Page 292 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

FIGURE 10.35
0
20
40
10.9 Underwater optics and visibility 281
Reflected Artificial + Ambient = Total light
Light penetration and total illumination of target.
Light remaining
100% 10% 1% .1%
0
20
40
wavelengths are absorbed within the uppermost 60 ft (18 m) (Figure 10.35), the yellow will disap- pear within 330 ft (100 m), but green light can still be recognized with the human eye down to more than 800 ft (244 m) below the surface. So, even at shallow depths, objects become monochro- matic when viewed through the camera of an ROV system. The only way to bring out the color of the object of interest is to reduce the water column from the light source to the object. If that light source is aboard the ROV system, the light will need to be near the object (taking backscatter into consideration) in order to illuminate it with full color reflection. An example of the absorption spectrum for pure water is shown in Figure 10.36.
10.9.5 ROV visual lighting and scattering
Observers agree that the absorption and scattering in clear ocean water are essentially the same as in clear distilled water, that some dissolved matter increases the absorption, and that suspended
FIGURE 10.36
Light absorption by wavelength.
Ambient
Depth (meters)
Depth (meters)
Artificial
Red
Blue
Blue-Green