The UAV surface modelwas on average about 1.9 cm higher than the
RTS surface model. Potential reasons for this observation are: (1) thickness
of the ground control points (for example: reference targets had a
height of 1 cm), (2) the general tendency of measuring too low with a
RTS (for example: having the surveying pole/rod slightly penetrating
the ground surface), (3) impact of vegetation and surface conditions
(for example: areas with standing water that cannot or hardly be measured
using a RTS), and (4) number of survey point (for example: a
higher number ofmeasured points eventuallymakes a UAV-basedmeasurement
techniquemore accurate since the measurement resolution is
denser). The latter two reasons were specifically observed and noted in
the field experiment.