摘要
地面测量点对遥感像元的代表性如何,怎样获取像元的相对真值,多大的空间分辨率可以真实地反映森林区域的叶面积指数(LAI),这些都是定量遥感中的重要问题.本研究计算LAI-2200和TRAC两种冠层分析仪测量的空间范围,并结合GF-2(4.1 m)、Sentinel-2(10 m)、Landsat-8(30 m)3种不同空间分辨率遥感影像,找到各尺度下像元的相对真值,在保持真值观测面积和遥感获取面积一致的条件下,基于一元指数和多元回归模型,对比分析不同空间分辨率影像对估算森林LAI的影响,并对3种影像模型进行30和100 m尺度下的检验以及各自数据集的空间代表性评价,比较得出最适合表达研究区域森林LAI的尺度.结果表明:对于森林来说,高分辨率并不一定能充分反映森林LAI.基于3种分辨率影像的统计模型都能很好地估测森林LAI,其中,基于Sentinel-2的反演精度最高,基于GF-2的反演精度最低.30和100 m尺度下的检验结果表明,基于GF-2反演模型高估了森林LAI,基于Landsat-8的反演模型低估了森林LAI,基于Sentinel-2分辨率的统计模型可以很好地估测研究区域森林LAI.
There are several important issues in quantitative remote sensing and product authenticity testing, including how well do the ground measurement points represent the remote sensing pixels, how to obtain the relative truth value of pixels, and how much spatial resolution can truly reflect fore-st leaf area index(LAI). In this study, the measured space scope of two plant canopy analyzers [LAI-2200 and tracing radiation and architecture of canopies(TRAC)] were calculated, which were combined with remote sensing images with three different spatial resolutions: GF-2 with 4.1 m spatial resolution, the Sentinel-2 with 10 m spatial resolution, and Landsat-8 OLI with 30 m spatial resolution, to get the relative true value of pixel at each scale. Under the condition of keeping the real observed area consistent with that obtained by remote sensing, the effects of different spatial resolution images for estimating forest LAI were compared and analyzed based on the unary exponential and multiple regression statistical models. Moreover, the optimal statistical models of the three images were tested on 30 m and 100 m scales and the spatial representation of dataset were evaluated, to find the most suitable scale for the description of forest LAI in the study area. The results showed that high resolution did not necessarily fully reflect LAI of forests. The statistical model based on three kinds of resolution images could well estimate forest LAI. Among the three models, the model based on the Sentinel-2 image had the highest accuracy, and the one based on the GF-2 images had the lowest. The test results at 30 and 100 m scales indicated that the forest LAI was overestimated by the GF-2 inversion model, and underestimated by the Landsat-8 inversion model. The statistical model based on Sentinel-2 could well estimated forest LAI in the study area.
引文
[1] Chen JM,Black TA.Defining leaf area index for non-flat leaves.Plant,Cell and Environment,1992,15:421-429
[2] Bonan GB.Land-atmosphere interactions for climate system models:Coupling biophysical,biogeochemical,and ecosystem dynamical processes.Remote Sensing of Environment,1995,51:57-73
[3] Tian JG,Wang SD,Zhang LF,et al.Evaluating Diffe-rent Vegetation Index for Estimating LAI of Winter Wheat using Hyperspectral Remote Sensing Data [EB/OL].(2017-01-03) [2017-12-12].https://ieeexplore.ieee.org/document/8075437
[4] Shang J.Estimating winter wheat biomass by assimilating leaf area index-derived from fusion of Landsat-8 and MODIS data.International Journal of Applied Earth Observations & Geoinformation,2016,49:63-74.
[5] Breda NJJ.Ground-based measurements of leaf area index:A review of methods,instruments and current controversies.Journal of Experimental Botany,2003,54:2403-2417
[6] Jan C,Lammert K,Marnix VDB.Using Sentinel-2 data for retrieving LAI and leaf and canopy chlorophyll content of a potato crop.Remote Sensing,2017,9:405-419
[7] Wu L,Qin QM,Liu XN,et al.Spatial up-scaling correction for leaf area index based on the fractal theory.Remote Sensing,2016,8:197-211
[8] Zou J (邹杰),Yan G-J (阎广建).Optical methods for in situ measuring leaf area index of forest canopy:A review.Chinese Journal of Applied Ecology (应用生态学报),2010,21(11):2971-2979 (in Chinese)
[9] Middinti S,Thumaty KC,Gopalakrishnan R,et al.Estimating the leaf area index in Indian tropical forests using Landsat-8 OLI data.International Journal of Remote Sensing,2017,38:6769-6789
[10] Baret F,Hagolle O,Geiger B,et al.LAI,fAPAR and fCover CYCLOPES global products derived from VEGETATION.Remote Sensing of Environment,2007,110:275-286
[11] Ganguly S,Schull M,Samanta A,et al.Generating vegetation leaf area index earth system data record from multiple sensors.Part 1:Theory.Remote Sensing of Environment,2008,112:4333-4343
[12] Abuelgasim AA,Fernandes RA,Leblanc SG.Evaluation of national and global LAI products derived from optical remote sensing instruments over Canada.IEEE Transactions on Geoscience and Remote Sensing,2006,44:1872-1884
