A new coding method

The principle of “waveform invariance” is used for velocity measurement of the correlation sonar, which has a bottom tracking capability for providing earth reference velocity. For earlier two-pulse sonar systems, trade-offs were made between maximum range and velocity variance due to the reason that pulse width is equal to or less than pulse repetition period. A new pulse coding technique for a single transmitted pulse is utilized in the paper with respect to the conflicting problem mentioned above. The method involves truncated Gold sequence which contains the same number of 0´s and 1´s. The nature of the coded pulse is such that the autocorrelation function of the pulse possesses a temporal autocorrelation peak at a predetermined time lag besides at 0.The method used will increase achievable range while velocity accuracy not be deteriorated because correlation delay is less than pulse width.