星载激光雷达在林业上的应用研究进展

简单介绍了星载激光雷达系统的特点及其工作原理和组成部分,重点阐述了基于GLAS数据对森林冠层高度、森林生物量进行估算的方法,以及基于GLAS数据在森林类型识别和郁闭度估算等方面的应用研究,并分析总结了星载激光雷达进行估测的研究进展及其一些局限性。     

星载LiDAR与HJ-1A/HSI高光谱数据联合估测区域森林冠层高度

【目的】将ICESat-GLAS波形数据与HJ-1A/HSI高光谱数据联合,借助HSI高光谱数据提供的连续高分辨率光谱信息,实现区域森林冠层高度的估测,降低由于GLAS光斑呈离散条带状分布无法覆盖整个研究区造成的估测误差。【方法】首先,从平滑后的ICESat-GLAS波形数据中提取波形参数(波形长度W和地形坡度参数TS),基于W和TS建立GLAS森林冠层高度估测模型,并利用此模型计算研究区所有GLAS光斑内的森林冠层高度;然后,采用最小噪声分离法(MNF)对HJ-1A/HSI高光谱数据进行降维,提取前3个MNF分量(MNF1,MNF2,MNF3);最后,基于支持向量回归机(SVR)算法,利用GLAS估测的森林冠层高度和3个MNF分量建立区域森林冠层高度SVR估测模型,并估测研究区内无GLAS光斑覆盖区域的森林冠层高度,生成森林冠层高度分布图。【结果】从ICESat-GLAS波形数据中提取的地形坡度参数TS与野外实测地形坡度具有显著线性关系(R2=0.78);基于W和TS建立的GLAS森林冠层高度估测模型的R~2=0.78,RMSE=2.51 m,模型验证的R~2=0.85,RMSE=1.67 m;基于支持向量回归机算法建立的SVR模型建模的R2=0.70,RMSE=3.62 m,模型验证的R2=0.67,RMSE=4.42 m。采用野外数据对最终得到的森林冠层高度分布图的估测误差进行分析,结果估测误差最大值为7.10 m,最小值为0.07 m,平均值为1.78 m,估测误差的标准差为1.49 m,Q1为0.75 m,Q3为2.31 m。【结论】从ICESat-GLAS波形数据中提取的地形坡度参数TS能够很好地反映地形坡度的变化,本研究建立的线性关系模型可克服对数关系模型在平坦地区解释困难的问题。基于支持向量回归机算法,将ICESat-GLAS波形数据与HJ-1A/HSI高光谱数据联合,可克服ICESat-GLAS由于光斑呈离散条带状分布无法实现区域森林冠层高度估测的不足,实现对区域森林冠层高度的高精度估测。     

激光雷达在森林垂直结构参数估算中的应用

激光雷达是近年来迅速发展的主动遥感技术, 激光脉冲对森林具有很强的穿透能力, 在森林垂直结构参数估测中具有巨大的潜力与优势。文中分别总结了小光斑和大光斑激光雷达在获取树高、生物量等森林参数中的应用及其优缺点, 同时分析比较了小光斑和大光斑激光雷达在估测森林参数上的不同; 最后重点介绍了目前唯一的星载大光斑激光雷达ICESat/GLAS系统, 总结分析了其在大面积森林空间结构参数估算中的应用现状, 并对激光雷达前景及其应用中存在的问题进行了探讨和展望。     

生物量估测中的遥感技术

论述了森林生物量的概念和发展历史,介绍了常规森林生物量的估算方法,并进一步较为详尽地分析了广泛应用于生物量估算的遥感模型以及它们的影响因素。最后对应用遥感技术估测森林生物量的发展趋势作了论述。     

