XU Qun,XU Huadong*,DI Yanan,et al.Investigation of the effect of probe insert depth on inversion accuracy of moisture content of Betula platyphylla Suk.standing trees using time domain reflectometry[J].Journal of Forestry Engineering,2019,4(04):120-126.[doi:10.13360/j.issn.2096-1359.2019.04.018]





Investigation of the effect of probe insert depth on inversion accuracy of moisture content of Betula platyphylla Suk.standing trees using time domain reflectometry
徐群徐华东*狄亚楠 李其哲
东北林业大学工程技术学院,哈尔滨 150040
XU Qun XU Huadong* DI Yanan LI Qizhe
College of Engineering and Technology, Northeast Forestry University, Harbin 150040, China
白桦 活立木 含水率 电磁波传播时间 探针插入深度 时域反射法 反演模型
Betula platyphylla Suk. starding trees moisture content electromagnetic wave propagation time probe insert depth time domain reflectometry(TDR) inversion model
时域反射法(time domain reflectometry,TDR)用于反演活立木含水率时颇具潜力,但是其反演精度依赖于探针插入深度的合理选取。利用白桦圆盘,分别在不同探针插入深度(2,4,6和8 cm)下,采用TDR设备测量试件在不同含水率(绝干至饱湿)时的电磁波传播时间,深入分析了电磁波传播时间与含水率及插入深度之间的关系,构建了不同深度下的含水率校准方程,比较了模型(校准方程)精度,并最终优选了合适的探针插入深度。研究表明:电磁波传播时间对含水率和探针插入深度具有良好的敏感性,随含水率和插入深度的增大而增加; 4,6,8 cm插入深度下,电磁波传播时间对不同试件和含水率均具有稳定一致的变化规律,而2 cm插入深度的数据规律不明显; 分别将4,6,8 cm插入深度下的传播时间和体积含水率数据综合到一起,各自随机选取70%的数据(24组)作为训练样本构建校准方程,其余30%(9组)作为验证样本,结果发现4 cm插入深度时预测值相比验证样本真实值的平均误差和均方根误差均最小,分别为2.97%和3.84%; 最后分别将4,6,8 cm插入深度下的所有数据用于构建校准方程,通过残差图去除异常点后,校准方程的决定系数 R2分别为0.96,0.92,0.89。这表明在应用所构建的校准方程测量白桦活立木树干含水率时,最佳的探针插入深度是4 cm,该条件下校准方程的预测精度和拟合精度最好,且与6和8 cm插入深度相比,可有效降低钻孔难度,减小对活立木树干的损伤。
Accurate measurement of the moisture content(MC)of standing tree sapwood is a problem for forestry researchers.Time domain reflectometry(TDR)is one of the most promising methods to solve this problem.However, its measurement accuracy depends on reasonable selection of probe insert depth(PID).In this paper, the TDR equipment was employed to measure electromagnetic wave propagation time(EWPT)of Betula platyphylla Suk.disk specimens at different MCs(from absolute dry to saturation)and different PIDs(2 cm, 4 cm, 6 cm and 8 cm).The relationship between EWPT and MC, at different PID conditions, was analyzed, then some MC prediction models were developed and their accuracies were compared and analyzed.The most effective PID was finally determined.The results showed that: EWPT was highly sensitive to MC and PID, which kept an upword tendency with the increase of MC and PID; when PID was 4 cm, 6 cm or 8 cm, all specimen's EWPT data rised up with the increase of MC, while it was abnormal when PID was 2 cm.By analyzing EWPT and volumetric MC data at 4 cm, 6 cm and 8 cm PID respectively, 70% of the data(24 groups)were randomly selected as training samples to construct calibration equations, and the remaining 30%(9 groups)were used as verification samples.It was indicated that the average error(2.97%)and root mean square error(3.84%)were the smallest when PID was 4 cm by comparing the predicted value with the true value of the verification sample.Finally, several calibration equations at each PID, with a corresponding R2=0.96, 0.92 or 0.89, were constructed after removing the abnormal points, respectively.It was revealed that the 4 cm PID was the best selection when the above calibration equations were used to measure the MC of Betula platyphylla Suk.sapwood in field, because its calibration equation's prediction accuracy and fitting accuracy were the highest.In addition, it can also effectively reduce drilling difficulty and the damage to standing tree trunks, compared with the 6 cm and 8 cm PID.


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收稿日期:2018-10-29 修回日期:2019-04-15
基金项目:国家自然科学基金面上项目(31870537); 中央高校基本科研业务费专项资金项目(2572018BL08); 哈尔滨市应用技术研究与开发项目(2017RAQXJ078)。
更新日期/Last Update: 2019-07-10