50 Years of Multibeam Sonar

First conceptual diagram of slant range and sonar observed area in BOMAS (Bottom Mapping Sonar) proposal to the US Navy from General Instruments, the system developer.

An article in Hydro International magazine tells the story of how multibeam sonar was developed in the early 1960s. Originally conceived as an airborne radar mapping system, the concept of beam formed imaging was proposed to the US Navy, which immediately understood its application for use in hydrographic surveys.

Diagram from General Instruments proposal to the US Navy.

BOMAS (Bottom Mapping Sonar), later called SASS (Sonar Array Sounding System), was first installed in 1963 aboard USS Compass Island, a Navy electronic system test vessel. SASS, developed by the contractor General Instruments, was intended to produce contour maps of the ocean bottom. Sixty-one beams, each one degree wide, fanned out beneath the ship. Gyro information was used to stabilize the return echoes for roll and pitch.

Contrary to reports elsewhere on the web, the first SASS survey ship deployment was on  USNS Michelson at the Brooklyn Navy Yard (NY Naval Shipyard) in early 1964. Michelson was to proceed directly to its new operating area in the Pacific, but as the SASS (and associated systems) required further testing. Operating out of ports in Florida, sea trials were conducted in the waters around the Bahamas during spring and summer of 1964. Michelson finally deployed to the Pacific in the autumn, via Panama. SASS was  subsequently installed aboard sister survey ships USNS Dutton and USNS Bowditch.

Usefulness of SASS was initially limited by the lack of  large scale digital data storage at that time. Increased computer power, digital signal processing and the use of GPS for control have improved multibeam sonar. Michelson's SASS was the grandfather of all survey systems, side scans and fish finders in use today.

Read the story in Hydro International here.