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Although the noticeable progress achieved by ground-based lidars, using lidars as an operational spaceborne instruments still poses issues to be solved. A key issue is the long-term stability of the instrument over the mission lifetime, as a whole as well as at the level of each subsystem; another important issue is related to the processes of calibration in pre-launch and operational phases. Ground truth validation is also a critical process. This paper covers some of these aspects and focus on the instrument calibration and validation with a view of ensuring accurate instrument data during the whole instrument lifetime. The proposed concept is based on a combined space-ground lidar multi-calibration experiment using five lidars. The lidar instrument will be engineered for use in two versions: for ground and, qualified, for space. The lidar will need to operate at two wavelengths (first and second Nd-YAG harmonics), with polarization capability. Five similar instruments need to be employed. A spaceborne lidar will operate together with three ground-based lidar located in the tropics, sub-tropics and midlatitudes. A fifth lidar will operate for four months each year at each ground site. Such sites will coincide with the satellite overpasses. The measurement schedule will consists of series of simultaneous ground and satellite measurements at each site satellite overpass. Additional measurements from other instruments and local sites capabilities could be added.
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