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      Prototyping Crop Traits Retrieval Models for CHIME: Dimensionality Reduction Strategies Applied to PRISMA Data

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          Abstract

          In preparation for new-generation imaging spectrometer missions and the accompanying unprecedented inflow of hyperspectral data, optimized models are needed to generate vegetation traits routinely. Hybrid models, combining radiative transfer models with machine learning algorithms, are preferred, however, dealing with spectral collinearity imposes an additional challenge. In this study, we analyzed two spectral dimensionality reduction methods: principal component analysis (PCA) and band ranking (BR), embedded in a hybrid workflow for the retrieval of specific leaf area (SLA), leaf area index (LAI), canopy water content (CWC), canopy chlorophyll content (CCC), the fraction of absorbed photosynthetic active radiation (FAPAR), and fractional vegetation cover (FVC). The SCOPE model was used to simulate training data sets, which were optimized with active learning. Gaussian process regression (GPR) algorithms were trained over the simulations to obtain trait-specific models. The inclusion of PCA and BR with 20 features led to the so-called GPR-20PCA and GPR-20BR models. The 20PCA models encompassed over 99.95% cumulative variance of the full spectral data, while the GPR-20BR models were based on the 20 most sensitive bands. Validation against in situ data obtained moderate to optimal results with normalized root mean squared error (NRMSE) from 13.9% (CWC) to 22.3% (CCC) for GPR-20PCA models, and NRMSE from 19.6% (CWC) to 29.1% (SLA) for GPR-20BR models. Overall, the GPR-20PCA slightly outperformed the GPR-20BR models for all six variables. To demonstrate mapping capabilities, both models were tested on a PRecursore IperSpettrale della Missione Applicativa (PRISMA) scene, spectrally resampled to Copernicus Hyperspectral Imaging Mission for the Environment (CHIME), over an agricultural test site (Jolanda di Savoia, Italy). The two strategies obtained plausible spatial patterns, and consistency between the two models was highest for FVC and LAI ( R 2 = 0.91, R 2 = 0.86) and lowest for SLA mapping ( R 2 = 0.53). From these findings, we recommend implementing GPR-20PCA models as the most efficient strategy for the retrieval of multiple crop traits from hyperspectral data streams. Hence, this workflow will support and facilitate the preparations of traits retrieval models from the next-generation operational CHIME.

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          Wrappers for feature subset selection

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            Principal component analysis: a review and recent developments.

            Large datasets are increasingly common and are often difficult to interpret. Principal component analysis (PCA) is a technique for reducing the dimensionality of such datasets, increasing interpretability but at the same time minimizing information loss. It does so by creating new uncorrelated variables that successively maximize variance. Finding such new variables, the principal components, reduces to solving an eigenvalue/eigenvector problem, and the new variables are defined by the dataset at hand, not a priori, hence making PCA an adaptive data analysis technique. It is adaptive in another sense too, since variants of the technique have been developed that are tailored to various different data types and structures. This article will begin by introducing the basic ideas of PCA, discussing what it can and cannot do. It will then describe some variants of PCA and their application.
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              Gaussian processes for machine learning

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                Author and article information

                Contributors
                Journal
                101624426
                Remote Sens (Basel)
                Remote Sens (Basel)
                Remote sensing
                2072-4292
                12 August 2022
                19 May 2022
                24 August 2022
                : 14
                : 10
                Affiliations
                [1 ]Image Processing Laboratory (IPL), University of Valencia, C/Catedrático José Beltran 2, 46980 Paterna, Valencia, Spain
                [2 ]Department of Geography, Ludwig-Maximilians-Universität München (LMU), Luisenstr. 37, 80333 Munich, Germany
                [3 ]Remote Sensing of Environmental Dynamics Laboratory (LTDA), University of Milano—Bicocca, Piazza della Scienza 1, 20126 Milano, Italy
                [4 ]Secretary of Research and Graduate Studies, Consejo Nacional de Ciencia y Tecnología, Universidad Autónoma de Nayarit, Tepic 63155, Nayarit, Mexico
                Author notes
                [* ] Correspondence: ana.b.pascual@ 123456uv.es
                Article
                EMS152688
                10.3390/rs14102448
                7613375
                36017157
                8e6c46bf-ca13-4621-ad5d-8c57ee7f9ebd

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license https://creativecommons.org/licenses/by/4.0/

                Categories
                Article

                prisma,chime,hybrid methods,biochemical and biophysical traits,gaussian process regression,active learning,principal component analysis,feature selection

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