宽带多普勒测速技术中跨周期模糊问题的研究

宽带声学多普勒流速剖面仪,利用伪随机编码调制发射脉冲信号以及复相关算法计算各水层反射回波的多普勒频移,进而达到测速的目的。复相关算法中,在排除模糊速度干扰的情况下,测速精度与脉冲信号的长度存在正比的关系。而脉冲宽度越长,所用来调制发射脉冲信号的编码阶数也越高,随之带来的便是速度模糊的问题。在复相关测频算法的基础上,针对长编码脉冲信号出现的周期性测频模糊情况,利用短编码脉冲信号的测频结果作为判别标准,选取恰当的周期性频偏作为计算结果,既提高了测速精度,又解决了精度提高所带来的周期性速度模糊问题,并且在实际应用中,提高了低信噪比条件下的测速精度。

Research on cross-period ambiguity in broad-band Doppler velocity measurement technology

In the broadband acoustic Doppler current profiler (BBADCP), the Doppler shifts of the echoes reflected from different water layers are calculated by using pseudo-random coded modulation and complex correlation algorithm to achieve the purpose of velocity measurement. It is known that in the complex correlation algorithm, there is a direct proportional relationship between the accuracy of velocity measurement and the length of pulse signal when the disturbance of ambiguous velocity is eliminated. However, for increasing pulse length, the higher coding order would be used to modulate the transmitting pulse signal, which brings the problem of velocity ambiguity. Based on the complex correlation frequency measurement algorithm and aiming at the periodic frequency measurement ambiguity of long-coded pulse signal, in this paper, a method by using the frequency measurement result of short-coded pulse signal as the discrimination criterion and choosing the appropriate periodic frequency offset as the calculation result is proposed, which can not only improve the velocity measurement accuracy, but also solve the problem of periodic velocity ambiguity while increasing precision. In practical application, the velocity measurement accuracy of this method is improved under low signal-to-noise ratio.