Polarization Spectral Image And Raman Spectral Characteristics Of Common Soybean Diseases And Pests

With the development of nondestructive spectral detection technology,more and more spectral detection methods are applied in all kinds of fields,especially in agricultural application.It is a hot spot to detect pests and diseases of crops using spectral technology.At present,it will take at least two days to identify soybean diseases using traditional detect method,which is not conducive for early detection and treatment.Rapid detection of soybean diseases has industrial demand,and it is also one of the most important steps to realize the establishment of intelligent and digital agriculture.In this paper,the polarization spectral imaging technique and Raman spectroscopy were used to identify and characterize the bacterial spot disease,bacterial spot disease,downy mildew and aphids in early soybean growth.Based on the detection principle of polarization bidirectional reflectance distribution function(PBRDF)and mathematical model,according to Stokes vector analysis method,the polarized and spectral characteristics of soybean leaves under early pest stress were studied.The image feature of the leaves with pests under different polarization states were analyzed.The difference of relative polarization spectral reflectance between healthy area and disease spot area of leaves was compared.Raman spectroscopy detection experiments were carried out in different spots and areas of soybean common diseases and insect pests.Based on the density functional theory(DFT),the molecular model of soybean bacterial disease markers was constructed by Gaussian software.The theoretical calculation and experimental results of Raman spectroscopy were analyzed.During the analysis of early soybean diseases and insect pests by polarized spectral imaging technology,the following characteristic spectral regions were obtained by a large number of experiments and comparative analysis.The spectral information of bacterial spot was collected from 505 nm to 565 nm at a polarization angle of 135°,90° parameter.The spectral information of bacterial rash was obtained from 670 nm to 680 nm at a polarization angle of 90°,0° parameter.The spectral information of downy mildew was got from 655 nm to 665 nm at a polarization angle of 45°,0° parameter.The spectral information of aphid damage was displayed from 655 nm to 665 nm at a polarization angle of 0°,0° and 135°,90° parameter.During the analysis of early diseases and insect pests of soybean by Raman spectroscopy,different characteristics of spectral full width at half maximum(FWHM)and frequency shift of each disease leaves were obtained.The internal characteristic information of diseased leaves was distinguished effectively.By combining the internal characteristics of Raman spectroscopy with the external characteristics of polarized spectrum image,the common diseases and pests of soybean can be quickly and early identified.The effectiveness of identification of soybean bacterial spots,bacterial rashes,downy mildew and aphids was verified by polarization spectral imaging technology and Raman spectroscopy technology.It provides a method for optical monitoring pests and diseases of crops.It is hoped that the optical detection technology can be more widely used in agriculture filed and provide scientific basis for safe and nondestructive detection for crops.