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Content archived on 2024-04-19

MArine RAdiometric Spectrometer: system deployment and application development programme


The marine radiometric spectrometer system MARAS has been developed to perform spectral radiometry in the ocean. By simultaneous collection of upwelling and downwelling scalar and vector spectral irradiance the apparent optical properties of a water body can be estimated. The multicollector system has collectors mounted at 2 depths so that it is relatively impervious to changes in the ambient light levels and only requires relative, rather than absolute, calibration of its sensor sensitivities.

The measurements of apparent optical properties are used in an inversion system which has been developed and tested by simulated radiative transfer models and can be shown to yield useful estimates of the inherent absorption and scattering properties of the ocean. The direct effect of ocean constituents on both the measurements themselves, and on the derived apparent and inherent optical properties are demonstrated.
The Marine Radiometric Spectrometer (MARAS) system is designed to characterise the optical properties of the marine environment. The system will enable scientists to study the effects of different marine constituents on these optical properties. Global monitoring of Earth's marine surface by future remote sensing ocean colour satellite systems will require a much better understanding of these optical properties, and also of the way in which these optical properties affect the spectral shape of Top of the Atmosphere (TOA) radiation.

After completion of the transmissiometer/scatterometer, the technical and scientific evaluation of the instrument will be performed in a series of test cruises designed to evaluate the system performance in open and coastal waters. The optimum approach to the use of spectral radiometer data has to be developed. Instrument calibration, the extraction of constituent estimates, the estimation of inherent optical properties, and the modelling of the radiative transfer process to produce TOA radiance estimates, are all elements of this validation programme. This programme will aim to establish the norms to be used in the exchange of optical data for ocean colour science and subsequently for the validation and vicarious calibration of future global monitoring satellite systems.

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