探针插入深度对时域反射法反演白桦树干含水率精度的影响
|
摘要
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.
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.
引文
[1]EDWARDS W R N,JARVIS P G. A method for measuring radial differences in water content of intact tree stems by attenuation of gamma radiation[J]. Plant Cell and Environment,1983,6(3):255-260. DOI:10.1111/1365-3040.ep11587650.
[2]RASCHI A,TOGNETTI R,RIDDER H W,et al. Water in the stems of sessile oak(Quercus petraca)assessed by computer tomography with concurrent measurements of sap velocity and ultrasound emission[J]. Plant Cell and Environment,1995,18(5):545-554. DOI:10.1111/j.1365-3040.1995.tb00554.x.
[3]MENON R S,MACKAY A L,HAILEY J R T,et al. An NMR determination of the physiological water distribution in wood during drying[J]. Journal of Applied Polymer Science,2010,33(4):1141-1155. DOI:10.1002/app.1987.070330408.
[4]赵荣军,霍小梅,上官蔚蔚,等.近红外光谱法预测粗皮桉木材气干密度的影响因素分析[J].光谱学与光谱分析,2011,31(11):1948-1951. DOI:10.3964/j.issn.1000-0593(2011)11-2948-04.ZHAO R J,HUO X M,SHANGGUAN W W,et al. Analysis of factors affecting air dry density of rough-skinned wood by near infrared spectroscopy[J]. Spectroscopy and Spectral Analysis,2011,31(11):1948-1951.
[5]CONSTANTZ J,MURPHY F. Monitoring storage moisture in tree using time domain reflectometry[J]. Journal of Hydrology,1990,119(1/2/3/4):31-42. DOI:10.1016/0022-1694(90)90032-S.
[6]赵燕东,高超,张新,等.基于驻波率原理的植物茎体水分无损检测方法研究[J].农业机械学报,2016,47(1):310-316.DOI:10.6041/j.issn.1000-1298.2016.01.042.ZHAO Y D,GAO C,ZHANG X,et al. Nondestructive detection method of plant stem moisture content based on standing wave rate principle[J]. Journal of Agricultural Machinery,2016,47(1):310-316.
[7]赵燕东,王海兰,胡培金,等.基于活立木介电特性的植物茎体含水量测量方法[J].林业科学,2010,46(11):179-183.DOI:10.11707/j.1001-7488.20101128.ZHAO Y D,WANG H L,HU P J,et al. Method for measuring moisture content of plant stems based on dielectric properties of standing trees[J]. Scientia Silvae Sinicae,2010,46(11):179-183.
[8]WULLSCHLEGER S D,HANSON P J,TODD D E. Measuring stem water content in four deciduous hardwood with a time domain reflectometry[J]. Tree Physiology,1996,16(10):809-815.DOI:10.1093/treephys/16.10.809.
[9]IRVINE J,GRACE J. Non-destructive measurement of stem water content by time domain reflectometry using short probes[J]. Journal of Experimental Botany,1997,48(3):813-818. DOI:10.1093/jxb/48.3.813.
[10]NADLER A,RAVEH E,YERMIYAHU U,et al. Evaluation of TDR use to monitor water content in stem of lemon trees and soil and their response to water stress[J]. Soil Science Society of America Journal, 2003,67(2):437-488. DOI:10. 2136/sssaj2003.4370.
[11]NADLER A,RAVEH E,YERMIYAHU U,et al. Stress induced water content variations in mango stem by time domain reflectometry[J]. Soil Science Society of America Journal,2006,70(2):510-520. DOI:10.2136/sssaj2005.0127.
[12]SANTANA V H,FERNANDEZ J M,MORAN C. Estimation of tree water stress from stem and soil water monitoring with time-domain reflectometry in two small forested basins in Spain[J].Hydrological Processes,2008,22:2493-2501. DOI:10. 1002/hyp.6845.
[13]SCHIMLECK L,MYERS K L,SANDERS J,et al. Measuring the moisture content of green wood using time domain reflectometry[J]. Forest Products Journal,2011,61(6):428-434. DOI:10.13073/0015-7473-61.6.428.
[14]DAHLEN J,ANTONY F,LI A,et al. Time-domain reflectometry for the prediction of Loblolly pine and Sweetgum moisture content[J]. BioResources,2015,10:4947-4960. DOI:10. 15376/biores.10.3.4947-4960.
[15]SAITO T,YASUDA H,SAKURAI M,et al. Monitoring of stem water content of native and invasive trees in arid environments using GS3 soil moisture sensors[J]. Vadose Zone Journal,2016,15(3):1-9. DOI:10.2136/vzj2015.04.0061.
[16]CASTIGLIONEP,SHOUSE P J,WRAITH J M. Multiplexer-induced interference on TDR measurements of electrical conductivity[J]. Soil Science Society of Americal Journal,2006,70(5):1453-1458. DOI:10.2136/sssaj2005.0169.
[17]JAMES W L. Dielectric properties of wood and hardboard:variation with temperature,frequency,moisture content and grain orienuation[R]. USDA Forest Service Research Paper, FPL245,1975.
[18]王玉婷,徐华东,周涵婷,等.环境温度对活立木内部含水率变化的影响[J].南京林业大学学报(自然科学版),2017,41(5):107-113.DOI:10.3969/j.issn.1000-2006.201606006.WANG Y T,XU H D,ZHOU H T,et al. Effects of environmental temperatures on internal moisture content of standing trees[J].Journal of Nanjing Forestry University(Natural Sciences Edition),2017,41(5):107-113.
[19]徐华东,王立海.温度和含水率对红松木材中应力波传播速度的影响[J].林业科学,2011,47(9):123-128. DOI:10.11707/j.1001-7488.20110921.XU H D,WANG L H. Effects of moisture content and temperature on propagation velocity of stress waves in Korean pine wood[J].Scientia Silvae Sinicae,2011,47(9):123-128.
