Estimation of the directional and whole apparent clumping index (ACI) from indirect optical measurements
Estimation of the directional and whole apparent clumping index (ACI) from indirect optical measurements
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通过间接光学测量估计方向和整体表观聚集指数 (ACI)
DOI：
10.1016/j.isprsjprs.2018.06.022
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发表时间：
2018-10
影响因子：
12.7
通讯作者：
Shanshan Wei
中科院分区：
文献类型：
--
作者：
Hongliang Fang;Weiwei Liu;Wenjuan Li;Shanshan Wei
冠层聚集指数（Canopy clustered index， CI）反映了叶片组分在空间上的非随机分布，是更好地理解冠层辐射传输过程的重要结构参数。利用LAI-2200植物冠层分析仪，采用对数间隙分数平均法计算了植被的表观聚集指数（ACI）。虽然LAI-2200计算不同圆锥环的间隙分数和ACI，但缺乏其他几何单位（例如角单元或方位角扇形）和仪器的ACI计算。本研究以LAI-2200 ACI为基础，比较了不同光学仪器对不同几何空间计算的ACI。利用LAI-2200、数字半球摄影（DHP）和AccuPAR在中国东北稻田进行的季节性连续测量获得的现场数据，计算了不同水平上的定向aci——方向单元（ΩA（θ，ϕ））、同心圆（ΩA(θ)）、方位扇区（ΩA（ϕ））和水平景观（ΩA(ν)）。采用角积分法、简单平均法、非线性校正法和方差均值比法，从定向aci出发计算整个aci。水稻的定向ACIs一般为ΩA(θ, φ) < ΩA（θ）和ΩA(φ) < ΩA(ν)，叶片随机性随线段大小的增加而增加。DHP估计的ΩA（θ，ϕ）表明冠层聚集在最精细的水平，与对数平均法（ΩLX）和比值法（有效叶面积指数（lae）除以LAI）估计的CIs一致。ACI指标扩展了现有的CI指标，可以用不同的光学仪器获得。扩展后的度量可以应用于其他植被生态系统的冠层辐射传输建模和冠层生物物理参数的估计。
Canopy clumping index (CI) indicates the non-random distribution of foliage components in space, and is an important structural parameter for better understanding the radiative transfer process in a canopy. The apparent clumping index (ACI), calculated using the logarithmic gap fraction averaging method, is reported by the LAI-2200 Plant Canopy Analyzer. While LAI-2200 calculates the gap fraction and ACI from different conical rings, calculation of ACI for other geometric units (e.g., an angular cell or an azimuth sector) and instruments has been lacked. Building upon the LAI-2200 ACI, this study compares the ACIs calculated for different geometric spaces from different optical instruments. The field data obtained from seasonal continuous measurements with LAI-2200, digital hemispheric photography (DHP), and AccuPAR at a paddy rice field in northeast China were used to calculate the directional ACIs at different levels—a directional cell (ΩA(θ,ϕ)), a concentric ring (ΩA(θ)), an azimuth sector (ΩA(ϕ)), and over the horizontal landscape (ΩA(ν)). The whole ACIs were calculated from the directional ACIs with an angular integration method, a simple averaging method, a non-linear correction method, and a variance-to-mean ratio method. The directional ACIs for paddy rice generally follow the order of ΩA(θ,ϕ) < ΩA(θ) and ΩA(ϕ) < ΩA(ν), displaying an increase of foliage randomness with the segment size. The ΩA(θ,ϕ) estimated from DHP indicates canopy clumping at the finest level and is consistent with the CIs estimated from the logarithmic averaging method (ΩLX) and the ratio method (the effective leaf area index (LAIe) divided by the LAI). The ACI metrics expand the current CI metrics and can be obtained with different optical instruments. The expanded metrics can be applied in the canopy radiative transfer modeling and in the estimation of canopy biophysical parameters for other vegetation ecosystems.
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使用归一化差异热点和暗点 (NDHD) 方法估计 MISR 和 MODIS 传感器的冠层丛集指数：BRDF 模型和太阳天顶角的影响
影响因子：
13.5
作者：
Wei Shanshan;Fang Hongliang
通讯作者：
Fang Hongliang
影响因子：
5.7
作者：
NORMAN, JM;JARVIS, PG
通讯作者：
JARVIS, PG
影响因子：
6.2
作者：
Garriques, S.;Shabanov, N. V.;Myneni, R. B.
通讯作者：
Myneni, R. B.
DOI：
10.1016/0002-1571(71)90092-6
发表时间：
1971-01-01
期刊：
AGRICULTURAL METEOROLOGY
影响因子：
--
作者：
NILSON, T
通讯作者：
NILSON, T
影响因子：
13.5
作者：
Chen, JM;Menges, CH;Leblanc, SG
通讯作者：
Leblanc, SG