POLYCHROMATIC TRANSMISSOMETER FOR IN-SITU MEASUREMENTS OF SUSPENDED PARTICLES AND GELBSTOFF IN WATER

The beam attenuation coefficient is an optical parameter that sensitiv ely depends on suspended and dissolved substances in water. Its measur ement is not only of interest for an understanding of the radiative tr ansfer in a water column. With appropriate algorithms for data interpr etation, it also allows a fast determination of absorbing and scatteri ng matter as time-series measurements or depth profiles that cannot ea sily be obtained with other methods. An instrument has been developed for measuring spectral attenuation coefficients over st wavelength ran ge from 340 to 785 nm. The optical path length can be set between 0 an d 400 min. This allows application in a wide range of turbidity in coa stal and inland (case 2 and case 3) waters and a calibration of the in strument during in-situ measurements. This makes the instrument suitab le for long-term applications in which signals from conventional instr uments would degrade owing to the biofouling of optical windows. From the data, the amount and the size distribution of suspended particles and the specific absorption of dissolved organic matter are derived in real time. Algorithms based on Monte Carlo methods are available for a classification of transparent particles and phytoplankton. (C) 1997 Optical Society of America.