What is Surface Water?
Water occupies about 71% of the Earth's surface, of which only 2.5% is freshwater in the form of lakes, reservoirs, and rivers. Hydrologic observations of rivers, lakes, and reservoirs are extremely important given humanity's reliance on freshwater for survival, and are of major importance to understand the global water cycle. Existing stream gauge systems are limited in many areas, especially remote and politically unstable environments where people are often most vulnerable to floods and droughts. Remote sensing techniques, such as altimetry and interferometry, enable measurements of surface water to understand the global water cycle on land, as well as provide a global inventory of water resources.