Empirical Quantification of Topobathymetric LiDAR System Resolution
using Modulation Transfer Function
Abstract
Topobathymetric scanning LiDAR deployed on unmanned aerial systems (UAS)
is a powerful tool for high-resolution mapping of the dynamic interface
between topography and bathymetry. However, standardized methods for
empirical resolution validation have not been widely adopted across
LiDAR applications. While theoretical models of idealized LiDAR sampling
resolution can be used to describe topographical resolution,
misrepresented or unknown behaviors in an instrument, platform, or
environment can degrade expected performance or introduce georeferencing
inaccuracies. Furthermore, bathymetric resolution is strongly dependent
on water surface and column conditions. Thus, only empirical methods for
evaluating resolution will provide reliable estimates for both
topographic and bathymetric surveys. Presented is an extension of
standard modulation transfer function (MTF) methods used by passive
imaging systems applied to high-resolution scanning LiDAR. Compact
retroreflectors characterized as point and line sources are employed to
empirically assess effective LiDAR system resolution through MTF
analysis in topographic and bathymetric scenes. These targets enable MTF
analyses using range-height measurements without reliance on intensity
data, promoting widespread applicability among LiDAR systems. Empirical
MTFs calculated using these targets are compared against theory-derived
counterparts as empirical measurements elucidate influences by elements
that are unknown or difficult to model. Simulated point cloud data were
incorporated into theoretical MTF descriptions to better represent
empirically-derived topographic MTFs, revealing mirror pointing
uncertainties in the across-track axis. Similarly, theoretical
bathymetric MTFs augmented with simulated, subaqueous data enabled water
surface slope estimation using empirical measurements of submerged
retroreflector targets, where rough water surfaces strongly influenced
beam steering and the corresponding point spread MTFs.