近红外土壤含水率传感器设计与试验

摘要

A near infrared reflection (NIR) soil water sensor was developed for rapid measurement of soil moisture content.Light emitting diodes (LEDs),at 1 940 nm and 1 800 nm respectively,were used as measurement and reference light sources.The photodiode received the light reflected from the soil surface to produce an output electronic signal,which was related to the soil moisture content.The received signals were put into a two stage pre-amplifier,an analogue/digital (A/D) transfer,and then were displayed and stored.A certain relationship was found between the output reflected light and soil moisture content.The experiment results showed that the distance from light sensor to soil surface had some influences on the intensity of received signal.According to the sensor structure,a certain distance could be chosen to make a better intensity and stability of reflected signal.The reflectance of the two light sources decreased with increase of soil particle size.There was a strong linear correlation between the relative absorption depth and soil moisture content,and the determination coefficient was 0.863.%设计了一种适用于快速测量土壤含水率的近红外传感器.发光二极管(LED)作为传感器的光源,中心波长为1 940 nm的光为测量光,l 800 nm为参考光,土壤含水率对这2个波长的光有不同的吸收特性.光源发出的光照射到土壤表面,经反射后进入光电转换器,将光信号转换为电信号,送至两级放大电路、模数转换器(A/D)、显示和存储设备,输出的反射光强与土壤含水率存在一定的关系.仪器性能试验表明:光源传感器到土壤表面的距离对采集信号的强度有一定影响,根据传感器的结构,可以选择一定的距离使反射信号的强度和稳定性最好.两波长光的反射光强随着土壤粒径的增大而减小；土壤含水率与相对吸收深度之间具有很好的线性相关性,回归分析的决定系数为0.863.