Toward high-spatial resolution gravity surveying of the mid-ocean ridges with autonomous underwater vehicles

The shallow ocean crust of the mid-ocean ridge (MOR) is a critical environment where important chemical and biological exchanges occur. Resolving the 3-D structure of the subsurface environment beneath MOR crests at spatial scales ranging from 1-1000 meters remains a continuing challenge in marine geophysics. Previous submerged gravity surveys have employed manned, remotely operated, or towed submersibles - to date, autonomous underwater vehicles (AUVs) have not been used. Obtaining sub-mGal gravity measurements requires highly accurate knowledge of vehicle depth, velocity, attitude, and attitude rate, and we report the impact that sensing errors have on obtaining accurate estimates of the vehicle acceleration measured by the gravimeter. We investigate the effect of AUV velocity on filtering of the gravity anomaly data and how this bounds the achievable spatial resolution of gravity surveys. These results demonstrate the limitations imposed on continuous gravity surveying by vehicle velocity and present navigation sensing. Precision gravimetry will significantly enhance the bathymetric, magnetic, and optical data currently obtained by the AUV, and the data obtained promises to advance our knowledge of a wide variety of processes occurring at MORs, as well as other structurally complex seafloor terrains.