Taking water temperature measurements from the zeppelin
Ocean eddies are small and short-lived and are therefore difficult to measure. Special cameras help to capture them with precision.
The large ocean currents such as the Humboldt Current in the South Pacific or the Gulf Stream in the North Atlantic heavily influence the weather and climate in their respective regions. They are driven by winds and tides but also by temperature and salinity variations.
In addition to the large ocean currents, there are also much smaller vortices. They are referred to as ocean eddies. There are few observations and analyses of these eddies because they are so small in size (the diameters are often only a few kilometres) and they only last a short time (a few hours up to one day). Satellites, though passing at regular intervals, pass only briefly over a particular region and can therefore hardly measure the ocean eddies as they have already collapsed by the time the satellites have flown over their position again.
Despite their small size and limited lifespan, eddies do play a crucial role in the energy budget of global ocean circulation. Furthermore, salinity and oxygen content as well as temperature variations in the water also influence the living conditions of microalgae, plankton and fish. It is therefore important in many respects to better understand how ocean eddies function as well as the effects they may have.
In early June 2016, scientists from the Helmholtz-Zentrum Geesthacht (HZG) will use a zeppelin for the first time in observing ocean eddies in the Baltic Sea from the air.
The zeppelin will fly at a height of approximately one thousand meters above the sea surface and as soon as it locates an interesting eddy, it will float in place over the location. It is equipped with infrared and hyperspectral cameras to measure temperature variations as well as salinity and chlorophyll content of the sea water.
The infrared camera, also known as the thermal imaging camera, however, doesn’t directly measure temperature, but simply depicts the radiation intensity in the infrared range and then converts this radiation into a visible image. Temperature differences of 0.03 °C can be reconstructed in such a way. Using the hyperspectral camera, on the other hand, salt and chlorophyll content can be determined. In contrast to a normal camera, which breaks down visible light in three colours (red, green and blue) to create images, the hyperspectral camera can measure and make visible to the human eye the invisible wavelengths from the ultraviolet range to the long wave infrared range. The respective content can then be calculated from chlorophyll’s and/or seawater’s varying reflectivity.
The formation mechanisms and temporal development of the ocean eddies from cooler (mostly forms the internal core) and/or warmer water (mostly forms the outer eddy) can thus be observed precisely over several hours. The influence of the eddy formation on microalgae and/or chlorophyll distribution should also be analysed in this manner.
The measurements taken from the air will be supplemented with current meters, wave and ocean gliders deployed from research ships, and also by a fast boat for data acquisition.
Text: Dr. Ute Münch, Science Platform Earth and Environment. Scientific Editor, Dr. Holger Brix (HZG)