Performance assessment of GEBCO_2023 gridded bathymetric data in selected shallow waters of Indian ocean using the seafloor from ICESat-2 photons

Bathymetric data represents estimated seafloor topography and aids in understanding the intricacies of earth and ocean interaction processes. The General Bathymetric Chart of the Oceans (GEBCO) released the GEBCO_2023 gridded bathymetric data as an interim dataset in connection with the ambitious task of producing the definitive ocean floor map for the globe by 2023. Evaluating the data of scientific importance is essential to ensure its fitness for the applications; however, the procedure needs qualified reference data of higher accuracy for comparison. This article discusses the methods and results of performance validation on GEBCO_2023 using the seafloor obtained from the ICESat-2 geolocated photons as a reference. The validation was carried out at three test sites containing shallow waters in the Indian Ocean. In two of the test sites, where the coastal waters have minimal influence from the continental sediment flux, the trend of the seafloor from both the data sources is similar, and the quantified accuracy of GEBCO_2023 in terms of RMSE is less than 3 m. In the extent of the third test site, where mostly perennial turbidity prevails, the accuracy of the GEBCO's seafloor depth in terms of RMSE and MAE is in the range of 5-6 m, with underestimation of the seafloor. The reasons for the errors in the GEBCO_2023 grid were analyzed based on the associated metadata, namely, the Type-Identifier grid that informs the source of depth data for a given grid cell. In summary, the GEBCO_2023 grid is the best available and resourceful bathymetric data in the present scenario where challenges and complications exist for mapping the ocean surface besides technological advancements.