The Role of the Atmosphere for Satellite Gravity Field Missions
The Role of the Atmosphere for Satellite Gravity Field Missions
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DOI：
10.1007/978-3-540-85426-5_13
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
T. Gruber;T. Peters;Lieselotte Zenner
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文献类型：
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作者：
T. Gruber;T. Peters;Lieselotte Zenner
传统上，在卫星导出的静态全球重力场模型中，地球的总质量被认为是固体地球质量和陆地（水文学）、海洋、冰（大陆冰和海冰）和大气中的水团的总和。总质量反映在GM值（重力常数乘以地球质量）中，该值通常是大地测量参考系的一个参数。由于整个系统地球是质量守恒的，因此GM在时间上应该是恒定的。GM的任何时间依赖性只能由GM的错误估计（或球谐级数的相应零度系数）引起。对于时变重力场的分析，情况更为复杂，因为质量在不同的时间和空间尺度上波动，并在地球系统的组成部分之间交换。忽略固体地球内部的质量变化（例如地震、地幔对流等）水循环是质量变化的主要来源，其中大气层起着最突出的作用（通过压力场变化、通过强迫海洋环流、通过降水和蒸发）。为了在重力场分析中考虑到这种时间变化，卫星使命及其传感器的采样模式也起着至关重要的作用。这意味着，在重力场恢复期间，相对于平均值的质量变化的已知部分必须被独立地建模和校正，以避免时间信号混叠到结果场中。与此相反，未知的时间变量的质量变化必须估计。本文介绍了利用卫星资料确定重力场的大气质量变化问题。在本文的主要部分，提供了对大气总质量及其随时间变化的估计，以及对垂直结构和大气场潜在误差的影响的分析。结果表明，在过去的20年里，大气总质量略有增加，这可能是全球变暖的一个暗示。误差分析的结果还表明，大气的垂直结构以及大气场的潜在误差是GRACE数据分析达到最终性能的关键
Traditionally, in satellite derived static global gravity field models, the total mass of the Earth is considered to be the sum of the solid Earth mass and the water masses in land (hydrology), oceans, ice (continental ice and sea ice) and atmosphere. The total mass is reflected in the GM value (gravity constant times Earth mass), which usually is a parameter of geodetic reference systems. As the whole system Earth is mass conserving in principle GM should be constant over time. Any time dependency of GM could only be caused by wrong estimates for GM (or the corresponding zero degree coefficient of the spherical harmonic series)For analysis of the time variable gravity field the situation is more complex, because masses are fluctuating at various temporal and spatial scales and are exchanged between components of the Earth system. Disregarding mass variations inside the solid Earth (e.g. by earthquakes, mantle convection, etc.) the water cycle represents the major source of mass variations, of which the atmosphere plays the most prominent role (by pressure field variations, by forcing ocean circulation, by precipitation and evaporation). In order to take into account such temporal variations for gravity field analysis the sampling pattern of the satellite mission and its sensors in addition play a crucial role. This means that during gravity field recovery the known part of mass variations with respect to the mean value have to be modelled independently and corrected for in order to avoid aliasing of temporal signals into the resulting fields. In contrast, unknown time variable mass variations have to be estimated. Both approaches are applied nowadays in the GRACE data analysis simultaneouslyThe paper introduces the problem of atmospheric mass variability for gravity field determination with satellite data. In the main part of the paper estimates for the total mass of the atmosphere and its variability in time as well as an analysis of the impact of the vertical structure and of potential errors in the atmospheric fields are provided. Results indicate, that the total atmospheric mass during the last 20 years slightly increased, what could be a hint to global warming. Results of error analysis also show, that for reaching the ultimate performance with GRACE data analysis, the vertical structure of the atmosphere as well as potential errors in the atmospheric fields are crucial