Horizontal Calibration of Vessel Lever Arms Using Non-Traditional Survey Methods

Casey O'Heran
Master's Defense
Ocean Engineering/Ocean Mapping
Friday, Apr. 17, 2020, 1:00pm

Knowledge of offset distances from sonars, mounted on vessels, to systems such as Inertial Measurement Units (IMUs) and Global Navigation Satellite Systems (GNSS) is crucial for accurate ocean mapping applications. Traditional survey methods, such as employing laser scanners or total stations, are used to determine professional vessel offset distances reliably. However, for vessels of opportunity that are collecting volunteer bathymetric data, it is beneficial to consider survey methods that are less time consuming, less expensive, and which do not involve bringing the vessel into a dry dock. Thus, this thesis explores three alternative methods that meet this criteria, for horizontally calibrating vessels With the development of Unmanned Aircraft Systems (UASs) in the field of mapping, more cost-effective and quicker surveys can be conducted. For standard mapping applications, the tradeoff in using UASs compared to traditional surveying instruments is that there is an increase in errors.

To investigate the potential of using UASs to accurately calibrate horizontal vessel offsets, UASs were utilized to calibrate a vessel with both Structure for Motion (SfM) photogrammetry and aerial lidar while the vessel was docked. Estimates of the horizontal deviations from ground truth, for both methods, were obtained by comparing the horizontal distances between targets on a vessel, acquired by the UAS methods, to ground-truth measurements of offset distances from survey-grade laser scanning of the vessel. In addition to the UAS methods, a seafloor reference technique that involves collecting single-beam echo sounder (SBES) data over a known bathymetric feature and using a grid search optimization on the datasets to estimate horizontal offsets of a vessel, was investigated. Errors for the seafloor reference method were on the meter level and therefore may only be relevant for larger offsets such as on larger ships. With the use of Ground Control Points (GCPs), however, UAS methods were able to achieve horizontal deviations on the order of centimeters.


Casey O’Heran is a young professional in the field of geospatial science. He earned his B.S. in Surveying Engineering from Ferris State University in Big Rapids, Michigan. During his time there, he participated in projects that exposed him to geospatial data acquisition using land surveying methods and data fusion. His studies also exposed him to the theory of multispectral LIDAR, echo sounders, and their ability to collect bathymetric data. This exposure sparked his interest in bathymetric data acquisition.

Casey is now pursuing a master’s degree in ocean engineering with a focus in ocean mapping at the University of New Hampshire (UNH). Additionally, he is a Research Assistant for the Center of Coastal and Ocean Mapping (CCOM) at UNH. During his time at UNH, Casey has conducted research that explores utilizing Unmanned Aircraft Systems (UASs) for hydrographic purposes. His thesis investigates the implementation of UASs to survey vessels while they are docked. Casey hopes to utilize developed skill sets in terrestrial, aerial, and hydrographic surveying throughout his career as a mapping professional.