I have a matrix of complex entries (it is the Fourier transform of an image. I shall refer to this as "signal", following the convention in radio astronomy). I'd like to calculate how the amplitude of the signal varies as a function of distance from the center of the signal, given the signal values as a matrix. Here, distance is the L2 norm of the index and amplitude is the norm of the signal values at that distance.
I am clueless as to how to get started with the problem - I keep hitting dead ends. A solution would be very helpful.