| 摘要 |
An echo measurement system transmits a transmitted-signal which is modulated over a period of time corresponding to a modulation duration. The modulation could be, for example, modulation to represent a coded signal. A transducer (2), which may be common between transmission and reception, receives a received-signal which is cross-correlated with the transmitted-signal. The transmitted-signal comprises a plurality of transmission periods separated by a plurality of transmission pauses. The modulation duration extends over two or more of the transmission periods and the duration of the transmission pauses is varied within a range of transmission pause duration. The technique seeks to improve the signal-to-noise ratio without imposing undesirable other constraints. |
