Use of a digital camera onboard a UAV to monitor spring phenology at individual tree level

The aim of this study is to assess the potential of imagery acquired from an Unmanned Aerial Vehicle (UAV) to track seasonal changes in leaf canopy at individual tree level. UAV flights were carried out over a deciduous woodland during the spring season of 2015, from which a temporal series of 5 cm spatial resolution orthophotos was generated. Initial results are presented in this paper. Four trees with different observed Start of Season (SOS) dates were selected to monitor UAV-derived Green Chromatic Coordinate (GCC). The chronological order when sudden increases of GCC values occurred matched with the chronological order of observed SOS. Trees with later observed SOS presented GCC values increasing slowly over time, which were associated with development of understory vegetation. It is concluded that UAV imagery has the potential to track leaf phenology at the individual tree level, but further studies are necessary to better understand this new level of information detected from UAVs.

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