Full-ocean-depth EM124 mapping of the Challenger Deep by R/V Hakuho-maru and depth-estimate sensitivity tests

The Challenger Deep in the Mariana Trench is the deepest known point on Earth, yet recent depth estimates still differ by several meters because of environmental and instrumental uncertainties. Here we present a new full-ocean-depth multibeam bathymetric dataset collected with a Kongsberg EM124 echosounder aboard R/V Hakuho-maru during the KH-23-9 cruise in 2023. The survey comprises east-west and north-south lines acquired at vessel speeds of 4-15 kt. Five seawater sound velocity models were constructed from contemporaneous XCTD data, historical full-depth CTD data, and a recent full-depth reference profile to test the sensitivity of depth estimates. After ping-by-ping editing and gridding, the preferred KH23XCTD+KH92CTD solution resolves three basins deeper than 10,900 m, with maximum depths of 10,926, 10,912, and 10,927 m in the western, central, and eastern basins, respectively. Alternative sound velocity models yield maximum depths from 10,914 to 10,932 m, illustrating the meter- to >10-m-scale sensitivity of full-ocean-depth multibeam estimates to the applied sound velocity structure. Cleaned point soundings, gridded bathymetric surfaces for each sound velocity model, and the gridding script are provided. The dataset enables assessment of how sound velocity structure, survey speed, and beam-footprint geometry influence depth estimates in full-ocean-depth multibeam mapping, and provides a new reference for cross-comparison of Challenger Deep bathymetry.