<title>NEARSCAT full-spectrum narrow forward-angle transmissometer-nephelometer</title>

Abstract

The crucial parameters required for the design of underwater optical systems are optical absorption and scattering as a function of location, depth, and wavelength in the ocean. DREV has developed, built, and deployed an underwater probe (NEARSCAT), whose sole purpose is to gather information about the underwater light field in the waters of interest to Canada. The instrument is unique in that it can scan all wavebands in the visible spectrum from 400 nm to 700 nm. It can also continuously sample up to 6 arbitrarily chosen wavelength bands simultaneously with a resolution of 10 nm. The instrument can separate the absorption and scattering components of seawater. This instrument was deployed at 16 locations along the East Coast of Canada, ranging from the north of Baffin Island to Cabot Strait. It was also deployed at 21 stations on the West Coast of Canada. The water column was sampled to a maximum depth of 300 m. The data was found to be extremely consistent and of high quality. We found that the waters were much less absorbing than was previously believed. A strong scattering layer was found to exist near the surface, and extending to a depth of 40 meters. This layer does not strongly absorb. The lack of absorption, the strong layering of scattering, and the predominance of narrow-angle forward scattering has important consequences for optical underwater systems as it implies that signal recovery techniques will be effective in the underwater environment and allow much better performance than was previously thought to be possible.