Using lidar waveforms to detect environmental hazards through visualization of the water column

摘要

Airborne bathymetric lidar (Light Detection and Ranging) systems measure the optical path (range and angle) between the sea surface and the seafloor. Lidar achieves this measurement by firing a laser from an aircraft and calculating the range based on the speed of light and the time it takes for the laser pulse to return. Measurements of photoelectrons at the photocathode of a returned laser pulse are collected frequently, such as once every nanosecond. The collected measurements of a single pulse in a time series are called a waveform. The laser pulse return (reflection) from the seafloor is visible in the waveform as a pronounced “bump” above the volume backscatter. Similarly, any floating or submerged objects in the water can also be seen in the waveform. Along with a voxelized 3D image cube visualization of the lidar data in terms of the returned backscatter from the sea surface to the seafloor, the water surface and underwater environmental changes can also be detected based on waveform analysis of airborne bathymetric lidar data. Oil spills on the water surface and leaks from sewers or other kinds of underwater pipes can be detected as well by analyzing the change in the water column volume. The paper demonstrates the possibility of utilizing this unique three-dimensional water column visualization tool to detect environmental hazards and carry out rapid environmental assessments.