other hand, this requires the correction of such signals to uncover others. To study the Earth’s deep interior and the on-going dynamic processes requires the correction of disturbing signals, and one of these signals is related to ocean tidal loading. Although new ocean tide models are being derived from current satellite missions, there are still uncertainties.In this paper we present an intercomparison ocean tide models to test their fit to world-wide observations. Therefore, three TOPEX/POSEIDON (T/P) satellite derived models (CSR3.0, FES95.2 and TPXO.2) beside the classical SCHW80 model were selected for an accuracy assessment study. The selected models have been subjected to an intercomparison test, tide gauge validation test and comparison to 59 tidal gravity stations.The intercomparison test shows a good agreement between the T/P-based models for the open ocean and remarkable disagreement between the selected models in the coastal regions indicating that such models are still problematic in these regions. The tide gauge validation shows that the T/P derived models fit tide gauges better than SCHW80, with a better fit for the semidiurnal constituents than for the diurnal constituents. Comparing the gravimetric ocean-tide loading computed from the selected models with the residuals from a set of 59 tidal gravity stations shows that there is an improvement of the T/P derived models with respect to the Schwiderski model, especially in M2. However, this improvement is not as significant as the result of the comparison with the pelagic data. The procedure developed for the comparison of T/P derived models with SCHW80 is presented. The results provide not only information and improvement with regard to SCHW80, but also information about the properties of the new models. It is intended to continue this work applying the very recent models to see how they perform compared to this study.With this study we provide boundary conditions for the improvement of new ocean-tide models in order to benefit from the gravity measurements now possible regarding the evaluation of Earth structures and dynamic processes.