Prediction of Soluble Solid Content of Korla Pears Based on CARS-MIV
ZHU Xiao-lin1, 2, LI Guang-hui1, 2*, ZHANG Meng1, 2
1. School of IOT Engineering, Jiangnan University, Wuxi 214122, China
2. Engineering Research Center of IOT Technology Applications, Ministry of Education, Wuxi 214122 China
Abstract：In order to classify and set different prices on the basis of soluble solid content (SSC) of korla pears and promote the development of post-harvest processing healthily in standardization and industrialization, a fast, precise and nondestructive method to detect soluble solid content of korla pears was determined by applying hyperspectral reflectance imaging technology. 157 korla pears freshly and with no surface damage were collected as samples. Hyperspectral images with a spectral range of 400~1000 nm of pears were acquired by hyperspectral imaging system. Then the region of interest (ROI) function of ENVI 5.3 software was used to conduct spectral data extraction from each hyperspectral image of pear. Totally, 157 pear samples were divided into calibration set (105) and prediction set (52) based on the Kennard-Stone（KS）sample set partitioning method. The research compared the influence of accuracy of modeling in terms of the spectrum pretreatment methods of original spectrum, standard normal variate (SNV), multiplicative scatter correction (MSC), first derivative (FD) and second derivative (SD). The SNV was applied for smoothing and denoising of the original hyperspectral data. A variable selection method combining competitive adaptive reweighted sampling and mean impact value (CARS-MIV) was utilized to extract the characteristic variables from full spectrum (FS). The modeled samples of competitive adaptive reweighted sampling (CARS) are generated by random selection of Monte Carlo sampling, and the regression coefficients of variables will change accordingly. The absolute value of regression coefficients cannot fully reflect the importance of variables, and affect the accuracy of the model. To lower the impact, the mean impact value (MIV) algorithm is applied to select the independent variables for secondary screening, and the variables with bigger correlation are selected for modeling and analysis. In this paper, the variables selected by CARS, successive projection algorithm (SPA) and Monte-Carlo uninformative variable elimination (MCUVE) were used for comparison. Finally, the spectral information selected from full wavelength and the spectral information selected from four characteristic wavelength selection method were taken as input vector to build support vector regression（SVR）model to predict soluble solid content of korla pears. The performances of the models were evaluated by the root of mean square of calibration (RMSEC), the root of mean square of prediction (RMSEP), the correlation coefficient of calibration (Rc) and the correlation coefficient of prediction (Rp). By means of comparison, the CARS-MIV-SVR models achieved the optimal performance with the Rc reaching 0.985 94 and Rp up to 0.946 31. The RMSEC and RMSEP are 0.185 85 and 0.403 33 respectively. These experimental results demonstrated that CSRS-MIV method can efficiently improve the stability and accuracy of wavelength selection, and optimize the precision of prediction model. The hyperspectral technique combined with CARS-MIV-SVR model can meet the needs of determination of soluble solid content and be used to classify and set different prices on the basis of SSC of korla pears.
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