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Jing M. Chen - One of the best experts on this subject based on the ideXlab platform.
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evaluating optical measurements of Leaf Area Index against litter collection in a mixed broadleaved korean pine forest in china
Trees-structure and Function, 2015Co-Authors: Zhili Liu, Guangze Jin, Jing M. ChenAbstract:Key message We evaluated the error caused by optical measurements of Leaf Area Index using a direct method in a mixed broadLeaf-coniferous forest in China.
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Leaf Area Index measurements
2014Co-Authors: Jing M. Chen, L Paul, Steven PlummerAbstract:Abstract. Leaf Area Index (LAI) is a key structural characteristic of forest ecosystems because of the role of green leaves in controlling many biological and physical processes in plant canopies. Accurate LA1 estimates are required in studies of ecophysiology, atmosphere-ecosystem interactions, and global change. The objective of this paper is to evaluate LA1 values obtained by several research teams using different methods for a broad spectrum of boreal forest types in support of the international Boreal Ecosystem-Atmosphere Study (BOREAS). These methods include destructive sampling and optical instruments: the tracing radiation and architecture of canopies (TRAC), the LAI-2000 plant canopy analyzer, hemispherical photography, and the Sunfleck Ceptometer. The latter three calculate LA1 from measured radiation transmittance (gap fraction) using inversion models that assume a random spatial distribution of leaves. It is shown that these instruments underestimate LA1 of boreal forest stands where the foliage is clumped. The TRAC quantifies the clumping effect by measuring the canopy gap size distribution. For deciduous stands the clumping Index measured from TRAC includes the clumping effect at all scales, but for conifer stands it only resolves the clumping effect at scales larger than the shoot (the basic collection of needles). To determine foliage clumping within conifer shoots, a video camera and rotational light table system was used. The major difficulties in determining the surface Area of small conifer needles have been largely overcome by the use of an accurate volume displacement method. Hemispherical photography has the advantage that it also provides a permanent image record of the canopies. Typically, LA1 falls in the range from 1 to 4 for jack pine and aspen forests and from 1 to 6 for black spruce. Our comparative studies provide the most comprehensive set of LA1 estimates available for boreal forests and demonstrate that optical techniques, combined with limited direct foliage sampling, can be used to obtain quick and accurate LA1 measurements. 1
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retrieving crown Leaf Area Index from an individual tree using ground based lidar data
Canadian Journal of Remote Sensing, 2011Co-Authors: Inian Moorthy, J R Miller, Jing M. ChenAbstract:Light detection and ranging (lidar) sensors, both at the terrestrial and airborne levels, have recently emerged as useful tools for three-dimensional (3D) reconstruction of vegetated environments. One such terrestrial laser scanner (TLS) is the Intelligent Laser Ranging and Imaging System (ILRIS-3D). The objective of this research was to develop approaches to use ILRIS-3D data to retrieve structural information of an artificial tree in a controlled laboratory experiment. The key crown-level structural parameters investigated in this study were gap fraction, Leaf Area Index (LAI), and clumping Index. Measured XYZ point cloud data from a systematically pruned tree were sliced to retrieve laser pulse return density profiles, which subsequently were used to estimate gap fraction, LAI, and clumping Index. Gap fraction estimates were cross-validated with traditional methods of histogram thresholding of digital photographs (r2 = 0.95). LAI estimates from lidar data were corrected for the confounding effects of w...
