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1.
多角度遥感观测是研究植被冠层BRDF (Bidirectional Reflectance Distribution Function)特性的重要手段,但目前对森林冠层进行连续间隔采样的多角度遥感观测及数据较少,热点方向的观测尤为缺乏。本研究基于无人机多角度高光谱成像系统,在主平面上对针叶林冠层以等角度连续间隔采样进行多角度观测,获取了主平面上多角度(包括热点和暗点)高光谱影像,并将观测结果与四尺度几何光学模型模拟结果进行对比分析。多角度观测获取的植被冠层反射率呈现出典型的植被方向反射特征,后向大部分角度观测的冠层反射率高于前向,在热点处出现峰值,在暗点附近方向出现最低值,观测天顶角VZA (View Zenith Angle)较大时表现出明显的"碗边效应"。结果表明:(1)观测的针叶林冠层反射率及BRDF特性与四尺度模型模拟基本一致,但红光波段模拟的热点反射率稍低于观测,前向观测VZA较大时模拟与观测结果差异稍大;(2)冠层结构及叶片光学特性的差异会导致观测到的BRDF特征不同;(3)观测的针叶林冠层BRDF呈现明显的光谱效应,不同波段呈现的各向异性特性不同,红光波段各向异性最强,近红外波段最弱;(4) BRDF的光谱效应差异导致观测到的植被指数也表现出各向异性,NDVI (Normalized Difference Vegetation Index)、PRI (Photochemical Reflectance Index)和MTCI(MERIS Terrestrial Chlorophyll Index)在热点方向最低,EVI (Enhanced Vegetation Index)在热点方向最高。本研究中无人机多角度成像观测提供的角度和高光谱信息,尤其是热点和暗点信息,在地物识别及分类、植被冠层结构反演及碳循环关键参数获取等研究方面具有较好的应用前景,在其它地物反射或热辐射等方向性特性研究中也具有较大的潜力。 相似文献
2.
植被结构及太阳／观测角度对NDVI的影响 总被引：1，自引：0，他引：1
在文献［１］中作者建立了计算多组分植被方向反射系数（ＢＲＦ）的综合解析模型。本文采用该模型研究植被空间结构对常用的归一化植被指数（ＮＤＶＩ）的影响，文中讨论了ＮＤＶＩ与叶（或植被其它组分）角分布（ＬＡＤ）、植被组分（如叶片）的特征尺度和它们在空间的散布方式，以及非叶器官面积在总面积中所占比例间的依赖关系，同时给出了ＮＤＶＩ随太阳／观测角度的变化情况。结果表明即使在叶面积指数（ＬＡＩ）固定不变时，冠层结构及植被组分光学性质的空间非均匀性对ＮＤＶＩ的大小及角分布也有十分显著的影响。通常ＮＤＷ随角度的变化是很大的，如果植被不同组分的光学性质差异很大，且事先不知道它们的空间散布方式时，那么利用ＤＮＶＩ就无法准确地估算出ＬＡＩ。但是对于组分随机分布的植被，利用远离“热点”区域的光谱资料可以使冠层其它结构参数的影响减至最小。 相似文献
3.
Mingchang Wang Xuefeng Niu Qian Yang Shengbo Chen Guodong Yang Fengyan Wang 《Journal of the Indian Society of Remote Sensing》2018,46(1):1-8
Hyper spectral remote sensing is widely used to identify ground objects as a result of the advantages of ground radiation intensity characteristics and spectral position characteristics, in which inversion of vegetation components is the difficult point and hotspot. In this study, Huma county of Heilongjiang Province was selected as the study area, the canopy spectra of four types of typical vegetation were measured in situ firstly, including mongolian oak, cotton grass, lespedeza and white birch. Then, on the basis of analyzing the canopy spectral characteristics and their parameterization, the spectral differences of different vegetations were located, and the parameterization method of characteristics identification was determined. Finally, Hyperion data were used to calculate the canopy albedos based on the bidirectional reflectance model of vegetation canopies, and to map the vegetation components in the study area by use of linear spectral mixture model. The results showed that inversion of vegetation components in high vegetation-covered area was accurate using the canopy albedos and liner spectral mixture model, and was identical with the field sampling, which validated the feasibility of canopy albedos and liner spectral mixture model for the inversion of vegetation components. 相似文献
4.
