1. N. M. Bilgutay (1981 ), Split spectrum processing for flaw-to-grain echo enhancement in ultrasonic detection . Ph.D. thesis , Purdue University, West Lafayette, Indiana.
2. Ch. Brockmann, and G. Shafer (1998 ), Design and construction of the Bang Na-Bang expressway , in, Rotterdam, vol. 1 , 275 -80 .
3. N. J. Carino (2001 ), Impact-echo method: An overview , in, American Society of Civil Engineers, Washington DC, 1 -18 .