SATELLITE REMOTE SENSING OF THE TERRESTRIAL WATER CYCLE

Land surface hydrology is a collection of complex processes. Precipitation is partitioned into infiltration and runoff depending on antecedent soil moisture conditions, the properties of the soil and its abilities to conduct water away from the surface, the slope of the land surface and the amount of atmospheric demand for evapotranspiration. The observed solar radiation and the computed downward longwave radiation drive the energy budget and evapotranspiration. However in reality the spatial variability both the land surface properties (soil and vegetation) as well as the meteorological inputs (precipitation and radiation) are never accurately known. This incurs errors in the computer simulations of water and energy budgets. Satellite remote sensing has a broad spatial view of the land surface and is able to average the heterogeneities and provide data for use in hydrology such as soil moisture, surface temperature and vegetation density. Land surface hydrology embeds in itself spatial and temporal heterogeneities making observation and modeling activities very difficult. In the past few decades satellite remote sensing has provided a simple way to observe the land surface hydrological cycle from space and provide "snapshot" observations. In my presentation I shall review various methods to observe the land surface - using microwave observations for soil moisture and precipitation; visible/near infrared for vegetation, gravity for groundwater and thermal observations for surface temperature. These are integrated to provide an understanding of the water cycle and above all help in understanding the available water resources in parts of the world where observations are lacking and economy is tied closely to water.