Design And Simulation About Optical System Of Active Crop Growth Monitor

Optical system is part of the core modules of crop growth spectrum monitoring equipment,which directly determines the accuracy and reliability of equipment.Based on crop growth spectrum monitoring principle,this paper presents a design scheme of the optical system for monitoring canopy spectrum of rice and wheat.A medium power,small angle LED is designed as the light source,and the diffusion film is used as the emission light path,so the low light source power,low spot uniformity and other key problems are solved.The research results have important significance to improve the overall performance of the crop growth monitor,to promote the application of intelligent equipment of crop cultivation,and to promote the independent innovation of precision agriculture in our country.Firstly,based on the principle of crop growth spectrum detection by using the research results about the sensitive band of rice-wheat growth information in 730nm and 810nm in recent years according to canopy structure characteristics of wheat and rice.The design scheme of optical system is proposed.The luminous system is irradiated to produce an elliptical uniform spot,and the light receiving system receives the light from the light reflected by the canopy.Secondly,the light emitting optical system is designed and simulated.Based on the theory of non-imaging optics,modeling and optimization parameters of lens(at the radius of sphere,height of cylinder)and the reflecting cup parameters(radius of the bottom and top radius),the power 400MW,half value angle of 100 LED as light source,to meet the light source power requirements,but also to enhance the portability of the monitor.Luminous light path design,the two band led a cross distribution,the purpose of which is to make two wavelength led to emit light in canopy overlap,irradiation of the same region;based on spot size(long axis is 30cm long,short axis 10 cm in length),comparison of different specifications of the diffusion sheet,select 100x300specifications diffusion film optical system.The simulation results show that spot uniformity of compared with the traditional cylindrical lens optical system was increased by 20%.In addition,the design and Simulation of the optical system are carried out.Based on the principle of geometrical optics,a Finel lens with a focal length of 15mm is designed as the core component of the light sensitive optical path.The photosensitive diode is selected as the light sensitive element,the verification result shows that the photosensitive diode works in the linear region,the R2 value reaches to 0.99,so the measuring accuracy is guaranteed.Lastly,the performance of the optical system designed in this paper is simulated and tested.At first,for simulation test,the LED optical file is obtained through the near field light source distribution test system.And the file should be imported into Tracepro optical simulation software to establish the system model and track the light.The spot irradiance distribution figure at different height is obtained.The uniformity can be calculated by formula and is compared with the uniformity of physical spot obtained by light source uniformity test platform.The results show that the uniformity of optical system designed in this paper is more than 80%,which can meet the test requirements.The standard reflectance gray scale test shows that,with height changing,the root mean square error(RMSE)of the ratio vegetation index RVI is 0.1081,while the RMSE of NDVI is 0.0192.The field experiment shows that NDVI and RVI obtained from the active crop growth monitor have a good correlation with ASD hyper-spectrometer and R2 is better than 0.82.It is indicated that the design of the optical system meets the requirements of field test in this paper.