Low-Light Camera Field Evaluation for Underwater Nighttime Operations

A low-light, underwater, charge coupled device (CCD) video camera with a unique lens was evaluated in near-zero surface lux for operational use at night as a function of depth in the ocean. The goal is real-time video for moving underwater operations, as standard cameras need stationary long exposures and a fixed scenery. CCD video cameras handle illumination variation with pixel uniformity in low light the best. The video camera observed objects at varying distances with a filtered low-light source in a tank, validating its ability to operate at low luxes automatically. The video camera and self-contained logger were attached to a frame with Secchi disks, and a Snellen eye chart was deployed in the ocean at night (lux less than 0.1). Edge detection was applied to Secchi disks in recorded images where outlines were observed to 12 m and 25 m depth in a harbor and ocean. The visual acuity is short-range and was significantly lower than night vision goggles at similar lux levels. Video results varied from the harbor with measured chlorophyll-a near 0 to10-40 microgram/L in the ocean, representing an algae bloom responsible for bioluminescence. The stirred motion of the frame induced bioluminescence that created varying effects on visibility.