Apt: An Instrument For Monitoring Seafloor Acceleration, Pressure, And Temperature With Large Dynamic Range And Bandwidth

A simple tool has been developed to facilitate the study of interrelated geodetic, geodynamic, seismic, and oceanographic phenomena in marine settings. It incorporates quartz pressure and triaxial acceleration sensors and a low-power, high-precision frequency counter. The sensors are housed in a 6-cm outside-diameter, 1-m-long pressure case that is pushed vertically into the seabed with a submersible or remotely operated vehicle, with no profile remaining above the seafloor to cause current-induced noise. The mass of the tool is designed to match that of the sediment it displaces to optimize coupling. Intrinsic measurement precision of the order of 10(-8) of full scale (in this instance, a pressure range equivalent to 4000 m of water depth and an acceleration range of +/- 3g) allows observations of pressure, acceleration, and tilt variations of 0.4 Pa, 0.6 mu m s(-2), and 0.06 mu rad, respectively. Temperature variations measured near the top and at the bottom of the instrument are resolved to better than 0.1 mK. With the large dynamic ranges, high sensitivities and broad bandwidth (10-Hz Nyquist to drift-limited zero-frequency DC), ground motion associated with microseisms, strong and weak seismic ground motion, tidal loading, and slow and rapid geodynamic deformation-all normally studied using disparate instruments-can be observed with this single tool. Examples of data are provided from four deployments with connections to the Ocean Networks Canada Northeast Pacific telemetred undersea networked experiment (NEPTUNE) observatory cable.