激光雷达回波模型辅助的坡地森林冠层高度反演
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摘要
大光斑激光雷达数据已广泛应用于森林冠层高度提取,但通常仅限于地形坡度小于20°的平缓地区。在地形坡度大于20°的陡峭山区,地形引起的波形展宽使得地面回波和植被回波信息混合在一起,给森林冠层高度提取带来巨大挑战。本文利用激光雷达回波模型和地形信息,提出了一种模型辅助的坡地森林冠层高度反演算法。该方法以激光雷达回波信号截止点为参考,定义了波形高度指数H50和H75,使用激光雷达回波模型与已知地形信息模拟裸地的激光雷达回波,将裸地回波信号截止点与森林激光雷达回波信号截止点对齐,利用裸地回波计算常用的波形相对高度指数RH50和RH75,对森林冠层高度进行反演。并与高斯波形分解法和波形参数法的反演结果进行了比较。研究结果表明:(1)利用所提取的波形指数RH50和RH75对胸高断面积加权平均高(Lorey’s height)进行了估算,在坡度小于20°时,高斯波形分解法、波形参数法和模型辅助法的估算结果与实测值线性拟合的相关系数(R2)分别为0.70,0.78和0.98,对应的均方根误差(RMSE)分别为2.90 m,2.48 m和0.60 m,模型辅助法略优于其他两种方法;(2)在坡度大于20°时,高斯波形分解法、波形参数法和模型辅助法的R2分别为0.14,0.28和0.97,相应的RMSE分别为4.93 m,4.53 m和0.81 m,模型辅助法明显优于其他两种方法;(3)在0°—40°时,模型辅助法对Lorey’s height估算结果与实测值的R2为0.97,RMSE为0.80 m。本研究提出的模型辅助法具有更好的地形适应性,在0°—40°的坡度范围内具备对坡地森林冠层高度反演的潜力。
Full waveform data of large-footprint LiDAR are widely used to retrieve global or regional forest canopy heights. However, most studies have focused on forests on relatively flat terrains where the slope is smaller than 20°. Estimating the canopy height of hillside forest stands over mountainous areas with large relief remains a challenge. A model-assisted method is proposed to estimate canopy heights of hillside forest stands by using LiDAR waveforms and overcome the effect of terrains. The adaptability of the method in 0° to 40° is evaluated. We propose a new method and redefine the height index. First, the LiDAR waveform of bare ground is simulated according to given terrain slopes. Second, the LiDAR waveforms of a forest stand and bare ground are aligned according to their signal ending points. Finally,the heights of quarter energy points(i.e., H50 and H75) of the LiDAR waveform of forests are defined relative to the signal ending points,and the heights of quarter energy points(i.e., Hg50 and Hg75) of the LiDAR waveform of bare ground are defined relative to the signal ending points. The relative height indices(i.e., RH50 and RH75) of the forest LiDAR waveform are defined as the difference in the corresponding index of the simulated waveform of forest and bare ground, namely, RH50=H50-Hg50 and RH75=H75-Hg75. The newly defined RH50 and RH75 are used to estimate forest canopy heights. The model-assisted method is validated within 0° to 40° terrain slopes and compared with Gaussian decomposition and edge-extent methods.(1) Within the 0° to 20° terrain slopes, the accuracies of estimating forest canopy heights using Gaussian decomposition, edge-extent,and proposed model-assisted methods are R2=0.70, 0.78, and 0.98 and root-mean-square error(RMSE)=2.90 m, 2.48 m, and 0.60 m, respectively. The performance of the proposed method is slightly better than that of the two other methods.(2) Within the 22° to 40° terrain slopes,the accuracies of estimating forest canopy heights using Gaussian decomposition, edge-extent, and proposed model-assisted methods are R2=0.14, 0.28, and 0.97 and RMSE=4.93 m, 4.53 m, and 0.81 m, respectively. The proposed model-assisted method is superior to the two other methods.(3) The estimation accuracy of the model-assisted method within the 0° to 40° terrain slopes is R2=0.97 and RMSE=0.80 m.This model can overcome the effect of the terrain and maintain high accuracy. The method will be further validated using spaceborne LiDAR data in future research. The proposed method can correct the effect of slope over hillsides, and the relative height indices extracted by this method are insensitive to terrain slopes. The proposed method shows a potential for use in the accurate estimation of forest canopy heights over hillsides.
