The Argus Island Project Artemis array has two specifications as the project moved from active to passive SOFAR application. source wikipedia:
shipboard active array:
50 ft (15 m) by 33 ft (10 m) and
weighed 400 tons. It consisted of
1440 individual transducers (200 pounds apiece) in a
48 by 30 configuration.
fixed passive receive array:
10 Mile long
ten strings of hydrophones mounted on
200 eighty-foot towers laid down the side of Plantagenet Bank in Bermuda.
The strings were laid on the side of the bank using the U.S. Navy large covered lighter YFNB-12, reconfigured with a long overhead boom to handle the towers. Each cable had special takeouts built into it at intervals from which wires to the hydrophones were connected. Each tower was clamped onto the special cable with takeouts. At the upper end of the approximately 4-inch (100 mm) cable a wire rope was attached and led to an explosively embedded anchor shot into the flat coral top of Plantagenet Bank. Tension of more than 40,000 lb was applied to the wire rope and cable to lay it down the side of the bank in the straightest line possible. At one point all further construction ceased while a stopper was placed on the special cable because most of the connection to the wire rope had broken and the string was being held by a few strands of wire on the double drum winch on YFNB-12. The YFNB-12 was held in place with four Murray and Tregurtha Diesel outboard engines placed on the corners and capable of 360 degree rotation, developing tremendous thrust in any direction. The cables led to Argus Island tower, from which the signal was conducted to the United States listening post located at Tudor Hill, Southampton, Bermuda ( ) that had opened on June 1, 1955. At the time the post was classified top secret. Tudor Hill Naval Facility Bermuda was closed in 1995. The facility shares a short road with the Pompano Beach Club.
Picture of the probable interim design.
Picture of the probable final design.
These two views may not be with the same hydrophone array. The second is obviously larger than the first. Given the resolution’s rough ability to count the elements, this makes for difficulty in determining their construction details. Focusing on the second, my first impression was to call each white spot in the field of frames an element. However, there are white square covers over some of what should be elements (I would speculate they were there to mark what element had not been inspected yet—or had failed a test), and these covers center on the black areas surrounding the white areas. Thus the white areas are part of the frame.
The first picture’s array is in 3×5 panels, each panel is of 5×12 elements (900 total elements), but this does not conform to the specification above in any way—even if additional panels were added. However, as this is a difficult interpretation given both the poor resolution and the camera angle, each panel could be composed of 6×12 elements, and the entire assembly is only short a row of panels. I would like to think this first picture is displaying the array under partial construction.
The second picture’s array shows 4×5 panels, each panel is of 6×12 elements (1440 total elements) which does conform in layout. This also conforms to the extract from Project Artemis Acoustic Source Performance Characteristics:
The Artemis acoustic source was designed to meet the requirements for an ocean surveillance study program. These requirements included a source level of 152 dB in a 100-Hz band centered at 400 Hz with a transducer operating depth of 1200 feet. The transducer, which was completed in June 1964, is a rectangular planar array 33 feet wide and 50 feet high.
The ocean surveillance study program, Project Artemis, initiated by the Office of Naval Research in 1958, required a very high power, deep acoustic source. The acoustic requirements established. for the projector called for a capability of radiating 1000 kW of acoustic power in a 100-Hz band centered at 400 Hz with pulse lengths of 10 to 60 seconds at a 10% duty cycle. Beamwidth to the half-power points was to be 20 degrees in the horizontal plane and 12.5 degrees in the vertical plane. This combination of power and beamwidth would result in a source level of approximately 152 decibels relative to 1 microbar at 1 yard (dB//1 gbar at 1 yd). The acoustic axis was to have a fixed orientation of 11 degrees above the horizontal plane.
Several proposals for the projector were considered, the final selection being a rectangular plane array 33 feet wide by 50 feet high composed of 1440 variable-reluctance transducer elements. Each element is nearly cubical, being 11-1/8 inches square on the radiating face and 11-3/4 inches deep. They are assembled in frames in which 72 elements are closely packed in 12 rows by six columns. Each assembly, referred to as a module, is approximately 6 feet wide. by 12 feet high. The completed array consists of far rows of modules with five modules in each row. The modules are mounted on a suitable array frame which provides the proper tilt angle of the radiating face and supports auxiliary components associated with the electrical input to the elements. Radiation to the rear of the array is suppressed by a system of pressure compensated, flattened, gas-filled tubes which serve as acoustic pressure releases on the rear faces of the elements.
Extracts from Project Artemis Acoustic Source Characteristics Of The Type TR-11F Transducer Element (which concerns itself with an upgrade in impedance to help with transmitter loading, and with diaphragm spring displacement):
The present configuration of the ARTEMIS source employs TR-11C elements with a parallel electrical connection of groups of six series connected elements.
(source unknown) The SOSUS application of these elements in an array suggest a receive sensitivity of 1W audio power at 1,000km.