Laser underwater ranging based on wavelet transform

Abstract

<sec>This paper proposes an underwater ranging method based on wavelet transform. First, according to the band-pass filtering characteristics of the wavelet transform, the time-domain signal is decomposed in the frequency domain. The wavelet basis functions with high similarity are established. These wavelet basis functions contain complete frequency domain information of time-domain signals. This method can improve the ability to decompose frequency domain of time-domain signals and extract the information about the effective frequency domain. Then, using the multiple frequency domain decomposition approximations, the effective frequency domain information contained in the time domain signal is completely extracted.</sec><sec>The time-frequency signal of wavelet time-frequency fusion ranging takes the energy consistency of the time-frequency domain signal as the link and uses the binary spline interpolation structure to realize the time-frequency combination of the signal. In this method, the time-domain signal is first decomposed and filtered by wavelet time-domain to obtain more complete time-domain effective information. But at this time, the time-domain signal is the superimposed form of frequency-domain information, so the energy domain information contained in the time-frequency signal is decomposed into the wavelet frequency domain through the binary spline interpolation, and the energy expression form of the time-frequency signal can be obtained. The target is locked by finding the position of the maximum value of energy corresponding to the time-frequency domain of the signal to achieve the purpose of precise ranging. By performing the wavelet multi-layer time-domain decomposition filtering first, the frequency domain decomposition range can be effectively reduced, thereby avoiding data redundancy and reducing the ability to realize the effective frequency domain resolution.</sec><sec>By using this method we successively carry out continuous light underwater ranging experiments with different attenuation length water bodies and different modulation frequencies, and analyze the influence of this method on continuous light underwater detection. Experiments verify that this ranging method successfully achieves the accurate measurement of targets within 8 attenuation lengths within an output power of 2.3 W, and its ranging accuracy is less than 1 cm; the use of wavelet time-frequency fusion ranging can pass the frequency domain energy decomposition capability enhancement, to a certain extent, compensates for the measurement error caused by the significant attenuation of the effective signal. Therefore, the ranging method can be applied to signals with complex frequency domain information or including a bandwidth.</sec>