Research Application Of Infrared Thermography On Disease Detection Of Crop At An Early Stage

Aiming to prevent disease and ensure the crop production, there is existed that the pesticides are overused in our country. This situation leads to soil and water pollution increasing in agricultural production. Meanwhile, the excessive use of pesticides brings the food safety issues. It has been widespread concern of the whole society. To protect the environment and realize sustainable development of agriculture, our country will control the use of water, fertilizer and pesticides. The government report on two sessions emphasized on March 5, 2015 said that “Synthetically control residues in pesticides and veterinary drugs, improve the quality of agricultural products and standard of food safety.” Among that the early detection and treatment of pests and diseases are an effective measure to reduce the dosage of pesticides.The traditional disease detection is mainly based on naked eye. In order to detect disease at an early stage, people have done a lot of exploration and research in recent years, such as microscopy techniques and spectroscopic technology. Their aim is to look for ways to detect disease at an early stage. In this article, the research is about infrared thermography on detection of crop diseases at an early stage.The main contents of this research are as follows:1. The first part summarized the domestic and international progress and current status of infrared thermography in aspects of crop diseases and stress detection. Then it analyzed the deficiencies in similar studies at home and abroad of this technology. Besides, it sketched out infrared thermography, focused on the principle and structure of uncooled infrared detector. After that it derived its flow equation of heat. Finally, it analyzed the relationship between the water changes and temperature in the crop after infecting diseases. This part drew a conclusion that it was feasible for infrared thermography to detect crop diseases.2. By reviewing a large amount of literature and consulting rice experts in Academy of Agricultural Sciences of Yangzhou and wheat experts in China Agricultural University, experimental team did many times of pre-tests and determined spray inoculation of rice blast and smearing inoculation of wheat stripe rust through comparison testing. The characteristics and mechanism of bacteria infection were analyzed. Experimental team generalized and sorted the preparation methods by actual practices on experimental material of rice and wheat. It concluded culture and infection of bacteria. In the formal experiment, experimental team selected rice blast and wheat stripe rust as test material.3. Experimental team built a system experiment of infrared thermal imaging by analyzing system requirement. It concluded Vario CAM®hr thermal infrared imager which was made in Germany, memory card of image, upper computer and visible image acquisition system. Before acquiring the formal images, experimental team collected infrared thermal images at different times throughout the day. Then experimental team analyzed and contrasted the effects of ambient temperature and moisture on the quality of images. Finally experimental team determined the sampling time and detection method of image.4. Under controlled conditions, experimental team utilized infrared thermography to detect rice leaves infected rice blast and wheat leaves infected wheat stripe rust in preliminary detection. Its aim was to analyze the impact of pathogeny to leaf in the infrared thermal images. Then experimental team used IRBIS 3, Infrared data analysis software, to analyze 200 acquired images. In the dry environment, the temperature difference in the infected leaves of rice was about 0.62℃~2℃ by extracting their eigenvalues while it was less than 0.2℃ in the healthy leaves. In the dry environment, the temperature difference in the infected leaves of wheat was about 1℃~1.5℃, however it was just less than 0.3℃ in the healthy leaves.5. Experimental team took advantage of IRBIS 3 to analyze more than 2,000 images, the results showed that:(1) By detecting continuously and non-destructively for nearly 80 samples whose rice leaves were infected rice blast, experimental team found that the temperature difference between affected site and healthy site in the same leaf was about 0.36℃~0.63℃. At that time, the lesions was difficult to observe under naked eye. It almost could be early detected about one day in advance before the symptom was shown.(2) After being infected by wheat stripe rust, the temperature of disease portion in leaf was lower than that of healthy portion. Before lesion of wheat leaves was obviously visible, when it was just entering the stage of chlorosis, the infected leaves did not produced spores yet at this point. At the marked point in the infrared images, experimental team could get the result that temperature eigenvalues of this point was about 0.62℃~0.87℃ lower than the surrounding normal parts after extracting infrared image feature.(3) Infrared thermography to detect crop diseases was used. Then experimental team used SPAD-502, leaf chlorophyll meter, to measure the content of their relative value of chlorophyll. After a comprehensive analysis of the temperature and disease progress of the blade, it was found that relative content of chlorophyll changed with the development of disease. The results of experiment showed that, the content of chlorophyll could be used as an indicator to identify whether the crop was infected under controlled conditions.These results indicated that infrared thermography could realize rapid, non-destructive detection for crop diseases. A theoretical basis of the development on rapid detection instruments and sensors of crop diseases was provided.