8 million phenological and sky images from 29 ecosystems from the Arctic to the tropics: the Phenological Eyes Network

We report long-term continuous phenologicaland sky images taken by time-lapse cameras through the PhenologicalEyes Network (http://www.pheno-eye.org. Accessed 29 May 2018) in various ecosystems from the Arctic to the tropics. Phenologicalimages are useful in recording the year-to-year variability in the timing of flowering, leaf-flush, leaf-coloring, and leaf-fall and detecting the characteristics of phenologicalpatterns and timing sensitivity among species and ecosystems. They can also help interpret variations in carbon, water, and heat cycling in terrestrial ecosystems, and be used to obtain ground-truthdata for the validation of satellite-observed products. Sky images are useful in continuously recording atmospheric conditions and obtaining ground-truthdata for the validation of cloud contamination and atmospheric noisepresent in satellite remote-sensing data. We have taken sky, forest canopy, forest floor, and shoot images of a range of tree species and landscapes, using time-lapse cameras installed on forest floors, towers, and rooftops. In total, 84 time-lapse cameras at 29 sites have taken 8 million images since 1999. Our images provide (1) long-term, continuous detailed records of plant phenologythat are more quantitative than in situ visual phenologicalobservations of index trees; (2) basic information to explain the responsiveness, vulnerability, and resilience of ecosystem canopies and their functions and services to changes in climate; and (3) ground-truthingfor the validation of satellite remote-sensing observations.