Characterization of Canopy Anisotropies Over a Forested Area using a
Multispectral Imager Integrated into an Unmanned Aerial System: the
Droniometer Experiment
Abstract
Challenges in remote sensing, including remote sensing of vegetation,
include the spectral characterization of objects over space and time.
One key aspect for this characterization involves the geometry of data
acquisition and positional relationships between light source, the
target and the remote sensor. Several configurations of goniometers have
been used to acquire spectral data as a function of this geometry and
this strategy has been particularly efficient when applied to the study
of short canopies (e.g., grasses). Tall canopies present logistical
challenges when conducting these analyses, which can be resolved by
replacing physical structures (rails) with flying systems capable to
conform to different canopy geometries and data acquisition
requirements. This work (the Droniometer Experiment) investigates
anisotropies of a forest using radiometrically calibrated images from a
multispectral camera (MicaSense RedEdge) mounted on a rotary-wing
unmanned aerial system programmed to follow a planned flight that
simulates data acquisition by a goniometer assembled over tall canopy.
The experiment used multiple planned flights, conducted to represent
changes in illumination, considering sun azimuth and elevation (multiple
flights per day and over the course of months). Multi-angle data
acquisition was addressed by controlling aircraft position and camera
pitch at regular intervals. This work presents the integration of the
droniometer system, including platform and camera requirements and
control, data acquisition and processing, and analyses of results for
target/vegetation characterization and to support information extraction
and multi-angle remote sensing. A radiative transfer model, the Soil
Canopy Observation, Photochemistry and Energy fluxes (SCOPE) was used
for comparative analysis and to further describe anisotropies in
spectral responses of tall canopies.