透地雷達應用於稻穀乾燥過程含水率監測

Abstract

本研究透過高頻透地雷達來偵測靜置條件下與連續乾燥過程中稻穀含水率之變化。在初步實驗中，透地雷達所量測到的稻穀介電常數會受到含水率顯著的影響，而不同稻穀穀層厚度在統計上對介電常數的影響並不顯著。研究顯示由Nelson與Noh發展的稻穀介電常數估計數學模式適合用來作為估計介電常數的理論依據。 在連續乾燥過程中，透地雷達所推估到的介電常數會受到溫度顯著的影響。當溫度變化時，在參考溫度24 °C下計算所得到的理論介電常數需要加上由Lawrence 等人所提供的溫度修正因子進行溫度效應的修正。當考量溫度修正因子後，利用透地雷達方式推估所獲得的介電常數與Nelson與Noh所發展的介電常數數學模式十分吻合。 在連續乾燥過程中，透地雷達所量測到的介電常數受到許多因素如含水率、溫度與密度的影響。本研究並透過在稻穀乾燥過程中，所量測到的溫度與透地雷達的波速，利用數值方法推估稻穀乾燥過程中的含水率。所推估的含水率與利用烤箱法所獲得的含水率比較，兩者有很好的配合度。因此可利用透地雷達的方式來進行稻穀乾燥過程中含水率的非破壞性即時監測。

In this study, GPR system was used to detect paddy moisture content in a static condition and a continuous drying process. In our preliminary experiments, the dielectric constant obtained by the GPR was influenced by the paddy moisture content and temperature, but the paddy thickness was statistically insignificant. The mathematical model for the dielectric constant of paddy by Nelson and Noh was found to be applicable in estimating the dielectric constant of paddy in our experiments. In the continuous drying experiment, the dielectric constant of paddy measured by the GPR was significantly influenced by temperature. As the temperature changed during the drying process, a temperature correction factor developed by Lawrence et al. [27] was adopted to model the temperature effect. After the introduction of the factor, the dielectric constants measured in this study matched well with the theoretical data calculated from the mathematical model by Nelson and Noh.[29] In a continuous drying process, the dielectric constant of paddy measured by the GPR is affected by many factors such as moisture content, temperature, and bulk density. In this study, a numerical method was used to estimate the real-time moisture content by measuring the dielectric constant and temperature during the paddy drying process. The estimated results showed good agreement with data obtained by the oven method. This demonstrates the potential of application of the GPR system in real time monitoring of paddy moisture content during the drying process.