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首页> 外文期刊>Agricultural and Forest Meteorology >Physiological interpretation of a hyperspectral time series in a citrus orchard
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Physiological interpretation of a hyperspectral time series in a citrus orchard

机译：柑橘园中高光谱时间序列的生理解释

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Hyperspectral remote sensing for monitoring horticultural production systems requires the understanding of how plant physiology, canopy structure, management and solar elevation affect the retrieved canopy reflectance during different stages of the phenological cycle. Hence, the objective of this study was to set up and to interpret a hyperspectral time series for a mature and healthy citrus orchard in the Western Cape province of South Africa considering these effects. Based on the remotely sensed data, biophysical parameters at the canopy level were derived and related to known observed physiological and phenological changes at the leaf level and to orchard management. Fractions of mature fruit, flowers, and sunburnt leaves were considered, and indices related to canopy structure chlorophyll content and canopy water status were calculated.Results revealed small cover fractions of mature fruit, flowers and sunburnt leaves of respectively 2.1%, 3.1% and 7.0%, but the high spectral contrast between flowers and leaves allowed a successful classification of flowering intensity. Furthermore, it was shown that canopy level time series of vegetation indices were sensitive to changes in solar elevation and soil reflectance which could be reduced by applying an empirical soil line correction for the most affected indices. Most trends in vegetation indices at the canopy level could be explained by a combination of changes at the leaf level (chlorophyll, carotenoids, dry matter), changes in canopy structure (leaf area index and leaf angle distribution) and changes in cover fractions of vegetative flushes, flowers and sunburnt leaves. The transformed chlorophyll absorption ratio index over the optimised soil adjusted vegetation index (MCARI/OSAVI) was best related to leaf level trends in chlorophyll content. Seasonal changes in the photochemical reflectance index (PRI) were linked to inverse changes in the carotenoid-to-chlorophyll ratio. Canopy structure indices (the modified triangular vegetation index or MTVI2 and the standardized leaf area index determining index or sLAIDI) were sensitive to changes in leaf area index, average leaf angle as well to management interactions (pruning and harvest). Canopy water status was highly impacted during the spring flush due to expanding leaves that concealed trends in the underlying mature leaves. Seasonal trends in soil and weeds reflectance were related to changes in volumetric soil water content and to the earlier and reduced growth period of non-irrigated weeds
机译：用于监视园艺生产系统的高光谱遥感需要了解植物生理，冠层结构，管理和太阳高度如何在物候周期的不同阶段影响检索到的冠层反射率。因此，本研究的目的是建立并解释考虑到这些影响的南非西开普省成熟而健康的柑橘园的高光谱时间序列。根据遥感数据，得出冠层水平的生物物理参数，并将其与已知的叶片水平的生理和物候变化以及果园管理联系起来。考虑成熟果实，花和炙叶的分数，计算与冠层结构叶绿素含量和冠层水分状况相关的指数，结果显示成熟果实，花朵和炙叶的覆盖率小，分别为2.1％，3.1％和7.0 ％，但是花和叶之间的高光谱对比度允许开花强度的成功分类。此外，结果表明，植被指数的冠层水平时间序列对太阳高度和土壤反射率的变化敏感，而对受影响最大的指数应用经验性土壤线校正可以减少这种变化。冠层水平上植被指数的大多数趋势可以用叶片水平（叶绿素，类胡萝卜素，干物质）的变化，冠层结构的变化（叶面积指数和叶角分布）以及植物覆盖率的变化共同解释。潮红，花朵和晒伤的叶子。优化的土壤调节植被指数（MCARI / OSAVI）上转化的叶绿素吸收比指数与叶面叶绿素含量趋势最相关。光化学反射指数（PRI）的季节性变化与类胡萝卜素与叶绿素比率的反向变化有关。冠层结构指数（改良的三角植被指数或MTVI2和标准化的叶面积指数确定指数或sLAIDI）对叶面积指数，平均叶角以及管理相互作用（修剪和收获）的变化敏感。春季冲洗期间，冠层水状况受到严重影响，这是由于叶片膨胀而掩盖了潜在的成熟叶片中的趋势。土壤和杂草反射率的季节性趋势与土壤含水量的变化以及非灌溉杂草生长的早期和减少有关。

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