TITLE: Phenocamera GCC daily average image composite collection from Laevasvagge, north-western Sweden.
SITES STATION: Tarfala Research Station
TIME PERIOD: 2021-08-07 10:00:00 - 2021-09-05 14:00:00
TIME RESOLUTION: DAILY
TIME ZONE: UTC +1 
SAMPLING POINT: Laevasvagge, Mast 4m Phenocam 01
LATITUDE: 68.042512
LONGITUDE: 18.959844
ALTITUDE: 952.71 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 a mosaic of Natural grassland (CORINE: 3.2.1) and Heathland (CORINE: 3.2.2) determined by the micro climate of a hummocky terrain in an arctic alpine valley.

SENSOR DESCRIPTION:
Data acquired with Mobotix M25 RGB phenology camera, with wide field of view (FOV) angle of 60 degrees. Images stored in JPG format.  

DATA ACQUISITION
The original images were acquired with a phenology camera on an observation mast, at a height of 4 m above ground, looking north-east (22.5 degrees) and an off-nadir angle of 59 degrees. The phenocamera acquired images from 9 a.m. to 3 p.m. every half an hour. The phenocamera operated between August and September.
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): 68.042512, 18.959844. 

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.