叶面积指数（LAI）和叶倾角分布（LAD）是决定植被冠层结构的重要参数。在计算机模拟植被冠层,两个参数是植被三维真实结构生成的重要控制因子。本论文中,结合计算机图像学理论,基于实验的地面实测结构参数数据利用可改写的扩展L-system方法生成草以及白杨树的真实三维场景。RGM（A radiosity-graphics combined model）模型是基于辐射度方法的计算机模拟模型,利用此模型来计算生成的三维场景可见光及近红外波段的冠层辐射特性,如冠层波谱以及方向反射特性等。在本研究中,模拟了两种不同下垫面的白杨林地：（1）下垫面只有土壤的白杨树场景;（2）下垫面包括土壤和草的白杨树。在特定的场景组分光学特性下,模拟得到两种情况的主平面冠层BRF（bi-di-rectional reflectance factor）,并对两者的差异进行了分析。可以看出,下垫面对冠层BRF的影响不可忽视。但是,由于白杨林地结构的复杂,大尺度的场景中必须由成千上万个面元组成,因此辐射度方法不能模拟大尺度的真实结构场景。为了拓展辐射度方法应用范围,根据白杨树树冠的特点,将其抽象为椭球体,从而减少场景组成面元个数,满足了辐射度方法的要求。并结合几何光学模型的思想,在对椭球体面元赋值加入了间隙率;并考虑了整个树冠的承照面以及阴影面的差异,模拟大尺度林地冠层BRF,且与GOMS模型结果符合的很好。通过以上研究,可以看出计算机模拟为遥感研究获取多角度数据信息提供了一种很好的手段。 相似文献
5.
J.G.P.W. Clevers L. KooistraM.E. Schaepman 《International Journal of Applied Earth Observation and Geoinformation》2008
Canopy water content (CWC) is important for mapping and monitoring the condition of the terrestrial ecosystem. Spectral information related to the water absorption features at 970 nm and 1200 nm offers possibilities for deriving information on CWC. In this study, we compare the use of derivative spectra, spectral indices and continuum removal techniques for these regions. Hyperspectral reflectance data representing a range of canopies were simulated using the combined PROSPECT + SAILH model. Best results in estimating CWC were obtained by using spectral derivatives at the slopes of the 970 nm and 1200 nm water absorption features. Real data from two different test sites were analysed. Spectral information at both test sites was obtained with an ASD FieldSpec spectrometer, whereas at the second site HyMap airborne imaging spectrometer data were also acquired. Best results were obtained for the derivative spectra. In order to avoid the potential influence of atmospheric water vapour absorption bands the derivative of the reflectance on the right slope of the canopy water absorption feature at 970 nm can best be used for estimating CWC. 相似文献
6.
利用激光雷达和多角度频谱成像仪数据估测森林垂直参数 总被引：3，自引：0，他引：3
植被的结构参数如植被高度、生物量、水平和垂直分布等，是影响陆地与大气能量交换乃至生物圈多样性的重要因素。多数遥感系统虽然可以提供植被水平结构的图像，但是不能提供植被成分垂直分布的信息。大尺度激光雷达仪器如LVIS产生的激光雷达信号，已成功地用于估计树高和森林生物量，然而大多数激光雷达仪器不具备图像能力，只能提供一个区域内的采样数据。其他的遥感数据如多角度高光谱、多频率多时相辐射计或雷达数据，可根据GLAS（Geoscience Laser Altimeter System）采样的测量用来推断出连续的森林结构区域覆盖参数。
MISR（Multi-angle Imaging Spectrometer）对陆表多角度的成像能力，可以通过BRDF的各向异性提供植被的结构信息。结合激光雷达的垂直采样和MISR的图像，区域内乃至全球性的森林空间参数的成像是可能的。ICESat卫星上的GLAS数据、Terra卫星上的MISR数据为区域或全球性森林结构参数提供了可能。本文的研究目的是评估GLAS数据，分析类似于MISR的数据对森林结构参数的估计能力。本文中使用了LVIS、AirMISR和GLAS数据。通过对GLAS树高的测量与GLAS像元内来自LVIS的平均树高对比，发现它们是高度相关的。同时还探讨了多角度频谱成像仪数据预测树高信息的能力，这将在今后区域内森林结构参数映射加以研究。 相似文献
7.
