Measuring the underwater light field with a modified drifting buoy

Recently, scientists deployed a so-called BGC float of the ICBM research group Marine Sensorsystems in the Mediterranean, between Nizza and the island of Corsica. For the first time, this kind of automated diving boy for biogeochemical (“BGC”) measurements was equipped with a multispectral RAMSES radiometer, provided by the German enterprise TriOS, a partner of the ICBM in the current project Spectral-Argo-N. These devices are able – in simplified words – to detect entire colour ranges of light or, to express it more precisely, to record entire wavelength ranges.

The BGC floats used so far were equipped with radiometers that could detect only four wavelenghts, or even less. In this configuration, the float serves as a diving robot which, depending on its construction, is able to dive to depths of several thousands of metres. Resurfacing at regular intervals, it automatically radios the collected measuring data to the marine science community. In the modified float, the hyperspectral sensor is part of the measuring equipment.

How deep light penetrates into the sea and how it changes in different water layers are important questions for marine researchers. Answers on these questions, knowing also the respective water temperatures, enables the scientists to draw conclusions on the biological activity underwater. The so-called light field strongly influences algal growth as well as zooplankton, fish and other organisms.

At present, the hyperspectral BGC float of the Marine Sensorsystems group undergoes a test run in the Mediterranean, doing for the first time high resolution underwater light field measurements. Moreover, the scientists are developing novel procedures for data evaluation and data management. Eventually, they want to collect comprehensive data on the underwater light field as well as to describe temporal and spatial changes and finally, to compare their results with current satellite data.

A second RAMSES equipped float is currently tested in the North Sea and will be deployed afterwards in the Baltic.