Werner Alpers - Academia.edu (original) (raw)

Werner Alpers

Pofessor emeritus at the University of Hamburg, Institute of Oceanography

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Papers by Werner Alpers

Research paper thumbnail of Synthetic Aperture Radar Observations of Sea Surface Signatures of Atmospheric Gravity Waves over Southeast Asian Coastal Waters

Research paper thumbnail of Study of a Winter Monsoon Front over the South China Sea by Multi-Sensor Satellite and Weather Radar Data, and a Numerical Model

Research paper thumbnail of Internal Waves Session

Research paper thumbnail of Dragon In Support To Harmonizing European and Chinese Marine Monitoring for Environment and Security System

Research paper thumbnail of Study of a Winter Monsoon Front and a Squall Line over the South China Sea by Synergetic Use of Synthetic Aperture and Weather Radar Data

Dragon 2 Final Results and Dragon 3 Kickoff Symposium, 2013

Research paper thumbnail of A comparison of ocean wave-radar modulation transfer functions at different radar frequencies and polarizations determined from tower and aircraft measurements

1995 International Geoscience and Remote Sensing Symposium, IGARSS '95. Quantitative Remote Sensing for Science and Applications

ABSTRACT

Research paper thumbnail of Evaluation of the Phase Velocity of the Ocean Dominant Wave Using an Airborne Coherent Radar System

Es wird ein Verfahren vorgeschlagen, das die Phasengeschwindigkeit der dominanten Ozeanwellen dur... more Es wird ein Verfahren vorgeschlagen, das die Phasengeschwindigkeit der dominanten Ozeanwellen durch die Anwendung der Reflektivitaetsversatzmethode (RDM) genau bestimmt. Dieses Verfahren ist mit SAR-Flugzeug-Daten erfolgreich bestaetigt worden und erweist eine Genauigkeit von ca. 2m/s.

Research paper thumbnail of Extraction of the Phase Velocity of the Dominant Ocean Wave from SAR Raw Data

A new method for determining the magnitude and the direction of the phase velocity of the dominan... more A new method for determining the magnitude and the direction of the phase velocity of the dominant ocean surface wave from synthetic aperture radar (SAR) raw data is proposed. This method is based on the Reflectivity Displacement Method (RDM).

Research paper thumbnail of On the Reflectivity Displacement Method for Measuring the Phase Velocity of the Dominant Ocean Wave

A new method for determining the magnitude and the direction of the phase velocity of the dominan... more A new method for determining the magnitude and the direction of the phase velocity of the dominant ocean surface wave from synthetic aperture radar (SAR) raw data is proposed. This method is based on the Reflectivity Displacement Method (RDM).

Research paper thumbnail of Progress Toward Demonstrating SAR Monitoring of Chinese Seas

Research paper thumbnail of The Rhine outflow plume studied by synthetic aperture radar data and numerical simulations

Research paper thumbnail of SAR Remote Sensing of Internal Solitary Waves in the Ocean

Advances in SAR Remote Sensing of Oceans, 2018

Research paper thumbnail of Ocean circulation modeling by use of radar altimeter data

Research paper thumbnail of Simulation of ocean waves imaging by an along-track interferometric synthetic aperture radar

IEEE Transactions on Geoscience and Remote Sensing, 1997

ABSTRACT

Research paper thumbnail of The Rhine outflow studied by the analysis of ERS1/2 SAR data and numerical simulations

