Crater detection using CGC A new circle detection method

"Constrained Gradient for Circle" (CGC) is a new circle detection algorithm based on the gradient of the intensity image. The method relies on two conditions. The "gradient angle compatibility condition" constrains the gradient of a given percentage of the pixels belonging to some digital circles having a radius in the range of radii to detect to point towards the centre of the circle or in the opposite direction. The "curvature compatibility condition" constrains the variation of the gradient angle of the same pixels in a range depending on the radius of the circle. These two conditions are sufficient to detect the core of circular shapes. The best-fitting circle is then identified. The method is applied to artificial and reference images and compared to state-of-the-art methods. It is also applied to water-filled crater detection in Cambodia: these craters that might indicate the presence of Unexploded Ordnance (UXO) dating from the US bombing produce dark circles on satellite panchromatic images.