Difference between revisions of "Template:This weeks featured article"

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(Classification of coastal profiles)
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==Classification of coastal profiles==
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==Bathymetry from inverse wave refraction==
  
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[[Image:01_echosoundings_enc.jpg|thumb|350px|right|Bathymetry of area of investigation acquired by multibeam echosounder.]]
  
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[[Image:exposed littoral a.jpg|thumb|right|Fig. 1a. Typical exposed littoral dune coast, the Danish North Sea Coast]]
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It is possible to determine the [[bathymetry]] of a certain area using radar data. On the Island of Sylt at the German Bight Coast, measurements are done during storm conditions. This data is processed based on inversion of the non-linear and linear wave theory. More about the area of investigation, data processing, result and discussion of the results can be found in the article.
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[[Image:exposed littoral b.jpg|thumb|right|Fig. 1b. Corresponding wave height distribution.]]
 
  
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The determination of the [[bathymetry]] in coastal environments by utilizing the ocean wave-shoaling photographic imagery, and the observed reduction of ocean wave phase speed with decreased water depth, is used since the WW-II (Williams 1946)<ref>Williams, W.W. 1946, The determination of gradients of enemy-held beaches. Geographical Journal 107, 76–93.</ref>. The last decade, with the expansion of different ground based instrumentations, mainly radar and video imagery, for the observation of the sea surface and the exponential increase of the computational power, several methodologies for the [[bathymetry]] reckoning have been published, e.g. Bell 1999<ref> P. Bell 1999, Shallow water bathymetry derived from an analysis of x-band radar images of waves, Coastal Engineering 3-4, pp. 513-527.</ref>, Seemann et al. 1999<ref>Seemann J., C. Senet, H. Dankert, Hatten, H., Ziemer, F. 1999, Radar image sequence analysis of inhomogeneous water surfaces, in proc. of the SPIE'99 Conference - Applications of Digital Image Processing XXII. vol. 3808, pp. 536-546.</ref>, Stockdon and Holman 2000<ref>Stockdon, H.F., Holman, R.A. 2000, Estimation of wave phase speed and nearshore bathymetry from video imagery. Journal of Geophysical Research 105 (C9), pp. 22015–22033.</ref>, Dankert 2003<ref>Dankert, H. 2003, Retrieval of Surface-Current Fields and Bathymetries using Radar-Image Se-quences, International Geoscience and Remote Sensing Symposium, Toulouse, France.</ref>, Bell et al. 2004<ref name="bell">Bell, P., J. Williams, S. Clark, B. Morris and A. Vila-Concejo 2004, Nested Radar Systems for Remote Coastal Observations, Journal of Coastal Research SI39, pp. 483-487.</ref>, Catalan and Haller 2008<ref>Catalan, P.A. and Haller, M.C., 2008, Remote sensing of breaking wave phase speeds with ap-plication to non-linear depth inversions. Coastal Engineering, 55(1), pp. 93-111.</ref>, Senet et al. 2008<ref name="sen">Senet, C. M., J. Seemann, S. Flampouris, F. Ziemer 2008, Determination of Bathymetric and Current Maps by the Method DiSC Based on the Analysis of Nautical X–Band Radar-Image Se-quences of the Sea Surface, IEEE Transaction on Geoscience and Remote Sensing 46(7), pp.1-9.</ref>. The core of the previously mentioned methods is the inversion of the wave characteristics by assuming the validity of linear or non-linear models for the propagation of the wavefield over uneven sea bottom.
  
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In the present investigation, twelve hourly radar datasets acquired during storm conditions are analyzed by two methods: The non-linear method of Bell et al. 2004<ref name="bell"/> (henceforth BW04), which is based on the inversion of the non-linear [[Dispersion (waves)|wave dispersion]] equation of Hedges (1976)<ref>Hedges, T.S. 1976, An empirical modification to linear wave theory, Proc. Inst. Civ. Eng., 61, pp. 575-579.</ref> and the Dispersive Surface Classificator (henceforth DiSC08), Senet et al. 2008<ref name="sen"/>, which is based on the inversion of the linear wave theory. The results are validated as bathymetric retrieving instruments and the two wave propagation theories are compared about their sensitivity to the local bathymetric relief. The two methods are compared under the assumption of fundamentally similar implemented algorithms.
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This page gives an overview of the existing types of coastal profiles around the world. Their classification, as given below, is based on the material present at the specific location and size of the water bodies at the location. The wave and wind conditions are related to the size of water body present and the wind and wave climate at the location. Several characteristics of the coastal profiles are mentioned. Links to articles with a detailed description of a coastal profile can be found in the see also paragraph.
 