Full waveform data of large-footprint LiDAR are widely used to retrieve global or regional forest canopy heights. However, most studies have focused on forests on relatively flat terrains where the slope is smaller than 20°. Estimating the canopy height of hillside forest stands over mountainous areas with large relief remains a challenge. A model-assisted method is proposed to estimate canopy heights of hillside forest stands by using LiDAR waveforms and overcome the effect of terrains. The adaptability of the method in 0° to 40° is evaluated. We propose a new method and redefine the height index. First, the LiDAR waveform of bare ground is simulated according to given terrain slopes. Second, the LiDAR waveforms of a forest stand and bare ground are aligned according to their signal ending points. Finally,the heights of quarter energy points(i.e., H50 and H75) of the LiDAR waveform of forests are defined relative to the signal ending points,and the heights of quarter energy points(i.e., Hg50 and Hg75) of the LiDAR waveform of bare ground are defined relative to the signal ending points. The relative height indices(i.e., RH50 and RH75) of the forest LiDAR waveform are defined as the difference in the corresponding index of the simulated waveform of forest and bare ground, namely, RH50=H50-Hg50 and RH75=H75-Hg75. The newly defined RH50 and RH75 are used to estimate forest canopy heights. The model-assisted method is validated within 0° to 40° terrain slopes and compared with Gaussian decomposition and edge-extent methods.(1) Within the 0° to 20° terrain slopes, the accuracies of estimating forest canopy heights using Gaussian decomposition, edge-extent,and proposed model-assisted methods are R2=0.70, 0.78, and 0.98 and root-mean-square error(RMSE)=2.90 m, 2.48 m, and 0.60 m, respectively. The performance of the proposed method is slightly better than that of the two other methods.(2) Within the 22° to 40° terrain slopes,the accuracies of estimating forest canopy heights using Gaussian decomposition, edge-extent, and proposed model-assisted methods are R2=0.14, 0.28, and 0.97 and RMSE=4.93 m, 4.53 m, and 0.81 m, respectively. The proposed model-assisted method is superior to the two other methods.(3) The estimation accuracy of the model-assisted method within the 0° to 40° terrain slopes is R2=0.97 and RMSE=0.80 m.This model can overcome the effect of the terrain and maintain high accuracy. The method will be further validated using spaceborne LiDAR data in future research. The proposed method can correct the effect of slope over hillsides, and the relative height indices extracted by this method are insensitive to terrain slopes. The proposed method shows a potential for use in the accurate estimation of forest canopy heights over hillsides.
引文
Allouis T,Durrieu S and Couteron P.2012.A new method for incorporating hillslope effects to improve canopy-height estimates from large-footprint lidar waveforms.IEEE Geoscience and Remote Sensing Letters,9(4):730-734[DOI:10.1109/LGRS.2011.2179635]
Cao L,Coops N C,Hermosilla T,Innes J,Dai J S and She G H.2014.Using small-footprint discrete and full-waveform airborne Li DARmetrics to estimate total biomass and biomass components in subtropical forests.Remote Sensing,6(8):7110-7135[DOI:10.3390/rs6087110]
Carabajal C C and Harding D J.2005.ICESat validation of SRTM C-band digital elevation models.Geophysical Research Letters,32(22):L22S01[DOI:10.1029/2005gl023957]
