Petitt Robert A.

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Petitt
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Robert A.
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  • Technical Report
    At Sea Test 2 deployment cruise : cruise 475 on board R/V Oceanus September 22 – 26, 2011 Woods Hole –Woods Hole, MA
    (Woods Hole Oceanographic Institution, 2011-10) Weller, Robert A. ; Lund, John M. ; von der Heydt, Keith ; Palanza, Matthew ; Lerner, Steven A. ; Scholz, Tim ; Begler, Christian ; Siddal, Gregg ; Ostrom, William M. ; Newhall, Kris ; Bouchard, Paul R. ; McMonagle, Kathleen ; Jamieson, Eric ; Petitt, Robert A. ; O’Brien, Jeff ; Cook, Gary
    The R/V Oceanus, on Cruise 475, carried out the deployment of three moorings for the Coastal and Global Scale Nodes (CGSN) Implementing Organization of the NSF Ocean Observatories Initiative. These three moorings are prototypes of the moorings to be used by CGSN at the Pioneer, Endurance, and Global Arrays. Oceanus departed from Woods Hole, Massachusetts on September 22, 2011 and steamed south to the location of the mooring deployments on the shelf break. Over three days, September 23-25, Oceanus surveyed the bottom at the planned mooring sites, deployed the moorings, and carried out on site verification of the functioning of the moorings and moored hardware. Oceanus returned to Woods Hole on September 26, 2011.
  • Technical Report
    Report of a workshop on technical approaches to construction of a seafloor geomagnetic observatory
    (Woods Hole Oceanographic Institution, 1995-09) Chave, Alan D. ; Green, Arthur W. ; Filloux, Jean H. ; Law, Lawrie K. ; Petitt, Robert A. ; Rasson, Jean L. ; Schultz, Adam ; Spiess, Fred N. ; Tarits, Pascal ; Tivey, Maurice A. ; Webb, Spahr C.
    This report considers the technical issues on sensors, data recording and transmission, control and timing, power, and packaging associated with constricting a seafloor geomagnetic observatory. Existing technologies either already in use for oceanographic purposes or adapted from terrestral geomagnetic observatories could be applied to measure the vector magnetic field components and absolute intensity with minimal development. The major technical challenge arises in measuring absolute direction on the seafloor because terrestral techniques are not transferrable to the deep ocean. Two solutions to this problem were identified. The first requires the development of an instrument which measures the instantaneous declination and inclination of the magnetic field relative to a north-seeking gyroscope and the local vertical. The second is a straightforward extension of a precision acoustic method for determining absolute position on the seafloor.
  • Technical Report
    SeisCORK engineering design study
    (Woods Hole Oceanographic Institution, 2006-05) Stephen, Ralph A. ; Pettigrew, Tom ; Petitt, Robert A.
    The goal of SeisCORKs is to make simultaneous and co-located seismic, pressure, temperature, pore water chemistry and pore water biology measurements in the seafloor. We want to see the small events in the vicinity of the borehole for three reasons: 1) After an event fluid may flow in the formation in response to the changing stress regime. Down to what magnitude of event do the pressure transients in the well respond? 2) Fluid flow causes small earthquakes. One mechanism for example is by changing the temperature of the rocks which expand and contract, altering the stress regime. We want to look for this fluid flow. 3) Laboratory studies of rock deformation show that shear fracture is preceded by the coalescence of interacting tensile microcracks which are observed as “acoustic emissions”. By placing high frequency geophones next to faults it may be possible to observe these “acoustic” precursors to rock failure. Since in reservoirs on land small events appear in the frequency band 400-800Hz, no one has yet tried to observe them in oceanic crust. SeisCORKs also obviate the considerable logistical, administrative, and clearance difficulties associated with scheduling a shooting ship to run offset VSPs. We resolved to start with a “tubing conveyed” SeisCORK configuration consisting of four three-component sondes at 50m separation lowered on the outside of 4.5in casing (or drill pipe) inside 10-3/4in casing.