Synthetic aperture radar (SAR) images acquired by the First and Second European Remote Sensing sa... more Synthetic aperture radar (SAR) images acquired by the First and Second European Remote Sensing satellites (ERS-1/2) over coastal waters near estuaries often show sea surface signatures of river outflow fronts. In particular, the analysis of 20 SAR images showing the Rhine outflow region indicates that the outflow front is visible as a narrow zone of high radar backscatter. Location and form of the outtlow front are strongly linked to the tidal phase, but they also depend, among others, on wind conditions, Rhine discharge, residual currents, and neap-spring tidal cycle. In order to simulate the dynamics of the Rhine plume in the outflow region, a two-layer, nonlinear numerical model based on the hydrostatic shallow water equations has been developed. Due to a numerical technique for the treatment of movable lateral boundaries, the model allows for the simulation of localized layers with an outcropping interface (front). The model is forced by imposing tidal and residual transport and river discharge at the open boundaries. The evolution of the Rhine plume as calculated by the numerical model is discussed with respect to the tidal phase. A simple radar imaging model which relates the modulation of the backscattered power to the surface velocity convergence in radar look direction is applied to the simulated surface velocity. Relative good agreement between model results and observed Rhine front signatures suggests that wave-current interaction probably represents the dominant element of the imaging mechanism for the Rhine plume front.

Research paper thumbnail of Investigation of Coastal Wind Fields over the Black Sea Using Envisat

The sea area off the east coast of the Black Sea is an area where often pronounced local winds ar... more The sea area off the east coast of the Black Sea is an area where often pronounced local winds are encountered. The most prominent one is the Novorossiyskaya bora, which is a strong wind blowing from the coastal mountains onto the Black Sea, which can attain speeds of up to 40 ms -1 . But also katabatic winds and foehn winds are often encountered in this area. We have analyzed seven coastal wind events by using synthetic aperture radar (SAR) images acquired by the Advanced Synthetic Aperture Radar (ASAR) onboard the European Envisat satellite. The winds modify the sea surface roughness and thus they become visible on SAR images. Information on the spatial extent and the fine-scale structure of the coastal wind fields can be obtained from these images. In particular, SAR images can be used to study 1) wind jets, wakes, and atmospheric eddies generated by the interaction of winds with coastal topography, 2) boundaries between the local and ambient wind fields, and 3) atmospheric gravi...

Research paper thumbnail of Fernerkundung der Meeresoberfläche von Satelliten aus

Research paper thumbnail of SAR observation of internal waves generated by sub-mesoscale eddies in the Strait of Sicily

Research paper thumbnail of The occurrence of sea slicks on the ocean surface and their influence on remote sensing signals

Research paper thumbnail of The modulation of the radar backscattering cross section by long ocean waves

Research paper thumbnail of Synthetic Aperture Radar Observations of Sea Surface Signatures of Atmospheric Gravity Waves over Southeast Asian Coastal Waters

Research paper thumbnail of Study of a Winter Monsoon Front over the South China Sea by Multi-Sensor Satellite and Weather Radar Data, and a Numerical Model

Research paper thumbnail of Internal Waves Session

Research paper thumbnail of Dragon In Support To Harmonizing European and Chinese Marine Monitoring for Environment and Security System

Research paper thumbnail of Study of a Winter Monsoon Front and a Squall Line over the South China Sea by Synergetic Use of Synthetic Aperture and Weather Radar Data

Dragon 2 Final Results and Dragon 3 Kickoff Symposium, 2013

Research paper thumbnail of A comparison of ocean wave-radar modulation transfer functions at different radar frequencies and polarizations determined from tower and aircraft measurements

1995 International Geoscience and Remote Sensing Symposium, IGARSS '95. Quantitative Remote Sensing for Science and Applications

ABSTRACT

Research paper thumbnail of Evaluation of the Phase Velocity of the Ocean Dominant Wave Using an Airborne Coherent Radar System

Es wird ein Verfahren vorgeschlagen, das die Phasengeschwindigkeit der dominanten Ozeanwellen dur... more Es wird ein Verfahren vorgeschlagen, das die Phasengeschwindigkeit der dominanten Ozeanwellen durch die Anwendung der Reflektivitaetsversatzmethode (RDM) genau bestimmt. Dieses Verfahren ist mit SAR-Flugzeug-Daten erfolgreich bestaetigt worden und erweist eine Genauigkeit von ca. 2m/s.

Research paper thumbnail of Extraction of the Phase Velocity of the Dominant Ocean Wave from SAR Raw Data

A new method for determining the magnitude and the direction of the phase velocity of the dominan... more A new method for determining the magnitude and the direction of the phase velocity of the dominant ocean surface wave from synthetic aperture radar (SAR) raw data is proposed. This method is based on the Reflectivity Displacement Method (RDM).

