The ocean environment is a time-varying system function, and the instability effect of single-frequency signal in the channel limits its application. However, the linear frequency modulation (LFM) signal has a certain bandwidth. Even if the loss of a frequency point is too large, the other frequency points are still returned by the echo energy, which can overcome the limitation of the instability effect of single frequency. When affected by Doppler in the ocean, it may cause the peak value to drop and widen. The hyperbolic frequency modulation (HFM) signal has Doppler invariance. Therefore, this paper uses the HFM signal for the target echo simulation and construction, which has a multi-highlight structure. This paper uses the up-sampling and down-sampling methods to achieve accurate time-delay. The situation of target without Doppler and different sizes of Doppler and different depths of the target are made, and the results of the target multi-highlight are proposed. This method can be useful in engineering application.
KEYWORDS: Signal detection, Acoustics, Active sonar, Signal processing, Signal attenuation, Pulse signals, Tunable filters, Oceanography, Frequency response, Acoustic waves
In the marine environment, the active sonar sends out the specific detection acoustic signal that is the input signal[1]. The detection acoustic signal changes over time and space and has a propagation loss during the propagation process. This propagation process can be thought of as a system. It is very important to find the output signal of the system. Since the energy of the signal is higher than the background noise, the conventional method is to find the maximum value according to the signal energy, but this method has certain shortcomings. This paper uses the method of Hilbert transform[2,3,4,5,6] to get the variable envelope. Then we find the rising edge and falling edge of the signal in the envelope. At last we find the starting point of the signal by the pulse width of the input signal.
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