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Measurement of 2-D Sea Surface Elevation Fields using Complex Synthetic Aperture Radar Data

Schulz-Stellenfleth, Johannes und Lehner, Susanne (2004) Measurement of 2-D Sea Surface Elevation Fields using Complex Synthetic Aperture Radar Data. IEEE Trans. Geosc. Rem. Sens., 42 (ISSN: 0196-2892) (6), Seiten 1149-1160.

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Kurzfassung

A method is presented to derive two-dimensional sea surface elevation fields from complex synthetic aperture radar (SAR) data. Applied to spaceborne SAR data as acquired by European Remote Sensing 2 (ERS-2) or the Environmental Satellite (ENVISAT), the method allows to analyze the structure of ocean wave fields, e.g., wave grouping or individual wave heights on a global scale. The technique, thus, provides wave parameters not obtained with common SAR wave retrieval schemes, which are designed to estimate the 2-D wave spectrum, i.e., second-order statistical moments of the wave field. Estimates of sea surface elevation fields are obtained based on the existing theory of SAR ocean wave imaging, i.e., the modulation of the SAR image intensity due real aperture radar and motion-related effects. A power series expansion is derived for SAR intensity images that enables the analysis of nonlinear effects as well as to derive a quasi-linear approximation of the SAR imaging model in the spatial domain. A statistical analysis is performed based on a global dataset of 2D wave spectra provided by the European Centre for Medium-Range Weather Forecast. Distributions are given for the relative error of the quasi-linear approximation in the spatial domain. It is shown that the error can be reduced by smoothing the SAR image in the azimuthal direction at the cost of lower resolution. Smoothed elevation fields are retrieved by the minimization of a cost function defined in the Fourier domain based on the quasi-linear approximation of the imaging process. A multilook technique is applied to infer the information on wave propagation directions, which is required because the SAR transfer function is non-Hermitian, i.e., the SAR image is not determined by the "frozen" sea surface, but wave motion has a significant impact. The method is applied to simulated SAR images as well as to data acquired by ERS-2. The errors of the retrieved wave field due to image noise, uncertainties in the SAR imaging model, and bandwidth limitations are analyzed. In particular, the fact that the estimated elevation field is smoothed due to the finite system resolution and smearing effects associated with wave motion is discussed. A statistical test is proposed to check the homogeneity of the SAR image. T- he method makes sure that atmospheric effects are not misinterpreted as being caused by ocean waves.

Dokumentart:Zeitschriftenbeitrag
Zusätzliche Informationen: LIDO-Berichtsjahr=2004,
Titel:Measurement of 2-D Sea Surface Elevation Fields using Complex Synthetic Aperture Radar Data
Autoren:
AutorenInstitution oder E-Mail-Adresse der Autoren
Schulz-Stellenfleth, JohannesNICHT SPEZIFIZIERT
Lehner, SusanneNICHT SPEZIFIZIERT
Datum:2004
Erschienen in:IEEE Trans. Geosc. Rem. Sens.
Referierte Publikation:Ja
In ISI Web of Science:Ja
Band:42 (ISSN: 0196-2892)
Seitenbereich:Seiten 1149-1160
Status:veröffentlicht
HGF - Forschungsbereich:Verkehr und Weltraum (alt)
HGF - Programm:Weltraum (alt)
HGF - Programmthema:W EO - Erdbeobachtung
DLR - Schwerpunkt:Weltraum
DLR - Forschungsgebiet:W EO - Erdbeobachtung
DLR - Teilgebiet (Projekt, Vorhaben):NICHT SPEZIFIZIERT
Standort: Oberpfaffenhofen
Institute & Einrichtungen:Institut für Methodik der Fernerkundung
Hinterlegt von: Bärbel Bolowski
Hinterlegt am:13 Feb 2006
Letzte Änderung:06 Jan 2010 22:26

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