基于微波频时域变换的土壤灌溉湿润锋检测技术

Soil Wetting Front Detection Based on Frequency Domain to Time Domain Conversion of Microwave

为有效解决传统TDR系统在确定土壤湿润锋位置时带宽小、上升沿时间长、分层界面位置测量误差大等问题,本文在研究TDR阻抗测量的基础上,利用微波频域、时域变换理论提出了一种基于便携式矢量网络分析仪的土壤湿润峰测量方法。利用ADS仿真分析验证了TDR波形重新建模方法,证明了不同阻抗交界面检测的可靠性。通过油水交界面、2层不同含水率土壤干湿交界面、3层不同含水率土壤干湿交界面位置的测量,与传统TDR方法测得的结果进行对比,结果表明基于便携式矢量网络分析仪建立的微波阻抗反射信号转换模型在实际应用中具有很好的准确性,可为土壤分布式含水率的测定提供理论借鉴。

Determining the location of the soil wetting front is of great significance for optimizing irrigation decision-making and realizing intelligent irrigation.The automatic device for detecting the soil wet-dry interface has not been commercialized at present.A soil wetting front measurement system was proposed with a vector network analyzer based on the research of TDR impedance measurement.Through TDR waveform reconstruction,the shortcomings of traditional TDR systems were effectively solved,such as insufficient bandwidth,long duration of rising edge of pulse and unclear boundary position detection.The reliability of the TDR waveform reconstruction method model was verified by simulation with ADS software.The locations of oil-water interface,dry-wet interface of two layers of soil with different moisture contents,and dry-wet interface of three layers of soil with different moisture contents were measured.The comparison between the results obtained by using the built model and the results obtained by the TDR method demonstrated the accuracy of the measurement.The theoretical simulation results carried out by ADS software showed that the TDR waveform converted from high frequency domain to time domain can accurately measure the position of impedance discontinuities.Through the two-layer and three-layer soil measurement experiments with different water contents,it was shown that this test method can be applied to actual production measurement.The accuracy of the reflection signal conversion model based on potable vector network analyzer in the actual application of determining the location of the soil moisture front provided a theoretical reference for the determination of the distributed soil moisture content.