Oceanic In situ Fraunhofer-Line Characteristics (Fraunhofer-Line Underwater eXperiment: FLUX).

摘要

Interest in making use of the existence of Fraunhofer lines to reduce solar background noise for the Satellite Laser Communications (SLC) program prompted the requirement for making underwater in situ characterizations of five Fraunhofer lines in the blue-green spectrum. Recent papers that discuss and attempt to explain frequent occurrences of high measured values for underwater irradiance raised concerns about the persistence of Fraunhofer lines. The effect of an increased light field could significantly reduce (potentially eliminate) the absorption depth of Fraunhofer lines and reduce their solar-rejection benefits to optical communications. These characterizations were made from a surface ship off the coast of Hawaii in August 1989. Fraunhofer lines at 420, 440, 486, 518, and 532 nm were characterized at the surface and at four discrete depths to a maximum depth of 90 m. These are the first known characterizations of Fraunhofer lines underwater. A high resolution scan from 450 to 550 nm was also made at a depth of 73 m. The results from this experiment showed no differences between the surface and underwater scans, suggesting the effects of interwavelength scattering is less than originally proposed.