Understanding something that is remotely sensible, scaling active chlorophyll fluorescence from leaves to canopies at ranges of ~50 metres
Remote sensing of photosynthetic activities in leaves from inaccessible plants and within canopies has long been a key element in the 'Holy Grail' of plant physiological ecology. The potential application of telescope/laser-based remote sensing systems for chlorophyll fluorescence was first explored by Chappelle et al. (1984) who searched for species-specific chlorophyll fluorescence spectra. On-the-leaf pulse amplitude modulated (PAM) systems have been available for some time (Schreiber et al. 1986). These have been modified for near remote sensing (FiPAM, Flexas et al. 2000, 2002; Laser-PAM, Ounis et al. 2001) and have been particularly successful in the diagnosis of water stress. Although long-term monitoring of individual leaves in leaf clips is now possible with MONIPAM (Porcar-Castell et al. 2008), we still await devices for non-intrusive, in-situ observations of active chlorophyll fluorescence in many patches of a canopy at distances beyond a few meters. On the other hand 'passive' remote sensing of suninduced chlorophyll fluorescence can now be monitored from space (Frankenberg et al. 2011) that, with improvements in spatial resolution, offers exciting prospects for bringing further molecular mechanistic insights to measurements of ecosystem scale processes.