Starek, MichaelMarques Freguete, Larissa2023-01-192023-01-192022-12https://hdl.handle.net/1969.6/95084Bathymetric data is a valuable type of information since it can be applied to diverse uses such as navigation hazards and updates on nautical charts, detection and classification of aquatic habitats based on bottom texture, monitoring of sediment transport in coastal areas, etc. The issue of monitoring bathymetry in coastal areas is that coastal hydrodynamic processes often occur within a small temporal scale which requires high-frequency data collection for a good understanding of sediment transport patterns and that can impede efficient coastal management. Uncrewed Aircraft System (UAS)-based photobathymetry techniques are the result of the combination of the versatility of remote sensing techniques and the flexibility of UAS, being perceived as a solution for a more flexible, cost-effective, time-consistent, spatially denser coastal bathymetry mapping. These techniques are very commonly used in coastal studies, but they still pose questions about their application capabilities. This study has the purpose of performing a comparative analysis of the main existing UAS based photobathymetry techniques (video-based linear depth inversion, optical inversion, and structure-from-motion / multi-view stereo (SfM-MVS) photogrammetry) and UAS-borne bathymetric light detecting and ranging (lidar) focusing on their technical characteristics and operational advantages and limitations. The comparison was based on the literature review of current studies on these techniques and on the results obtained from field experiments for performance assessment of UAS-based video-based linear depth inversion and SfM-MVS photogrammetry techniques as they present opposite conceptualizations: while the first technique depends on wave properties and requires fairly turbid water, the last strictly requires optically clear and calm water. The field experiments consisted of a UAS flight in hovering mode at a wave-dominated sandy beach along the southern Texas coastline for the video-based linear depth inversion, and three UAS flights over wave-protected bayside areas of St. George Island, FL, and Mustang Island, TX, for the SfM-MVS photogrammetry. The flights on the bayside areas were set to evaluate the effect of three flight parameters on the UAS-based SfM-MVS photogrammetry’s performance: camera orientation, solar elevation, and GSD. The flight experiment for the video-based technique resulted in a digital surface model (DSM) with a spatial resolution of 2 m, dimensions of 390 m x 400 m, and absolute vertical accuracy of 0.21 m. From the field experiments for UAS-based SfM-MVS photogrammetry, it was concluded that flights with camera orientation set to 30o off-nadir, orientated along the sun azimuth, at a time with high solar elevation, and at altitudes of 100 m AGL will provide the best accuracy. The addition of refraction correction improved the bathymetric accuracy lowering the RMSE to 0.15 m. According to what was observed from the field experiments combined with the findings presented in the reviewed literature, it was concluded that UAS-borne bathymetric lidar, SfM MVS photogrammetry, and optical inversion techniques are the opposite of video-based linear depth inversion, where water clarity and low wave activity are the determining factors for their success while linear depth inversion requires turbid waters and can only be applied in ambient with high wave activity. Each technique has its particularities regarding drawbacks and advantages and a summarized table is provided in this work offering recommendations for use and flight practices.197 pagesen-USAttribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/bathymetric mappingcBathy algorithmcoastal shallow watersSfM-MVS photogrammetryUASUAS-based photobathymetry techniquesText