| 摘要 |
A method of modelling a surface of an object by using ultrasonic waves transmitted along the surface comprises the steps of: transmitting the ultrasonic waves along paths along the surface, and determining travel times of the ultrasonic waves along the paths. At least some of the ultrasonic waves exhibit an S0 mode and have a frequency-dependent velocity. This velocity (c) is relatively high for frequencies up to a first bending point (BP1), decreasing relatively rapidly for frequencies between the first bending point (BP1) and a second bending point (BP2), and relatively low for frequencies beyond the second bending point (BP2). The ultrasonic waves have a frequency range which lies at or below the first bending point (BP1). |