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Leaf Area Index measurements at fluxnet canada forest sites
Agricultural and Forest Meteorology, 2006Co-Authors: Jing M. Chen, Oliver Sonnentag, Ajit Govind, Yongqin Zhang, Alan G Barr, Brian D AmiroAbstract:Leaf Area Index (LAI) measurements made at 17 forest sites of the Fluxnet Canada Research Network are reported here. In addition to LAI, we also report other major structural parameters including the effective LAI, element clumping Index, needle-to-shoot Area ratio, and woody-to-total Area ratio. Values of the fraction of photosynthetically active radiation (FPAR) absorbed by green leaves in these stands at noon of 15 August are also provided, and a procedure is suggested for using the effective LAI for estimating FPAR at various times of the day and year. Labour-intensive laboratory measurements of the needle-to-shoot Area ratio were made for five conifer sites. For each site, 45 shoot samples were measured at three heights from three trees. LAI-2000, TRAC and digital hemispherical photography (DHP) were used in the field, and good agreements between these techniques were obtained. In particular, the low cost DHP technique agreed within 21% of LAI-2000 in terms of effective LAI measurements and 12% of TRAC in terms of element clumping Index measurements, suggesting a possibility of using DHP alone for indirect LAI measurements. However, LAI-2000 and TRAC are still found to be more reliable than DHP because of some remaining technical issues with DHP. We confirm the correct method for determining the photographic exposure proposed in previous studies and suggest optimum zenith angle ranges in photograph processing to estimate the effective LAI and the clumping Index.
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Algorithm for global Leaf Area Index retrieval using satellite imagery
IEEE Transactions on Geoscience and Remote Sensing, 2006Co-Authors: Feng Deng, Stephen Plummer, Jing M. Chen, Mingzhen Chen, Jan PisekAbstract:Leaf Area Index (LAI) is one of the most important Earth surface parameters in modeling ecosystems and their inter- action with climate. Based on a geometrical optical model (Four- Scale) and LAI algorithms previously derived for Canada-wide applications, this paper presents a new algorithm for the global retrieval of LAI where the bidirectional reflectance distribution function (BRDF) is considered explicitly in the algorithm and hence removing the need of doing BRDF corrections and nor- malizations to the input images. The core problem of integrating BRDF into the LAI algorithm is that nonlinear BRDF kernels that are used to relate spectral reflectances to LAI are also LAI dependent, and no analytical solution is found to derive directly LAI from reflectance data. This problem is solved through de- veloping a simple iteration procedure. The relationships between LAI and reflectances of various spectral bands (red, near infrared, and shortwave infrared) are simulated with Four-Scale with a multiple scattering scheme. Based on the model simulations, the key coefficients in the BRDF kernels are fitted with Chebyshev polynomials of the second kind. Spectral indices—the simple ratio and the reduced simple ratio—are used to effectively combine the spectral bands for LAI retrieval. Example regional and global LAI maps are produced. Accuracy assessment on a Canada-wide LAI map is made in comparison with a previously validated 1998 LAI map and ground measurements made in seven Landsat scenes.
Steven W Running - One of the best experts on this subject based on the ideXlab platform.
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a regional phenology model for detecting onset of greenness in temperate mixed forests korea an application of modis Leaf Area Index
Remote Sensing of Environment, 2003Co-Authors: Sinkyu Kang, Jonghwan Lim, Maosheng Zhao, Chanryul Park, Steven W Running, Rachel A LoehmanAbstract:Abstract A regional phenology model for detecting onset of vegetation greenness was developed using year 2001MODIS land products in temperate mixed forests in Korea. The model incorporates a digital elevation model (DEM), moderate resolution imaging spectroradiometer (MODIS) landcover and Leaf Area Index (LAI) products, and climate data from weather-monitoring stations. MODIS-based onset of greenness varied spatially and showed significant correlation with air temperature (r=−0.70, p
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measuring fractional cover and Leaf Area Index in arid ecosystems digital camera radiation transmittance and laser altimetry methods