It is very important to know the spectral characteristics for the sake of understanding the remote sensing data. The reflectance characteristics of paddy field canopies vary with time or observational conditions (solar zenith angle, solar azimuth angle, and view zenith angle). A number of field studies have clarified the effects of these conditions on grain canopy reflectance. Most of the field data used in these study, however, were conducted only through the growing season in one year or by grains planted in pots. A series of authors’ experiments were initiated in 1982 and continued from the spring to the autumn every year to 1987. In this study we describe that the remotely sensed spectral data measured on the ground are influenced not only by the grain type, observational conditions, and growing season but also by the solar zenith angle, solar azimuth angle and view zenith angle in relation to scene. In this paper we report the results from the investigation of these various fundamental properties. 相似文献
8.
Abstract Environmental data are often utilized to guide interpretation of spectral information based on context, however, these are also important in deriving vegetation maps themselves, especially where ecological information can be mapped spatially. A vegetation classification procedure is presented which combines a classification of spectral data from Landsat‐5 Thematic Mapper (TM) and environmental data based on topography and fire history. These data were combined utilizing fuzzy logic where assignment of each pixel to a single vegetation category was derived comparing the partial membership of each vegetation category within spectral and environmental classes. Partial membership was assigned from canopy cover for forest types measured from field sampling. Initial classification of spectral and ecological data produced map accuracies of less than 50% due to overlap between spectrally similar vegetation and limited spatial precision for predicting local vegetation types solely from the ecological information. Combination of environmental data through fuzzy logic increased overall mapping accuracy (70%) in coniferous forest communities of northwestern Montana, USA. 相似文献
9.
Monitoring biophysical and biochemical vegetation variables in space and time is key to understand the earth system. Operational approaches using remote sensing imagery rely on the inversion of radiative transfer models, which describe the interactions between light and vegetation canopies. The inversion required to estimate vegetation variables is, however, an ill-posed problem because of variable compensation effects that can cause different combinations of soil and canopy variables to yield extremely similar spectral responses. In this contribution, we present a novel approach to visualise the ill-posed problem using self-organizing maps (SOM), which are a type of unsupervised neural network. The approach is demonstrated with simulations for Sentinel-2 data (13 bands) made with the Soil-Leaf-Canopy (SLC) radiative transfer model. A look-up table of 100,000 entries was built by randomly sampling 14 SLC model input variables between their minimum and maximum allowed values while using both a dark and a bright soil. The Sentinel-2 spectral simulations were used to train a SOM of 200 × 125 neurons. The training projected similar spectral signatures onto either the same, or contiguous, neuron(s). Tracing back the inputs that generated each spectral signature, we created a 200 × 125 map for each of the SLC variables. The lack of spatial patterns and the variability in these maps indicate ill-posed situations, where similar spectral signatures correspond to different canopy variables. For Sentinel-2, our results showed that leaf area index, crown cover and leaf chlorophyll, water and brown pigment content are less confused in the inversion than variables with noisier maps like fraction of brown canopy area, leaf dry matter content and the PROSPECT mesophyll parameter. This study supports both educational and on-going research activities on inversion algorithms and might be useful to evaluate the uncertainties of retrieved canopy biophysical and biochemical state variables. 相似文献
10.
