SPOT-4 VEGETATION INSTRUMENT - VEGETATION MONITORING ON A GLOBAL-SCALE

Vegetation plays a major role in global climatic change. It is a major contributor to the hydrological cycle and carbon exchanges between the Earth's surface and the atmosphere. A new space-based system dedicated to vegetation would be a boom to climatic and environmental studies. The additional possibilities of evaluating agricultural, pasture and forest production would be major contributions to improved natural resources management and a special benefit to agriculture and the general economy in developing countries. A space mission for monitoring terrestrial vegetation at global and local. levels is proposed for inclusion in the Spot-4 payload, scheduled for launch around 1997. The ''vegetation'' concept is more than just an on-board package; it is a complete system with its own space and ground segments. The vegetation instrument (VI) on-board package is designed as an add-on payload that is quite independent of the host satellite. In addition to the basic imaging instrument, the add-on payload includes a solid-state recorder, an image telemetry subsystem and a computer to manage the work plan, To accommodate future long-term missions and achieve a lifetime in excess of 5 years, no moving parts are included in either the imaging instrument proper or the recorder subsystem. The innovative, large field-of-view(101 degrees) imaging instrument features telecentric lenses and focal-plane illumination compensation. Despite the large FOV, pixel size varies extremely little across the swath. Overall, the instrument offers an excellent revisit capability at the highest resolution. The inclusion of the VI package alongside Spot-4's prime payload of two HRVIR (high resolution Visible and i.r.) imaging instruments will open the way to studies requiring both high accuracy satellite imagery and short revisit intervals. The combination of HRVIR and VI imagery will pave the way to powerful new multi-scale interpretation models, particularly as the instruments will share the same spectral bands, have a common reference frame and be synchronized in time.