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首页> 外文期刊>IEEE Geoscience and Remote Sensing Letters >Spatial Scale and Landscape Heterogeneity Effects on FAPAR in an Open-Canopy Black Spruce Forest in Interior Alaska
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Spatial Scale and Landscape Heterogeneity Effects on FAPAR in an Open-Canopy Black Spruce Forest in Interior Alaska

机译：阿拉斯加内陆开放式黑云杉林中FAPAR的空间尺度和景观异质性影响

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Black spruce forests dominate the land cover in interior Alaska. In this region, satellite remote sensing of ecosystem productivity is useful for evaluating black spruce forest status and recovery processes. The fraction of absorbed photosynthetically active radiation (FAPAR) by green leaves is a particularly important input parameter for ecosystem models. ${rm FAPAR}_{1d}$ is computed as the ratio of absorbed photosynthetically active radiation $({rm APAR}_{3d})$ to the incident photosynthetically active radiation at the horizontal plane above the canopy $({rm PAR}_{1d}, {rm FAPAR}_{1d} = {rm APAR}_{3d}/{rm PAR}_{1d})$ . The parameter ${rm FAPAR}_{1d}$ is scale dependent and can be larger than 1 as a result of laterally incident PAR. We investigated the dependence of ${rm FAPAR}_{1d}$ on spatial scale in an open-canopy black spruce forest in interior Alaska. We compared ${rm FAPAR}_{1d}$ with ${rm FAPAR}_{3d}( = {rm APAR}_{3d}/{rm PAR}_{3d})$, the latter of which considers incident PAR as actinic flux (spheradiance) $({rm PAR}_{3d})$. Our results showed the following: 1) landscape scale ${rm FAPAR}_{3d}(30times 30 hbox{m}^{2})$ was always larger (0.39–0.43) than ${rm FAPAR}_{1d}$ (0.19–0.27) due to the landscape heterogeneity and incident PAR regime, and 2) at the individual tree sc- le, ${rm FAPAR}_{1d}$ was highly variable, with 34% (day of year [DOY] 180) to 52% (DOY 258) of ${rm FAPAR}_{1d} > 1$, whereas ${rm FAPAR}_{3d}$ varied across a much narrower range (0.2–0.5). The spatial-scale dependence of the ratio of ${rm PAR}_{3d}$ to ${rm PAR}_{1d}$ converged at the pixel size larger than 5 m. Thus, a 5-m or coarser resolution was necessary to ignore the lateral PAR effect in the open-canopy black spruce forest.
机译：黑色的云杉林在阿拉斯加内部占主导地位。在该区域，卫星遥感的生态系统生产力对评估黑云杉林的状况和恢复过程很有用。绿叶吸收的光合作用活性辐射（FAPAR）的比例是生态系统模型特别重要的输入参数。 $ {rm FAPAR} _ {1d} $计算为吸收的光合有效辐射$（{rm APAR} _ {3d}）$与冠层上方水平面$（{rm PAR } _ {1d}，{rm FAPAR} _ {1d} = {rm APAR} _ {3d} / {rm PAR} _ {1d}）$。参数$ {rm FAPAR} _ {1d} $与比例有关，并且由于横向入射PAR而可能大于1。我们调查了阿拉斯加内部一个开放遮盖的黑色云杉林中$ {rm FAPAR} _ {1d} $对空间尺度的依赖性。我们将$ {rm FAPAR} _ {1d} $与$ {rm FAPAR} _ {3d}（= {rm APAR} _ {3d} / {rm PAR} _ {3d}）$进行了比较，其中后者考虑了事件PAR作为光化通量（散射度）$（{rm PAR} _ {3d}）$。我们的结果显示以下内容：1）景观尺度$ {rm FAPAR} _ {3d}（30×30 hbox {m} ^ {2}）$始终比$ {rm FAPAR} _ {1d}大（0.39–0.43） $（0.19–0.27）由于景观异质性和入射PAR制度，以及2）在单个树桩上，$ {rm FAPAR} _ {1d} $具有很大的可变性，为34％（每年[天] ] 180）到$ {rm FAPAR} _ {1d}> 1 $的52％（DOY 258），而$ {rm FAPAR} _ {3d} $的变化范围更窄（0.2-0.5）。 $ {rm PAR} _ {3d} $与$ {rm PAR} _ {1d} $之比的空间尺度相关性在大于5 m的像素大小处收敛。因此，需要5m或更粗的分辨率才能忽略开阔的黑云杉林的横向PAR效应。

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