Carabajal C C and Harding D J.2006.SRTM C-band and ICESat laser altimetry elevation comparisons as a function of tree cover and relief.Photogrammetric Engineering and Remote Sensing,72(3):287-298[DOI:10.14358/PERS.72.3.287]
Chen Q.2010.Retrieving vegetation height of forests and woodlands over mountainous areas in the Pacific Coast region using satellite laser altimetry.Remote Sensing of Environment,114(7):1610-1627[DOI:10.1016/j.rse.2010.02.016]
Chi H.2011.Research on Forest Aboveground Biomass Estimation in China Based on ICESat/GLAS and MODIS Data.Beijing:Institute of Remote Sensing Applications Chinese Academy Sciences(池泓.2011.基于ICESat/GLAS和MODIS数据的中国森林地上生物量估算研究.北京:中国科学院遥感应用研究所)
Drake J B,Dubayah R O,Clark D B,Knox R G,Blair J B,Hofton MA,Chazdon R L,Weishampel J F and Prince S.2002.Estimation of tropical forest structural characteristics using large-footprint lidar.Remote Sensing of Environment,79(2/3):305-319[DOI:10.1016/s0034-4257(01)00281-4]
Dubayah R O and Drake J B.2000.Lidar remote sensing for forestry.Journal of Forestry,98(6):44-46
Duong V H,Lindenbergh R,Pfeifer N and Vosselman G.2008.Single and two epoch analysis of ICESat full waveform data over forested areas.International Journal of Remote Sensing,29(5):1453-1473[DOI:10.1080/01431160701736372]
En?le F,Heinzel J and Koch B.2014.Accuracy of vegetation height and terrain elevation derived from ICESat/GLAS in forested areas.International Journal of Applied Earth Observation and Geoinformation,31:37-44[DOI:10.1016/j.jag.2014.02.009]
Field C B and Raupach M R.2004.The Global Carbon Cycle:Integrating Humans,Climate,and the Natural World.Washington:Island Press
Harding D J,Lefsky M A,Parker G G and Blair J B.2001.Laser altimeter canopy height profiles:methods and validation for closedcanopy,broadleaf forests.Remote Sensing of Environment,76(3):283-297[DOI:10.1016/S0034-4257(00)00210-8]
Hayashi M,Saigusa N,Oguma H and Yamagata Y.2013.Forest canopy height estimation using ICESat/GLAS data and error factor analysis in Hokkaido,Japan.ISPRS Journal of Photogrammetry and Remote Sensing,81:12-18[DOI:10.1016/j.isprsjprs.2013.04.004]
Hilbert C and Schmullius C.2012.Influence of surface topography on ICESat/GLAS forest height estimation and waveform shape.Remote Sensing,4(8):2210-1125[DOI:10.3390/rs4082210]
Lee S,Ni-Meister W,Yang W Z and Chen Q.2011.Physically based vertical vegetation structure retrieval from ICESat data:validation using LVIS in White Mountain National Forest,New Hampshire,USA.Remote Sensing of Environment,115(11):2776-2785[DOI:10.1016/j.rse.2010.08.026]
Lefsky M A,Harding D J,Keller M,Cohen W B,Carabajal C C,Del Bom Espirito-Santo F,Hunter M O and De Oliveira Jr R.2005.Estimates of forest canopy height and aboveground biomass using ICESat.Geophysical Research Letters,32(22):L22S02[DOI:10.1029/2005GL023971]
Lefsky M A,Keller M,Pang Y,De Camargo P B and Hunter M O.2007.Revised method for forest canopy height estimation from geoscience laser altimeter system waveforms.Journal of Applied Remote Sensing,1(1):013537[DOI:10.1117/1.2795724]
Nie S,Wang C,Zeng H C,Xi X H and Xia S B.2015.A revised terrain correction method for forest canopy height estimation using ICESat/GLAS data.ISPRS Journal of Photogrammetry and Remote Sensing,108:183-190[DOI:10.1016/j.isprsjprs.2015.07.008]
Pagnutti M and Ryan R E.2009.Automated DEM validation using ICESat GLAS data//Proceedings of ASPRS/MAPPS 2009 Fall Conference.San Antonio,Texas:ASPRS
Pang Y,Lefsky M,Andersen H E,Miller M E and Sherrill K.2008.Validation of the ICEsat vegetation product using crown-areaweighted mean height derived using crown delineation with discrete return lidar data.Canadian Journal of Remote Sensing,34(S2):S471-S484[DOI:10.5589/m08-074]
