Analysis of the polarizing video images of the sea surface

Konstantinov O.G.
V.I. Il'ichev Pacific Oceanological Institute FEB RAS
43 Baltiyskaya St., 690041 Vladivostok, Russia
Phone: 7-4232-312-158 Fax: 7-4232-312-573
olegkon@poi.dvo.ru

ABSTRACT

Characteristics of the sea surface contain information on many dynamic phenomena and processes in the ocean-atmosphere system and can be used for their investigation. To extract maximum information about spatial temporal and spectral characteristics of the surface with high accuracy a hardware/software complex was developed at the POI. It is designed for reception and analysis of the polarizing video images of the sea surface. Polarizing characteristics of light, which are formed by the image elements most fully reflect the geometrical characteristics of the surface. The complex includes several systems, which are distinguished by means of video image reception. The analysis of transient processes and small-scale roughness was carried out with a video system. In the system, three images on reception matrix of a CCD camera are formed by light, passed through polarizer-analyzers with three different orientations of the main axes. The angles of the main axes with respect to a vertical plane passing through an optical system axis were +45°, 0°, and –45°. An angle of incidence was chosen in the range from 20° to 70°. The analysis of the large-scale sea surface roughness was performed with another video system. In the system, a polarizer-analyzer whose orientation changed synchronously with the video signal was installed in front of an objective. It allows receiving three Stokes parameters of light reflected by the sea surface elements. Then three images obtained with positive, zero, and negative polarizer angles were matched and R, G, and B components of a colour image (by analogy with RGB image) were replaced by the appropriate polarizing components. Such read-out allows carrying out image analysis, using a rich arsenal of means of computer image processing. The information on polarizing characteristics of the elements of the sea surface allows the retrieval of their spatial orientation, slope dispersion, spatial and temporal autocorrelation functions and relief of the sea surface roughness, temporal and spatial spectra etc. The spatial scales accessible to the analysis depend on a focal length of an objective and the distance to the sea surface and changed from several millimetres to hundreds metres at temporal resolution of 80 Hz. Experimental data were obtained at the POI Marine station in the Peter the Great Bay, Japan Sea. The results of data processing illustrate the characteristics of the developed system. The results retrieved from polarization video images recorded at different wind speeds are compared with data taken by a system of small floats and other devices.

Last Update: 2005-03-16