Remote Characterization of Turbid Water Using a Novel Lidar Technique

Active remote sensing systems, such as Lidar, allow for range-resolved, non-contact probing of water properties and submerged objects. A new Lidar technique has been developed to measure water depth and subaqueous terrain in shallow waters where many Lidar systems suffer. To further advance this new capability, the influence of water turbidity must be addressed. Lidar systems are in use around the world to observe oceanic parameters, but retrievals primarily rely on a single-scattering assumption which breaks down in optically dense media, such as in turbid water. Multiple scattering of laser light by suspended particles can be exploited to identify levels of turbidity and particle size by recognizing the altering effects such scatter has on the polarization properties of light. For example, identifying regions by the amount the transmitted polarized laser light is depolarized enables differential detection of single-and multiple-scattered photons from optically dense media. Thus, a non-invasive, Lidar remote-sensing technique for determining the properties of turbid water is being developed. Through the use of a self-developed Monte Carlo code, we investigate a) how the angular spread and altered polarization caused by multiple scattering of returned photons depends on recorded range, b) what new information this can provide about the particles doing the multiple scattering, and c) whether this can be incorporated into a Lidar transmitter/receiver using current technologies. This Monte Carlo code has wide implications for polarization-sensitive Lidar systems with multiple-field-of-view capabilities. Results from the theoretical Monte Carlo simulations indicate that a polarization-sensitive Lidar system is able to retrieve optical depth and particle size of the turbid/cloudy medium, enabling remote characterization of turbid waters.