地基激光雷达的玉兰林冠层叶面积密度反演 总被引：1，自引：0，他引：1
叶面积密度LAD(Leaf Area Density)是表征冠层内部叶面积垂直分布的重要参数,其分布廓线的准确反演对研究植被碳氮循环、初级生产力和生物量估算等具有重要意义。本文在电子科技大学校内建立实验样区,利用地基激光雷达Leica Scan Station C10和数码相机获取玉兰林高分辨率3维激光点云数据和真彩色影像。利用监督分类将真彩色影像中枝干等非光合组织与叶片分离,再将像素分类信息映射给点云数据,从而提取叶片点云。通过点云数据体元化,并引入2维凸包算法确定垂直方向分层树冠边界,获取激光接触冠层的频率;随机选择不同高度的多个叶片,利用特征值法进行叶片平面拟合,估算出叶倾角,并结合天顶角估算叶倾角校正因子;最后基于体元的冠层分析VCP(Voxel-based Canopy Profiling)方法实现树林冠层LAD反演。结果表明体元化的叶片点云数据能准确确定树林冠层边界和统计接触频率实现LAD反演;反演的LAD变化走势与区域林木冠层叶片垂直分布相吻合,在冠层中下部随着高度的增加叶面积密度也随之增加,在4 m高度处达到最大值1 m2/m3,之后随着高度的增加叶面积密度逐渐降低。根据LAD计算得到的累积叶面积指数LAI为3.20 m2/m2,与LAI-2200实测的叶面积指数相比,相对误差为1.26%。 相似文献
11.
柑橘植株冠层氮素和光合色素含量近地遥感估测 总被引：1，自引：0，他引：1
柑橘植株营养状况的遥感监测是实现果树轻简高效管理和优质丰产的重要手段,但迄今有关基于低空遥感信息的果树营养诊断研究鲜见报道。本文采用具有490 nm、550 nm、570 nm、671 nm、680 nm、700 nm、720 nm、800 nm、840 nm、900 nm、950 nm等11个波段光谱的八旋翼飞行器(UAV)载多光谱遥感系统,获取距地面100 m高度的哈姆林甜橙植株春季冠层近地遥感信息,对比分析基于多元散射校正(MSC)和标准正态变量(SNV)两种预处理光谱和原始光谱(OS)的偏最小二乘(PLS)、多元线性回归(MLR)、主成分回归(PCR)及最小二乘支持向量机(LS-SVM)等4种模型对冠层叶片氮素、叶绿素a、叶绿素b和类胡萝卜素含量预测精度的影响。结果显示,距地面100 m高度的多光谱信息,通过SNV光谱预处理和MLR建模对冠层叶片氮素、叶绿素a和叶绿素b含量的预测效果均较好,预测集相关系数(Rp)值分别达0.8036、0.8065和0.8107,预测均方根误差(RMSEP)值分别为0.1363、0.0427和0.0243;而在SNV光谱预处理基础上的LS-SVM建模对冠层类胡萝卜素含量预测效果更优,Rp值达到了0.8535,RMSEP值为0.0117。表明利用机载多光谱图像信息可实现对柑橘植株冠层全氮及叶绿素a、叶绿素b和类胡萝卜素含量的较好估算,为大规模柑橘园植株冠层营养状况的精准和高效监测提供了一条新途径。 相似文献
12.
Although its use is widespread in several other scientific disciplines, the theory of tensor invariants is only marginally
adopted in gravity field modeling. We aim to close this gap by developing and applying the invariants approach for geopotential
recovery. Gravitational tensor invariants are deduced from products of second-order derivatives of the gravitational potential.
