Underwater 3D Measurement Technology Based On Fast Empirical Mode Decomposition

With the further development and utilization of marine resources by humans,the underwater three-dimensional measurement technology will have huge application prospects.In this thesis,an underwater measurement system is built using a camera,a mini projector,and a transparent glass cylinder.The projector projects standard sinusoidal grating stripes to the measurement field to produce phase modulation.The camera collects deformed grating fringe patterns,and combines the fast empirical mode decomposition algorithm and Fourier transform profilometry to realize the three-dimensional measurement technology.In order to improve the measurement accuracy,it is necessary to suppress the interference noise of the fringe pattern and remove the zero frequency component to expand the measurement range.Due to the particularity of the underwater measurement environment,the refraction and scattering phenomena need to be solved to improve the measurement accuracy.The content of this article is arranged as follows:First,the basic principles of two common phase recovery algorithms,the phase shift method and the Fourier transform method,are analyzed to derive the wrapped phase solution process.Because the Fourier transform method has the advantage of obtaining threedimensional data of the object in a single acquisition,the choice is more The efficient and convenient Fourier transform method is used as the phase recovery algorithm in this subject.Secondly,the improved fast empirical mode decomposition algorithm is applied to the underwater three-dimensional measurement technology,and the modal aliasing phenomenon is reduced by the boundary extension;the morphological evaluation method is used to replace the traditional interpolation method to improve the efficiency of the algorithm;the Hilbert spiral is added The function enhances the quality of the fringe pattern,making it more suitable for sinusoidal grating projection 3D measurement technology.The improved fast empirical mode decomposition algorithm removes the background component of the deformed fringe pattern,expands the measurement range of the Fourier transform method,and improves the measurement accuracy.Simulation results prove the superiority of this method.Finally,the underwater measurement system is calibrated,the underwater refraction nonlinear imaging model is established,and the measurement experiment is completed.The height measurement error in the weakly scattered water is 1.21%;when there are more scattering particles in the water,the measurement error is larger.After introducing the image enhancement algorithm based on the hybrid wavelet and directional filter bank,the height measurement error of the circular table in the strong scattering water is effectively reduced.The experimental results show the advantages of the improved rapid empirical mode decomposition 3D measurement technology in the field of underwater 3D measurement.The underwater 3D measurement system built in the experiment can achieve higher accuracy measurements.