The acoustic projector sends high frequency (642 kilohertz) sound into the water. 

 Objects reflect the sound waves in patterns that are dependent on their shape. The acoustic 

 detector (48 by 96 elements in a 2-foot [0.6 meter] square) senses, processes, and stores the 

 sound pattern as an acoustic hologram, which is then digitized and transferred to the holo- 

 graphic reconstructor, a digital minicomputer. The minicomputer processes the hologram to 

 form an image which is then displayed on a screen. All electronics inside the underwater 

 housing are pressure tolerant, that is, the housing does not withstand the ambient pressure, 

 but transmits it directly to the electronic components themselves within the oil-filled, 

 pressure-compensated container. 



The acoustic imaging system is envisioned as being very useful in two scenarios. As 

 a classification system in conjunction with a search sonar, it will provide target identifica- 

 tion, as would a television, but with greater range and less sensitivity to water turbidity. As 

 a visual system, it provides visibility for the operation of underwater work systems, even 

 when there is turbidity caused by the mud turned up by the work system. 



REAL-TIME OPTICAL MAPPING SYSTEM (ROMS) 



The concept behind the development of ROMS was to combine the qualities of (1) 

 high optical resolution, (2) a large swath width, and (3) a real-time readout to produce a 

 real-time optical picture of the ocean bottom for fast seafloor search and mapping. It 

 thus bridges the gap between existing acoustic systems, which offer long range and real-time 

 operation but are limited by low resolution; and photographic systems, which offer high 

 resolution but are not capable of real-time operation. 



ROM's capabilities depend upon a set of rotating, three-faceted mirrors mounted on 

 a single shaft (figure 9). The first mirror sweeps an argon laser beam across a 120-degree 

 (2.09 radians) angle. The second, synchronized with the first, receives a portion of the beam 

 returned from the seafloor and reflects it through a focusing system to a photomultiplier. 

 The photomultiplier signal is preamplified and processed before it is transmitted to the 

 surface, where it is further processed to make it compatible with a cathode-ray-tube (CRT) 

 display. The CRT display is arranged to provide a "waterfall," two-dimensional, map-type 

 display, and the data are permanently recorded on hard copy for postrun analysis. The 

 operator can control the display and adjust its contrast or zoom-in on an object of interest. 

 The receiving mirror is mounted in a water-filled, acrylic housing to minimize light losses 

 at the water-window-air interface. Its field of view is restricted to a region near the seafloor 

 to minimize first-order backscatter. Backscatter is sufficiently reduced to make the system 

 power limited. 



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