机载林业探测大光斑激光雷达系统的设计与应用

激光雷达以其独特的穿透能力在大面积的林业探测中越来越受到重视。以国家林业局调查规划设计院和北京遥测技术研究所共同设计研发的大光斑激光雷达系统为基础,详细介绍了该系统的工作原理、模块组成、设备安装、参数设计、数据处理等,并对该系统的飞行试验数据进行了分析,结果显示,该系统下得到的波形数据可对建筑、农田、森林等地物进行精确地刻画。进一步利用Matlab 2014b软件对大光斑激光雷达回波波形估测森林样地最大冠层高度,并利用与之对应的小光斑激光雷达数据提取的森林最大冠层高度对比,总体平均精度达到89.24%。利用SPSS软件做配对样本T检验,结果表明,该系统下获得的大光斑波形数据估测的森林最大冠层高度与小光斑估测的森林冠层高度的差异显著性为0.366,大于0.05,无明显差异,直接证明了大光斑激光雷达估测森林最大冠层高度的独特性能。因此,在未来的林业探测中,可用该系统对大面积的森林资源进行探测,为大面积估测林分最大高、平均高、郁闭度、生物量、蓄积量、叶面积指数等一系列森林参数创造了条件。     

森林背景反射率对乔木层地上生物量遥感估算的影响研究——以大兴安岭林区为例

遥感技术能够大面积覆盖和动态监测森林冠层叶片特征,森林乔木层地上生物量(AGB)与叶生物量之间存在良好的统计关系,根据遥感数据提取森林有效叶面积指数(LAIe)以估算叶生物量、进而估算AGB是可行的。然而,利用遥感数据提取森林LAIe时会受到林下植被等背景信息的影响。因此,论文以我国东北大兴安岭林区为研究区,利用中分辨率成像光谱仪(MODIS)数据和四尺度模型定量研究森林背景反射率对冠层LAIe和乔木层AGB遥感估算的影响。结果表明:背景反射率对森林LAIe遥感反演和AGB估算影响显著,利用遥感数据提取的背景反射率对背景影响订正后,反演的LAIe与基于高分辨率专题制图仪(TM)影像反演出的LAIe之间的相关性明显提高,决定系数(R~2)由0.32(n=25,p0.10)增大到0.48(n=25,p0.01),遥感估算的AGB与利用森林一类清查数据估算的AGB之间R~2由0.52(n=10,p0.05)上升到0.86(n=10,p0.01),LAIe和AGB高估现象得到明显纠正。     

基于遥感信息的森林生物量估算研究进展

遥感技术已被广泛应用于植被和生态系统的定量研究中,特别是利用遥感技术快速准确地估算森林生物量已取得了突破性的进展。综述了遥感技术在森林生物量估算中的现状,分析了各种遥感数据源在森林生物量估算中的优缺点,并简要总结了遥感技术在森林生物量估算应用方面的发展趋势。     

基于ICESat-GLAS数据和回波仿真原理识别森林类型

[目的]利用星载激光雷达波形数据对森林类型识别时,受地形、噪声和林层结构等因素影响,针叶林、阔叶林和混交林森林类型识别精度较低,为提高森林类型识别精度,需提取与森林类型相关的波形特征参数.[方法]结合回波仿真原理与林分冠层特征对GLAS回波波形进行理论分析,提出了与森林类型相关的波形特征参数147R-cafit-、K1...     

基于仿真大光斑激光雷达和多层感知器的森林地上生物量估算模型构建

森林是全球重要的陆地生态系统,各国普遍采用地面样地调查的方法评估其资源量和生物量。随着激光雷达技术的发展,采用星载大光斑激光雷达估算大区域森林地上生物量将成为另一种选择。为探索利用大光斑激光雷达估算森林地上生物量的方法,提出了一种基于仿真大光斑激光雷达和多层感知器的森林地上生物量估算模型。比较仿真大光斑激光雷达波形参数13种组合拟合森林地上生物量的效果后,认为多层感知器的估测精度高于多元线性回归。与样地实测地上生物量相比,多元线性回归估测结果的偏差范围为-34.96~23.28t/hm²,多层感知器估测结果的偏差范围更小,为-19.09~20.19t/hm²。因此,多层感知器估测森林地上生物量的效果优于多元线性回归。     

