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.
Funding
Australian Research Council
History
Publication title
Surveys in Geophysics
Volume
40
Pagination
631-656
ISSN
0169-3298
Department/School
School of Geography, Planning and Spatial Sciences
Publisher
Kluwer Academic Publ
Place of publication
Van Godewijckstraat 30, Dordrecht, Netherlands, 3311 Gz
Rights statement
Copyright 2019 Springer Nature B.V.
Repository Status
Restricted
Socio-economic Objectives
Assessment and management of Antarctic and Southern Ocean ecosystems; Expanding knowledge in the biological sciences; Expanding knowledge in the environmental sciences