GEOGRAPHICAL, BIOLOGICAL AND REMOTE-SENSING ASPECTS OF THE HYDROLOGICATMOSPHERIC PILOT EXPERIMENT IN THE SAHEL (HAPEX-SAHEL)

HAPEX Sahel (Hydrologic Atmospheric Pilot Experiment in the Sahel) was an international program focused on the soil-plant-atmosphere energy, water and carbon balance in the west African Sahel. It was intended t o improve our understanding of the interaction between the Sahel and t he general atmospheric circulation, both at present and in the future, providing a base line for studies of climate change. It was carried o ut in a 1 degrees X 1 degrees area of west Niger over a 3-4 year perio d with an 8-week intensive observation period from August to October 1 992. HAPEX-Sahel was funded by a wide range of agencies in seven parti cipating countries. Over 170 scientists visited and worked in the fiel d. An interdisciplinary approach was adopted with contributed studies in hydrology and soil moisture surface fluxes and vegetation, remote s ensing science, and meteorology and mesoscale modeling Detailed field measurements were concentrated at 3 ''supersites'' and 3 ancillary sit es. Four aircraft were used for remote sensing and flux measurement. O bservations from space were acquired from nine sensors on seven differ ent satellite platforms. Conditions in 1992 turned out to be average f ar the last decade with good gradients of precipitation and a variety of vegetation productivities between the study sites. An information s ystem has been established to provide a data base to disseminate the m easurements. An active program of meetings, workshops, and interdiscip linary studies is now in progress.