Line of Light Aid to Navigation

Abstract : The Coast Guard Research and Development Center evaluated the feasibility of using collimated, horizontal beams of light to mark shipping channels. The original concept called for the beams to be directed, at some fixed height above the water, down the channel centerline from an appropriate transmission point. Mariners would endeavor to safely transit the channel by steering to keep the beams overhead. Several source types were considered; the large beam divergence of incandescent sources made them unsuitable for ranges in excess of several hundred yards. Only lasers were found to offer the required intensity and beam divergence characteristics for a workable system. However, eye safety considerations limited the allowable output power density to unacceptable levels. At the allowable irradiance levels, light scattering calculations predicted poor beam visibility, except under ideal viewing conditions. Additionally, the high-powered lasers required would be expensive, unreliable, and difficult to maintain. A recommendation was made to remove the 'line of sight' concept from consideration due to negative safety, cost, performance, maintenance, and reliability aspects.