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Monitoring the constantly changing shape of the sea surface is important for scientific and societal applications such as ocean current forecasting, climate research, ship routing, cable laying, and debris tracking.<\/p>\n
A project supported by the Discovery element of ESA\u2019s Basic Activities recently investigated a new technique to measure sea surface topography very precisely. The project was based on an idea<\/a> submitted by the Institute for Space Studies of Catalonia (IEEC<\/a>) through the Open Space Innovation Platform (OSIP<\/a>) \u2013 ESA\u2019s place for your space ideas.<\/p>\n The technique involves looking at satellite navigation (GNSS) signals that have been reflected off of the sea surface at very low angles. At these so-called grazing angles, waves and surface roughness have very little impact on the reflection process; the sea surface acts as a very smooth mirror.<\/p>\n IEEC\u2019s Estel Cardellach, principal investigator and submitter of the OSIP idea explains: \u201cIn a mirror-like reflection the phase of the signal can be tracked \u2013 it is continuous. Different surface heights result in different phase measurements. It gives a very precise measurement of the surface altitude at a few centimetres\u2019 precision.\u201d<\/p>\n The ESA-funded activity involved developing a GNSS receiver and setting up an experiment in the Balaeric Islands to collect GNSS signals reflected off the sea surface. The team \u2013 made up of IEEC, imedea<\/a>, SOCIB<\/a> and DLR<\/a> \u2013 then processed the signals for optimised measurements of the shape of the sea surface.<\/p>\n \u201cThanks to OSIP and ESA Discovery we have been able to conduct this experiment on grazing GNSS reflectometry under monitored conditions,\u201d says Manuel Martin-Neira, ESA technical officer for the project. \u201cWe have linked the coherence of the reflected signals to wave height and elevation angle of GNSS satellites. These results have been very useful for preparing the PRETTY mission.\u201d<\/p>\n