The relationship between the internal waves on the sea surface in satellite radar images and Gabor filter parameters

Abstract

Radar satellite images are a valuable source of information about the thermal structure of waters and the dynamics of oceanic and atmospheric processes such as internal waves (IW) particularly in areas used for fishing. Internal wave generation is due to stream-velocity horizontal gradients, which modulate the sea surface roughness and result in the redistribution of suspended sediment, plankton and surfactant (surface-active agent) films and that is reflected in radar images as quasi-periodic linear structures with brightness below or above the background. The transition areas between the deep-water ocean areas and continental shelf, where the interaction of the tide and underwater appendages take place, are distinct in increased intensity of internal waves. Varying wind speed in atmospheric cyclonic motions and radar parameters add to complexity and spatial inhomogeneity of IW field in radar images. Digital processing of radar images of the sea surface was done using Gabor filter in the process. There was analyzed relationship between the filter parameters and IW surface development properties such as wave-train dimension and waves’ number in it, crest width and the interval between crests, crest length of the guiding wave, minimum and maximum wavelength in the train-wave, phase velocity. The paper provides examples of the impact of Gabor filter parameters on the outlining patterns with different IW geometry. Each example contains filter parameters’ values, the filter geometric image, the initial snapshot and visualization result of its processing. Using Gabor filter for processing radar wave images enables to detect internal waves of various geometry and origin, to identify the areas of their generation, as well as to reconstruct the incoming wind velocity. Thus, that makes this method high-potential in IW research.