Experimental Study And Error Correction On The Effect Of Temperature On The Measurement Of Soil Moisture Content By TDR Method

The time domain reflectometer(TDR, in brief) real-time method of measuring soil water content has been widely applied in the field of geotechnical engineering and agricultural soil and water engineering because of the characteristics of simple operation and can got the available data results in a short time. The measurement precision of soil water content using TDR method has been the focus issue emphasized by domestic and international scholars. Its precision mainly determined by the time delay measurement of electromagnetic wave and calibration of the relationship between the delay and soil water content. It has achieved progress to measure the time delay of electromagnetic wave, however, in the field of calibration of the relationship between the delay and soil water content, there is no systematic analysis of the soil water content measure errors caused by temperature change. As we known, it should not be ignored to consider the temperature effect on measuring soil water content using TDR method. In order to study the temperature effect on measuring soil water content using TDR method, and establish a set of calibration method of the relationship between measuring soil water content and the actual water content, the basic principle of TDR method measuring soil water content is analyzed, the remolded silty clay and silt sample that are 20% water content was prepared, which are the two common soil in Daqing area. TDR method and oven drying method were used respectively to measure the two soil samples in 0 ~ 20 ℃ within 11 control moisture value of the temperature. Based on oven drying moisture content measurement, the error distribution of two kinds of the soil moisture content with temperature using the TDR method were analyzed of, and the error correction formula were fitted. The correctness of the method was verified by experiment, and the enlarged sample was considered in the temperature error correction formula of silty clay water content.The research results show that the error of TDR method under different low positive temperature is more obvious. Through statistical analysis of the deviations of 3 groups, the following conclusions were extracted, with the temperature increasing,the measuring deviations of silty clay water content using TDR method has decreased,; but the trend of the measuring deviations of silt water content with temperature is inconspicuous. The results modified by revised formula of water content silty clay are better than the original measured results.