Development And Application Of Plant Chlorophyll Fluorescence Imaging System Based On CMOS Camera

Chlorophyll fluorescence is known as the probe of non-destructive plant detection,and is closely related to the photosynthesis of plants,so chlorophyll fluorescence detection technology is an important means to monitor plant growth status and physiological information.However,the current chlorophyll fluorescence detection technology is limited by the light source and fluorescence detection sensor,resulting in most of the chlorophyll fluorescence detection is point measurement or limited to the surface measurement of a single leaf,there is a certain probability of error;and the equipment for large area chlorophyll fluorescence measurement is expensive and can not be used in actual production.To solve the above problems,this paper develops a modulated chlorophyll fluorescence imaging system based on CMOS camera according to chlorophyll fluorescence excitation and detection wavelengths,and investigates the classification of drought stress in cucumber.The main research contents and results of this paper have the following parts:(1)Modulated chlorophyll fluorescence imaging system light source designTo solve the problem of small detection area due to the small irradiation area of the current chlorophyll fluorescence imaging system,a pulse width modulated(PWM)excitation light source for chlorophyll fluorescence imaging system was designed.The light source power was determined by Light Tools optical simulation software,and the evaluation function was used to determine the installation angle and the size of the uniform light bar structure according to the spatial coordinates of the LED light source to further improve the uniformity of the illumination area;PWM was used to control the light source to emit different intensities of excitation light.After the actual measurement of the instrument,it is found that the intensity of the system measures light is1μmol/8)/,the intensity of the photochemical light is 890μmol/8)/ and the intensity of the saturated pulsed light is 6277μmol/8)/,this system achieves the requirement of modulated chlorophyll fluorescence excitation light,and the uniformity of illumination in the detection area of 250mm×250mm is about 91.8%,which achieves the uniform illumination of large area with high light intensity.(2)Design of chlorophyll fluorescence imaging system based on CMOS cameraIn order to solve the problem of small measurement area and high cost of the current chlorophyll fluorescence detection system,a chlorophyll fluorescence imaging system for plants with a cooled CMOS camera with low cost and noise has been built,and the pulse synchronization timing of the system has been developed.To solve the synchronization problem between CMOS camera and LED measuring light,the external trigger pulse timing of CMOS camera is designed based on embedded system,and the electrical isolation of input and output signals is realized by combining with optocoupler isolation circuit,which effectively improves the anti-interference ability of the system.The pulse timing output of the master controller is verified,and the results show that the master controller achieves the synchronization of the external trigger pulse timing of CMOS camera and LED pulse timing,which ensures the accurate acquisition of chlorophyll fluorescence images during the detection process.(3)Software development for data analysis of chlorophyll fluorescence imaging systemThe data analysis software of the chlorophyll fluorescence imaging system was developed,and the imaging parameters of the chlorophyll fluorescence detection system were set using UART serial communication;the OTSU image segmentation algorithm and Open CV2 library functions were used to segment and calculate the chlorophyll fluorescence images acquired by the system,and the chlorophyll fluorescence parameter values and common chlorophyll fluorescence grayscale images were obtained;the PYQT image interface was used to visualize the pseudo-color imaging results and realize the integrated management of chlorophyll fluorescence imaging system detection control,data processing and data result visualization display.The comparison with IMAGING-PAM shows that the system can realize the detection of plant chlorophyll fluorescence,, /,, ′,(4 and other physiological parameters.(4)Drought stress study of cucumber based on chlorophyll fluorescence parameters and imagesUsing cucumber as the experimental material,the system was used to image and detect chlorophyll fluorescence of cucumber leaves under different irrigation conditions,and suitable chlorophyll fluorescence characteristic parameters were screened for drought stress diagnosis of cucumber.By studying the fluorescence distribution and parameter value trends of chlorophyll fluorescence images under different drought stress levels of cucumber,the classification models of drought stress levels based on extreme gradient boosting algorithm,radial basis neural network algorithm and random forest classification algorithm were constructed,and the extreme gradient boosting algorithm was screened as the drought stress diagnosis model,and the experimental results showed that the constructed model was able to accurately classify and diagnose different degrees of drought in cucumber.