Pang Y,Lefsky M,Sun G Q and Ranson J.2011.Impact of footprint diameter and off-nadir pointing on the precision of canopy height estimates from spaceborne lidar.Remote Sensing of Environment,115(11):2798-2809[DOI:10.1016/j.rse.2010.08.025]
Popescu S C,Zhao K G,Neuenschwander A and Lin C.2011.Satellite lidar vs.small footprint airborne lidar:comparing the accuracy of aboveground biomass estimates and forest structure metrics at footprint level.Remote Sensing of Environment,115(11):2786-2797[DOI:10.1016/j.rse.2011.01.026]
Ranson K J,Sun G,Knox R G,Levine E R,Weishampel J F and Fifer S T.2001.Northern forest ecosystem dynamics using coupled models and remote sensing.Remote Sensing of Environment,75(2):291-302[DOI:10.1016/s0034-4257(00)00174-7]
Rosette J A,North P R J,Suárez J C and Armston J D.2009.A comparison of biophysical parameter retrieval for forestry using airborne and satellite Li DAR.International Journal of Remote Sensing,30(19):5229-5237[DOI:10.1080/01431160903022944]
Rosette J A B,North P R J and Suárez J C.2008.Vegetation height estimates for a mixed temperate forest using satellite laser altimetry.International Journal of Remote Sensing,29(5):1475-1493[DOI:10.1080/01431160701736380]
Smith T M and Urban D L.1988.Scale and resolution of forest structural pattern.Vegetatio,74(2/3):143-150[DOI:10.1007/BF00044739]
Sun G,Ranson K J,Kimes D S,Blair J B and Kovacs K.2008.Forest vertical structure from GLAS:an evaluation using LVIS and SRTM data.Remote Sensing of Environment,112(1):107-117[DOI:10.1016/j.rse.2006.09.036]
Sun G Q and Ranson K J.2000.Modeling lidar returns from forest canopies.IEEE Transactions on Geoscience and Remote Sensing,38(6):2617-2626[DOI:10.1109/36.885208]
Sun G Q,Ranson K J,Guo Z,Zhang Z,Montesano P and Kimes D.2011.Forest biomass mapping from lidar and radar synergies.Remote Sensing of Environment,115(11):2906-2916[DOI:10.1016/j.rse.2011.03.021]
Wang C,Tang F X,Li L W,Li G C,Cheng F and Xi X H.2013.Wavelet analysis for ICESat/GLAS waveform decomposition and its application in average tree height estimation.IEEE Geoscience and Remote Sensing Letters,10(1):115-119[DOI:10.1109/lgrs.2012.2194692]
Wang X Y,Huang H B,Gong P,Liu C X,Li C C and Li W Y.2014.Forest canopy height extraction in rugged areas with ICESat/GLAS data.IEEE Transactions on Geoscience and Remote Sensing,52(8):4650-4657[DOI:10.1109/tgrs.2013.2283272]
Wulder M A,White J C,Nelson R F,N?sset E,?rka H O,Coops N C,Hilker T,Bater C W and Gobakken T.2012.Lidar sampling for large-area forest characterization:a review.Remote Sensing of Environment,121:196-209[DOI:10.1016/j.rse.2012.02.001]
Xing Y Q,De Gier A,Zhang J J and Wang L H.2010.An improved method for estimating forest canopy height using ICESat-GLASfull waveform data over sloping terrain:a case study in Changbai mountains,China.International Journal of Applied Earth Observation and Geoinformation,12(5):385-392[DOI:10.1016/j.jag.2010.04.010]
Yang W Z,Ni-Meister W and Lee S.2011.Assessment of the impacts of surface topography,off-nadir pointing and vegetation structure on vegetation lidar waveforms using an extended geometric optical and radiative transfer model.Remote Sensing of Environment,115(11):2810-2822[DOI:10.1016/j.rse.2010.02.021]
Cao L,Coops N C,Hermosilla T,Innes J,Dai J S and She G H.2014.Using small-footprint discrete and full-waveform airborne Li DARmetrics to estimate total biomass and biomass components in subtropical forests.Remote Sensing,6(8):7110-7135[DOI:10.3390/rs6087110]
