光学仪器法测定叶面积指数季节变化的误差分析

doi:10.11707/j.1001-7488.20160902

摘要/Abstract

摘要： [目的] 以黑龙江凉水国家级自然保护区人工林地为研究区，探讨影响间接法（光学仪器法）测定森林叶面积指数（LAI）季节变化精度的因素，为更准确地运用该方法测定LAI提供科学依据。[方法] 以红松人工林和兴安落叶松人工林为研究对象，利用直接法和半球摄影法（DHP）及LAI-2000植物冠层分析仪2种间接法测定其LAI季节变化（5-10月），并研究光学仪器法测定LAI精度的误差源（木质部、冠层水平上的集聚效应、簇内集聚效应和自动曝光设置）产生偏差的季节性变异。[结果] 对于红松人工林，DHP和LAI-2000在不同时期测定的LAI均低于直接法测定值，分别低估55%~68%和19%~35%；对于兴安落叶松人工林，DHP和LAI-2000在大部分时期低于直接法测定值，但在叶凋落后期均高于直接法测定值。不同误差源的校正参数及其对光学仪器法产生的偏差均存在明显的季节性差异。对于红松人工林，不同时期所有误差源产生的总偏差分别平均解释DHP，LAI-2000与直接法测定的LAI间差异的84%和79%。对于兴安落叶松人工林，利用Photoshop（PS）法校正木质部产生误差的情况下，不同时期所有误差源产生的总偏差对DHP、LAI-2000与直接法测定的LAI间差异的平均解释率分别为80%和65%，而利用背景值法校正木质部产生误差时，相应的平均解释率均低于5%。[结论] 2种针叶林内，经过校正后DHP均比LAI-2000更适于测定LAI的季节变化；同时利用PS法校正2种光学仪器法在测定LAI季节变化时木质部产生误差的效果优于背景值法。

关键词: 叶面积指数, 半球摄影法, LAI-2000植物冠层分析仪, 木质比例, 集聚效应, 自动曝光

Abstract: [Objective] The objective of this study was mainly to quantify the bias in measuring the seasonal variation of optical LAI due to different error sources and to explore which one is the most important for affecting the accuracy of LAI measurements by different optical methods in planation forests in the Heilongjiang Liangshui National Nature Reserve, in order to provide the theoretical basis for accurately estimating LAI by optical methods. [Methods] This study was conducted in a Korean pine (Pinus koraiensis) plantation and a Dahurian larch (Larix gmelinii) plantation. The seasonal changes of LAI were estimated using direct and optical methods including digital hemispherical photography (DHP) and LAI-2000 plant canopy analyzer. Further, the measurements bias of seasonal changes were analyzed due to error sources (i.e., woody materials, clumping effects beyond shoot level, clumping effects within shoot or automatic exposure setting) with optical methods. [Result] As for Korean pine plantation, the LAI values measured with DHP and LAI-2000 were all lower than that measured with direct LAI measurement method in different periods by 55%~68% and 19%~35%, respectively. As for Dahurian larch plantation, the LAI values measured with DHP and LAI-2000 were also lower than that measured with direct LAI measurement method in most periods, but the LAI from DHP and LAI-2000 were larger than that with direct LAI measurement in late leaf fall period. The bias due to different error sources with the optical methods showed clear seasonal dynamics. For Korean pine plantation, the total bias due to all error sources during all periods approximately explained averagely 84% and 79% of the differences between DHP or LAI-2000 and direct LAImeasurement, respectively. For Dahurian larch plantation, in the case of correcting the error caused by xylem by Photoshop (PS) method, the total bias due to all error sources during all periods approximately explained averagely 80% and 65% of the differences between DHP or LAI-2000 and direct LAI measurement, respectively; In contrast, when correcting the error caused by xylem using a background method, the corresponding explanation ratios were all less than 5%. [Conclusion] For the two coniferous forests, DHP is more suitable for estimating the seasonal changes of LAI than LAI-2000 after correlation, and PS method is more useful in correcting the error caused by xylem in estimating seasonal changes of LAI using the two optical methods than the background method.

Key words: leaf area index (LAI), digital hemispherical photography (DHP), LAI-2000 plant canopy analyzer, woody-to-total area ratio, clumping effects, automatic exposure

中图分类号:

S718.55

刘志理, 金光泽. 光学仪器法测定叶面积指数季节变化的误差分析[J]. 林业科学, 2016, 52(9): 11-21.

Liu Zhili, Jin Guangze. Bias Analysis of Seasonal Changes of Leaf Area Index Derived from Optical Methods[J]. Scientia Silvae Sinicae, 2016, 52(9): 11-21.

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