A Geographic Segmentation Approach for Satellite-derived Bathymetry

Juliane Affonso
Master's Defense

Earth Sciences/Ocean Mapping

Thursday, Aug. 25, 2022, 11:00am

Safety of navigation depends on our knowledge of seabed and its features, and, as such, any improvements in deriving bathymetry for nautical chart updating are of major importance. Satellite-Derived Bathymetry (SDB) is an alternative to traditional surveys using ship and airborne sensors, particularly for mapping remote and shallow areas, due to its reduced cost and the absence of any navigational risks in very shallow and unsurveyed areas. However, the accuracy of SDB can be judged as relatively low for nautical charting purposes and, therefore, is mostly used for reconnaissance or/and for filling gaps in remote or very shallow areas. One of the reasons may be that the conventional approaches assume that bottom type and water quality are constant and negligible within the entire image, and consequently, a global and linear model (such as that proposed by Dierssen) is performed to retrieve bathymetric information. To address the spatial heterogeneity within a scene and with the aim to increase the accuracy and coverage of estimated depths, this work investigates the segmentation of the scene, both horizontally and vertically, into smaller spatial units, and of an extended Dierssen model to account for water column and sea bottom variations. The proposed Geographic Segmentation method is evaluated in two test beds in Dry Tortugas, Florida, and St. Thomas East and Reserve, U.S. Virgin Islands, and the results are compared to those of the conventional global Dierssen. As the results illustrate, the accuracy of the proposed Geographic Segmentation approach may be considerably improved, compared to the conventional global approach, particularly with the use of a vertical (by depth) segmentation of the scene that demonstrated an improvement of over 40% in the accuracy of the estimated depths. Furthermore, the coverage of the SDB is also increased as the Geographic approach allows the extraction of bathymetry beyond the effective optical depth of the conventional global approach.

Advisors: Christos Kastrisios and Christopher Parrish
Committee members: Christos Kastrisios, Christopher Parrish, and Brian Calder


Juliane Affonso is pursuing an M.S. in Ocean Mapping at UNH with interest in satellite-derived bathymetry. She is also a Brazilian Navy Officer and has some experience with cartographic database maintenance, raster/paper chart/ENC production, GIS, riverine mapping, etc. Juliane holds a B.Eng in Cartographic Engineering from UNESP (2011) and a technical in Geomatics degree from UNICAMP (2006). She stands contentedly at the crossroads of Hydrography and looks forward to helping at the Brazilian Navy Hydrographic Center with new approaches for mapping shallow waters.