Hall, F. G., K. Bergen, J. B. Blair, R. Dubayah, R. Houghton, G. Hurtt, J. Kellndorfer, M. Lefsky, J. Ranson, S. Saatchi, H. H. Shugart, and D. Wickland. 2011. Characterizing 3D vegetation structure from space: Mission requirements. Remote Sensing of Environment 115:2753-2775.