冠层高度对江西69种阔叶树小枝单叶生物量与出叶强度关系的影响

【目的】研究阔叶树不同冠层高度对当年生小枝上单叶生物量与出叶强度之间关系的影响,以期探明森林内光照环境变化对树木小枝性状的影响,为揭示阔叶树林冠生长对光环境变化的响应机制提供理论依据。【方法】采用标准化主轴回归估计(standardized major axis estimation,SMA)方法对江西省阳际峰自然保护区内69种阔叶树不同冠层高度的单叶生物量(ILM)与出叶强度(单位茎生物量的叶片数量与单位茎体积的叶片数量,Lim与Liv)的异速生长关系(树木本身某一部分的相对增长)进行研究,分析不同冠层高度(上冠层与下冠层)对亚热带常绿阔叶林内常绿和落叶树种的单叶生物量与出叶强度之间关系的影响。【结果】1)常绿和落叶树种的Liv、比叶面积和单叶面积均存在显著差异(P0.05),但两者的叶片数量、ILM、Lim和茎密度均无显著差异(P 0.05)。常绿树种在不同冠层高度处的叶片数量、Liv、比叶面积、Lim和茎密度均存在显著差异(P0.05),但落叶树种在不同冠层高度处仅与比叶面积存在显著差异(P0.05)。2)常绿和落叶树种不同冠层高度当年生小枝的单叶生物量与出叶强度之间均为负等速关系;冠层高度对常绿树种小枝ILM-Lim的异速生长指数(方程斜率)无显著影响(P=0.95),但上冠层小枝ILM-Lim的异速生长常数(方程截距)显著高于下冠层(分别为1.24、1.05);冠层高度对落叶树种当年生小枝ILM-Lim的异速生长指数(P=0.65)与异速生长常数(P=0.83)均无显著影响。3)冠层高度对常绿树种当年生小枝ILM-Liv的异速生长指数(P=0.43)与异速生长常数(P=0.16)均无显著影响,对落叶树种当年生小枝ILM-Liv的异速生长指数(P=0.69)与异速生长常数(P=0.28)也无显著影响。【结论】冠层高度对常绿和落叶树种当年生小枝的单叶生物量与出叶强度之间的负等速关系未产生影响,但冠层高度对常绿树种的异速生长常数则产生显著影响,表明在一定的出叶强度下,上冠层具有更高的单叶生物量,这可能是受当年生小枝在不同冠层高度处的枝、叶资源获取策略不同所引起。     

星载激光雷达波形长度提取与林业应用潜力分析

森林是重要的环境资源,作为陆地生态系统的主体,森林是陆地上面积最大、分布最广、组成结构最复杂、物质资源最丰富的生态系统.我国虽然是一个森林资源相对较少的国家,森林生物量依然是陆地植被总生物量的主要组成部分.鉴于森林的重要性,世界各国都投入很大的力量对森林资源进行保护,每隔一定年限对其进行调查和监测.     

Estimating canopy closure density and above-ground tree biomass using partial least square methods in Chinese boreal forests

Boreal forests play an important role in global environment systems. Understanding boreal forest ecosystem structure and function requires accurate monitoring and estimating of forest canopy and biomass. We used partial least square regression (PLSR) models to relate forest parameters, i.e. canopy closure density and above ground tree biomass, to Landsat ETM+ data. The established models were optimized according to the variable importance for projection (VIP) criterion and the bootstrap method, and their performance was compared using several statistical indices. All variables selected by the VIP criterion passed the bootstrap test (p<0.05). The simplified models without insignificant variables (VIP <1) performed as well as the full model but with less computation time. The relative root mean square error (RMSE%) was 29% for canopy closure density, and 58% for above-ground tree biomass. We conclude that PLSR can be an effective method for estimating canopy closure density and above-ground biomass.     

