| As the more widely use of lidar for underwater detection, more attentions have been focused on the serious backscattering noised during detection. How to restrain the backscattering signal has become the core problem of the lidar technology.Recently modulated-pulse lidar has been raised as an advanced technic to restrain the backscattering noise. As the target reflection signal can keep the frequency characters of the detection signal, and backscattering noise the reflection of randomly distributed scattering volume, the overlaps of lots of randomly reflection can make the scattering signal to show a low-frequency character. This method takes advantage of this character, and combines the mature coherent detection technology and the water-penetrating ability, and introduces the method of using frequency filtering to restrain the backscattering signal. This is a method to modulate the detection signal to a high frequency at the transmitter, do frequency detection at the receiver, and use bandpass filter to cease the low frequency signal.In order to exam the correctness of this method, this paper analyzed the whole transmission process of photon from transmitter to receiver, constructed the underwater transmission model of photon, and simulated the whole transmission process and signal processing part with software based on Monte Carlo method. By this simulation, it shows the contrast of the target reflection signal has been enhanced. This way, the feasibility of this method is proved from the micro-level.Moreover, this paper studied the influence of the bandwidth of the filter and the modulating frequency to the whole system by comparing the target resolution with different modulating frequency with fixed bandwidth, and different bandwidth with fixed modulating frequency. Considering the actual conditions, a proper modulating frequency and filter bandwidth has been given. This gives theory research and theoretical support for the actual application. |
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