Plant Structure and Carbon Storage Assessment Utilizing Drone-Borne
Lidar and Deep Learning Technologies in a Danish Agricultural Expanse.
Abstract
The increase of vegetation greenness in the Northern latitudes suggests
a rise in the fixation of CO2 by photosynthesis, but the observed upward
trends in respiration could compensate for elevated uptake by
photosynthesis, necessitating the monitoring of variation in vegetation
structure and carbon (C) storage at very high spatio-temporal
resolution. Compared to passive optical remote sensing, Light Detection
and Ranging (Lidar) scanners may improve the quantification of C sink by
providing 3D information of plant structures without apparent sign of
saturation of spectral response over dense canopies. We evaluate a novel
approach to precisely map C sequestration and key metrics describing the
3D canopy structure of a temperate agricultural expanse by implementing
drone-borne Lidar scanner technology and deep learning (DL)
architectures potentially capable of detecting individual plants and
associated geometrical properties while deriving their above ground
biomass (AGB) from point cloud datasets originating from the scanner. An
intensive aerial and field campaign was carried out over an Integrated
Carbon Observation System (ICOS) class 1 station site (60 ha) in Denmark
to remotely measure the horizontal and vertical canopy structure at
15-day intervals during the vegetation growing period, and to collect
ground truth data of crop growth in terms of height, density, AGB and
green area index of more than 1200 plants. The point cloud data are
processed using pattern recognition tools to remove noise and classify
them to ground and non-ground points. Two DL models specifically
designed to handle the irregular structure of raw point clouds are
trained to extract features of vegetation by labeling the processed
point cloud data; DL’s suitability for assigning semantic information on
3D data representing cropland is assessed by validating them with the
field-based observations. In combination with tower-based flux data, the
application of Lidar and DL technologies appear to offer a
characterization of the dynamic interaction between climatic conditions,
vegetation growth, C sink, water and CO2 fluxes suitable to the
challenge of assessing the rapidly changing northern landscapes.