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首页> 外文期刊>International journal of remote sensing >Mapping gap fraction, LAI and defoliation using various ALS penetration variables
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Mapping gap fraction, LAI and defoliation using various ALS penetration variables

机译：使用各种ALS渗透变量绘制间隙分数，LAI和脱叶图

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摘要

Four alternative airborne laser scanning (ALS) canopy penetration variables were compared for their suitability for mapping of gap fraction, leaf area index and disturbances in a Scots pine forest. The variables were based on either echo counting or intensity, and on either first or first and last echoes. ALS data and field-measured gap fraction and effective leaf area index (LAI_e) were gathered before and after a severe insect defoliation by pine sawflies. LAI_e is a commonly used form of leaf area index that is mathematically derived from gap fraction, and includes the areas of foliage, branches and trunks, and which is not corrected for the clumping of foliage. The ALS penetration variables were almost equally strongly related to field-measured gap fraction and LAI_e. The estimated slopes in the LAI_e models varied from 0.94 to 2.71, and had coefficient of determination R~2 values of 0.92-0.94. They were strongly correlated to each other (R~2 values of 0.95-0.98) and agreed fairly well for temporal changes of LAI_e during the summer and the insect defoliation (R~2 values of 0.82-0.95). Counting of first and last echoes produced penetration rates close to the gap fraction, and this penetration variable was able to penetrate tree crowns. Ground-only echoes represented mostly between-tree gaps, and canopy-first-ground-last pulses represented mostly within-canopy gaps. However, the penetration variables based on first and last echoes suffered from the problem that a second echo might be impaired both in low and in tall canopies. In low canopies, two adjacent echoes from the same pulse would be too close in time to be separated by the sensor, while in tall canopies the pulse might apparently be fragmented down through the canopy. The intensity-based penetration variables needed to be supplemented with reflectance values, or at least the ratio between reflectance of the canopy and the ground, and this ratio was estimated from the data. The study demonstrated that one might be able to distinguish between disturbance types, e.g. between defoliation and cutting, by comparing alternative ALS penetration variables. Insect defoliation was dominated by an increase in within-canopy gaps and, correspondingly, the fraction of partly penetrating canopy-first-ground-last pulses. Tree removals from cutting were dominated by increases in between-tree gaps and the corresponding fraction of ground-only pulses.
机译：比较了四个替代的机载激光扫描（ALS）机盖穿透变量，以比较它们在绘制苏格兰松树森林中的空隙率，叶面积指数和扰动方面的适用性。这些变量基于回声计数或强度，以及第一个或第一个和最后一个回声。在严重的松叶虫昆虫脱叶之前和之后，收集了ALS数据以及现场测量的间隙分数和有效叶面积指数（LAI_e）。 LAI_e是叶面积指数的一种常用形式，它是通过数学方法从间隙分数中得出的，包括叶子，树枝和树干的面积，并且没有针对叶子的结块进行校正。 ALS渗透变量几乎与现场测量的间隙分数和LAI_e密切相关。 LAI_e模型中的估计斜率在0.94到2.71之间变化，确定系数R〜2值为0.92-0.94。它们相互之间具有很强的相关性（R〜2值为0.95-0.98），并且对于夏季LAI_e的时间变化和昆虫脱叶（R〜2值为0.82-0.95）相当一致。计数第一个和最后一个回波会产生接近间隙分数的穿透率，并且该穿透变量能够穿透树冠。仅地面回波主要代表树间间隙，而冠层先接地后脉冲主要代表冠层内间隙。但是，基于第一回声和最后回声的穿透力变量存在一个问题，即在低矮的树冠和高矮的树冠中第二回声都可能受到损害。在低冠层中，来自同一脉冲的两个相邻回波会在时间上过于接近而无法被传感器分开，而在高冠层中，脉冲显然会通过冠层被分解。基于强度的穿透变量需要补充反射率值或至少冠层与地面反射率之间的比率，并且该比率是根据数据估算的。这项研究表明，人们也许能够区分出各种干扰类型，例如通过比较其他ALS渗透变量，在脱叶和切割之间进行比较。昆虫的脱叶主要是冠层内部间隙的增加以及相应地部分穿透冠层先发地后脉冲的分数所致。砍伐树木的原因主要是树木之间的间隙和相应的仅地面脉冲部分的增加。

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  • 来源
    《International journal of remote sensing》 |2010年第5期|1227-1244|共18页
  • 作者

    SVEIN SOLBERG;

  • 作者单位

    Norwegian Forest and Landscape Institute, 1431 As, Norway;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
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