Ocean eddy tracking with circlets

We present a new method for detecting circles on digital images. This transform is called the circlet transform and can be seen as an extension of classical 1D wavelets in 2D: each basic element is a circle convolved by a 1D wavelet. In comparison with other circle-detector methods, mainly the Hough transform, the circlet transform takes into account the finite frequency aspect of the data: a circular shape is not restricted to a circle but has a certain width. The transform operates directly on image gradient and does not need further binary segmentation. The implementation is efficient as it consists of a few Fast Fourier Transforms. We apply the method to detect eddies on remote sensing images of chlorophyll from the Gulf of Lion (North Western Mediterranean Sea). The results show the effectiveness of the method to deal with real images with blurry edges.