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Fiducial markers are widely used for ground and air robot localization and navigation. The markers provide a tertiary reference for the robot when Global Positioning System (GPS) and inertial navigation are unreliable. These markers require a camera, software, and low-cost customizable tags to implement on a system. As these markers and the process for using them for ground and air systems has been explored extensively, very little research has been done on implementing these for underwater applications. This thesis investigates the feasibility of actively backlighting the markers and using a non-lighted imaging system. Using the BlueROV2—a commercial remotely operated vehicle (ROV), the Robot Operating System (ROS), AprilTag fiducial markers, and the open-source AprilTag2 detection software, experiments were conducted in air and underwater with ambient lighting and without ambient lighting. For the low-light tests, the markers were backlit by submersible LED lights. After conducting several tests in clear fresh water, the markers were able to be consistently identified out to 4 meters. The proposed marker design was then tested in the San Diego Bay as a proof of concept and demonstrated that the actively lit marker was detectable in open water with low ambient lighting. The experiments provided conclusive evidence that this method of using active fiducial markers underwater is not only feasible but can be easily implemented and has great potential with future research.

A combination of experiments and modeling are used to address the vibration durability of structures subjected to different random vibration environments. Presented in this work are a set of experimental data comparing the rate of change of the first natural frequency and the measured time to failure, of simple structural members under repetitive shock (RS) vibration, single-axis electrodynamic (ED) vibration and multi-axis ED vibration. It was found that multi-axis testing is more severe than single-axis testing at the same level. In addition the RS system low frequency amplitude is often too weak to efficiently propagate the crack. Smoothing of the input power spectral density (PSD) or poor line resolution was also shown to change the time to failure of a test. A poor correlation was shown between the PSD and the rate of natural frequency change (RFC) over a wide frequency shift. The change in natural frequency caused the initial PSD to be ineffective in determining the total time to failure. A predictive, analytic methodology to quantify the RFC was developed to predict the fatigue life of a structure experiencing random vibration excitation. This method allows the estimation of fatigue life using the frequency domain, where only the input power spectral density, damping factor and structural information are required. The methodology uses linear elastic fracture mechanics for fatigue crack propagation and accounts for the frequency shifting that occurs due to fatigue crack evolution. The analytic model has been shown to compare favorably to both finite element analysis (FEA) and experimental results, for mild-steel cantilever beams. Monte Carlo simulations have been conducted to assess the sensitivity of the model predictions to uncertainties in the input parameters. In addition a semi-empirical model was developed whereby the input PSD and damping factor are measured from life tests, and the resulting time to failure and the acceleration factors between differen

Fiducial markers are widely used for ground and air robot localization and navigation. The markers provide a tertiary reference for the robot when Global Positioning System (GPS) and inertial navigation are unreliable. These markers require a camera, software, and low-cost customizable tags to implement on a system. As these markers and the process for using them for ground and air systems has been explored extensively, very little research has been done on implementing these for underwater applications. This thesis investigates the feasibility of actively backlighting the markers and using a non-lighted imaging system. Using the BlueROV2—a commercial remotely operated vehicle (ROV), the Robot Operating System (ROS), AprilTag fiducial markers, and the open-source AprilTag2 detection software, experiments were conducted in air and underwater with ambient lighting and without ambient lighting. For the low-light tests, the markers were backlit by submersible LED lights. After conducting several tests in clear fresh water, the markers were able to be consistently identified out to 4 meters. The proposed marker design was then tested in the San Diego Bay as a proof of concept and demonstrated that the actively lit marker was detectable in open water with low ambient lighting. The experiments provided conclusive evidence that this method of using active fiducial markers underwater is not only feasible but can be easily implemented and has great potential with future research., http://archive.org/details/feasibilityofusi1094564023, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.