An in situ optical beam attenuance meter

The design, construction, and use of an oceanographic instrument which measures in situ the optical beam attenuance coefficient of sea water in the range of 0.1 to 4.5 m^-1 for any one of six defined spectral bands is described. The instrument is readily calibrated using pure water and has been designed to maintain its calibration over a period of several weeks despite lamp changing and the shocks received during normal shipboard handling. Data from some field trials are presented, indicating the potential of the instrument.