Application of filtering method in frequency domain to modulated LIDAR system for underwater detection

To improve underwater target contrast, spectrum characteristics of the sea water have been studied. The result shows backscattering signal has a low-pass characteristic while target reflection signal is less frequency-dependent. Modulation frequency of the incident optical signal is high enough, so target reflection signal exceeds backscattering signal at high frequency. Filtering method in frequency is used to filter out most energy of the backscattering signal and the white noise. As a result, time domain signal shows that underwater target contrast improves more than 8 times when the modulation frequency is 1.5 GHz and 11 times when the modulation frequency is 3 GHz.