Modulation Laser Radar Detection Of The Simulation Research Of Underwater

As airborne lidar underwater target detection plays an important role in military and civilian, many countries in the world are studying this advanced technology. In order to improve resolution and sensitivity of the underwater target, this paper simulates lidar underwater detection system. Backscattering noise signal dominates target reflection signal in the detector, so underwater target is very difficult to distinguish. Restraining the backscattering noise signal and improving the resolution of the underwater target are the main tasks of this paper.Based on the existing theory on seawater channel equation, backscattering channel spectrum shows a low-pass characteristic and the target reflection channel spectrum does not change with frequency, amplitude of the target reflection channel is bigger than the backscattering one’s in high frequency. If the spectrum of the target signal is moved to high frequencies, the underwater target resolution will be improved, based on this idea, a method, which modulates laser pulse with microwave signal and filters out the noise signal in frequency domain, is proposed. Frequency modulation and amplitude modulation are studied in this paper and the latter achieves good result. Several important system parameters are designed with this method. Their optimal values are given out with maximum signal to noise ratio and target reflection to backscattering peak ratio. Microwave signal frequency lies in1.5-3.5GHz, bandwidth of the filter lies in200-400MHz and so on.FP modulation, mirrored flip FP modulation, dual cosine superimposed amplitude modulation are also studied in the paper and the dual cosine superimposed amplitude modulation obtains the best result. The target reflection to backscattering peak ratio is close to1. Compared with the echo signals without frequency filtering processing, the peak power of the backscattering signal attenuates about23times and target reflection signal attenuates only3times. This method has a significant effect on suppression of the backscattering noise signals.Compared with traditional lidar underwater detection system, a conclusion can be drawn that modulation technology and filtering method in frequency domain are effective methods to improve resolution of the underwater target and they have guiding significance to improve detection depth and precision for airborne lidar system.