[2]RASCHI A,TOGNETTI R,RIDDER H W,et al. Water in the stems of sessile oak(Quercus petraca)assessed by computer tomography with concurrent measurements of sap velocity and ultrasound emission[J]. Plant Cell and Environment,1995,18(5):545-554. DOI:10.1111/j.1365-3040.1995.tb00554.x.
[3]MENON R S,MACKAY A L,HAILEY J R T,et al. An NMR determination of the physiological water distribution in wood during drying[J]. Journal of Applied Polymer Science,2010,33(4):1141-1155. DOI:10.1002/app.1987.070330408.
[4]赵荣军,霍小梅,上官蔚蔚,等.近红外光谱法预测粗皮桉木材气干密度的影响因素分析[J].光谱学与光谱分析,2011,31(11):1948-1951. DOI:10.3964/j.issn.1000-0593(2011)11-2948-04.ZHAO R J,HUO X M,SHANGGUAN W W,et al. Analysis of factors affecting air dry density of rough-skinned wood by near infrared spectroscopy[J]. Spectroscopy and Spectral Analysis,2011,31(11):1948-1951.
[5]CONSTANTZ J,MURPHY F. Monitoring storage moisture in tree using time domain reflectometry[J]. Journal of Hydrology,1990,119(1/2/3/4):31-42. DOI:10.1016/0022-1694(90)90032-S.
[6]赵燕东,高超,张新,等.基于驻波率原理的植物茎体水分无损检测方法研究[J].农业机械学报,2016,47(1):310-316.DOI:10.6041/j.issn.1000-1298.2016.01.042.ZHAO Y D,GAO C,ZHANG X,et al. Nondestructive detection method of plant stem moisture content based on standing wave rate principle[J]. Journal of Agricultural Machinery,2016,47(1):310-316.
[7]赵燕东,王海兰,胡培金,等.基于活立木介电特性的植物茎体含水量测量方法[J].林业科学,2010,46(11):179-183.DOI:10.11707/j.1001-7488.20101128.ZHAO Y D,WANG H L,HU P J,et al. Method for measuring moisture content of plant stems based on dielectric properties of standing trees[J]. Scientia Silvae Sinicae,2010,46(11):179-183.
[8]WULLSCHLEGER S D,HANSON P J,TODD D E. Measuring stem water content in four deciduous hardwood with a time domain reflectometry[J]. Tree Physiology,1996,16(10):809-815.DOI:10.1093/treephys/16.10.809.
[9]IRVINE J,GRACE J. Non-destructive measurement of stem water content by time domain reflectometry using short probes[J]. Journal of Experimental Botany,1997,48(3):813-818. DOI:10.1093/jxb/48.3.813.
[10]NADLER A,RAVEH E,YERMIYAHU U,et al. Evaluation of TDR use to monitor water content in stem of lemon trees and soil and their response to water stress[J]. Soil Science Society of America Journal, 2003,67(2):437-488. DOI:10. 2136/sssaj2003.4370.
[11]NADLER A,RAVEH E,YERMIYAHU U,et al. Stress induced water content variations in mango stem by time domain reflectometry[J]. Soil Science Society of America Journal,2006,70(2):510-520. DOI:10.2136/sssaj2005.0127.
[12]SANTANA V H,FERNANDEZ J M,MORAN C. Estimation of tree water stress from stem and soil water monitoring with time-domain reflectometry in two small forested basins in Spain[J].Hydrological Processes,2008,22:2493-2501. DOI:10. 1002/hyp.6845.
[13]SCHIMLECK L,MYERS K L,SANDERS J,et al. Measuring the moisture content of green wood using time domain reflectometry[J]. Forest Products Journal,2011,61(6):428-434. DOI:10.13073/0015-7473-61.6.428.
[14]DAHLEN J,ANTONY F,LI A,et al. Time-domain reflectometry for the prediction of Loblolly pine and Sweetgum moisture content[J]. BioResources,2015,10:4947-4960. DOI:10. 15376/biores.10.3.4947-4960.
[15]SAITO T,YASUDA H,SAKURAI M,et al. Monitoring of stem water content of native and invasive trees in arid environments using GS3 soil moisture sensors[J]. Vadose Zone Journal,2016,15(3):1-9. DOI:10.2136/vzj2015.04.0061.
[16]CASTIGLIONEP,SHOUSE P J,WRAITH J M. Multiplexer-induced interference on TDR measurements of electrical conductivity[J]. Soil Science Society of Americal Journal,2006,70(5):1453-1458. DOI:10.2136/sssaj2005.0169.
[17]JAMES W L. Dielectric properties of wood and hardboard:variation with temperature,frequency,moisture content and grain orienuation[R]. USDA Forest Service Research Paper, FPL245,1975.
[18]王玉婷,徐华东,周涵婷,等.环境温度对活立木内部含水率变化的影响[J].南京林业大学学报(自然科学版),2017,41(5):107-113.DOI:10.3969/j.issn.1000-2006.201606006.WANG Y T,XU H D,ZHOU H T,et al. Effects of environmental temperatures on internal moisture content of standing trees[J].Journal of Nanjing Forestry University(Natural Sciences Edition),2017,41(5):107-113.
[19]徐华东,王立海.温度和含水率对红松木材中应力波传播速度的影响[J].林业科学,2011,47(9):123-128. DOI:10.11707/j.1001-7488.20110921.XU H D,WANG L H. Effects of moisture content and temperature on propagation velocity of stress waves in Korean pine wood[J].Scientia Silvae Sinicae,2011,47(9):123-128.