Canopy Phenology and Greenness Indices at 13 Sites across North America 2003-2012

This data set contains camera-derived color index data, which serve as a proxy for canopy phenology. The data set spans 13 geographically distinct research sites, including 17 different cameras it total, each of which was mounted on a eddy flux tower for intercomparison of canopy and photosynthesis phenology. Each site was dominated by one of three PFTs: deciduous broadleaf forest, evergreen needleleaf forest, and grassland/crops (see HF215-01 for details). On each eddy covariance tower, a digital camera was installed in a fixed position, with a view across the top of the canopy. Most cameras collected photos, which were saved in 24-bit JPEG format, at 30-60 minute intervals, 12-24 hours a day. Time series were first visually inspected for camera shifts and changes in field of view. Noting these changes, we processed the image archives to extract regions of interest (ROI) that encompassed all portions of the full canopy within the foreground. To quantify canopy greenness, we calculated the green chromatic coordinate (GCC), which is widely used to monitor canopy development and identify phenological phase changes, as follows: GCC = DNG / (DNR + DNG + DNB) where DN is the digital number and R, G and B denote the red, green and blue channels, respectively. The Excess Green (ExG) index was then calclated as follows: ExG = 2 * DNG - (DNR + DNB) To characterize canopy coloration in fall, the red chromatic coordinate (RCC) was calculated using the same form as GCC, substituting DNR in the numerator. Indices have been smoothed along a 3-day interval, using a 90th percentile filter (Sonnentag et al. 2012). For each deciduous broadleaf site, there are three files – one each for GCC, ExG and RCC. For the grassland and evergreen needleleaf sites, there are two files, one each for GCC and ExG.