Demonstration of innovative seabed visualization technology that uses visible laser (green) × invisible laser (ultraviolet)
― New developments in the optical exploration of the seabed using a high-performance underwater laser scanner ―

1. Key Points

• Sonars are a conventional technology used for visualizing the seabed and can measure long and wide areas. However, the image resolution is relatively low with acoustic interference from other acoustic devices and systems. Cameras are a similar technology and have high resolution, but they can only visualize the limited area that light can reach and require proximity to the seabed, leading to safety and efficiency issues.

• Therefore, a world-class high-performance underwater laser scanner with a much higher image resolution than sonars and an overwhelmingly longer and wider measurement range than cameras was developed (Fig. 1). It performed better than existing underwater laser scanners in the following areas.
  [Measurement range] Achieved a visible laser-based seabed laser ranging^※1 distance of ≥60 m (round-trip propagation distance: ≥120 m)
  [Image resolution] Successfully generated ultra-high-resolution scanning images of deep seafloor with horizontal resolution of ≥8,000 pixels

• In addition, the deep seabed was simultaneously measured with a laser using visible light^※2 (green) and invisible light^※2 (ultraviolet) (simultaneous generation of a laser scan image of the seabed.).Measuring the reflection of the ultraviolet laser on the seabed is expected to make the previously “invisible expressions of the seafloor” visible.

Figure 1. Positioning of high-performance underwater laser scanner relative to conventional seabed visualization technology and outcomes of this announcement

2. Overview

Shojiro Ishibashi and his colleagues of the Maring Engineering Science Group from the Engineering Department in Japan Agency for Marine-Earth Science and Technology (JAMSTEC) have collaborated with Mitsubishi Electric Defense and Space Technologies Corp. and Hamamatsu Photonics K.K. to develop two deep-sea demonstrator models (green-laser demonstrator and UV-laser demonstrator) of a high-performance underwater laser scanner that uses a laser with visible light (green, wavelength 532 nm) and invisible light (ultraviolet, wavelength 355 nm), respectively. In deep-sea tests, each demonstrator was mounted on an underwater vehicle and achieved innovative performance that far exceeded conventional technologies.

The green-laser demonstrator recorded a laser ranging distance of ≥60 m (round-trip laser propagation distance including the reflection at the seabed: ≥120 m) for the deep seabed. This is in the order of magnitude of the world’s longest measurement range for this technology. Using the green-laser demonstrator and the UV-laser demonstrator, ultra-high-resolution laser scanning images of the deep seabed with a horizontal resolution of ≥8,000 pixels were achieved. This is also in the order of the world’s highest resolution levels, including those of existing seabed visualization technologies. Both demonstrators were used to simultaneously measure the seabed and generate laser scanning images that visualized the reflectance properties of the seabed at different laser wavelengths, specifically in the visible laser (green) and invisible laser (ultraviolet). This visual demonstration applying ultraviolet laser reflection on the deep seabed is the first of its kind, and interesting differences were found compared to the measurement results obtained using a visible laser. These results demonstrate the innovative performance that has been considered difficult to achieve when using lasers in seabed visualization technology, and they are expected to lead to new developments in the optical exploration of the seabed.

This research was supported by the “Security Technology Promotion Program JPJ004596” implemented by the Acquisition, Technology ＆ Logistics Agency.