Research paper thumbnail of On the Reflectivity Displacement Method for Measuring the Phase Velocity of the Dominant Ocean Wave

A new method for determining the magnitude and the direction of the phase velocity of the dominan... more A new method for determining the magnitude and the direction of the phase velocity of the dominant ocean surface wave from synthetic aperture radar (SAR) raw data is proposed. This method is based on the Reflectivity Displacement Method (RDM).

Research paper thumbnail of Progress Toward Demonstrating SAR Monitoring of Chinese Seas

Research paper thumbnail of The Rhine outflow plume studied by synthetic aperture radar data and numerical simulations

Research paper thumbnail of SAR Remote Sensing of Internal Solitary Waves in the Ocean

Advances in SAR Remote Sensing of Oceans, 2018

Research paper thumbnail of Ocean circulation modeling by use of radar altimeter data

Research paper thumbnail of Simulation of ocean waves imaging by an along-track interferometric synthetic aperture radar

IEEE Transactions on Geoscience and Remote Sensing, 1997

ABSTRACT

Research paper thumbnail of The Rhine outflow studied by the analysis of ERS1/2 SAR data and numerical simulations

Synthetic aperture radar (SAR) images acquired by the First and Second European Remote Sensing sa... more Synthetic aperture radar (SAR) images acquired by the First and Second European Remote Sensing satellites (ERS-1/2) over coastal waters near estuaries often show sea surface signatures of river outflow fronts. In particular, the analysis of 20 SAR images showing the Rhine outflow region indicates that the outflow front is visible as a narrow zone of high radar backscatter. Location and form of the outtlow front are strongly linked to the tidal phase, but they also depend, among others, on wind conditions, Rhine discharge, residual currents, and neap-spring tidal cycle. In order to simulate the dynamics of the Rhine plume in the outflow region, a two-layer, nonlinear numerical model based on the hydrostatic shallow water equations has been developed. Due to a numerical technique for the treatment of movable lateral boundaries, the model allows for the simulation of localized layers with an outcropping interface (front). The model is forced by imposing tidal and residual transport and river discharge at the open boundaries. The evolution of the Rhine plume as calculated by the numerical model is discussed with respect to the tidal phase. A simple radar imaging model which relates the modulation of the backscattered power to the surface velocity convergence in radar look direction is applied to the simulated surface velocity. Relative good agreement between model results and observed Rhine front signatures suggests that wave-current interaction probably represents the dominant element of the imaging mechanism for the Rhine plume front.

Research paper thumbnail of Investigation of Coastal Wind Fields over the Black Sea Using Envisat

The sea area off the east coast of the Black Sea is an area where often pronounced local winds ar... more The sea area off the east coast of the Black Sea is an area where often pronounced local winds are encountered. The most prominent one is the Novorossiyskaya bora, which is a strong wind blowing from the coastal mountains onto the Black Sea, which can attain speeds of up to 40 ms -1 . But also katabatic winds and foehn winds are often encountered in this area. We have analyzed seven coastal wind events by using synthetic aperture radar (SAR) images acquired by the Advanced Synthetic Aperture Radar (ASAR) onboard the European Envisat satellite. The winds modify the sea surface roughness and thus they become visible on SAR images. Information on the spatial extent and the fine-scale structure of the coastal wind fields can be obtained from these images. In particular, SAR images can be used to study 1) wind jets, wakes, and atmospheric eddies generated by the interaction of winds with coastal topography, 2) boundaries between the local and ambient wind fields, and 3) atmospheric gravi...

Research paper thumbnail of Fernerkundung der Meeresoberfläche von Satelliten aus

Research paper thumbnail of SAR observation of internal waves generated by sub-mesoscale eddies in the Strait of Sicily

Research paper thumbnail of The occurrence of sea slicks on the ocean surface and their influence on remote sensing signals

Research paper thumbnail of The modulation of the radar backscattering cross section by long ocean waves

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