The benefit of the method presented arises from its independence of the gradiometer instrument’s orientation in space. Thus,
we refrain from the classical methods for satellite gravity gradiometry analysis, i.e., in terms of individual gravity gradients,
in favor of the alternative invariants approach. The invariants approach requires a tailored processing strategy. Firstly,
the non-linear functionals with regard to the potential series expansion in spherical harmonics necessitates the linearization
and iterative solution of the resulting least-squares problem. From the computational point of view, efficient linearization
by means of perturbation theory has been adopted. It only requires the computation of reference gravity gradients. Secondly,
the deduced pseudo-observations are composed of all the gravitational tensor elements, all of which require a comparable level
of accuracy. Additionally, implementation of the invariants method for large data sets is a challenging task. We show the
fundamentals of tensor invariants theory adapted to satellite gradiometry. With regard to the GOCE (Gravity field and steady-state
Ocean Circulation Explorer) satellite gradiometry mission, we demonstrate that the iterative parameter estimation process
converges within only two iterations. Additionally, for the GOCE configuration, we show the invariants approach to be insensitive
to the synthesis of unobserved gravity gradients. 相似文献
13.
Jesús Delegido Luis AlonsoGonzalo González José Moreno 《International Journal of Applied Earth Observation and Geoinformation》2010
The Normalized Area Over reflectance Curve (NAOC) is proposed as a new index for remote sensing estimation of the leaf chlorophyll content of heterogeneous areas with different crops, different canopies and different types of bare soil. This index is based on the calculation of the area over the reflectance curve obtained by high spectral resolution reflectance measurements, determined, from the integral of the red–near-infrared interval, divided by the maximum reflectance in that spectral region. For this, use has been made of the experimental data of the SPARC campaigns, where in situ measurements were made of leaf chlorophyll content, LAI and fCOVER of 9 different crops – thus, yielding 300 different values with broad variability of these biophysical parameters. In addition, Proba/CHRIS hyperspectral images were obtained simultaneously to the ground measurements. By comparing the spectra of each pixel with its experimental leaf chlorophyll value, the NAOC was proven to exhibit a linear correlation to chlorophyll content. Calculating the correlation between these variables in the 600–800 nm interval, the best correlation was obtained by computing the integral of the spectral reflectance curve between 643 and 795 nm, which practically covers the spectral range of maximum chlorophyll absorption (at around 670 nm) and maximum leaf reflectance in the infrared (750–800 nm). Based on a Proba/CHRIS image, a chlorophyll map was generated using NAOC and compared with the land-use (crops classification) map. The method yielded a leaf chlorophyll content map of the study area, comprising a large heterogeneous zone. An analysis was made to determine whether the method also serves to estimate the total chlorophyll content of a canopy, multiplying the leaf chlorophyll content by the LAI. To validate the method, use was made of the data from another campaign ((SEN2FLEX), in which measurements were made of different biophysical parameters of 7 crops, and hyperspectral images were obtained with the CASI imaging radiometer from an aircraft. Applying the method to a CASI image, a map of leaf chlorophyll content was obtained, which on, establishing comparisons with the experimental data allowed us to estimate chlorophyll with a root mean square error of 4.2 μg/cm2, similar or smaller than other methods but with the improvement of applicability to a large set of different crop types. 相似文献
14.
Abstract Bidirectional reflectance characteristics of a wheat and a rice canopy were studied using radiometric measurements over the two canopies with an Exotech Radiometer Model 100AX. For both rice and wheat, the measurements exhibited significant variations in reflectance amplitude for varying viewing zenith angles and their values decreased from backward to forward scattering direction. Reflectance obtained its maximum value in the backscatter direction for the viewing angle that corresponds approximately to the solar zenith angle at the time of measurements. Canopy background condition (irrigated or non‐irrigated) was an important determining factor of canopy reflectance particularly in the near‐infrared region of the solar spectrum. Furthermore, bidirectional response characteristics of a vegetation canopy were influenced by the amount of vegetation cover. 相似文献
15.
