TITLE: Phenocamera GCC daily average image composite collection from Abisko Observatory, north-western Sweden.
SITES STATION: Abisko Scientific Research Station
TIME PERIOD: 2010-11-09 10:00:00 - 2010-11-28 14:00:00
TIME RESOLUTION: DAILY
TIME ZONE: UTC +1 
SAMPLING POINT: Abisko Scientific Research Station, Mast 4.5m Phenocam 01
LATITUDE: 68.353921
LONGITUDE: 18.789888
ALTITUDE: 381 m a.s.l.

FILE RETRIVED FROM: https://data.fieldsites.se Link to metadata landing page is available in separate file in the downloaded zip.
DATA POLICY: SITES data is licensed under a Creative Commons Attribution 4.0 international license (http://creativecommons.org/licenses/by/4.0/).

PARAMETERS & UNITS: Spectral Vegetation Index (fraction)

DESCRIPTION: 
Collection of phenocamera Green Chromatic Coordinate (GCC) index image composites averaged daily from quality-filtered images between 10 a.m. to 2 p.m.
The phenocamera pointed to Mount Nuolja. The ecosystems in the images are subalpine birch forest (Betula pubescens var. czerepan) and alpine shrubland (mainly Salix spp., Empetrum nigrum, and Vaccinium vitis–idaea) in the upper slope of Mount Nuolja.

SENSOR DESCRIPTION:
Data acquired with Nikon D300s RGB phenology camera, with wide field of view (FOV) angle of 60 degrees. Images stored in JPG format. 

DATA ACQUISITION
The original photos were acquired with phenology camera mounted on the rooftop of the observation house, at a height of 4.5 m above ground, looking west (270 degrees) and an off-nadir angle of 59 degrees. The phenocamera acquired images from 10 a.m. to 2 p.m. every two hours. The phenocamera was operated only during November.
The area surveyed by the phenocamera projects a footprint on the ground, the centroid of which is approximately defined by the following coordinate (latitude, longitude in GCS WGS84, decimal degrees): 68.353921, 18.789888.

PROCESSING METHODS:
Low quality images were filtered out manually from the original image collection. Low quality refers to images that contain sun glare, rain droplets, fog, or shadows, or represent low-light or blurry conditions.
For phenology purposes, all images from 10 a.m. to 2 p.m. were averaged per band (RGB) and pixel, daily. GCC composites were calculated from RGB daily averages and exported as 8 bit grayscale images. Digital range of GCC image layers is 0 - 255 and should be scaled down using a factor of 1/255 to get pixel values in physical range.
GCC is defined as: DNgreen / (DNred + DNgreen + DNblue) (Toomey et al., 2015)

REFERENCES
Richardson, Andrew D., Koen Hufkens, Tom Milliman, Donald M. Aubrecht, Min Chen, Josh M. Gray, Miriam R. Johnston et al. "Tracking vegetation phenology across diverse North American biomes using PhenoCam imagery." Scientific data 5 (2018): 180028.

Toomey, Michael, Mark A. Friedl, Steve Frolking, Koen Hufkens, Stephen Klosterman, Oliver Sonnentag, Dennis D. Baldocchi et al. "Greenness indices from digital cameras predict the timing and seasonal dynamics of canopy-scale photosynthesis." Ecological Applications 25, no. 1 (2015): 99-115.




