Laser Line Imaging

Brief Description

Illustration of a Laser Line Scan system emitting laser beams as it is towed above the bottom. Courtesy: 
Science Applications International Corporation
The basic system consists of the towed underwater optical sensor and the topside control console. Display options include video, frame-grabbed stills, and photographic hard copy. The LLS functions by illuminating a small spot on the target plane with a laser beam and recording the reflected energy with a photo-multiplier tube on a synchronous scanner. The transmitted and reflected laser beams are swept through a 70° sector using a rotating pair of prisms, building an image pixel by pixel in each scan line. The resultant scan lines are viewed as a waterfall display on a standard black and white video monitor and are recorded as an analog video signal.

See NOAA's summary table at summary view of laser line imaging technique. (149 KB PDF)

 

 

 

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Laser line imaging

Laser line scan image of a large group of fish congregating around an isolated rock outcrop.
      Courtesy: NOAA Ocean Exploration Underwater light sensors can be used to create images of the seafloor in deeper or turbid water that cannot be surveyed from the air. A Laser Line Scan (LLS) sensor, towed behind a ship, uses a laser to concentrate intense light over a small area. The laser beam scans the seafloor and the sensor records the reflected energy. The continuous laser scans create a detailed image at millimeter to centimeter resolution. The resolution and area (width) covered by the images vary with water clarity – the clearer the water, the higher the sensor can be towed above the bottom, and the greater the width of optical coverage. LLS is a useful tool for investigating spatial relationships among fish, invertebrates, and the seafloor over larger areas, which conventional video and photographic systems cannot do.

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