Project PRECIPITABLE WATER is a joint effort of one Greek and one Chinese Institute and one Greek Company aiming at providing accurate PW spatial distribution maps over Greece, capable of being used in regional and local studies.

Water vapor plays a key role in the earth-atmosphere system. Through its distribution and variation, it provides an important link connecting the various components of the hydrological cycle and modulates the earth's energy budget. An important water vapor parameter currently being obtained from satellite and radiosonde measurements is precipitable water (PW).

Precipitable Water is the total atmospheric water vapor contained in a vertical column of unit cross-sectional area extending from the surface to the top of the atmosphere.
Due to the lack of radiosondes at the spatial and temporal resolution that is appropriate for climatic studies, the estimation of PW needs to be performed from satellite measurements, which provides spatially and temporally continuous data. PW estimation from satellite data is performed through the atmospheric attenuation caused by the amount of water vapor in a vertical column in the thermal infrared region.