The accuracy of Kirchhoff's approximation in describing the far field speckles produced by random self-affine fractal surfacesC. X. Liu, C. F. Cheng, X. R. Ren, S. Y. Teng and Z. Z. XuEur. Phys. J. D, 36 1 (2005) 105-110DOI: https://doi.org/10.1140/epjd/e2005-00210-x