The eddy hunters head for the sky

A flight with the oceanographic magnifying glass – on the lookout for ocean eddies in the airship

Photo: iStock/ Hiob

From below it seems enormous. But despite its seventy-five metre length, it’s elegant. Just ten metres away from me, it lands almost silently. Like a boat, it orients itself on a mooring line with the wind. Yet another reason a zeppelin is referred to as an ’airship‘ and not an ’airplane‘.

The personnel on the ground wave and give the command to board quickly because the next scientific flight will begin right after its short stop. Today I’m accompanying Prof. Burkard Baschek, Director at the Institute of Coastal Research of the Hereon and his colleagues in the Department of Remote Sensing during the last zeppelin test flight over Lake Constance. The airship rises again briskly and the pilot steers us away from the Friedrichshafen Airport to the mouth of the Rhine River at Lake Constance.

The Zeppelin has actually been used in sightseeing flights nearly every day since the nineties, so a journey for the two-person crew from the Zeppelin Luftschifftechnik GmbH is almost routine. The situation is different for the researchers of the Helmholtz-Zentrum Hereon.

The Geesthacht Coastal Researchers

"We fly out in the mornings and don’t know until we land what new scientific questions
await us." - Prof Burkard Baschek. Photo: Hereon/ Torsten Fischer

Today the Geesthacht researchers are studying small ocean eddies and are testing the zeppelin as well as their equipment for a future research expedition over the Baltic Sea. While large ocean currents, such as the Gulf Stream, have been studied for many years, what is known about small ocean eddies, with a diameter ranging from one hundred metres to five kilometres, is still relatively little. It is an oversight in the truest sense of the word: environmental satellites with a resolution of one kilometre cannot detect each eddy, which often only exist for six to twenty four hours. Although the small eddies, in comparison to gigantic ocean currents, seem small, they are of great importance.

The zeppelin serves as a central interface from which other measurement instruments as well as vessels are coordinated. Currents are calculated and small eddies are detected with
the help of cameras. Photo: Hereon/ Torsten Fischer

The wind drives large global ocean currents, which are regarded as the heat pump of global climate. This energy is lost again in increasingly smaller eddies. Furthermore, scientists assume that half of the world’s entire microscopically small sea algae, known as phytoplankton, rely on these eddies. This phytoplankton is at the bottom of the food chain and provides a large portion of the oxygen in the atmosphere. “We assume that the small eddies also influence fish migrations,” explains Baschek. “Maybe we should park here now?” The pilot of the zeppelin brakes and we hover at a near standstill over Lake Constance.

It’s a good view from the zeppelin: the water from the Rhine churns different colours and shades. Photo: Hereon/ Torsten Fischer

The water from the Rhine churns different colours and shades beneath us. The scientists use two special cameras for their work. A highly sensitive infrared camera provides temperature maps of the water surface, capturing one hundred images per second. The thermal imaging camera measures even small temperature differences of 0.035 degrees Celsius. The currents are calculated and small eddies are detected using these tools. “The advantage is that, as opposed to airplane expeditions or satellite measurements, the zeppelin can permanently remain above the eddy and can measure it with an accuracy of under one meter in high pixel resolution,“ explains Wolfgang Cordes, scientist at the Institute of Coastal Research, who has been studying water surfaces from the air for many years. His colleagues simultaneously observe the eddy with what is known as a hyperspectral camera. This device records up to one thousand different light spectrum bands and is thus able to determine the ’colour‘ of the water. “This data helps us to differentiate, for example, green algae from red algae,” explains Dr Rüdiger Röttgers, who heads the Department of Remote Sensing at the Hereon. “We hope we can come to conclusions from the air about the condition and growth of the algae in the long-run,“ he adds. New eddies are detected again and again, we change altitude, and the technology is put to the test.

The scientists are tracking the eddies with highly sensitive cameras in this hovering laboratory.
The scientists seem content, the tension visibly decreasing. Their measurement instruments are functioning. Photo: Hereon/ Torsten Fischer

Burkard Baschek finally gives the command and the pilot begins the journey back to the airfield. The scientists seem content, the tension visibly decreasing. Their measurement instruments are functioning. “It’s obvious that we still need to adjust our cameras a bit, but we’re pleased with the first tests and with using the zeppelin as a research platform,“ says Baschek, summing up his days in Friedrichshafen. There’s still some time remaining before we land, and we enjoy the view of the Swiss mountains while the scientists discuss plans for the coming year. “We hope to use the zeppelin in summer 2016 for an eddy expedition in the Baltic Sea. It will not only be equipped with our cameras, like a sort of flying microscope, but it will also direct the ships below.” To additionally facilitate studying the interior of the eddies, colleagues on the water will steer fast boats and the Hereon‘s research ship the Ludwig Prandtl to the eddies themselves. Measurement instruments are dragged through the water at different depths and automated gliders will be put into use. These tools supply a multitude of additional oceanographic data.

Photo: Hereon/ Torsten Fischer

The zeppelin lands as gently as it had ascended. The airship is moored and moved to the airport’s hangar. The work for the coastal researchers on the ground isn’t nearly over: the data must still be evaluated in Geesthacht. The measurement instruments, however, must first be unmounted and loaded into the truck. Rüdiger Röttgers adds, “Our work doesn‘t just include collecting and analysing data. A coastal researcher also needs to know how to pack boxes.”