Abstract
Radiative transfer model (RTM) inversion allows for the quantitative estimation of vegetation biochemical composition from satellite sensor data, but large uncertainties associated with inversion make accurate estimation difficult. The leaf structure parameter (Ns) is one of the largest sources of uncertainty in inversion of the widely used leaf-level PROSPECT model, since it is the only parameter that cannot be directly measured. In this study, we characterize Ns as a function of phenology by collecting an extensive dataset of leaf measurements from samples of three dicotyledon species (hard red wheat, soft white wheat, and upland rice) and one monocotyledon (soy), grown under controlled conditions over two full growth seasons. A total of 230 samples were collected: measured leaf reflectance and transmittance were used to estimate Ns from each sample. These experimental data were used to investigate whether Ns depends on phenological stages (early/mid/late), and/or irrigation regime (irrigation at 85%, 75%, 60% of the initial saturated tray weight, and pre-/post-irrigation). The results, supported by the extensive experimental data set, indicate a significant difference between Ns estimated on monocotyledon and dicotyledon plants, and a significant difference between Ns estimated at different phenological stages. Different irrigation regimes did not result in significant Ns differences for either monocotyledon or dicotyledon plant types. To our knowledge, this study provides the first systematic record of Ns as a function of phenology for common crop species.
Highlights
Terrestrial biogeochemical cycles are primarily driven by plant physiological and ecological processes involving the exchange of matter and energy, such as photosynthesis and evapotranspiration [1,2,3]
This paper presents the results of an extensive experiment aimed at the assessment of the PROSPECT radiative transfer model leaf parameter (Ns) as a function of phenological class, and whether water content would indirectly influence the estimation of the Ns parameter
The results indicate a significant difference between Ns estimated on the considered monocotyledon and dicotyledon plants, and new findings of a significant difference between Ns estimated at different phenological stages
Summary
Terrestrial biogeochemical cycles are primarily driven by plant physiological and ecological processes involving the exchange of matter and energy, such as photosynthesis and evapotranspiration [1,2,3]. Knowledge of plant canopy biochemical composition provides critical information towards understanding and predicting the flow of energy and matter within terrestrial biogeochemical cycles [4,5]. Empirical methods, which rely on statistical relationships of observed phenomena with remote sensing measurements, are widely applied as being simple and computationally efficient. With this approach, multispectral reflectances are combined into vegetation indices, designed to maximize the sensitivity to parameters of interest while minimizing the influence of unrelated factors, including soil or atmospheric effects [9,10]. The vegetation indices are subsequently correlated to biochemical variables such as photosynthetically active pigments, water, and biomass
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