Carabajal C C and Harding D J.2005.ICESat validation of SRTM C-band digital elevation models.Geophysical Research Letters,32(22):L22S01[DOI:10.1029/2005gl023957]
Carabajal C C and Harding D J.2006.SRTM C-band and ICESat laser altimetry elevation comparisons as a function of tree cover and relief.Photogrammetric Engineering and Remote Sensing,72(3):287-298[DOI:10.14358/PERS.72.3.287]
Chen Q.2010.Retrieving vegetation height of forests and woodlands over mountainous areas in the Pacific Coast region using satellite laser altimetry.Remote Sensing of Environment,114(7):1610-1627[DOI:10.1016/j.rse.2010.02.016]
Chi H.2011.Research on Forest Aboveground Biomass Estimation in China Based on ICESat/GLAS and MODIS Data.Beijing:Institute of Remote Sensing Applications Chinese Academy Sciences(池泓.2011.基于ICESat/GLAS和MODIS数据的中国森林地上生物量估算研究.北京:中国科学院遥感应用研究所)
Drake J B,Dubayah R O,Clark D B,Knox R G,Blair J B,Hofton MA,Chazdon R L,Weishampel J F and Prince S.2002.Estimation of tropical forest structural characteristics using large-footprint lidar.Remote Sensing of Environment,79(2/3):305-319[DOI:10.1016/s0034-4257(01)00281-4]
Dubayah R O and Drake J B.2000.Lidar remote sensing for forestry.Journal of Forestry,98(6):44-46
Duong V H,Lindenbergh R,Pfeifer N and Vosselman G.2008.Single and two epoch analysis of ICESat full waveform data over forested areas.International Journal of Remote Sensing,29(5):1453-1473[DOI:10.1080/01431160701736372]
En?le F,Heinzel J and Koch B.2014.Accuracy of vegetation height and terrain elevation derived from ICESat/GLAS in forested areas.International Journal of Applied Earth Observation and Geoinformation,31:37-44[DOI:10.1016/j.jag.2014.02.009]
Field C B and Raupach M R.2004.The Global Carbon Cycle:Integrating Humans,Climate,and the Natural World.Washington:Island Press
Harding D J,Lefsky M A,Parker G G and Blair J B.2001.Laser altimeter canopy height profiles:methods and validation for closedcanopy,broadleaf forests.Remote Sensing of Environment,76(3):283-297[DOI:10.1016/S0034-4257(00)00210-8]
Hayashi M,Saigusa N,Oguma H and Yamagata Y.2013.Forest canopy height estimation using ICESat/GLAS data and error factor analysis in Hokkaido,Japan.ISPRS Journal of Photogrammetry and Remote Sensing,81:12-18[DOI:10.1016/j.isprsjprs.2013.04.004]
Hilbert C and Schmullius C.2012.Influence of surface topography on ICESat/GLAS forest height estimation and waveform shape.Remote Sensing,4(8):2210-1125[DOI:10.3390/rs4082210]
Lee S,Ni-Meister W,Yang W Z and Chen Q.2011.Physically based vertical vegetation structure retrieval from ICESat data:validation using LVIS in White Mountain National Forest,New Hampshire,USA.Remote Sensing of Environment,115(11):2776-2785[DOI:10.1016/j.rse.2010.08.026]
Lefsky M A,Harding D J,Keller M,Cohen W B,Carabajal C C,Del Bom Espirito-Santo F,Hunter M O and De Oliveira Jr R.2005.Estimates of forest canopy height and aboveground biomass using ICESat.Geophysical Research Letters,32(22):L22S02[DOI:10.1029/2005GL023971]
Lefsky M A,Keller M,Pang Y,De Camargo P B and Hunter M O.2007.Revised method for forest canopy height estimation from geoscience laser altimeter system waveforms.Journal of Applied Remote Sensing,1(1):013537[DOI:10.1117/1.2795724]
Nie S,Wang C,Zeng H C,Xi X H and Xia S B.2015.A revised terrain correction method for forest canopy height estimation using ICESat/GLAS data.ISPRS Journal of Photogrammetry and Remote Sensing,108:183-190[DOI:10.1016/j.isprsjprs.2015.07.008]
Pagnutti M and Ryan R E.2009.Automated DEM validation using ICESat GLAS data//Proceedings of ASPRS/MAPPS 2009 Fall Conference.San Antonio,Texas:ASPRS
