Remote sensing in hydrological sciences

Space age, and with it the era of earth observation, is generally considered to have begun more than 50 years ago with the launch of Sputnik-1 on 4 October 1957 (Kramer, 2002). Sputnik’s beeping radio signals did not only serve to demonstrate the technological capabilities of the Soviet Union, they were also used to gather information about the electron density of the ionosphere. In legacy of Sputnik, most of the Earth observation satellite missions that were to follow served multiple purposes. Unfortunately, up to this day, political and technological motives may be more important drivers for the design of remote sensing missions than the requirements and needs of the geoscientific community. It is probably for this reason that remote sensing continues to be underutilized in many Earth science applications. Hydrology is not an exception. This mismatch of technological capabilities and use of remotely sensed data has increasingly been recognised in the 1990s. Consequently, an increasing number of space-related programmes with the goal to bridge the gap between remote sensing data providers and users have been initiated. One example is GMES1 (Global Monitoring for Environment and Security), a joint programme of the European Commission and the European Space Agency (ESA) designed to establish a European capacity for the provision and use of operational information for monitoring and management of the environment and for civil security. Another example is GEOSS2 – the Global Earth Observation System of Systems – aiming at creating a comprehensive, coordinated and sustained ob-