Buoy and Experiment Systems

You can expect this page to grow as we progress through the project design phase.

The buoy:

Our buoy started off as a salvaged piece of Surlyn foam used before on a Naval Research Labs round-bottom buoy and stored at a warehouse near Chesapeake Beach, MD. Oceaneering Incorporated of Upper Marlboro, MD will complete the design and construction of a new deck structure, keel, and electronics well. Oceaneering will also host the integration of the other buoy and experiment components.

Fiberglass Antenna Housing:

In order to protect our set of four VLF antennas and help to reduce sea ice buildup on the superstructure of our buoy, we will mount an 8 ft. diameter, 9.5 ft. tall fiberglass housing on the buoy. This unique item is being constructed by Marine Design and Composites, of Owings, MD.

6500m Mooring System:

In order to reliably anchor the buoy in 5400 meters of water for two years or more, an extensive and well engineered mooring system must be used. Mooring Systems Incorporated, of Cataumet, MA will build and deliver such a system based on the proven inverse catenary design.

This design is characterized by three component sections. At the top, a 2000 meter 7/16" wire rope section provides tension at the keel, durable performance, and protection from fish bite. Next, a 2500 meter 1" nylon rope section absorbs shock and is more dense than the sea water. The lower section is 2000 meters of 1.5" polypropylene rope which is less dense than the seawater. The net result is a mid-section S-shape common to the inverse catenary design.

Experiment and Telemetry Systems:

We face several unique challenges to run our experiment remotely on the open ocean. These go beyond the ordinary complexities of a highly sensitive VLF receiver.

• The experiment operates on a sea that never calms.
  • In addition to sampling ELF/VLF fields, we must also simultaneously determine the buoys three dimensional orientation.
  • Tilt sensors can give two of the three, but not yaw.
  • A digital magnetic compass has several problems. We are currently considering several options including flux-gate magnetometers and reverse direction finding to known Navy transmitters with our antenna array.
• Limited ability to isolate electronic noise from VLF measurements.
  • Our existing VLF line receivers employed at sites in Alaska require 200 ft. of separation from the antennas to eliminate interference with the received signal. This interference is mainly due to digital components and switching power supplies in the line receiver box.
  • On the buoy, we will have up to 4 ft of maximum separation from the antenna array.
  • To work around this, we will use a mu-metal enclosure that attenuates the magnetic field by 87-93 dB in the frequency range of interest.
• Experiment must run for a long duration on a limited power supply.
  • Most common method of power generation: diesel, solar. Both have problems at our location.
  • We will use twenty 6V AGM marine batteries that can support a low power design for at least a year.
  • Solar panels will replenish the battery bank during the summer months and give us more operational flexibility.
  • The batteries will weigh 1400 pounds, but will be placed below the buoy's center of buoyancy. This will contribute to the buoy’s stability.
• Data must be brought back through the Iridium satellite communication system.
  • Cannot risk leaving data on the buoy for one or two years until revisiting the site.
  • Iridium data modems are the solution for near-real time data and telemetry monitoring.
  • Reconfiguration and scheduling on the fly, from Stanford or HAARP.
  • Coverage at our southerly location with an omni-directional antenna.
  • Relatively low power compared to other SATCOM systems and Iridium is a solvent company.
  • Drawback is low data rate. -> need for onboard data processing.

You can see how we plan to integrate the various subsystems in the following PDF document.