THE WORK OF THE CSIRO SCIENTISTS

Magnus Wettle and David Blondeau-Patissier

David and Magnus were aboard the Pelican for one week in order to measure the optical properties of coral waters in the GBR. The purpose of these measurements was to help to allow us to understand how visible light (the signal detected by a satellite) is affected by the water overlying the corals. Ultimately, this will allow us to better interpret satellite data, which in turn can be a powerful tool for monitoring the extent and/or severity of coral bleaching throughout the whole Great Barrier Reef.

The two main variables that describe how light as we see it from the satellite is affected by the water are absorption (a) and backscattering (b). Absorption changes the colour of the light as well as decreases its intensity (as seen from a satellite in space), whereas backscattering increases the perceived intensity of light as well as changing its colour.

We have deployed a suite of underwater optical instruments at various sites throughout the first week, and are satisfied that we have collected a suitable and useful data set. Various technical complications arose along the way, but that was only to be expected with the complexity of the instrumentation.

The waters measured on this trip are exceptionally clear, which can be seen in the two graphs: both absorption and backscattering are considerably lower in the GBR coral waters compared to waters measured last year in the Daintree in the Northern Territory. All the terrestrial particles in the Daintree waters result in high backscattering, which is why these waters look brown in the photo. Because of the unusually clear waters in coral environments, these waters need to be properly measured in order to account for them in the algorithms used to interpret satellite image data.

Apart from the obvious mission for us to collect data, it was very beneficial to spend some time with the GBRMPA team. After all, our work on developing methods for monitoring coral bleaching using satellites is only relevant if it is useful for people like Paul and his team. The opportunity to discuss what they need and what we can and cannot do has been very beneficial to us, and we are grateful for the invitation to come along.

Seeing the endless fields of bleached corals at the Keppel Isles was an astounding if depressing experience, and put this work into stark context.

And aside from all this science stuff, hanging out with Ewan, Matty, Frank and Peda has been great fun. I have thoroughly enjoyed having my horizons broadened from all the new things I have learned from them.

From writings by Magnus Wettle and David Blondeau-Patissier (edited by Nick Kelly)