Lake water levels from 1992 to present derived from satellite observations

This dataset provides lake water levels for 251 selected lakes on four continents derived from satellite radar altimetry. Lake water level information is traditionally obtained via ground-based observation systems and networks that suffer from well-known inherent problems: high cost, sparse coverage (often limited to political local/national instead of geographical/hydrological boundaries), slow dissemination of data, heterogeneous temporal coverage, destruction of the stations during floods, absence of stations in remote areas, absence of management strategy, etc.
Although originally conceived to study open ocean processes, the radar altimeter satellites have nevertheless acquired numerous useful measurements over lakes. With this technique, the Lake Water Level is defined as the height, in meters above the geoid (the shape that the surface would take under the influence of the gravity and rotation of Earth) of the reflecting surface. It is observed by space radar altimeters that measure the time it takes for radar pulses to reach the ground targets, directly below the spacecraft (nadir position), and return. Hence, only lakes located along the satellite's ground tracks can be monitored, with a quality of measurement that not only depends of the size of the lake, but also on the reflecting targets in its surroundings such as topography or vegetation. For each of the key lakes monitored in the C3S Lakes production system, the Level-3 Water Level is provided in separate file along with the corresponding uncertainty.
This altimetric technique, that can complement ground-based observations systems, potentially provides a major improvement in the field of continental hydrology, due to the global coverage (however limited to Earth’s portion at nadir of the orbital ground tracks), regular temporal sampling and short delivery delays.
The Lake Water Level is a recognized Essential Climate Variable (ECV) by the Global Climate Observing System (GCOS). Lake Water Level products are generated by CLS on behalf of the Copernicus Climate Change Services, the Earth Observation Programme of the European Commission.

本数据集提供了四大洲251个选定湖泊的水位数据，这些数据源自卫星雷达高度计。传统上，湖泊水位信息通过地面观测系统和网络获取，然而这些系统普遍存在诸多固有缺陷：成本高昂、覆盖范围稀疏（通常局限于政治区域而非地理或水文边界）、数据传播缓慢、时间覆盖不均、观测站可能在洪水中被摧毁、偏远地区缺乏观测站、缺乏管理策略等。尽管最初是为了研究开放海洋过程而设计，雷达高度计卫星仍在此类湖泊上获取了大量有用测量数据。通过这一技术，湖泊水位被定义为相对于地球椭球面（在地球重力及自转影响下地表所呈现的形状）的高度，单位为米。它通过太空雷达高度计进行观测，该高度计测量雷达脉冲从卫星下方（子午点位置）到达地面目标并返回所需的时间。因此，只有位于卫星地面轨迹上的湖泊可以被监测，其测量质量不仅取决于湖泊的大小，还取决于其周围反射目标，如地形或植被。在C3S湖泊生产系统中监测的关键湖泊，均提供了单独的第三级水位文件及其相应的测量不确定性。这种高度测量技术，可作为地面观测系统的补充，由于具有全球覆盖范围（尽管限于地球轨道地面轨迹的子午点部分）、规律的时间采样和短时间交付延迟，有望在大陆水文学领域带来重大改进。湖泊水位被全球气候观测系统（GCOS）认定为基本气候变量（ECV）。湖泊水位产品由CLS代表Copernicus气候变化服务（欧洲委员会的地球观测计划）生成。