为削弱混合像元对植被参数反演的影响,提出了基于混合像元分解理论反演路域植被等量水厚度的方法。利用PRO4SAIL模型正演获得的高光谱窄波段数据,模拟Landsat 8遥感影像宽波段植被冠层光谱数据,并进行等量水厚度的敏感植被指数的筛选;对覆盖研究区域的Landsat 8遥感影像进行线性混合像元分解,获取更加精确的植被冠层光谱反射率;同时,利用支持向量机构建等量水厚度估测模型,实现对路域植被等量水厚度的遥感反演。研究结果表明,利用混合像元分解后得到的植被冠层光谱参与模型反演得到的路域植被等量水厚度更加符合实际情况,为遥感影像反演植被参数提供了有效数据。 相似文献
16.
This study presents a hybrid framework for single tree detection from airborne laser scanning (ALS) data by integrating low-level image processing techniques into a high-level probabilistic framework. The proposed approach modeled tree crowns in a forest plot as a configuration of circular objects. We took advantage of low-level image processing techniques to generate candidate configurations from the canopy height model (CHM): the treetop positions were sampled within the over-extracted local maxima via local maxima filtering, and the crown sizes were derived from marker-controlled watershed segmentation using corresponding treetops as markers. The configuration containing the best possible set of detected tree objects was estimated by a global optimization solver. To achieve this, we introduced a Gibbs energy, which contains a data term that judges the fitness of the objects with respect to the data, and a prior term that prevents severe overlapping between tree crowns on the configuration space. The energy was then embedded into a Markov Chain Monte Carlo (MCMC) dynamics coupled with a simulated annealing to find its global minimum. In this research, we also proposed a Monte Carlo-based sampling method for parameter estimation. We tested the method on a temperate mature coniferous forest in Ontario, Canada and also on simulated coniferous forest plots with different degrees of crown overlap. The experimental results showed the effectiveness of our proposed method, which was capable of reducing the commission errors produced by local maxima filtering, thus increasing the overall detection accuracy by approximately 10% on all of the datasets. 相似文献
17.
机载激光雷达（LiDAR）强度数据在获取过程中受多种因素影响,各因素影响的有效量化及校正对机载LiDAR强度校正及应用具有重要意义。本文以雷达方程为基础,分别采用距离、入射角及距离和入射角对LiDAR点云强度进行校正,从中提取冠层总强度和强度比值两类参数,用于估测森林叶面积指数（LAI）,以期量化各影响因素强度校正对不同类型参数估测森林LAI的影响。结果表明：强度经距离校正能够提高森林LAI的估测精度,而强度经数字高程模型衍生入射角校正非但没能提高估测精度,反而降低了估测精度。强度经距离和入射角综合校正虽能提高森林LAI的估测精度,但结果却低于距离单独校正的结果。与此同时,对冠层总强度参数而言,强度校正前后森林LAI估测结果的差异较为明显,而对强度比值参数而言,强度校正前后森林LAI估测结果差异不大。综上可知,不同因素强度校正对森林LAI估测的影响不同,且影响程度与所用参数变量类型密切相关。因此,在未来强度应用研究中,应根据变量参数类型选择合适的校正方式,以避免不恰当校正造成的成本浪费及精度降低。 相似文献
18.
Use of principal components of UAV-acquired narrow-band multispectral imagery to map the diverse low stature vegetation fAPAR 总被引：1，自引：0，他引：1
The fraction of absorbed photosynthetically active radiation (fAPAR) is an important plant physiological index that is used to assess the ability of vegetation to absorb PAR, which is utilized to sequester carbon in the atmosphere. This index is also important for monitoring plant health and productivity, which has been widely used to monitor low stature crops and is a crucial metric for food security assessment. The fAPAR has been commonly correlated with a greenness index derived from spaceborne optical imagery, but the relatively coarse spatial or temporal resolution may prohibit its application on complex land surfaces. In addition, the relationships between fAPAR and remotely sensed greenness data may be influenced by the heterogeneity of canopies. Multispectral and hyperspectral unmanned aerial vehicle (UAV) imaging systems, conversely, can provide several spectral bands at sub-meter resolutions, permitting precise estimation of fAPAR using chemometrics. However, the data pre-processing procedures are cumbersome, which makes large-scale mapping challenging. In this study, we applied a set of well-verified image processing protocols and a chemometric model to a lightweight, frame-based and narrow-band (10 nm) UAV imaging system to estimate the fAPAR over a relatively large cultivated land area with a variety of low stature vegetation of tropical crops along with native and non-native grasses. A principal component regression was applied to 12 bands of spectral reflectance data to minimize the collinearity issue and compress the data variation. Stepwise regression was employed to reduce the data dimensionality, and the first, third and fifth components were selected to estimate the fAPAR. Our results indicate that 77% of the fAPAR variation was explained by the model. All bands that are sensitive to foliar pigment concentrations, canopy structure and/or leaf water content may contribute to the estimation, especially those located close to (720 nm) or within (750 nm and 780 nm) the near-infrared spectral region. This study demonstrates that this narrow-band frame-based UAV system would be useful for vegetation monitoring. With proper pre-flight planning and hardware improvement, the mapping of a narrow-band multispectral UAV system could be comparable to that of a manned aircraft system. 相似文献
19.
