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The Topography of the Mediterranean Sea - GPS reflection measurements with the German Research Aircraft HALO

Measurements of GPS signals that are reflected off the sea surface allow the detection of sea surface height differences with centimetre precision. Scientists from the German Research Centre for Geosciences GFZ together with colleagues from the Leibniz University Hannover, the Technical University Dresden and the Institute for Space Sciences in Barcelona gathered these data with dedicated GPS receivers aboard the German research aircraft (HALO) and demonstrated for the first time that GPS reflection measurements can resolve anomalies of the sea surface topography.

These measurements were part of the GEOHALO flight experiment that focused on the investigation of different geoscientific topics in the Mediterranean region. Using reflected GPS signals for ocean surface monitoring is a rather new field of geoscientific research. Compared to established radar or laser altimeter measurements, the use of GPS reflections offers a significantly higher ocean coverage. This is due to simultaneous observations along multiple reflection tracks that are provided by the different navigation satellites, whereas established sensors provide only one track.

The ambition of the GFZ researchers is even higher and is focused on the International Space Station ISS. The successful aircraft campaign is an important step towards the application of GPS reflectometry aboard satellites for global observations of the ocean surface. Possible applications hereby comprise, e.g., the potential early detection of tsunamis, that have only small amplitudes in the open ocean and can hardly be located with today's observation coverage. Even our understanding of climate change can profit from GPS reflectometry. Mesoscale oceanic currents (eddies) with extentions between 10 and 100 km are crucial for the climate relevant ocean's energy transport, and currently cannot be sufficiently explored. These global scale challenges are recently studied by the GFZ scientists to prepare the reflectometry experiment aboard the ISS in cooperation with the European Space Agency ESA.

Semmling, A. M.; Beckheinrich, J.; Wickert, J.; Beyerle, G.; Schön, S.; Fabra, F.; Pflug, H.; He, K.; Schwabe, J., and Scheinert, M. (2014): “Sea surface topography retrieved from GNSS reflectometry phase data of the GEOHALO flight mission”, Geophysical Research Letters, 2014, 41, doi:10.1002/2013GL058725

Figures related to GEOHALO in printable resolution can be found in:

www.gfz-potsdam.de/medien-kommunikation/bildarchiv/halo/

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