Leaf weight per area and leaf size of 85 Estonian woody species in relation to shade tolerance and light availability

Leaf weight per area (LWA) and leaf size were examined in 85 species of woody plants representing 83% of Estonian native flora.

Average values of 68.6 g m⁻² for LWA and 6.62 cm² for leaf size were estimated for the medium light availability. Mean LWA values can be used to correct for the bias in estimating foliage functional properties in forest stand models and for converting leaf biomass into foliage area. LWA increased with relative light availability (1 minus stand canopy cover) and species light demand, indicating that LWA was higher at the same light availability for more intolerant species. Leaf size is a canopy parameter that should be considered when canopy radiative balance and distribution of solar radiation is of interest. Mean leaf size was not so closely related to light availability as LWA, decreasing with species light demand and increasing with total plant height. Variation in leaf size is discussed in terms of species shade tolerance and height growth.     

基于无人机影像的森林生物量估测与制图

【目的】森林生物量的精确测定,对于全球气候变化和碳循环研究具有重要的意义。【方法】以东北林业大学城市林业示范基地为研究区域,首先利用无人机平台获取整个研究区域的高分辨率无人机影像;然后在研究区域四种人工林样地中分别选取20 m×20 m的4块建模样方和4块测试样方,通过每木检尺法实测建模样方内林木的树高和胸径数据,建立H-DBH(树高-胸径)估算模型,并结合已有的DBH-SB(胸径-树干生物量)模型得到测试样方的森林生物量数据;在处理后的数字冠层高度模型(DCHM)基础上利用局部最大值法提取树高与树冠中心点位置,建立一种结合无人机影像提取树高与H-SB(树高-树干生物量)经验模型的森林生物量制图方法。【结果】不同样方的H-DBH模型R2均大于0.70,测试样方的总地上生物量平均值为6915.85 kg,总的估测精度为87%。通过ArcGIS软件结合本研究提出的方法快速得到了整个研究区域的地上生物量分布图,估测总地上生物量为4396.18 t。【结论】研究结果可为快速准确的进行森林生物量的估测提供基础数据和技术参考。     

Small area estimation of forest attributes in the Norwegian National Forest Inventory

The Norwegian National Forest Inventory (NNFI) provides estimates of forest parameters on national and regional scales by means of a systematic network of permanent sample plots. One of the biggest challenges for the NNFI is the interest in forest attribute information for small sub-populations such as municipalities or protected areas. Frequently, too few sampled observations are available for such small areas to allow estimates with acceptable precision. However, if an auxiliary variable exists that is correlated with the variable of interest, small area estimation (SAE) techniques may provide means to improve the precision of estimates. The study aimed at estimating the mean above-ground forest biomass for small areas with high precision and accuracy, using SAE techniques. For this purpose, the simple random sampling (SRS) estimator, the generalized regression (GREG) estimator, and the unit-level empirical best linear unbiased prediction (EBLUP) estimator were compared. Mean canopy height obtained from a photogrammetric canopy height model (CHM) was the auxiliary variable available for every population element. The small areas were 14 municipalities within a 2,184 km² study area for which an estimate of the mean forest biomass was sought. The municipalities were between 31 and 527 km² and contained 1–35 NNFI sample plots located within forest. The mean canopy height obtained from the CHM was found to have a strong linear correlation with forest biomass. Both the SRS estimator and the GREG estimator result in unstable estimates if they are based on too few observations. Although this is not the case for the EBLUP estimator, the estimators were only compared for municipalities with more than five sample plots. The SRS resulted in the highest standard errors in all municipalities. Whereas the GREG and EBLUP standard errors were similar for small areas with many sample plots, the EBLUP standard error was usually smaller than the GREG standard error. The difference between the EBLUP and GREG standard error increased with a decreasing number of sample plots within the small area. The EBLUP estimates of mean forest biomass within the municipalities ranged between 95.01 and 153.76 Mg ha^?1, with standard errors between 8.20 and 12.84 Mg ha^?1.     