Remote Sensing of Environment, 2000Co-Authors: Michael A White, Gregory P Asner, Ramakrishna R Nemani, J L Privette, Steven W RunningAbstract:Abstract Field measurement of shrubland ecological properties is important for both site monitoring and validation of remote sensing information. During the May 1997 NASA Earth Observing System Jornada Prototype Validation Exercise, we calculated plot-level plant Area Index, Leaf Area Index, total fractional cover, and green fractional cover with data from four instruments: (1) a Dycam Agricultural Digital Camera (ADC), (2) a LI-COR LAI-2000 plant canopy analyzer, (3) a Decagon sunfleck Ceptometer, and (4) a laser altimeter. Estimates from the LAI-2000 and Ceptometer were very similar (plant Area Index 0.3, Leaf Area Index 0.22, total fractional cover 0.19, green fractional cover 0.14), while the ADC produced values 5% to 10% higher. Laser altimeter values, depending on the height cutoff used to establish total fractional cover, were either higher or lower than the other instruments' values: a 10-cm cutoff produced values
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estimation of global Leaf Area Index and absorbed par using radiative transfer models
IEEE Transactions on Geoscience and Remote Sensing, 1997Co-Authors: Ranga B Myneni, Ramakrishna R Nemani, R Ramakrishna, Steven W RunningAbstract:A simple method for the estimation of global Leaf Area Index (LAI) and fraction of photosynthetically active radiation absorbed by the vegetation (FAPAR) from atmospherically corrected Normalized Difference Vegetation Index (NDVI) observations is described. Recent improvements to the authors' three dimensional radiative transfer model of a vegetated surface are described. Example simulation results and a validation exercise are discussed. The model was utilized to derive land cover specific NDVI-LAI and NDVI-FAPAR relations. The method therefore requires stratification of global vegetation into cover types that are compatible with the radiative transfer model. Such a classification based on vegetation structure is proposed and a simple method for its derivation is presented. Proof-of-concept results are given to illustrate the feasibility of the proposed method.
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forest ecosystem processes at the watershed scale sensitivity to remotely sensed Leaf Area Index estimates
International Journal of Remote Sensing, 1993Co-Authors: Ramakrishna R Nemani, Lars E Pierce, Steven W RunningAbstract:Abstract Recent research has shown that general trends in forest Leaf Area Index along regional climatic gradients can be adequately characterized by using ratios of near-infrared and red reflectances. However it has proven difficult to represent properly the spatial distribution of Leaf Area Index (LAI) at sub-regional scales such as small catchments. The key problem at Thematic Mapper scale is the variation in canopy closure and understorey contribution, which dramatically influences near-infrared reflectance from conifer forests, [n this paper, a new spectral Index is presented to estimate LAI of conifer forests using a combination of Red, NIR and mid-IR reflectances from the Landsat Thematic Mapper (TM). A simulation system (RHESSys) was used first, to generate potential vegetation patterns around a watershed in order to test them against remotely-sensed vegetation patterns, and secondly, to test the sensitivity of forest ecosystem processes to LAT estimated from combinations of the Thematic Mapper da...
Guang Zheng - One of the best experts on this subject based on the ideXlab platform.
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derivation validation and sensitivity analysis of terrestrial laser scanning based Leaf Area Index
Canadian Journal of Remote Sensing, 2016Co-Authors: Qinghua Guo, Guang Zheng, Shengli Tao, Kaiguang Zhao, Baolin XueAbstract:Abstract. Terrestrial laser scanning (TLS) is a promising tool, used to retrieve Leaf Area Index (LAI). However, the accuracy of LAI estimations based on TLS is still difficult to validate, because high-fidelity destructive measurements of Leaf Area are lacking. A comprehensive analysis of the sensitivity of TLS-based LAI estimates against various influencing factors (e.g., noise points, woody points, and voxel size) has yet to be reported. We acquired the true LAI by destructively measuring all leaves of 17 magnolia trees. We also improved a voxel-based method to estimate the LAI from the TLS data. We further assessed the sensitivity of LAI estimates against denoising, separation of woody points from foliage points, and voxel size. Our results showed that TLS-based LAI estimations were significantly related to the destructively sampled LAI (R2 = 0.832, RMSE = 0.693). Denoising improved the TLS-based LAI accuracy with a decrease of 0.415 in RMSE. Conversely, wood-Leaf separation showed little effect on th...
