The Southampton underwater multiparameter optical-fibre spectrometer system (SUMOSS)

Abstract

The SUMOSS was designed to measure simultaneously a number of inherent and apparent optical properties at high spectral resolution (<5 nm). The sensors consist of a transmissometer to measure beam attenuation, plane irradiance sensors (to measure reflectance, Kd and Ku) and a scalar irradiance sensor for calculating the absorption coefficient. The SUMOSS was designed to minimize the effects of self-shading of the sensors. The radiometric stability of the instrument across the visible spectrum (350-720 nm) was assessed in a series of dark room experiments. The linearity of the response of the passive sensors was evaluated over a range of intensities and was found to be stable to within 1%. The spectral resolution was measured using red and green lasers on the passive channels (FWHM 4 nm, sampling interval 0.4 nm). Radiometric calibrations showed that there was minimal variability in the spectral response over time. The SUMOSS has been deployed in three optically different water masses (the Baltic, Mediterranean and UK) and the spectral quality and intensity of the readings is interpreted using measurements of the concentrations of suspended particulate material and chlorophyll.