基于遥感的区域尺度森林地上生物量估算研究 总被引：1，自引：0，他引：1
森林是陆地生态系统最大的碳库,精确估算森林生物量是陆地碳循环研究的关键。首先从机载LiDAR数据中提取高度和密度统计量,采用逐步回归模型进行典型样区生物量估算;然后利用机载LiDAR数据估算的生物量作为样本数据,与多光谱遥感数据Landsat8 OLI的波段反射率及植被指数建立回归模型,实现区域尺度森林地上生物量估算。实验结果显示,机载LiDAR数据估算的鼎湖山样区生物量与地面实测生物量的相关性R2达0.81,生物量RMSE为40.85 t/ha,说明机载LiDAR点云数据的高度和密度统计量与生物量存在较高的相关性。以机载LiDAR数据估算的生物量为样本数据,结合多光谱遥感数据Landsat8 OLI估算粤西北地区的森林地上生物量,精度验证结果为:R2为0.58,RMSE为36.9 t/ha;针叶林、阔叶林和针阔叶混交林等3种不同森林类型生物量的估算结果为:R2分别为0.51(n=251)、0.58(n=235)和0.56(n=241),生物量RMSE分别为24.1 t/ha、31.3 t/ha和29.9 t/ha,估算精度相差不大。总体上看,利用遥感数据可以开展区域尺度的森林地上生物量估算,为森林固碳监测提供有力的参考数据。 相似文献
20.
In recent years, airborne LiDAR sensors have shown remarkable performance in the mapping of forest vegetation. This experimental study looks at LiDAR data at the scale of individual pulses to elucidate the sources behind interpulse variation in backscattering. Close-range photogrammetry was used for obtaining the canopy reference measurements at the ratio scale. The experiments illustrated different orientation techniques in the field, LiDAR acquisitions and photogrammetry in both leaf-on and leaf-off conditions, and two-waveform recording LiDAR sensors. The intrafootprint branch silhouettes in zenith-looking images, in which the camera, footprint, and LiDAR sensor were collinear, were extracted and contrasted with LiDAR backscattering. An enhanced planimetric match (refinement of strip matching) was achieved by shifting the pulses in a strip and searching for the maximal correlation between the silhouette and LiDAR intensity. The relative silhouette explained up to 80–90% of the interpulse variation. We tested whether accounting for the Gaussian spread of intrafootprint irradiance would improve the correlations, but the effect was blurred by small-scale geometric noise. Accounting for receiver gain variations in the Leica ALS60 sensor data strengthened the dependences. The size of the vegetation objects required for triggering a LiDAR observation was analyzed. We demonstrated the use of LiDAR pulses adjacent to canopy vegetation, which did not trigger a canopy echo, for canopy mapping. Pulses not triggering an echo constitute the complement to the actual canopy. We conclude that field photogrammetry is a useful tool for mapping forest canopies from below and that quantitative analysis is feasible even at the scale of single pulses for enhanced understanding of LiDAR observations from vegetation. 相似文献