Evaluation of shipboard and satellite-derived bathymetry and gravity data over seamounts in the north Pacific Ocean

The Earth's surface topography/bathymetry and gravity provide important information on crustal structure and the tectonic processes that act on it due, for example, to plate flexure and mantle convection. Such studies require, however, high accuracy in the topography/bathymetry and gravity field at a wide range of spatial scales. Shipboard bathymetry measurements using single beam 3.5 kHz and 12 kHz echo sounders have been in operation on research vessels since the mid 40s. It is now possible using hull mounted multibeam systems, for example, to obtain accuracies of 1-2 m and insonify the seafloor over widths up to 2.5 times the available water depth. Shipboard gravity measurements using beam-type gravimeters mounted on gyro-stabilized platforms have been in operation since the early 60s. It is now possible using vertically constrained accelerometers and modern GPS navigation, for example, to obtain accuracies of 1-2 mGal at a resolution of 2-10 km, depending on sea state. Similarly, satellite-derived bathymetry and gravity data have seen significant improvement in the past few decades, owing to the non-repeat cycles of Jason-1/2, Cryosat-2 and SARAL/AltiKa and altimeter-derived gravity data have been used to recover bathymetry to a high degree of accuracy (~180 m RMS). Surprisingly, there have been comparatively few studies that have compared shipboard and satellite-derived bathymetry and gravity data. During April-June, 2019 we had the opportunity onboard R/V Marcus G. Langseth to compare data acquired with an EM120 Koninsberg swath bathymetry system and a refurbished Bell Aerospace BGM-3 gravimeter with a recent (SRTM15+V2.0) combined ship/satellite-derived bathymetry and gravity field over the Musician and Emperor seamounts in the north Pacific Ocean. We show here that while the recovery of bathymetry and gravity from satellite data has been impressive, discrepancies of up to several mGal and hundreds of meters exist between the shipboard and satellite-derived data. Shipboard bathymetry and gravity data will therefore continue to be required, especially over features with a high wavenumber content (such as seamounts) beyond that recoverable by bathymetric and gravimetric prediction.