Malenovský Zbyněk, Homolová Lucie, Lukeš Petr, Buddenbaum Henning, Verrelst Jochem, Alonso Luis, Schaepman Michael E, Lauret Nicolas, Gastellu-Etchegorry Jean-Philippe
Surveying and Spatial Sciences Group, School of Technology, Environments and Design, University of Tasmania, Private Bag 76, Hobart, TAS 7001, Australia.
Global Change Research Institute CAS, Remote Sensing Department, Bělidla 986/4a, 603 00 Brno, Czech Republic.
Surv Geophys. 2019;40:631-656. doi: 10.1007/s10712-019-09534-y. Epub 2019 May 9.
Imaging spectroscopy of vegetation requires methods for scaling and generalizing optical signals that are reflected, transmitted and emitted in the solar wavelength domain from single leaves and observed at the level of canopies by proximal sensing, airborne and satellite spectroradiometers. The upscaling embedded in imaging spectroscopy retrievals and validations of plant biochemical and structural traits is challenged by natural variability and measurement uncertainties. Sources of the leaf-to-canopy upscaling variability and uncertainties are reviewed with respect to: (1) implementation of retrieval algorithms and (2) their parameterization and validation of quantitative products through in situ field measurements. The challenges are outlined and discussed for empirical and physical leaf and canopy radiative transfer modelling components, considering both forward and inverse modes. Discussion on optical remote sensing validation schemes includes also description of a multiscale validation concept and its advantages. Impacts of intraspecific and interspecific variability on collected field and laboratory measurements of leaf biochemical traits and optical properties are demonstrated for selected plant species, and field measurement uncertainty sources are listed and discussed specifically for foliar pigments and canopy leaf area index. The review concludes with the main findings and suggestions as how to reduce uncertainties and include variability in scaling vegetation imaging spectroscopy signals and functional traits of single leaves up to observations of whole canopies.
植被成像光谱学需要能够对光学信号进行尺度转换和推广的方法，这些光学信号在太阳波长范围内从单叶反射、透射和发射，并通过近距离传感、机载和卫星光谱辐射计在冠层水平上进行观测。成像光谱学在植物生化和结构特征反演及验证中所涉及的尺度上推，面临着自然变异性和测量不确定性的挑战。本文从以下两个方面综述了从叶片到冠层尺度上推的变异性和不确定性来源：（1）反演算法的实施；（2）通过实地测量对定量产品进行参数化和验证。针对经验性和物理性的叶片及冠层辐射传输建模组件，考虑正向和反向模式，概述并讨论了其中的挑战。关于光学遥感验证方案的讨论还包括对多尺度验证概念及其优势的描述。针对选定的植物物种，展示了种内和种间变异性对叶片生化特征和光学特性的实地和实验室测量结果的影响，并特别列出和讨论了叶面色素和冠层叶面积指数的实地测量不确定性来源。综述最后给出了主要研究结果以及关于如何减少不确定性、将变异性纳入从单叶植被成像光谱信号及功能特征到整个冠层观测的尺度转换中的建议。
