Monitoring the temporal changes in the gravity field, oceans, land water and ice masses in North America by means of integrated satellite data

科学研究表明，联合国政府间气候变化专门委员会(IPCC)关于地球气候的第五份评估报告断言，我们正在看到气候系统发生数百年有记录以来前所未有的变化。冰川和冰盖正在减少，海平面正在上升，水循环正在改变，仅举几例。预计会出现更极端的天气事件、严重的沿海洪水，甚至水资源枯竭，这些气候变化将持续几个世纪。来自地球观测卫星的数据是在全球范围内监测、模拟和预测这种变化及其将造成的自然灾害的宝贵工具。拟议的研究计划将通过对其中一些影响进行量化和建模，重点放在加拿大和北美，为这一长期目标做出贡献。它将允许对上述气候变化的影响进行适当评估，从而使政府能够在知情的情况下做出缓解这些影响的决定。特别是，这项研究将侧重于确定大地水准面(地球重力场的等势面与理想的静止海洋重合)、海平面、陆地水和冰块的时间变化。这主要是通过使用GRACE卫星任务的数据来实现的，GRACE卫星探测到与地球流体和固体中的地球物理过程有关的质量重新分配所引起的综合重力变化。其中包括水文、大气和海洋质量变异性、由于冰川均衡调整(GIA)造成的粘弹性地球变形、以及主要由与气候有关的冰块变化引起的弹性变形。所有这些信号的识别、分离和解释是一项非常艰巨的任务，也将是这项研究计划的一个关键方面。 第一个主要目标是确定地球系统中总的时间质量再分配，特别是它对北美大地水准面的影响。由于大地水准面被用作陆地和海洋高度/深度(垂直基准面)的参考面，因此，对大地水准面的监测对于了解海洋、冰和陆地水水平的变化至关重要，因此与本研究的其他三个目标的研究密切相关。此外，这将支持加拿大和美国政府最近决定通过使用基于大地水准面的垂直基准面来更新其高度系统，并为其提供信息。第二个主要目标是研究海洋的平均海面(MSS)如何随时间变化，这是了解洪水和风暴潮等沿海灾害的重要因素。雷达和激光卫星测高任务的数据将被合并，以计算变化的MSS，并更好地了解海洋环流。第三个主要目标是将GRACE数据与水文学模型结合使用，用于区域和全球水文学研究，并用于确定北美地区的GIA。从土壤湿度和海洋盐度(SMOS)以及GRACE卫星数据和水文学模型获得的知识将加强对洪水(甚至干旱和热浪)等危险事件以及北美陆地水等宝贵自然资源变化的预测和可能的预测。第四个主要目标是利用GRACE以及诸如NASA的ICESat和ESA的CryoSat任务等冰测高任务的卫星数据来确定北半球的冰块质量损失及其对海平面上升的贡献。还将研究海冰消退，因为如果持续下去，将产生巨大的经济影响，因为它将使加拿大北极地区的航行和资源勘探成为可能。

Scientific research has shown, and the fifth assessment report on the Earth's climate of the UN’s Intergovernmental Panel on Climate Change (IPCC) has asserted, that we are seeing changes in the climate system unprecedented in records spanning hundreds of years. The glaciers and ice caps are diminishing, sea level is rising and the water cycle is changing, just to name a few. More extreme weather events, severe coastal inundation and even depletion of water resources are forecasted, as is the persistence of these climate changes for centuries. Data from Earth-observing satellites are an invaluable tool for monitoring, modeling and predicting such changes, and the natural hazards they will cause, on a global scale. The proposed research program will contribute to this long-term goal by quantifying and modeling some of these effects, with focus in Canada and North America. It will allow proper assessment of the aforementioned effects of climate change, and thus will enable informed government decisions for their mitigation. In particular, this research will focus on the determination of temporal changes in the geoid (the equipotential surface of the Earth’s gravity field coinciding with the idealized oceans at rest), sea level, land water and ice masses. This has become possible primarily through the use of data from the GRACE satellite mission, which senses the integrated gravity change induced by the redistribution of masses related to geophysical processes in the fluid and solid Earth. These include hydrological, atmospheric and oceanic mass variability, viscoelastic Earth deformation due to glacial isostatic adjustment (GIA), and elastic deformation due primarily to climate-related ice mass changes. The identification, separation and interpretation of all these signals is a very daunting task and will be a key aspect of this research program. The first major objective is to determine the total temporal mass redistribution in the Earth System and in particular its effect on the geoid in North America. Since the geoid surface is used as the reference surface for land and ocean heights/depths (vertical datum), its monitoring is essential for understanding changes in the level of the oceans, ice and land water, and is therefore intimately related to the study of the other three objectives of this research. In addition, this will support and inform the Canadian and US governments’ recent decision to modernize their height systems by use of a geoid-based vertical datum. The second major objective is to study how the mean sea surface (MSS) of the oceans changes over time, an important factor for understanding coastal hazards such as flooding and storm surges. Data from radar and laser satellite altimetry missions will be merged to compute the changing MSS, and to better understand ocean circulation. The third major objective is the use of GRACE data together with hydrology models for regional and global hydrology studies and for GIA determination in North America. The knowledge gained from the Soil Moisture and Ocean Salinity (SMOS) and GRACE satellite data and hydrology models will strengthen forecasting and possibly predicting hazardous events such as floods (and even droughts and heat waves) and changes in precious natural resources such as land water over North America. The fourth major objective is to use satellite data from GRACE as well as from ice altimetry missions, such as NASA’s ICESat and ESA’s CryoSat missions, to determine the ice mass loss in the northern hemisphere and its contribution to sea level rise. Retreating sea ice will also be studied because, if sustained, it will have a tremendous economic impact since it will make navigation and resource exploration possible in the Arctic regions of Canada.