Abstract
Bathymetry maps can be produced with high accuracy by using active acoustic and laser sensing systems. Various acoustic systems such as side-scan sonar, single and multi-beam echosounder are difficult to operate in shallow waters, and measurement with laser systems depends on the presence of appropriate optical transparency. Disadvantages such as workload, time, and economic costs should also be mentioned in the implementation of the two systems. On the other hand, bathymetry maps can be obtained in shallow waters up to a depth of 15 m at an affordable cost with multispectral images covering larger areas and remote/inaccessible locations. This method, known as the experimental approach, requires however sufficient field depth data. In this study, bathymetric map of a study area was generated by combining external depth measurements obtained from ICESat-2 ATL03 photon heights and Sentinel-2 multispectral images. This study aimed to test the accuracy of this bathymetric map against an existing map. Reflectance values measured in Sentinel-2’s coastal aerosol, blue and green bands were modelled under multiple linear regression by using both log-linear and log-rational approaches, and as a result a relative depth map was obtained. The resultant non-metric map is scaled by refraction corrected ICESat-2 depth values building the model’s training set. The bathymetry map was calculated with the multiple linear regression model obtained from this training set and compared with the existing side-scan sonar bathymetric map of the test area. The comparison tests revealed that the atmospheric correction did not improve the results, and better accuracy values were achieved with the log-linear approach compared to the log-rational approach. A root mean square error of ±1.6 m was calculated from the comparisons to the acoustic bathymetry map. The number of differences having absolute values of 5 m and below constituted 94% of the total comparison points. Although the expected accuracy for navigation is not met, bathymetric maps of shallow areas with high optical transparency can still be obtained at a low cost by combining two independent satellite-based datasets for research and other applications.