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spatial variability of terrestrial laser scanning based Leaf Area Index
International Journal of Applied Earth Observation and Geoinformation, 2012Co-Authors: Guang Zheng, Monika L MoskalAbstract:Abstract Forest stand point clouds generated from multiple scan locations using terrestrial laser scanning (TLS) have diverse range of spatial distribution patterns. These in turn have an effect on the direct Leaf Area Index (LAI) estimation from the point cloud. However, the most effective placement of the scanning equipment in homogeneous vs. heterogeneous stands has not been investigated. In this research, TLS was used to sample an evenly planted Douglas-fir (Pseudotsuga menziesii) seedling forest stand and a mature heterogeneous forest stand dominated by Douglas-fir (P. menziesii) and Western hemlock (Tsuga heterophylla). A new method, circular point cloud slicing, was developed to explore the spatial variation of point density for both azimuthal angular and radial directions. The results show that alone, a central location 360° scan data, does not capture all of the stand characteristics and less than 50% of variation of the estimation of effective Leaf Area Index (LAIe) of a mature heterogeneous stand. Thus, reducing occlusion, by incorporating additional lateral side view scans, is necessary to comprehensively represent the canopy structure, and structural variation of the heterogeneous forest stand. It was also shown, based on the assumption that the comprehensive scan combination can fully represent the forest stand, and that LAIe estimated from the comprehensive multi-direction mosaiced dataset are higher by twofold compared to the result from central scan only.
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computational geometry based retrieval of effective Leaf Area Index using terrestrial laser scanning
IEEE Transactions on Geoscience and Remote Sensing, 2012Co-Authors: Guang Zheng, L M MoskalAbstract:Quantifying the 3-D forest canopy structure and Leaf Area Index of an individual tree or a forest stand is challenging. The canopy structural information implicitly contained within point cloud data (PCD) generated from terrestrial laser scanning (TLS) makes it possible to characterize directly the spatial distribution of foliage elements. In this paper, a new voxel-based method titled “point cloud slicing” is presented to retrieve the biophysical characteristics of the forest canopy including extinction coefficient, gap fraction, overlapping effect, and effective Leaf Area (ELA) from PCD. These extractions were performed not only from the whole canopy but also from layers of the canopy to depict the distribution patterns of foliage elements within the canopy. The results showed that the TLS-based ELA estimation method could explain 88.7% (rmse = 0.007, p <; 0.001, and n = 30) variation of the destructive-sample-based Leaf Area measurement results. It was found that the sampling resolution was a key parameter in defining the dimension of a single voxel. Furthermore, the TLS-based method can also serve as a calibration tool for airborne laser scanning application with ground sampling.
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retrieving Leaf Area Index lai using remote sensing theories methods and sensors
Sensors, 2009Co-Authors: Guang Zheng, Monika L MoskalAbstract:The ability to accurately and rapidly acquire Leaf Area Index (LAI) is an indispensable component of process-based ecological research facilitating the understanding of gas-vegetation exchange phenomenon at an array of spatial scales from the Leaf to the landscape. However, LAI is difficult to directly acquire for large spatial extents due to its time consuming and work intensive nature. Such efforts have been significantly improved by the emergence of optical and active remote sensing techniques. This paper reviews the definitions and theories of LAI measurement with respect to direct and indirect methods. Then, the methodologies for LAI retrieval with regard to the characteristics of a range of remotely sensed datasets are discussed. Remote sensing indirect methods are subdivided into two categories of passive and active remote sensing, which are further categorized as terrestrial, aerial and satellite-born platforms. Due to a wide variety in spatial resolution of remotely sensed data and the requirements of ecological modeling, the scaling issue of LAI is discussed and special consideration is given to extrapolation of measurement to landscape and regional levels.
Monika L Moskal - One of the best experts on this subject based on the ideXlab platform.
