Research On High Precision Refractive Index Measurement Technology Based On Linear Array CCD Sensor

Refractive index is a basic physical property,which can reflect the solute solution concentration information,such as salinity,density,sugar content,concentration and other parameters.With the development of industrialization,in order to reduce labor costs and ensure product quality,real-time,accurate,online automation requirements have been put forward for refractive index measurement devices.Based on the requirement of an automated refractive index measuring instrument,this thesis completes the design of a refractive index measuring system based on a linear array CCD.The image processing algorithm is used to analyze the images collected by the linear array CCD to realize the refractive index measurement.In the direction of measurement resolution,a corresponding sub-pixel algorithm is designed,and the image processing technology is used to improve the resolution of the system device.First,the thesis discusses the measurement methods of refractive index.In the comparison and induction of the existing technology,the linear array CCD is combined with the critical angle method to measure the refractive index,and this thesis successfully designed the critical angle system based on the requirements of automated measurement technology.The selection and parameter design of each component of the system device were successfully completed.And according to the work flow of the system device,this thesis realized the automatic software program design.Aiming at the noise in the linear array CCD digital image,a combination of median filtering and wavelet filtering algorithms is used for processing.Based on the image processing algorithm of the system device and the type of CCD noise,this thesis constructed a reflectivity simulation model,which is applied to the filtering algorithm.And by the way of evaluating SNR,the median filtering and wavelet filtering algorithm parameters are designed.In this thesis,the process of linear array CCD image processing in critical angle method is introduced,and the algorithm design of refractive index information extraction based on Fresnel reflectance curve is designed.To extract the refractive index information,the differential method is used.In view of the limitation of the single pixel accuracy of the differential method,parabolic interpolation and centroid sub-pixel extraction algorithms are designed.And the thesis adopted the reflectivity simulation model to evaluate and design the sub-pixel algorithm.Finally,according to the seawater salinity measurement needs of the linear array CCD system device,relevant verification experiments are designed.This thesis configure high-resolution salinity reference solution,and verify the anti-noise performance of the sub-pixel algorithm through repeatability experiments.And we achieve the accuracy measurement of the salinity reference solution with sub-pixel algorithm.