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The [[theoretical equilibrium profile]] is often recognised in the real coastal profiles, but deviations often occur due to variations in the seabed material and the presence of bars and due to the influence of tide, etc. Another reason can be that the actual profile has not yet reached the [[equilibrium profile|equilibrium shape]], which is important information in relation to the analysis of the predominant processes at a specific site. Rocky coastlines that exist adjacent to littoral coastal profiles have only a minor influence on the coastal profile but may have a major influence on the shape and stability of the shoreline.
 

Revision as of 15:19, 19 January 2009

Bathymetry from inverse wave refraction

Bathymetry of area of investigation acquired by multibeam echosounder.

It is possible to determine the bathymetry of a certain area using radar data. On the Island of Sylt at the German Bight Coast, measurements are done during storm conditions. This data is processed based on inversion of the non-linear and linear wave theory. More about the area of investigation, data processing, result and discussion of the results can be found in the article.

The determination of the bathymetry in coastal environments by utilizing the ocean wave-shoaling photographic imagery, and the observed reduction of ocean wave phase speed with decreased water depth, is used since the WW-II (Williams 1946)[1]. The last decade, with the expansion of different ground based instrumentations, mainly radar and video imagery, for the observation of the sea surface and the exponential increase of the computational power, several methodologies for the bathymetry reckoning have been published, e.g. Bell 1999[2], Seemann et al. 1999[3], Stockdon and Holman 2000[4], Dankert 2003[5], Bell et al. 2004[6], Catalan and Haller 2008[7], Senet et al. 2008[8]. The core of the previously mentioned methods is the inversion of the wave characteristics by assuming the validity of linear or non-linear models for the propagation of the wavefield over uneven sea bottom.

In the present investigation, twelve hourly radar datasets acquired during storm conditions are analyzed by two methods: The non-linear method of Bell et al. 2004[6] (henceforth BW04), which is based on the inversion of the non-linear wave dispersion equation of Hedges (1976)[9] and the Dispersive Surface Classificator (henceforth DiSC08), Senet et al. 2008[8], which is based on the inversion of the linear wave theory. The results are validated as bathymetric retrieving instruments and the two wave propagation theories are compared about their sensitivity to the local bathymetric relief. The two methods are compared under the assumption of fundamentally similar implemented algorithms.
  1. ↑ Williams, W.W. 1946, The determination of gradients of enemy-held beaches. Geographical Journal 107, 76–93.
  2. ↑ P. Bell 1999, Shallow water bathymetry derived from an analysis of x-band radar images of waves, Coastal Engineering 3-4, pp. 513-527.
  3. ↑ Seemann J., C. Senet, H. Dankert, Hatten, H., Ziemer, F. 1999, Radar image sequence analysis of inhomogeneous water surfaces, in proc. of the SPIE'99 Conference - Applications of Digital Image Processing XXII. vol. 3808, pp. 536-546.
  4. ↑ Stockdon, H.F., Holman, R.A. 2000, Estimation of wave phase speed and nearshore bathymetry from video imagery. Journal of Geophysical Research 105 (C9), pp. 22015–22033.
  5. ↑ Dankert, H. 2003, Retrieval of Surface-Current Fields and Bathymetries using Radar-Image Se-quences, International Geoscience and Remote Sensing Symposium, Toulouse, France.
  6. ↑ 6.0 6.1 Bell, P., J. Williams, S. Clark, B. Morris and A. Vila-Concejo 2004, Nested Radar Systems for Remote Coastal Observations, Journal of Coastal Research SI39, pp. 483-487.
  7. ↑ Catalan, P.A. and Haller, M.C., 2008, Remote sensing of breaking wave phase speeds with ap-plication to non-linear depth inversions. Coastal Engineering, 55(1), pp. 93-111.
  8. ↑ 8.0 8.1 Senet, C. M., J. Seemann, S. Flampouris, F. Ziemer 2008, Determination of Bathymetric and Current Maps by the Method DiSC Based on the Analysis of Nautical X–Band Radar-Image Se-quences of the Sea Surface, IEEE Transaction on Geoscience and Remote Sensing 46(7), pp.1-9.
  9. ↑ Hedges, T.S. 1976, An empirical modification to linear wave theory, Proc. Inst. Civ. Eng., 61, pp. 575-579.
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