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spatial variability of terrestrial laser scanning based Leaf Area Index
International Journal of Applied Earth Observation and Geoinformation, 2012Co-Authors: Guang Zheng, Monika L MoskalAbstract:Abstract Forest stand point clouds generated from multiple scan locations using terrestrial laser scanning (TLS) have diverse range of spatial distribution patterns. These in turn have an effect on the direct Leaf Area Index (LAI) estimation from the point cloud. However, the most effective placement of the scanning equipment in homogeneous vs. heterogeneous stands has not been investigated. In this research, TLS was used to sample an evenly planted Douglas-fir (Pseudotsuga menziesii) seedling forest stand and a mature heterogeneous forest stand dominated by Douglas-fir (P. menziesii) and Western hemlock (Tsuga heterophylla). A new method, circular point cloud slicing, was developed to explore the spatial variation of point density for both azimuthal angular and radial directions. The results show that alone, a central location 360° scan data, does not capture all of the stand characteristics and less than 50% of variation of the estimation of effective Leaf Area Index (LAIe) of a mature heterogeneous stand. Thus, reducing occlusion, by incorporating additional lateral side view scans, is necessary to comprehensively represent the canopy structure, and structural variation of the heterogeneous forest stand. It was also shown, based on the assumption that the comprehensive scan combination can fully represent the forest stand, and that LAIe estimated from the comprehensive multi-direction mosaiced dataset are higher by twofold compared to the result from central scan only.
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retrieving Leaf Area Index lai using remote sensing theories methods and sensors
Sensors, 2009Co-Authors: Guang Zheng, Monika L MoskalAbstract:The ability to accurately and rapidly acquire Leaf Area Index (LAI) is an indispensable component of process-based ecological research facilitating the understanding of gas-vegetation exchange phenomenon at an array of spatial scales from the Leaf to the landscape. However, LAI is difficult to directly acquire for large spatial extents due to its time consuming and work intensive nature. Such efforts have been significantly improved by the emergence of optical and active remote sensing techniques. This paper reviews the definitions and theories of LAI measurement with respect to direct and indirect methods. Then, the methodologies for LAI retrieval with regard to the characteristics of a range of remotely sensed datasets are discussed. Remote sensing indirect methods are subdivided into two categories of passive and active remote sensing, which are further categorized as terrestrial, aerial and satellite-born platforms. Due to a wide variety in spatial resolution of remotely sensed data and the requirements of ecological modeling, the scaling issue of LAI is discussed and special consideration is given to extrapolation of measurement to landscape and regional levels.
J Cihlar - One of the best experts on this subject based on the ideXlab platform.
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retrieving Leaf Area Index of boreal conifer forests using landsat tm images
Remote Sensing of Environment, 1996Co-Authors: Jing M. Chen, J CihlarAbstract:Abstract Vegetation indices, including the simple ratio (SR) and the normalized difference vegetation Index (NDVI), from Landsat TM data were correlated to ground-based measurements of LAI, effective LAI, and the crown closure in boreal conifer forests located near Candle Lake and Prince Albert, Saskatchewan and near Thompson, Manitoba, as part of the Boreal Ecosystem-Atmosphere Study (BOREAS). The measurements were made using two optical instruments: the Plant Canopy Analyzer (LAI-2000, LI-COR) and the TRAC (Tracing Radiation and Architecture of Canopies). The TRAC was recently developed to quantify the effect of canopy architecture on optical measurements of Leaf Area Index. The stands were located on georeferenced Landsat TM images using global positioning system (GPS) measurements. It is found that late spring Landsat images are superior to summer images for determining overstory LAI in boreal conifer stands because the effect of the understory is minimized in the spring before the full growth of the understory and moss cover. The effective LAI, obtained from gap fraction measurements assuming a random distribution of foliage spatial positions, was found to be better correlated to SR and NDVI than LAI. The effective LAI is less variable and easier to measure than LAI, and is also an intrinsic attribute of plant canopies. It is therefore suggested to use effective LAI as the most important parameter for radiation interception considerations.
