Saturday, July 2, 2011

An ocean view from space

- Fabrício S. C. Oliveira (University of Sao Paulo, Brazil)

Firstly, I'd like to thank our Chief Scientist, Scott Miller, for the invitation to participate on this cruise. This will be an opportunity to learn techniques for making air-sea interaction measurements and applying these techniques in studies of the same nature in Brazil. I was extremely curious in participating on a cruise that has as its purpose measuring air-sea gas exchange, since that is totally new for me.  At the moment, I don't work with air-sea gas flux (yet), so what am I doing here?

I'm a physical oceanographer specialized in ocean remote sensing meso- and large-scale and a beginner in ocean modeling. However, if we are studying areas with high primary productivity (phytoplankton blooms) nothing is better than satellite data to monitor these blooms. The main advantages in using satellite data are the wide spatial coverage, synopticity, and the high sample frequency of the data. Regions with a high oceanic primary productivity can be easily monitored from space using ocean color images. The oceans are composed of different kinds of components, dissolved or particulate. They can be optically active, that is, interacting with electromagnetic radiation from the sun; they are responsible for the different colors in the oceans.

The majority of sensors monitoring the ocean color operate in the visible band, a narrow band of the electromagnetic spectrum that is used for us to distinguish the color of the objects. The most important application of these sensors is the estimation of chlorophyll-a concentration, because from it is possible to estimate the phytoplanktonic biomass and primary productivity in an area. Good… it seems intuitive to use this data for monitoring bloom regions, right? Gotcha!!! As nothing is perfect, a big problem is that the clouds are totally opaque to the radiation in these wavelengths and a high cloud coverage means no data. This high cloud coverage has been common along the cruise. To minimize the effect of the cloud coverage I have tried to do some simple image processing, such as an averaged composite between two different ocean color sensors.

Finally, as an oceanographer, it is fair that I participate on the team charged with making the CTD casts, the CTDers, as we are known. I'm totally familiar with this operation, but I've never seen a CTD cast so organized (congrats to the crew and SSSG team). Also, I've never seen such fast CTD casts in the deep-sea because the CTD only goes down to 100m, but I'm not complaining because the sooner the better. The CTDers are always in a good mood, event at 1am, when we are closely monitored by the squids and small fishes (maybe needlefishes, i'm not sure about that).