The commissioning phase and the calibration/validation activities

Envisat is designed to provide measurements of the atmosphere, ocean, land and ice over a five-year period. After the launch, a six-month Commissionin g Phase is foreseen. This first period is dedicated to instrument switch-on and in-flight calibration and to the first validation of the Envisat produ cts. There is general consensus that the calibration and especially the val idation activities represent a long-term effort, which extends far beyond t he duration of the Commissioning Phase and gradually shifts into algorithm improvement. The Commissioning Phase is the period that ESA has available t o check out and verify the complete data chain (instruments and ground-proc essing algorithms) before releasing the Envisat data to the wide user commu nity. At the end of the Commissioning Phase, the data quality is guaranteed by the Agency. In addition to ESA and its industrial partners in the Envisat Consortium, m any other companies and research institutes are contributing to the calibra tion and validation programme. A major contribution is being made by the Pr incipal Investigators of approved proposals submitted to ESA in response to the worldwide 'Announcement of Opportunity for the Exploitation of Envisat Data Products' issued in 1998. Teams have been formed in which the various participants are working side-by-side to achieve the ambitious calibration and validation programme objectives.