| The weed is a kind of herbaceous plant that grow randomly and doesn't need actively cultivation of human beings.Rape,which has large acreage in China,is seriously impacted by weeds,in general years weeds may lead to reduction of rapeseed output by 10% to 20%,and in some extreme conditions due to the impact of the weed reduction of rape output even reached more than 50%.In view of the serious damage of weeds caused on crops production,weeds in the field often need to be taken the active control.And the spraying of chemical herbicides because of its simple operation and good effect on weed control has been widely used,however,scholars found that the use of herbicides in the past many years in a large area of extensive evenly spraying will cause serious adverse damage on the ecological environment and the human health.Therefore,the method of target variable spraying with the spatial selectivity is the most ideal method of herbicide application,and the precondition of realizing the target spraying is to solve the problem of automatic identification of weeds.The sensor based on spectral analysis principle due to its good real-time detection performace,no damage to sample and relatively low instrument cost advantage has become a research hotspot in the field of automatic identification of weeds,and the commercial application of sensor based on this technology is available.However,because of the principle of the sensor itself,the sensor is easy to be affected by the interference of environmental stray light to reduce the recognition accuracy.Optical modulation and demodulation techniques can eliminate the environmental stray light DC component that is superimposed on the detection signal by modulation and demodulation of the intensity of light based on discrete Fourier transform,so that reduce the environmental impact of stray light on the detection accuracy of spectrum detection instrument.In the paper the weeds in winter rape at seedling stage is as research object,based on the preliminary research of the project group,using the four detection wavelength of 590 nm,710nm,750 nm and 940 nm and the optical modulation anddemodulation techniques,a set of field weed spectrum recognition test system was established,and the ability of anti environmental stray light was tested.The main research contents are as follows:1.Analysis of the factors affecting the accuracy of weed recognitionThe sensor itself factors and the external environment interference factors were analyzed relatively.The factors of sensor itself mainly were the unreasonable design of the optical system,the noise in the photoelectric device working process and the error of the signal acquisition and processing system in the sampling process;the external environment interference factors were the interference on the sensor caused by the sky background light and artificial light when the sensor is working.2.Establishment of field weed spectrum recognition test system based on optical modulation and demodulationThe optical modulation technology was introduced briefly,and the function of modulation of the optical signal on suppressing the interference of stray light and eliminating the noise caused by the detector itself was discussed.Using four preferred characteristic wavelengths(590nm,710 nm,750nm and 940nm),a set of experimental system based on optical modulation and demodulation technique was designed.This experiment system mainly included experimental equipment(optical modulation device and photoelectric signal acquisition device)and data processing program of LabVIEW.The experiment system adopted the active LED light source and modulated its luminous intensity,and adopted a gain adjustable integrated detector based on photoelectric diode to detect the reflected light signal intensity,adopted IPC(Industrial Personal Computer)to AD-sample the real-time detector signal.Using LabVIEW the experiment data processing program was written.The program mainly realized waveform data sampling,waveform data collection,waveform digital filter,spectrum measurement on filtered waveform data and extraction of the signal amplitude(that is characterized reflectance value of tested sample)at modulated frequency.3.Test on the environmental stray light interference removal effect of using light modulation and demodulationIn order to verify the experimental results of the application of the opticalmodulation and demodulation technology in the removal of environmental stray light using established experimental system,two groups of verification tests were carried out.The results of verification test on eliminating environmental stray light interference show that the experiment system can get stable characterized reflectance value when the environment stray light change slowly and change dramatically,indicating that the optical modulation and demodulation techniques greatly enhance the signal-to-noise ratio and provide a new way of thinking on improving the measurement accuracy of sensor based on the principle of spectrum.4.Static performance test of test systemA series of relative experiments had been carried out using established experimental system,including system repeatability testing,verification test on eliminating environmental stray light interference,calibration experiment with spectrometer and relative verification test.The CV(coefficient of variation)of the experimental system repeatability test results is less than 1.5%,which shows that the experimental results are consistent,the stability of the experimental system is good,and the anti-interference ability is strong.At the end,the calibration test on the experimental system was carried out,and the determination coefficient of calibration equation under four central wavelength were 0.8692,0.9817,0.9812,0.9812.Verification test using winter rape samples was carried out,and the relative error of test results are less than 10%,the maximum is 8.82%,of which the relative error of750 nm and 940 nm test results is relatively small,in less than 3%,the maximum is3.08%.The experimental results show that the measured reflectance is closely related to the actual spectral reflectance of the measured samples,and the actual spectral reflectance values,which eliminate the affect of environmental stray light,can be obtained by calibration equation. |
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