Evaluation of Shipboard and Satellite‐Derived Bathymetry and Gravity Data Over Seamounts in the Northwest Pacific Ocean

Abstract

Earth's surface topography/bathymetry and gravity fields provide important constraints 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 measurements at a wide range of spatial scales. During the past few decades much progress has been made in the acquisition of bathymetry and gravity data using both shipboard and satellite altimeter methods. Surprisingly, there have been few comparisons of these data. During April–June, 2019 we had the opportunity onboard a R/V Marcus G. Langseth cruise in the northwest Pacific Ocean to compare data acquired with an EM122 Kongsberg swath bathymetry system and a refurbished Bell Aerospace BGM‐3 gravimeter with the most recent global bathymetry and gravity fields. We find that while the recovery of bathymetry and gravity from satellite radar altimeter data in areas of sparse shipboard data has been impressive, root mean square discrepancies in the range 175.5–303.4 m and 2.6–6.3 mGal exist between shipboard and satellite‐derived data. While these discrepancies are small, they are highly correlated and therefore have implications for the density structure, rock type and geological processes occurring on the deep seafloor. Shipboard data should continue to be acquired, especially over features such as seamounts, banks, and ridges that are associated with short wavelength (<25 km wavelength) bathymetric and gravimetric features beyond that is recoverable in satellite‐derived data.

Seismic Structure, Gravity Anomalies and Flexure Along the Emperor Seamount Chain

“…Watts et al. (2020) obtained a similar result in their study of shipboard BGM‐3 and satellite‐derived gravity data over Jimmu, and other seamounts in the northwest Pacific. We therefore use shipboard rather than satellite‐derived gravity anomaly data in this paper.…”

“…The median filtered shipboard BGM-3 data show a strong correlation with the swath bathymetry and better resolves the small-scale features of Earth's gravity field than currently available global satellite-derived fields such as DTU10 (Andersen et al, 2010) and V28.1 (Sandwell et al, 2019). Watts et al (2020) obtained a similar result in their study of shipboard BGM-3 and satellite-derived gravity data over Jimmu, and other seamounts in the northwest Pacific. We therefore use shipboard rather than satellite-derived gravity anomaly data in this paper.…”

Ocean‐depth measurement using shallow‐water wave models

“…10 Despite the success of satellite-gravity-based bathymetry, 11 recent work suggests that shipboard data are more reliable to detect sharp relief features with characteristic length-scales less than 25 km. 12 An alternative approach employs fluid dynamical principles to model the motion of an incompressible fluid, bounded below by a solid impermeable surface. With the rise in availability and quality of satellite imagery, fluid dynamical methods for ocean-depth measurement offer a way to survey large parts of the coastlines and oceans.…”

“…These methods work on the principle that the additional mass due to a seamount increases the strength of the local gravitational field causing a bulge in the surface height of the water directly above 10 . Despite the success of satellite‐gravity‐based bathymetry, 11 recent work suggests that shipboard data are more reliable to detect sharp relief features with characteristic length‐scales less than 25 km 12 …”

Ocean-depth measurement using shallow-water wave models

“…These methods work on the principle that the additional mass due to a seamount increases the strength of the local gravitational field causing a bulge in the surface height of the water directly above [48]. Despite the success of satellitegravity based bathymetry [49], recent work suggests shipboard data is more reliable to detect sharp relief features with characteristic length-scales less than 25km [52].…”