In this paper, quantitative studies of water vapor Meteosat imagery, based on an accurate transmittance and radiance model are described. Using conventional radiosonde data, a linear relation between cloudless radiances and digital counts is obtained. It is shown that the distribution with altitude of the peak contribution to the radiances varies from about the 550 mb level to about the 450 mb level for pictures acquired in July over the western part of Europe and Mediterranean Sea. The influence of the temperature profile on the altitude of the maximum contribution layer is pointed out. A relation between the radiative field and the water vapor mass above the 600 mb level is found.