Development and Field Deployment of a Novel AUV Gravimeter


DOEI and Access to the Sea co-funded Research: 2010


Scientists currently possess few techniques capable of obtaining quantitative fine-spatial resolution data of the shallow oceanic crust.  Sonar surveys provide valuable bathymetric information on seafloor structure, and recent advances in sonar technology and underwater vehicle navigation have significantly improved the precision of these surveys.  Optical surveys provide imagery of the seafloor, enabling scientists to identify geological and biological features.  While bathymetric sonar and optical camera surveys provide valuable observations of the seafloor they provide limited information on sub-seafloor structure.  Near-bottom magnetic surveying by deeptow, submersible or ROV has been shown to be useful in measuring the magnetic properties of the shallow ocean crust in a decameter scale Gravity measurements can provide valuable information about the density and porosity of the sub-seafloor structure, and provide crucial additional constraints on the shallow oceanic crustal structure.  Gravity anomalies are routinely measured from ships and satellites however the large distance between the gravimeter precludes using this approach for resolving small-scale and low amplitude density anomalies and motivates employing autonomous underwater vehicles (AUVs) to obtain near-bottom gravity measurements.  Presently, there is no gravimeter suitable for use on an AUV.  This proposal investigates using a new class of accelerometers to develop and test a new AUV gravimeter.  We propose three investigations: (1) determine the ultimate sensitivity of the accelerometer and test it side-by- side with a standard ship gravimeter; (2) investigate the potential of strap-down gravimetry; and (3) integrate the sensor into the Sentry AUV and use it on a previously cruise to the Southern Kermadec Arc in Spring 2011.  This new sensing capability will augment and enhance the instrumentation already on the Sentry AUV and motivate new investigations in using gravimetry to improve our understanding of the shallow oceanic crust.  Finally, results from this research will also motivate future research in using this new class of accelerometers to develop low-cost, high-precision inertial navigation systems — an application area with broad implications for ocean, land, and aerial robotics.