﻿TITLE: Phenocamera GCC daily average composite images collection from SAFE-A, southern Sweden.
SITES STATION: Lönnstorp Research Station
TIME PERIOD: 2018-03-21 2018-12-31
TIME RESOLUTION: DAILY
TIME ZONE: UTC +1 
LATITUDE: 55.668516
LONGITUDE: 13.110039
ALTITUDE: 295 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 index (GCC) daily composite images, calculated from daily average RGB composites,from quality-filtered photos between 10 a.m. and 2 p.m.
The phenocamera is pointing to an experimental arable land, composed by a perennial cropland system (Intermediate wheat grass, Medicago sativa), harvested in 2018-09-03.

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

DATA ACQUISITION
The original photos were acquired with a phenology camera on a observation tower, at a height of 10 m above ground, looking east (85 degrees) and a zenith angle of  80 degrees. On March 10th 2019, there was a change in the camera configuration, in terms of time of acquisition, frequency and photo dimensions. Before that date, the phenocamera collected photos from 6 a.m. to 7 p.m. and took one photo per hour. After that date, the phenocamera was configured to take photos from 9 a.m. to 3 p.m. every 30 min. The phenocamera operates all year long. 
The area surveyed by the phenocamera projects a footprint on the ground defined by the following coordinates (GCS WGS84, degrees decimal): 55.668116, 13.114852; 55.671798, 13.118552; 55.668509, 13.109611; 55.668106, 13.108658.

PROCESSING METHODS:
Low quality photos were filtered from the original phenology photo collection using thresholds to the spectral signal of the photos (DN), as defined by Richardson et al., 2018. Low quality refers to photos that present sun glare, rain droplets, fog or shadows, or represent low-light or blurry conditions. 
For phenology purposes, all photos from 10 a.m. to 2 p.m. were averaged per band (RGB) and pixel, daily. GCC composites were calculated from RGB daily averages.
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.