[13] Fang H,Jiang C,Li W,et al.Characterization and intercomparison of global moderate resolution leaf area index (LAI) products:Analysis of climatologies and theoretical uncertainties.Journal of Geophysical Research:Biogeosciences,2013,118:529-548
[14] Morisette JT,Baret F,Privette JL,et al.Validation of global moderate-resolution LAI products:A framework proposed within the CEOS land product validation subgroup.IEEE Transactions on Geoscience and Remote Sensing,2006,44:1804-1817
[15] Pisek J,Chen JM.Comparison and validation of MODIS and VEGETATION global LAI products over four BigFoot sites in North America.Remote Sensing of Environment,2007,109:81-94
[16] Chen JM,Pavlic G,Brown L,et al.Derivation and vali-dation of Canada-wide coarse-resolution leaf area index maps using high-resolution satellite imagery and ground measurements.Remote Sensing of Environment,2002,80:165-184
[17] Xu B,Li J,Liu Q,et al.Evaluating spatial representativeness of station observations for remotely sensed leaf area index products.IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing,2016,9:3267-3282
[18] Zhang R-H (张仁华),Tian J (田静),Li Z-L (李召良),et al.Spatial scaling and information fractal dimension of surface parameters used in quantitative remote sensing.Scientia Sinica Terrae (中国科学:地球科学),2010,40(2):211-222 (in Chinese)
[19] Zhu G-L (朱高龙),Ju W-M (居为民),Chen J-M (陈镜明),et al.Forest canopy leaf area index in Maoershan Mountain ground measurement and remote sensing retrieval.Chinese Journal of Applied Ecology (应用生态学报),2010,28(1):2117-2124 (in Chinese)
[20] Welles JM,Norman JM.Instrument for indirect measurement of canopy architecture.Agronomy Journal,1991,83:818-825
[21] Manuel CT,García HF,Lorenzo B,et al.A Critical comparison of remote sensing leaf area index estimates over rice-cultivated areas:From Sentinel-2 and Landsat-7/8 to MODIS,GEOV1 and EUMETSAT polar system.Remote Sensing,2018,10:763-782
[22] Chen X-F (陈新芳),Chen J-M (陈镜明),An S-Q (安树青) ,et al.Comparison of effects of different atmospheric correction methods on remote sensing estimation of forest leaf area index.Chinese Journal of Eco-logy (生态学杂志),2006,25(7):769-773 (in Chinese)
[23] Jiang JL,Ji XS,Yao X,et al.Evaluation of three techniques for correcting the spatial scaling bias of leaf area index.Remote Sensing,2018,10:221-240
[24] Wang LJ,Zhang GM,Lin H,et al.Estimation of leaf area index using an angular vegetation index based on in situ measurements and CHRIS/PROBA data.ISPRS-International Archives of the Photogrammetry,Remote Sensing and Spatial Information Sciences,2016,XLI-B7:121-128
[25] Liu F (刘帆),Wang C-K (王传宽),Wang X-C (王兴昌),Monitoring temporal dynamics in leaf area index of the temperate broadleaved deciduous forest in Maoershan region,Northeast China with tower-based radiation measurement.Chinese Journal of Applied Ecology (应用生态学报),2016,27(8):2409-2419 (in Chinese)
[26] Kamel S,Christophe F,Maire GL,et al.Comparative analysis of IKONOS,SPOT,and ETM+ data for leaf area index estimation in temperate coniferous and deciduous forest stands.Remote Sensing of Environment,2006,102:161-175
[27] Xie QY,Huang WJ,Liang D,et al.Leaf area index estimation using vegetation indices derived from airborne hyperspectral images in winter wheat.IEEE Journal of Selected Topics in Applied Earth Observations & Remote Sensing,2017,7:3586-3594
[28] Wang Q (王卿),Liu J (刘健),Yu K-Y (余坤勇).Inversion of Masson pine forest LAI by multiple-perspective vegetation index.Plant Science Journal (植物科学学报),2017,35(1):48-55(in Chinese)
[29] Li-Cor Inc.LAI-2200 Plant Canopy Analyzer Operating Manual.Lincoln,NE,USA:Li-Cor Inc,2012
[30] Kobayashi H,Ryu Y,Baldocchi DD,et al.On the correct estimation of gap fraction:How to remove scattered radiation in gap fraction measurements?Agricultural and Forest Meteorology,2013,174-175:170-183
[31] Liang S,Fang H,Chen M,et al.Validating MODIS land surface reflectance and albedo products:Methods and preliminary results.Remote Sensing of Environment,2002,83:149-162
[32] Leblanc SG,Chen JM,MK.Tracing radiation and architecture of canopies.Gastroenterology,2002,78:722-727
[33] Li C-G (李崇贵),Zhao X-W (赵宪文),Li C-G (李春干).Theory and Realization of Estimating Forest Stock Volume by Remote Sensing.Beijing:Science Press,2006 (in Chinese)
[34] Zhang R-H (张仁华).Key Scientific Issues of Quantitative Remote Sensing.Beijing:Higher Education Press,2016 (in Chinese)
