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Investigation of terrain illumination effects on vegetation indices and VI-derived phenological metrics in subtropical deciduous forests

机译：地形照明对亚热带落叶林植被指数和VI物候指标的影响

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摘要

We used RapidEye and Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra data to study terrain illumination effects on 3 vegetation indices (VIs) and 11 phenological metrics over seasonal deciduous forests in southern Brazil. We applied TIMESAT for the analysis of the Enhanced Vegetation Index (EVI) and the Normalized Difference Vegetation Index (NDVI) derived from the MOD13Q1 product to calculate phenological metrics. We related the VIs with the cosine of the incidence angle i (Cos i) and inspected percentage changes in VIs before and after topographic C-correction. The results showed that the EVI was more sensitive to seasonal changes in canopy biophysical attributes than the NDVI and Red-Edge NDVI, as indicated by analysis of non-topographically corrected RapidEye images from the summer and winter. On the other hand, the EVI was more sensitive to terrain illumination, presenting higher correlation coefficients with Cos i that decreased with reduction in the canopy background L factor. After C-correction, the RapidEye Red-Edge NDVI, NDVI, and EVI decreased 2%, 1%, and 13% over sunlit surfaces and increased up to 5%, 14%, and 89% over shaded surfaces, respectively. The EVI-related phenological metrics were also much more affected by topographic effects than the NDVI-derived metrics. From the set of 11 metrics, the 2 that described the period of lower photosynthetic activity and seasonal VI amplitude presented the largest correlation coefficients with Cos i. The results showed that terrain illumination is a factor of spectral variability in the seasonal analysis of phenological metrics, especially for VIs that are not spectrally normalized.
机译：我们使用RapidEye和中等分辨率成像光谱仪（MODIS）/ Terra数据研究了巴西南部季节性落叶林上3种植被指数（VI）和11种物候指标对地形照明的影响。我们将TIMESAT用于分析从MOD13Q1产品获得的增强植被指数（EVI）和归一化差异植被指数（NDVI），以计算物候指标。我们将VI与入射角i的余弦（Cos i）相关联，并检查了地形C校正前后VI的百分比变化。结果表明，EVI比NDVI和Red-Edge NDVI对冠层生物物理属性的季节性变化更为敏感，这是通过对夏季和冬季非地形校正的RapidEye图像进行分析而得出的。另一方面，EVI对地形照明更敏感，与Cos i的相关系数更高，随着冠层背景L因子的减小而降低。经过C校正后，RapidEye Red-Edge NDVI，NDVI和EVI在阳光照射的表面上分别减少了2％，1％和13％，在阴影表面上分别增加了5％，14％和89％。与EVI相关的物候指标也比NDVI得出的指标受地形影响更大。在这11个度量标准集中，有2个描述了较低的光合活性和季节性VI幅度，与Cos i的相关系数最大。结果表明，在物候指标的季节性分析中，地形照度是光谱变异性的一个因素，尤其是对于未进行光谱归一化的VI。

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  • 来源
    《GIScience & remote sensing》 |2016年第3期|360-381|共22页
  • 作者

    Galvao Lenio Soares; Breunig Fabio Marcelo; Teles Thiago Sousa; Gaida William; Balbinot Rafaelo;

  • 作者单位

    Inst Nacl Pesquisas Espaciais, Div Sensoriamento Remoto, Caixa Postal 515, BR-12227010 Sao Jose Dos Campos, SP, Brazil;

    Univ Fed Santa Maria, Dept Engn Florestal, CESNORS UFSM, Linha Sete Setembro S-N,Sala 59,Bloco Apoio 4, BR-98400000 Frederico Westphalen, RS, Brazil;

    Inst Nacl Pesquisas Espaciais, Div Sensoriamento Remoto, Caixa Postal 515, BR-12227010 Sao Jose Dos Campos, SP, Brazil;

    Univ Fed Santa Maria, Dept Engn Florestal, CESNORS UFSM, Linha Sete Setembro S-N,Sala 59,Bloco Apoio 4, BR-98400000 Frederico Westphalen, RS, Brazil;

    Univ Fed Santa Maria, Dept Engn Florestal, CESNORS UFSM, Linha Sete Setembro S-N,Sala 59,Bloco Apoio 4, BR-98400000 Frederico Westphalen, RS, Brazil;

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  • 关键词

    MODIS; topographic effects; subtropical forests; phenological metrics; vegetation indices; RapidEye;

    机译：MODIS;地形影响;亚热带森林;物候指标;植被指数;快速眼;

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