Robert A. Petitt

Hawaii‐2 observatory pioneers opportunities for remote instrumentation in ocean studies

Beneath 5000 m of water midway between Hawaii and California, the Hawaii-2 Observatory (H20) rests on the seafloor (Figure 1). Telemetry and power come to this pioneer, deep-ocean scientific observatory via a retired telephone cable, Hawaii-2, donated by AT&T to the Incorporated Research Institutions for Seismology (IRIS) Consortium for the benefit of the scientific community. H20 is the first Global Seismographic Network (GSN) station on the seafloor.With a suite of wet-mateable connectors on a junction box (j-box), H20 offers marine scientists a new opportunity to deploy and operate remote instrumentation in the middle of the ocean.

A network-based telemetry architecture developed for the Martha's Vineyard Coastal Observatory

Underwater observatories with real-time data and virtually unlimited power transmission capabilities compared to traditional oceanographic moorings are beginning to provide scientists with continuous access to the coastal and open ocean. However, for any coastal observatory to serve as a cost-effective system for the collection of long-term scientific and environmental data, it must have a simple, upgradeable power and telemetry system and an instrument interface that is compatible with existing standards. It must be designed for extended environmental exposure and ease of service to avoid high maintenance costs. Most importantly, the observatory must be accessible to all potential users, including students, scientists, engineers, and policy makers. This strategy was applied to the design of the Marthas Vineyard Coastal Observatory on the south shore of the island of Marthas Vineyard. The new facility, and in particular its system architecture, as developed by the Woods Hole Oceanographic Institution with support from the National Science Foundation, are described.

The Martha's Vineyard Coastal Observatory: a long term facility for monitoring air-sea processes

The desire to gain a better understanding of coastal processes over the past decade has led to an increased focus on coastal research in the scientific community. As an estimated 50% of humanity lives within 100 miles of a coastline and as national defense initiatives shift towards littoral regions, this interest in coastal processes will continue to grow. The south shore of the island of Marthas Vineyard is an ideal location for the study of the near-shore environment, due to its uninterrupted, south-facing beach with open ocean exposure. This area is frequented by all types of weather systems, including winter storms, hurricanes, and calm summer conditions. The seasonal variations provide a wide range of biological activity as well. To support long-term research in these areas, the Woods Hole Oceanographic Institution (WHOI), supported by the National Science Foundation, is currently developing and installing a coastal observatory system on the south shore of the Vineyard in Edgartown, Massachusetts.

Report of a workshop on technical approaches to construction of a seafloor geomagnetic observatory

Funding was provided by the National Science Foundation under grant EAR94-21712 and the National Aeronautics and Space Administration.

A fast response, stable CTD for gliders and AUVs

A new CTD has been designed for gliders and other AUVs. It uses a four-electrode conductivity cell with internal temperature sensor to achieve excellent dynamic response and high spatial resolution. The design is rugged, has low drag and is resistant to fouling. No pump is required and the electronics are self-calibrating and free of thermal drifts. Results of a comparison with an un-pumped Seabird SBE-41cp CTD on a glider show superior performance in all temperature gradient situations

Technology For The Measurement Of Oceanic Low Frequency Electric Fields

Low frequency ( ~ 0 . 0 1 Hz) electric field data from the Ocean have wide applications in basic research into the structure of the solid earth, in exploration geophysics, in studies of the depth-averaged velocity structure of ocean currents, and in tactical oceanography. However, a number of unique problems caused by the oceanic environment must be overcome to achieve stable measurements to frequencies as low as Hz. First, the high conductivity (3-5 S/m) of seawater results in substantially weaker electric fields in the ocean than in other geological materials. This means that precision, low noise electronics must be used and that even the faint fields generated by corrosion of metallic parts may be capable of swamping the signal of interest. Second, even the best non-polarizing electrodes exhibit a time variable offset voltage which is often much larger than that produced by the external electric field. Finally, the very long period nature of oceanic electric field phenomena places extreme stability requirements on instrument electronics. None of these problems are as important for electric field measurements on land, and a very different approach is required in the oceanic environment. As a case history, this paper will describe instrumentation that has overcome these obstacles in a low power package capable of multiyear deployments in the deep ocean. The electric potential is measured between the ends of orthogonal, 3 m long pairs of seawater-filled plastic pipes or salt bridges. The inner ends of the salt bridge are connected to a mechanical DPDT fluid switch or water chopper which physically reverses the electrodes during the measurement cycle. As the switch changes position, a set of non-polarizing silver-silver chloride electrodes are alternately connected to opposite ends of the salt bridge. This not only removes electrode drift, but eases the necessity for ultra stable analog electronics. After amplification by a low power differential amplifier, analog-to-digital conversion is achieved using a voltage controlled oscillator followed by a simple counter. A low power microcontroller handles all basic instrument functions including data storage in EEPROM memory. All of the electronics, including batteries, orientation compass, and a radio transmitter for recovery location, are contained in a single 17 inch glass sphere pressure case. The least count sensitivity of this instrument is 20 nVim, corresponding to an electric potential of 60 nV across the 3 m salt bridge. Based on spectral analysis of seafloor records, the real instrument noise level is substantially lower than this figure. The baseline stability over long deployments is compar-

Instrumentation to measure electromagnetic fields on continental shelves

The authors have constructed a set of instruments designed explicitly for shallow water electromagnetic measurements. These units record (with sixteen bit accuracy on EPROM memory cards) the vector horizontal electric field, the vector variations of the magnetic field, pressure, temperature and two components of tilt at a nominal sample rate of 2 Hz for a month. This could be extended to 10 Hz for short experiments as the sensors are easily capable of operation to this point.<<ETX>>

Power system for the new Jason ROV

Jason II/Medea is a remotely operated vehicle (ROV) system built and operated by the Woods Hole Oceanographic Institution (WHOI) for oceanographic research to depths of 6500 m. Jason II/Medea is a two-body system: Medea operates at the end of the 10 km electro-optical tether cable and decouples Jason from surface ship motion. Jason II is connected to Medea by a 35 m long neutrally buoyant umbilical. The free swimming Jason II is propelled by six DC brushless electric thrusters that provide about 500 lbs of thrust in each of three axes of motion. Jason II features dual manipulators, a detachable sample sled, workspace lighting, still and video cameras and navigation and science survey instruments. Jason II also provides a payload capacity for mission-specific scientific instruments and tools. The new power system delivers, controls and monitors all the power used on the vehicle under the command of the control system software.

A new vehicle for measuring deep ocean mixing

The High Resolution Profiler II (HRP-II) is a unique free vehicle developed at WHOI to measure a range of scales of ocean mixing, from turbulence to advection. On-board mission control software allows autonomous operation during data acquisition profiles to depths of up to 6000 meters. The new profiler was exercised in deep water during a successful test cruise in January 2004.

Power systems for the Coastal and Global Scale Nodes of the Ocean Observatories Initiative

The Ocean Observatories Initiative (OOI) includes mooring power systems development for the Coastal and Global Scale Nodes (CGSN). This paper summarizes the current status and results of the CGSN power systems development effort primarily concentrating on the surface moorings which include wind generators, photovoltaic arrays, rechargeable batteries and power control electronics. Higher power versions of these mooring power systems, currently in the design phase, are also described.