Multi-satellite determination of global and regional geoid and sea level variations

加拿大和美国最近决定分别在2010年和2018年之前建立基于大地水准面的垂直基准。大地水准面是理想海洋静止时的等势面，因此可作为高程的参考面（基准面）。因此，它的精确确定和完善是大地测量学的一个持续研究课题，因为它在制图、导航、海洋学、空间数据的地理参照和地质灾害监测以及研究地球内部的物理、海平面变化、海洋环流、冰的运动和气候变化方面都是不可或缺的。垂直基准面要求精确了解大地水准面、地壳和平均海面及其随时间的变化。只有将空间观测与其他陆地/海洋信息结合起来才能获得这类知识。最重要的是专门用于（a）确定地球重力场的卫星（CHAMP、GRACE和即将发射的GOCE）和（B）监测地球海洋和冰盖的卫星（各种激光测高卫星、即将发射的CryoSat-2等）提供的数据。目前和今后这类数据的丰富为推进大地测量研究及其应用提供了巨大的机会。因此，拟议研究的主要目标和预期成果是，通过制定联合利用来自各种地球观测卫星的数据进行海洋环流监测和重力场测定的方法，提高加拿大对地球系统进行遥感的能力。第一个主要目标是确定大陆和全球范围内精确的高分辨率大地水准面及其时间和误差特征。对于第二个主要目标，将合并来自当前和未来飞行任务的多卫星海洋和冰测高数据，以计算高分辨率的平均海面和冰盖对全球平均海平面上升的影响。将这两个目标结合起来，将有助于成功建立以大地水准面为基础的垂直基准。这项研究的其他重要成果将是使用GRACE和其他数据进行水文研究和冰后期回弹测定在加拿大。

Canada and the US have recently decided to establish geoid-based vertical datums by 2010 and 2018, respectively. The geoid is the equipotential surface of the idealized oceans at rest and thus serves as the reference surface (datum) for elevations. Therefore, its precise determination and refinement is an on-going subject of research in geodesy, as it is indispensable in mapping, navigation, oceanography, geo-referencing of spatial data and geo-hazards monitoring, and for studying the physics of the Earth's interior, sea level changes, ocean circulation, ice motion, and climate changes. A vertical datum requires precise knowledge of the geoid, the Earth's crust and the mean sea surface, together with their variations in time. Such knowledge can only be obtained by combining space-borne observations with other terrestrial/oceanic information. Of primary importance are the data provided by satellites dedicated (a) to the determination of the Earth's gravity field (CHAMP, GRACE, and the soon-to-be-launched GOCE) and (b) to the monitoring of the Earth's oceans and ice caps (various laser altimetry satellites, the soon-to-be-launched CryoSat-2, etc.). The abundance of such data presently and in the future provides tremendous opportunities for advancing geodetic research and its applications. Therefore, the main goal, and expected outcome, of the proposed research is to enhance Canada's capacity in remote sensing of the Earth system by developing methods for the joint exploitation of data from various Earth-observing satellites for ocean circulation monitoring and gravity field determination. The first major objective is to determine an accurate high-resolution geoid at continental and global scales, and its temporal and error characteristics. For the second major objective, multi-satellite sea and ice altimetry data from current and future missions will be merged to compute a high-resolution mean sea surface and the contribution of ice sheets to the mean global rise in sea level. Combining both objectives will lead to the successful establishment of a geoid-based vertical datum. Other important outcomes of this research will be the use of GRACE and other data for hydrology studies and for postglacial rebound determination in Canada.