Airborne Lidar Bathymetry Beam Diagnostics Using An Underwater Optical Detector Array
Master of Science Defense
Ocean Engineering–Ocean Mapping
The geometry of the air-water interface is an important factor in optical ray-path calculations for applications such as Airborne Lidar Bathymetry (ALB), and optical communication through the water surface. Previous studies on lidar laser beams refracting through a complex water surface have been dependent solely on theoretical models and simulations. However, these studies lack validation from empirical measurements that were conducted under well-controlled conditions. This work presents an empirical approach using a 6x6 array of photodiodes as a spatial detector unit to perform laser beam diagnostics below the surface of the water. Beam patterns that resulted from intersection between the underwater laser beam light field and the detector array were modeled and used to calculate changes in beam position and orientation at various water surface conditions. In this study, the effects of small capillary and capillary-gravity waves with wavelengths less than 10 cm were considered. Results of the study were compared to ALB ray-path geometry calculations and corrections over a flat water surface. In addition, uncertainty attributed to the air-water interface was evaluated and implemented in total propagated uncertainty (TPU) models for ALB measurements.
Matt Birkebak received a B.S. in mechanical engineering from UNH in 2015. During his undergraduate time, he participated in a summer SURF fellowship at CCOM in 2013. He worked on spectral restoration of underwater cameras under Drs. Shachak Pe’eri and Yuri Rzhanov. Through this experience, he became interested in ocean optics and bathymetric Lidar. At CCOM, Matt has pursued a master's degree where he is looking at bathymetric Lidar uncertainty caused by ripples in the air-water interface.