Seasonal variation of leaf area index (LAI) over paddy rice fields in NE China: Intercomparison of destructive sampling, LAI-2200, digital hemispherical photography (DHP), and AccuPAR methods
Seasonal variation of leaf area index (LAI) over paddy rice fields in NE China: Intercomparison of destructive sampling, LAI-2200, digital hemispherical photography (DHP), and AccuPAR methods
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中国东北稻田叶面积指数（LAI）季节变化：破坏性采样、LAI-2200、数字半球摄影（DHP）和 AccuPAR 方法的比较
DOI：
10.1016/j.agrformet.2014.08.005
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发表时间：
2014-11-01
影响因子：
6.2
通讯作者：
Jiang, Chongya
中科院分区：
文献类型：
--
作者：
Fang, Hongliang;Li, Wenjuan;Jiang, Chongya
叶面积指数（LAI）的连续测量对于LAI遥感产品的有效性验证变得越来越重要。2012年在中国东北地区进行了一项季节性田间活动，以连续测量水稻田的叶面积指数。三个间接的光学方法，LAI-2200，数字半球摄影（DHP），AccuPAR，进行了比较，同时进行破坏性采样方法。对聚集效应的修正应用于从间接光学测量估计的有效植物面积指数（派（eff））。LAI-2200和DHP在整个季节产生一致的派（eff）估计（R-2 = 0.76，RMSE = 0.97）。从DHP获得的丛生指数（CI）值一般随植物生长而降低，在一年中的第191-230天（DOY）的生长高峰期，其范围在0.63和0.74之间。从DHP照片检索的CI值一般随着视角的增加而减小。用LAI-2200和DHP估算的光学派和LAI值与DOY 230前的破坏值吻合得很好（PAI的R-2 = 0.75，RMSE = 1.15; LAI的R-2=0.78，RMSE = 0.74），相对误差分别小于10%和5%。对于LAI-2200省略环5在旺季期间产生非常准确的派和LAI估计。然而，AccuPAR低估了派（eff），派和LAI值从其他方法（高达30%）。在DOY 231之后，由于叶片衰老和DHP分类困难，破坏性方法和光学方法检测派的能力显著降低。因此，在适当考虑聚集效应的情况下，利用LAI-2200和DHP可以较准确地估算水稻衰老前的派。本研究所获得的季节性连续叶面积指数的测量结果对叶面积指数遥感产品的验证具有重要的参考价值。(C)2014爱思唯尔有限公司版权所有。
Continuous field leaf area index (LAI) measurement has become increasingly important for the validation of remote sensing LAI products. A seasonal field campaign was carried out to take continuous LAI measurements over paddy rice fields in NE China in 2012. Three indirect optical methods, LAI-2200, digital hemispherical photography (DHP), and AccuPAR, were compared with a destructive sampling method conducted concurrently. Corrections for the clumping effect were applied to the effective plant area indices (PAI(eff)) estimated from the indirect optical measurements.Both LAI-2200 and DHP produce consistent PAI(eff) estimates over the season (R-2 = 0.76, RMSE = 0.97). The clumping index (CI) values obtained from DHP generally decrease with plant growth and range between 0.63 and 0.74 during the peak growing period from day of year (DOY) 191-230. The CI values retrieved from DHP photos generally decrease with increasing view angles. The optical PAI and LAI values estimated from LAI-2200 and DHP correspond very well with the destructive values before DOY 230 (R-2 = 0.75, RMSE = 1.15 for PAI and R-2=0.78, RMSE = 0.74 for LAI), and the relative errors are less than 10% and 5%, respectively, for the two instruments. Omitting ring 5 for LAI-2200 generates very accurate PAI and LAI estimations during the peak season. Nevertheless, AccuPAR underestimates the PAI(eff), PAI, and LAI values obtained from other methods (up to 30%). After DOY 231, the capability to detect PAI decreases significantly for both destructive and optical methods due to the leaf senescence and the DHP classification difficulty. In general, rice PAI could be accurately estimated with LAI-2200 and DHP before senescence if the clumping effect could be properly taken into account. The seasonal continuous LAI measurements obtained from this study are valuable for the validation of remote sensing LAI products. (C) 2014 Elsevier B.V. All rights reserved.