Airborne Lidar Bathymetry (ALB) waveforms provide a time log for the interaction of the laser pulse with the environment (water surface, water column and seafloor) along its ray-path geometry. Using the water surface return and the bottom return, it is possible to calculate the water depth. In addition to bathymetry, the ALB bottom return can provide information on seafloor characteristics. The main environmental factors that contribute to the ALB bottom return measurements are: slope, roughness, vegetation, and mineral composition of the surface geology. Both the environment and the ALB hardware affect the bottom return and contribute to the measurement uncertainties. In this study, the ALB bottom return waveform was investigated spatially (i.e., area contributing to the return) and temporally (i.e. the shape of the waveform return) for seafloor characterization. A system-agnostic approach was developed in order to distinguish between the spatial variations of different bottom characteristics. An empirical comparison of bottom characteristics was conducted near the Merrimack River Embayment, Gulf of Maine, USA. The study results showed a good correlation to acoustic backscatter collected over the same area.
As part of the research to development an optical communication design of a leader-follower formation between unmanned underwater vehicles (UUVs), this paper presents light field characterization and design configuration of the hardware required to allow the use of distance detection between UUVs. The study specifically is targeting communication between remotely operated vehicles (ROVs). As an initial step in this study, the light field produced from a light source mounted on the leader UUV was empirically characterized and modeled. Based on the light field measurements, a photo-detector array for the follower UUV was designed. Evaluation of the communication algorithms to monitor the UUV’s motion was conducted through underwater experiments in the Ocean Engineering Laboratory at the University of New Hampshire. The optimal spectral range was determined based on the calculation of the diffuse attenuation coefficients by using two different light sources and a spectrometer. The range between the leader and the follower vehicles for a specific water type was determined. In addition, the array design and the communication algorithms were modified according to the results from the light field.