﻿TITLE: Phenocamera GCC daily average composite image collection from SAFE-A, southern Sweden.
SITES STATION: Lönnstorp Research Station
TIME PERIOD: 2019
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 several plots of experimental arable land, covering three different cropping systems. On the right side of the scene there is agro-forestry system composed by rows of apple and hedges intercropped with organic crop rotation. The varieties of apple (Malus pumila) are varieties Topaz, Aroma and Santana. Hedges are blueberry honeysuckle (Lonicera caerulea var. Ezochi and var. stubbaröd), Sea buckthorn (Hippophae rhamnoides), Vosges whitebeam (Sorbus mougeotii), Black elder (Sambucus nigra), Goat willow (Salix caprea) and two varieties (comomn and Cecilia) of Cherry plum (Prunus cerasifera). In 2019, the organic crop was sugar beet, until harvest in October 30th. 
In the foreground of the image there is a perennial wheat grass plot (Thinopyram intermedium), which was harvested in September 16th. 
In the background of the image, there are four plots for rotational cropping system. The crops rotate every year. In summer 2019, from front to the back of the scene, the crops were winter wheat (between 2018-10-14 and 2018-08-15), winter oilseed rape (between 2018-08-22 and 2019-07-29), spring barley (between 2019-04-09 and 2019-08-12) and sugar beet (between 2019-04-10 and 2019-10-30).
In winter 2019, from front to the back of the scene, the crops were grass legume ley (since 2019-05-08), winter wheat (since 2019-09-25), winter oilseed rape (since 2019-08-30) and bare soil.

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 west-north-west (293 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): 55.672876, 13.101675; 55.670907, 13.101306; 55.668129, 13.103690; 55.667438, 13.105746; 55.667524, 13.107720; 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.




