Sea Surface Current Measurements Using Along-Track Interferometric SAR
Licentiatavhandling, 2018

Ocean currents affect the weather, the climate and the marine ecosystem. Observing ocean currents is important for understanding the upper-ocean layer dynamics and its interaction with the other components of the climate system. In-situ measurements are sparse and their deployment and maintenance is costly. Satellite remote sensing with large spatial coverage offers a good complement to the in-situ observations.
In this work we have studied the spaceborne Along-Track Interferometric SAR (ATI-SAR) for measuring sea surface currents. The measurement principle is based on the fact that the phase difference between two SAR acquisitions is directly related to radial (line-of-sight) velocity of the illuminated surface. Previous studies based on similar systems were carried out in areas with well defined and strong tidal currents ( 1 -3 m /s). In this work we demonstrate the capability of ATI-SAR, through several study cases, in areas with weak currents ( <0.5 m /s). This is challenging for the satellite measurements of surface currents because it requires very accurate processing and retrieval algorithms. In addition, it has been found that wave motion contribution, systematically dominates the measured ATI-SAR radial velocity in these weak current areas. Estimation of the wave motion  contribution relies on high-resolution and accurate wind data. Thus, a wind speed retrieval algorithm from SAR is needed to support the ATI-SAR current retrieval. We have shown that with an appropriate processing of the ATI-SAR phase and with applying the necessary corrections to the measured velocity a good agreement with ocean circulation models is achieved (rmse = 0.1 m/s). These corrections include phase calibration and wind  compensation to correct for instrument and geophysical systematic errors, respectively. Finally, a novel method for removing the wind direction ambiguity, based on the ATI-SAR phase, is presented. In previous methods, the wind ambiguity removal was based on external information, e.g. an atmospheric model or on visual observation of wind shadows.

Synthetic aperture radar

Ocean remote sensing


Along-track InSAR

Sea surface currents

Room EB, Edit building
Opponent: Dr. Martin Gade, University of Hamburg, Germany


Anis Elyouncha

Chalmers, Rymd-, geo- och miljövetenskap, Mikrovågs- och optisk fjärranalys

Wind-wave effect on ATI-SAR measurements of ocean surface currents in the Baltic Sea

36th IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2016; Beijing; China; 10-15 July 2016,; Vol. 2016-November(2016)p. 3982-3985

Paper i proceeding

Phase calibration of TanDEM-X ATI-SAR data for sea surface velocity measurements

International Geoscience and Remote Sensing Symposium (IGARSS),; (2017)p. 922-925

Paper i proceeding

Wind direction ambiguity removal using along-track InSAR: A case study

International Geoscience and Remote Sensing Symposium (IGARSS),; Vol. Volume 2018-July(2018)p. 3262-3265

Paper i proceeding

A. Elyouncha, L. E. B. Eriksson, R. Romeiser and L. M. H. Ulander, ”Measurements of Sea Surface Currents in the Baltic Sea Region using Spaceborne Along-Track InSAR,”. Manuscript submitted to IEEE Transactions on Geoscience and Remote Sensing.

Understanding ocean surface dynamics with satelite data

Rymdstyrelsen (167/14), 2015-01-01 -- 2019-03-31.




Oceanografi, hydrologi, vattenresurser


Grundläggande vetenskaper



Room EB, Edit building

Opponent: Dr. Martin Gade, University of Hamburg, Germany

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