Pang Y,Lefsky M,Andersen H E,Miller M E and Sherrill K.2008.Validation of the ICEsat vegetation product using crown-areaweighted mean height derived using crown delineation with discrete return lidar data.Canadian Journal of Remote Sensing,34(S2):S471-S484[DOI:10.5589/m08-074]
Pang Y,Lefsky M,Sun G Q and Ranson J.2011.Impact of footprint diameter and off-nadir pointing on the precision of canopy height estimates from spaceborne lidar.Remote Sensing of Environment,115(11):2798-2809[DOI:10.1016/j.rse.2010.08.025]
Popescu S C,Zhao K G,Neuenschwander A and Lin C.2011.Satellite lidar vs.small footprint airborne lidar:comparing the accuracy of aboveground biomass estimates and forest structure metrics at footprint level.Remote Sensing of Environment,115(11):2786-2797[DOI:10.1016/j.rse.2011.01.026]
Ranson K J,Sun G,Knox R G,Levine E R,Weishampel J F and Fifer S T.2001.Northern forest ecosystem dynamics using coupled models and remote sensing.Remote Sensing of Environment,75(2):291-302[DOI:10.1016/s0034-4257(00)00174-7]
Rosette J A,North P R J,Suárez J C and Armston J D.2009.A comparison of biophysical parameter retrieval for forestry using airborne and satellite Li DAR.International Journal of Remote Sensing,30(19):5229-5237[DOI:10.1080/01431160903022944]
Rosette J A B,North P R J and Suárez J C.2008.Vegetation height estimates for a mixed temperate forest using satellite laser altimetry.International Journal of Remote Sensing,29(5):1475-1493[DOI:10.1080/01431160701736380]
Smith T M and Urban D L.1988.Scale and resolution of forest structural pattern.Vegetatio,74(2/3):143-150[DOI:10.1007/BF00044739]
Sun G,Ranson K J,Kimes D S,Blair J B and Kovacs K.2008.Forest vertical structure from GLAS:an evaluation using LVIS and SRTM data.Remote Sensing of Environment,112(1):107-117[DOI:10.1016/j.rse.2006.09.036]
Sun G Q and Ranson K J.2000.Modeling lidar returns from forest canopies.IEEE Transactions on Geoscience and Remote Sensing,38(6):2617-2626[DOI:10.1109/36.885208]
Sun G Q,Ranson K J,Guo Z,Zhang Z,Montesano P and Kimes D.2011.Forest biomass mapping from lidar and radar synergies.Remote Sensing of Environment,115(11):2906-2916[DOI:10.1016/j.rse.2011.03.021]
Wang C,Tang F X,Li L W,Li G C,Cheng F and Xi X H.2013.Wavelet analysis for ICESat/GLAS waveform decomposition and its application in average tree height estimation.IEEE Geoscience and Remote Sensing Letters,10(1):115-119[DOI:10.1109/lgrs.2012.2194692]
Wang X Y,Huang H B,Gong P,Liu C X,Li C C and Li W Y.2014.Forest canopy height extraction in rugged areas with ICESat/GLAS data.IEEE Transactions on Geoscience and Remote Sensing,52(8):4650-4657[DOI:10.1109/tgrs.2013.2283272]
Wulder M A,White J C,Nelson R F,N?sset E,?rka H O,Coops N C,Hilker T,Bater C W and Gobakken T.2012.Lidar sampling for large-area forest characterization:a review.Remote Sensing of Environment,121:196-209[DOI:10.1016/j.rse.2012.02.001]
Xing Y Q,De Gier A,Zhang J J and Wang L H.2010.An improved method for estimating forest canopy height using ICESat-GLASfull waveform data over sloping terrain:a case study in Changbai mountains,China.International Journal of Applied Earth Observation and Geoinformation,12(5):385-392[DOI:10.1016/j.jag.2010.04.010]
Yang W Z,Ni-Meister W and Lee S.2011.Assessment of the impacts of surface topography,off-nadir pointing and vegetation structure on vegetation lidar waveforms using an extended geometric optical and radiative transfer model.Remote Sensing of Environment,115(11):2810-2822[DOI:10.1016/j.rse.2010.02.021]