Water Cycle

Water Cycle

Although Earth's water cycle is dominated by the ocean, understanding its land-based component is vitally important. These waters directly affect human societies through food consumption, agriculture, and industrial activities. Conversely, they are impacted by human activities such as groundwater pumping and storage within reservoirs.

Continental waters need to be monitored, especially in association with flood or drought events. This is a challenge given that there are millions of water bodies around the globe. This situation is exacerbated by the dwindling number of in-situ gauges, along with a decrease in access to these data across the world. For this reason, satellite measurements provide a valuable source of information. For decades, satellite radar altimeters have proven their ability to observe water level variations of lakes, rivers, and floodplains.

In some regions – particularly remote lakes – altimetry data have been used in combination with, or substituted for, in situ data. Such remote water bodies can present a unique opportunity to study environmental trends. For example, with mean altitudes of 4,500 m (14,800 ft), some lakes in Tibet have been largely immune to rare human interference. Thus, variations in their water levels can be largely attributed to natural causes such as monsoons, El Niño events, or climate change.

Radar altimetry has some limitations for monitoring land hydrology because of relatively low spatial and temporal resolutions. Nevertheless, improvements in nadir altimetry sensor performance – coupled with the long-term stability, reliability, and accuracy of the measurements – have supported a broad scope of hydrological science applications. The promise demonstrated by altimetry contributed to the need for the Surface Water and Ocean Topography (SWOT) mission. With new interferometric technology to augment its nadir-looking altimeter, SWOT will provide a global inventory of all terrestrial water bodies (lakes, reservoirs, wetlands) whose surface area exceeds 250 m by 250 m (820 ft by 820 ft) and rivers whose widths exceed 100 m (330 ft).

Some of the applications that benefit from satellite altimetry data:

Click here to access Global Reservoirs/Lakes (G-REALM) data from the U.S. Department of Agriculture's Foreign Agricultural Service in cooperation with NASA and the University of Maryland. G-REALM utilizes radar altimeter data over inland water bodies to produce surface elevation products in an operational manner.

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