Two months stay at the University of Hamburg

4 March 2024, by Nannan Zi

On January 12, 2024, I arrived in Hamburg, marking my first time aboard. Before my arrival, I had joined the project of Welcome-Buddy of the University of Hamburg, and my assigned welcome-buddy picked me up at the airport.

 During my time at the Institute of Ocean- ography at the University of Hamburg, I mainly worked on our joint collaborative manuscript on the topic of SAR ocean eddies, with Dr. Martin Gade and my supervisor in China, Prof. Dr. rer. nat. Li Xiao-Ming. The following figure shows beautiful black eddies and white eddies on SAR imagery. Over the open sea, ocean eddies manifest in SAR images mainly due to two mechanisms, namely surfactant accumulation and wave/current interaction. The former mechanism is dominant at surface wind speeds below 6 m/s, when natural films on the ocean surface tend to accumulate in the convergence zones associated with the spiral flows. The surfactants dampen short Bragg waves, thereby leading to a reduction in radar backscattering from the sea surface, making the eddies visible as spiral dark lines on SAR images, hence they are often called ‘black’ eddies. At higher wind speeds, the surfactant film breaks up and black spirals disappear, and wave/current interactions become the dominant mechanism, through which eddies are visible on SAR imagery. As they cause bright lines of increased radar backscatter, they are often called ‘white’ eddies.

Martin is not only my teacher but also a dear friend. February 9th was New Year's Eve in China, and on that day, Martin and I celebrated this special holiday with a delicious hot pot dinner. I also did some sightseeing with Martin, and he served as my tour guide. There are many old buildings in his hometown, Lüneburg, which are so impressive. We climbed the tallest building, and then I got the whole view of the city. 

Soon after, my supervisor, Xiao-Ming, arrived at the University of Hamburg. (I changed majors when I started my Ph.D., and at that time I knew nothing about remote sensing, but he still chose me as his student without a second thought. I hold a deep respect for him because he teaches me a lot). Together, we visited the DLR in Bremen where I did a presentation and met with many scientists. They asked me some interesting and valuable questions. That day, I also took pictures of two handsome gentlemen.

On my last day here, Eleanor Frajka-Williams (the head of the group; I've benefited from every discussion she's had with me), Emelie (whom I shared an office with), Martin, and I went to the Miniatur-Wunderland, which is a major attraction in Hamburg. The models there are so realistic and fine.

I had a great time in Hamburg. The people here are very kind, and the city is beautiful with historical buildings. I sincerely hope to return someday!