Modelling heights of sparse aquatic reed (Phragmites australis) using Structure from Motion point clouds derived from Rotary- and Fixed-Wing Unmanned Aerial Vehicle (UAV) data

Abstract

Aquatic reed beds consisting of Phragmites australis play an important role in lake ecosystems. Digital Elevation Models (DEM) provide essential information in identifying and quantifying these stocks. This study modelled sparse aquatic reed beds with aerial images collected from Rotary (RW) and Fixed Wing (FW) Unmanned Aerial Vehicles (UAV) by the same imaging system. Image processing was executed in a Structure from Motion (SfM) environment and based on bundle adjustment. The DEMs were referenced with Ground Control Points (GCPs) and validated with independent Reference Points (RPs) of heights from reed and flat surfaces. Root Mean Squared (RMS) reprojection error showed that imagery taken with FW could be better aligned than the RW dataset. Quality assessment proved that RW gathers sharper data and lowers image blur resulting in slightly more accurate DEM, while FW showed better area coverage. The results from both configurations proved the efficiency of the methodology in deriving diagnostic relevant features for monitoring sparse aquatic reed beds.