A forest biomass yield table based on an empirical model

We report an empirical model for estimating unutilized wood biomass, and its application to Cryptomeria japonica D. Don and Larix kaempferi in Tohno City, Iwate Prefecture, northeast Japan. Outputs from the model are the quantity of unutilized wood biomass and merchantable volume produced by timber harvest. The unutilized wood biomass is divided into stumps, tops, branches, foliages, small trees, and unutilized stems due to their defects. Inputs to the model are mean diameter at breast height (DBH), mean tree height, trees per unit area, and timber utilization standards. DBH distribution, DBH–height curve, stem form, bark thickness, and relationship of stem biomass to foliage and branch biomass could be described by the proposed model, indicating its validity. The proposed model enables us to develop the forest biomass yield tables modified from the existing stem volume yield tables. The developed forest biomass yield tables indicated that the unutilized wood biomass due to defects accounted for the largest part of the whole unutilized wood biomass, and that the ratio of unutilized parts in stem volume to total stem volume could vary with stand age and site productivity class. Based on a comparison of the developed forest biomass yield tables with those reported previously, we concluded that the proposed model-based forest biomass yield table would be useful for estimating the quantity of unutilized wood biomass.     

Model performance of tree height-diameter relationships in the central Congo Basin

Key message

Tree heights in the central Congo Basin are overestimated using best-available height-diameter models. These errors are propagated into the estimation of aboveground biomass and canopy height, causing significant bias when used for calibration of remote sensing products in this region.

Context

Tree height-diameter models are important components of estimating aboveground biomass (AGB) and calibrating remote sensing products in tropical forests.

Aims

For a data-poor area of the central Congo Basin, we quantified height-diameter model performance of local, regional and pan-tropical models for their use in estimating AGB and canopy height.

Methods

At three old-growth forest sites, we assessed the bias introduced in height estimation by regional and pan-tropical height-diameter models. We developed an optimal local model with site-level randomizations accounted for by using a mixed-effects modeling approach. We quantified the error propagation of modeled heights for estimating AGB and canopy height.

Results

Regional and pan-tropical height-diameter models produced a significant overestimation in tree height, propagating into significant overestimations of AGB and Lorey’s height. The pan-tropical model accounting for climatic drivers performed better than the regional models. We present a local height-diameter model which produced nonsignificant errors for AGB and canopy height estimations at our study area.

Conclusion

The application of general models at our study area introduced bias in tree height estimations and the derived stand-level variables. Improved delimitation of regions in tropical Africa with similar forest structure is needed to produce models fit for calibrating remote sensing products.

     

激光雷达技术及其在林业上的应用

激光雷达是近年来国际上发展十分迅速的主动遥感技术,在森林参数的定量测量和反演上取得了成功的应用。激光雷达具有与被动光学遥感不同的成像机理,对植被空间结构和地形的探测能力很强,特别是对森林高度的探测能力,具有其他遥感数据无法比拟的优势。介绍激光雷达遥感的基本原理、大光斑和小光斑激光雷达系统的特点,对它们在林业上的应用现状进行评述,重点分析激光雷达反演森林参数的方法,对激光雷达的林业应用前景进行分析和展望。     

小光斑激光雷达数据估测森林生物量研究进展

小光斑激光雷达可以直接获取森林的垂直和水平结构参数,因此广泛应用于森林树高、生物量和郁闭度等结构参数估计。本文主要分析小光斑激光雷达在森林生物量估测中的应用,根据研究尺度的不同,分别对小光斑激光雷达在单木、样方水平森林生物量的反演技术和方法进行详细分析,并对小光斑激光雷达与其他类型遥感数据进行融合,共同用于森林生物量研究的潜能进行阐述,通过对上述分析得出小光斑激光雷达用于森林生物量研究中存在的问题进行总结并对其未来的研究进行展望。