激光相干场成像散斑噪声复合去噪方法

Compound denoising method of laser speckle noise in laser inherent field imaging

噪声是影响激光相干场高分辨成像系统像质的重要因素,激光相干场成像系统既受背景光加性噪声影响,又受激光乘性散斑噪声影响.为解决激光相干场成像系统受激光乘性散斑噪声和背景光加性噪声叠加引起的成像像质退化效应问题,从噪声抑制角度提高激光相干场系统高分辨成像像质,研究建立了激光散斑乘性噪声和背景光加性噪声对大气下行链路激光回波场信号影响干扰模型,并基于该模型提出了一种基于同态滤波和稀疏基追踪级联复合去噪算法.首先基于同态滤波理论将激光乘性散斑噪声转化为加性噪声,再由高通滤波器滤除散斑噪声,最后采用基追踪稀疏理论方法抑制背景光等加性噪声对像质的影响.研究表明,较现有单一去噪方法,该级联复合去噪方法可一次性消除激光乘性散斑噪声和背景加性噪声两种不同性质的噪声,有效改善了激光相干场成像质量.

Noise is an important factor affecting the image quality of laser coherent field high resolution imaging system.And there exists not only background light additive noise but also laser multiplicative speckle noise in a laser coherent field imaging system.Both of the above noise affect the imaging quality of laser coherent field system.In order to improve the imaging quality from the perspective of noise suppression and settle the imaging quality degradation problem of laser multiplicative speckle noise and background additive noise in the laser coherent field imaging system,the model for the influence of multiplicative speckle noise and background additive noise on laser echo field demodulated signal is established in atmospheric downlink.Then,based on the model,a novel homomorphic filter and sparse matrix trace cascade compound de-noising algorithm is put forward.Firstly,based on the homomorphic filtering theory,the laser multiplicative speckle noise in the laser echo demodulated signal is converted into the additive noise by logarithmic transformation.Then the lowfrequency laser multiplicative speckle noise is filtered by the high-pass filter,and the high-frequency demodulated signal is retained.The logarithmic inverse transform is used to obtain the laser echo demodulation signal after the multiplicative speckle noise has been filtered out.Next,the phase random disturbance of atmosphere in laser echo demodulated signal is suppressed by phase closure technology and the imaging spectrum component is reconstructed by the spectrum iterative reconstruction method.Then the high resolution image is obtained by spectrum component inverse Fourier transform.Finally,the effect of background additive noise on the image quality is suppressed by the sparse base tracking theory.The simulated and outdoor experiment result are used to verify the denoising effect and image quality enhancement effect of the composite de-noising method.Compared with the existing single denoising method,the composite denoising method is shown to be able to effectively eliminate laser multiplicative speckle noise and background additive noise at one time.The proposed method can improve image contrast and promote the Strehl ratio of imaging quality in a coherent imaging system.It provides a theoretical basis for improving imaging quality and denosing laser multiplicative speckle noise and background additive noise in coherent field imaging system.