Mapping 3D Water Turbidity with LiDAR Bathymetry: a Contribution to Water Quality Assessment

Abstract Water turbidity is an important indicator of water quality, as it allows for conclusions on the particles contained in the water. Suspended matter, sediments, algae and other particles in the water column influence the light transmission, oxygen content, nutrient supply and productivity of a water body. Information on water turbidity is therefore relevant for a wide range of limnological and oceanographic questions. In particular, the vertical turbidity stratification plays an important role in understanding the ecological relationships within a water body. Conventional in-situ measurement methods provide only isolated, point-based turbidity profiles, which fail to capture the overall turbidity conditions throughout the entire water body, including all small-scale lateral and vertical variations. Hence, the utilization of Light Detection and Ranging (LiDAR) bathymetry data for assessing area-wide depth-resolved water turbidity information shows great potential. By analysing the waveform of the backscattered LiDAR signal, information about the turbidity of the water can be derived. In this paper we present a signal analysis approach that allows to derive depth resolved turbidity parameter fields from LiDAR bathymetry data. The methodology was tested on a pre-alpine mountain lake using a UAV LiDAR bathymetry system. For validation purposes, a comprehensive set of in-situ water property measurements is available, which were collected at the same day as the bathymetric data. The results show that the turbidity parameters determined from the LiDAR data generally correspond to the trends observed in the conventional water property measurements, although local deviations are present.