Shallow Water Lidar for Target Morphology: Impacts of Surface Roughness and Turbidity
Jeffrey Thayer | Atmospheric & Space Technology Research Associates, LLC
The problem to be addressed by this project, is to develop technologies that detect, classify, and remediate military munitions found in aquatic environments such as ponds, lakes, rivers, estuaries, and coastal and open ocean areas. A specific need is for technology to operate in depths less than five meters. This shallow-water domain includes an assortment of unexploded ordnance that are the most likely to be encountered by the public and are expected to experience the most mobility. Many sensor technologies designed to detect, classify, and remediate munitions are challenged by this unique environment and suffer in performance, access, navigation, deployment, viewing, sensor standoff distance, and possible damage by changing bottom topography or obstructions.
The objective of this project is to research by modeling and experiment the interactions of polarized, pulsed laser light with the (wavy) water surface and the (turbid) water column. The purpose of this research is to investigate water conditions that might impact the feasibility of using the new, patented above-water lidar technology for the classification of the aquatic environment and the identification of munitions in waters less than five meters deep with vertical and horizontal resolutions of centimeters.
The research team has performed initial work in this area and has proven the measurement concept by building two early bathymetric lidar prototypes, and making measurements of water depth in various indoor settings with a depth resolution of 1 cm. The technical approach in this project is to advance lidar observations using polarimetry, coupled with system performance modeling, to investigate the feasibility of employing target morphometry for detecting and classifying both munitions and the environment around munitions in shallow waters. Project activities will involve system-to-target modeling of polarized laser light propagation and scattering, lidar research and lab tests, and field tests and demonstrations to understand how the applied methods are influenced by the uncertainties introduced by various water conditions, including surface roughness and turbidity, as well as object scattering, and lidar system attributes. Researchers will use the existing lidar equipment for testing and validating model results, measurement demonstrations, and for optimizing performance.
The outcome of this research will be an improved understanding of how polarized laser light can be employed for shallow water detection of submerged objects. It will lead to a demonstration of the feasibility of a lidar system for the classification of the aquatic environment and the identification of munitions in waters less than five meters deep with vertical and horizontal measurement resolutions of centimeters. The research will advance the understanding of environmental impacts on lidar bathymetric measurements (water depth, turbidity, land-water transitions, and bottom topologies) in shallow waters. This research will be of great interest to the Department of Defense (DoD) and scientific communities in that it impacts a wide variety of shallow-water aquatic environments. An additional benefit of the research results is that researchers will make advancements in applying lidar returns through polarimetry to provide a new way of characterizing underwater objects.
The results will further address DoD needs by fully establishing a new technology with the ability to detect, range, and classify underwater objects with high vertical and horizontal resolution (~1cm) in shallow water (<5m) – without touching the water. Relative to existing lidar systems, the resulting lidar will provide improved depth resolution, and better hydrography, thus making survey results more useful. It also uses less expensive and less complex lidar components, which reduces the system cost and cost compared to other bathymetric lidar systems. Finally, the data processing can be done in real-time, making surveys quicker, more reliable and less costly. The system can also be extended to water depths beyond five meters if needed.