EAPSI: The Effect of Seasonal Hydrological Loading on Vertical GPS Time Series

最近，连续GPS时间序列使得研究各种地面变形源成为可能。弹性载荷的季节性变化是非构造形变源，对GPS垂直时间序列尤其重要。例如，当水库每年在空和满之间循环时，就会发生这种情况。如果能够模拟和理解水负荷对GPS时间序列的贡献，就有可能仅从GPS测量就对地表水储存作出及时、准确和局部有用的估计。为此，本研究旨在确定缅甸连续GPS测量中地表水负荷的组成部分。已知该数据集中的垂直GPS信号包含世界上一些最大的年度振荡，可能是由于亚洲季风。然而，地表水储量的变化在多大程度上可以解释GPS振荡仍然未知。这项工作将由新加坡地球天文台GPS大地测量学的首席研究员Emma Hill教授完成。这项研究还将受益于与希尔博士研究小组的许多研究人员的合作，他们正在对缅甸大地测量数据进行大规模研究。本项目将通过加载模型将GPS时间序列分解为弹性载荷和其他来源的分量。GRACE卫星任务的重力测量将用于约束地表水负荷。然后，使用参考地球结构为每个GPS站建立弹性变形模型。本文认为，GPS垂直时间序列的季节变化主要是由水文负荷引起的，其振幅可达5 cm/年。本工程将产生季节性荷载对变形场影响的具体模型。GPS和GRACE时间序列之间的相关性还应提供缅甸每个连续GPS站的当地具体储水量估计。该奖项由美国国家科学基金会和新加坡国家研究基金会共同资助，隶属于东亚和太平洋暑期研究所项目，支持一名美国研究生进行暑期研究。

Continuous GPS time series have recently enabled the study of a variety of ground deformation sources. One non-tectonic deformation source, particularly important for vertical GPS time series, is seasonal changes in elastic loading. For example, this can occur when water reservoirs annually cycle between empty and full. If the contributions of water loading to the GPS time series can be modeled and understood, it is possible to make timely, accurate, and locally useful estimates of surface water storage simply from GPS measurements. To that end, this study aims to identify the components of surface water loads in the continuous GPS measurements from Myanmar. The vertical GPS signals in this dataset are known to contain some of the largest annual oscillations in the world, likely due to the Asian Monsoon. However, the degree to which changes in surface water storage can explain the GPS oscillations remains unknown. This work will be completed with Professor Emma Hill, a leading researcher in GPS geodesy at the Earth Observatory of Singapore. This research will also benefit from collaboration with the many researchers in Dr. Hill's research group who are working on a large-scale study of geodetic data from Myanmar. This project will decompose the GPS time series into components from elastic loading and other sources through a loading model. Gravity measurements from the GRACE satellite mission will be used to constrain surface water loads. The elastic deformation will then be modeled for each GPS station using a reference earth structure. It is hypothesized that much of the seasonal variation in the vertical GPS time series, which can reach 5 cm/year in amplitude, is due to hydrologic loading. This project will produce a specific model of the seasonal loading effects on the deformation field. The correlations between the GPS and GRACE time series should also provide locally specific estimates of water storage levels at each continuous GPS station in Myanmar. This award, under the East Asia and Pacific Summer Institutes program, supports summer research by a U.S. graduate student and is jointly funded by NSF and the National Research Foundation of Singapore.