Bathymetric Depth Sounder with Novel Echo Signal Analysis Based on Exponential Decomposition

摘要

We present a laser rangefinder specifically designed for bathymetric surveying tasks. The compact and lightweight instrument is capable of measuring through the water surface, ideally suited for generating profiles of waterbodies when operated from a UAV. The topo-bathymetric LiDAR sensor comprises a tilt compensation, an IMU/GNSS unit with antenna, a control unit, and supports triggering of external digital cameras. The laser range finder sends out laser pulses at a rate of 4 kHz. The echo signal for each laser pulse is digitized and recorded for the entire range gate of 50 m. This means that predetection averaging of the waveforms can be performed in post processing, increasing the depth performance. The averaging rate can be chosen after the flight on basis of measurement conditions. The waveforms are processed by a full waveform processing algorithm based on exponential decomposition which uses segments of an exponential function as base functions to model the backscatter cross-section of the target objects. Water surface, water column, and ground targets are modeled using a set of base functions of which an optimization selects the most suitable combination to fit the echo signal. This leads to high accuracy of the points and to automatic target classification.