Clara Smart

A pipeline for structured light bathymetric mapping

This paper details a methodology for using structured light laser imaging to create high resolution bathymetric maps of the sea floor. The system includes a pair of stereo cameras and an inclined 532nm sheet laser mounted to a remotely operated vehicle (ROV). While a structured light system generally requires a single camera, a stereo vision set up is used here for in-situ calibration of the laser system geometry by triangulating points on the laser line. This allows for quick calibration at the survey site and does not require precise jigs or a controlled environment. A batch procedure to extract the laser line from the images to sub-pixel accuracy is also presented. The method is robust to variations in image quality and moderate amounts of water column turbidity. The final maps are constructed using a reformulation of a previous bathymetric Simultaneous Localization and Mapping (SLAM) algorithm called incremental Smoothing and Mapping (iSAM). The iSAM framework is adapted from previous applications to perform sub-mapping, where segments of previously visited terrain are registered to create relative pose constraints. The resulting maps can be gridded at one centimeter and have significantly higher sample density than similar surveys using high frequency multibeam sonar or stereo vision. Results are presented for sample surveys at a submerged archaeological site and sea floor rock outcrop.

Detection of diffuse seafloor venting using a structured light laser sensor: 1. Development of a classification based detection method

Systematic and remote detection of diffuse hydrothermal venting is complex yet necessary to establish a comprehensive understanding the distribution, contribution, and context of fluid flow within hydrothermal systems. Diffuse flow is characterized by both low temperature and low flow rates and cannot be consistently distinguished during extensive systematic surveys using current vehicle-mounted visual, acoustic, or environmental sensors. The ROV-mounted structured light laser sensor is sensitive to fluid density anomalies and seafloor characteristics. Presented advancements to the detection algorithm include the development and implementation of intensity normalization routines and a support vector machine (SVM) classification algorithm. The resulting comprehensive maps establish the spatial distribution of potential hydrothermal vents and associated bacteria within a vent field.

Detection of diffuse seafloor venting using a structured light laser sensor: 2. Evaluation of detection sensitivity and limitations

Algorithms to detect diffuse hydrothermal vent fluids using the structured light laser sensor have proven to be successful. However, potential limitations due to survey parameters, including altitude and vehicle heading, have not been explored and are the focus of this study. Data from twelve surveys conducted over a single hydrothermal vent at three different altitudes (2.7m, 4.2m, and 6.2m) and four different headings are analyzed. Increasing survey altitude decreases the resolution and intensity of the imaged laser line, therefore range dependent processing considerations to maintain detection sensitivity are presented. Analysis of these surveys suggest minimal degradation of vent detection capabilities from survey altitudes up to 6m. Additionally, the shape and location of the detected distortion is dependent on survey heading and altitude and is presented as a potential indication of plume shape and rise height. The effects of range and survey heading are important for future applications of this sensor which may include surveying from higher, faster flying autonomous underwater vehicles (AUV).