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Fiducial reference measurements for vegetation bio-geophysical variables: An end-to-end uncertainty evaluation framework

Fiducial reference measurements for vegetation bio-geophysical variables: An end-to-end uncertainty evaluation framework
Fiducial reference measurements for vegetation bio-geophysical variables: An end-to-end uncertainty evaluation framework
With a wide range of satellite-derived vegetation bio-geophysical products now available to users, validation efforts are required to assess their accuracy and fitness for purpose. Substantial progress in the validation of such products has been made over the last two decades, but quantification of the uncertainties associated with in situ reference measurements is rarely performed, and the incorporation of uncertainties within upscaling procedures is cursory at best. Since current validation practices assume that reference data represent the truth, our ability to reliably demonstrate compliance with product uncertainty requirements through conformity testing is limited. The Fiducial Reference Measurements for Vegetation (FRM4VEG) project, initiated by the European Space Agency, is aiming to address this challenge by applying metrological principles to vegetation and surface reflectance product validation. Following FRM principles, and in accordance with the International Standards Organisation’s (ISO) Guide to the Expression of Uncertainty in Measurement (GUM), for the first time, we describe an end-to-end uncertainty evaluation framework for reference data of two key vegetation bio-geophysical variables: the fraction of absorbed photosynthetically active radiation (FAPAR) and canopy chlorophyll content (CCC). The process involves quantifying the uncertainties associated with individual in situ reference measurements and incorporating these uncertainties within the upscaling procedure (as well as those associated with the high-spatial-resolution imagery used for upscaling). The framework was demonstrated in two field campaigns covering agricultural crops (Las Tiesas–Barrax, Spain) and deciduous broadleaf forest (Wytham Woods, UK). Providing high-spatial-resolution reference maps with per-pixel uncertainty estimates, the framework is applicable to a range of other bio-geophysical variables including leaf area index (LAI), the fraction of vegetation cover (FCOVER), and canopy water content (CWC). The proposed procedures will facilitate conformity testing of moderate spatial resolution vegetation bio-geophysical products in future validation exercises.
CCC, FAPAR, FRM, Upscaling, Validation
2072-4292
Brown, Luke
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Camacho, Fernando
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García-Santos, Vicente
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Origo, Niall
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Fuster, Beatriz
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Morris, Harry
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Pastor-Guzman, Julio
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Sánchez-Zapero, Jorge
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Morrone, Rosalinda
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Ryder, James
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Nightingale, Joanne
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Boccia, Valentina
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Dash, Jadunandan
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Brown, Luke
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Camacho, Fernando
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García-Santos, Vicente
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Origo, Niall
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Fuster, Beatriz
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Morris, Harry
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Pastor-Guzman, Julio
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Sánchez-Zapero, Jorge
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Morrone, Rosalinda
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Ryder, James
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Nightingale, Joanne
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Boccia, Valentina
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Dash, Jadunandan
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Brown, Luke, Camacho, Fernando, García-Santos, Vicente, Origo, Niall, Fuster, Beatriz, Morris, Harry, Pastor-Guzman, Julio, Sánchez-Zapero, Jorge, Morrone, Rosalinda, Ryder, James, Nightingale, Joanne, Boccia, Valentina and Dash, Jadunandan (2021) Fiducial reference measurements for vegetation bio-geophysical variables: An end-to-end uncertainty evaluation framework. Remote Sensing, 13 (16), [3194]. (doi:10.3390/rs13163194).

Record type: Article

Abstract

With a wide range of satellite-derived vegetation bio-geophysical products now available to users, validation efforts are required to assess their accuracy and fitness for purpose. Substantial progress in the validation of such products has been made over the last two decades, but quantification of the uncertainties associated with in situ reference measurements is rarely performed, and the incorporation of uncertainties within upscaling procedures is cursory at best. Since current validation practices assume that reference data represent the truth, our ability to reliably demonstrate compliance with product uncertainty requirements through conformity testing is limited. The Fiducial Reference Measurements for Vegetation (FRM4VEG) project, initiated by the European Space Agency, is aiming to address this challenge by applying metrological principles to vegetation and surface reflectance product validation. Following FRM principles, and in accordance with the International Standards Organisation’s (ISO) Guide to the Expression of Uncertainty in Measurement (GUM), for the first time, we describe an end-to-end uncertainty evaluation framework for reference data of two key vegetation bio-geophysical variables: the fraction of absorbed photosynthetically active radiation (FAPAR) and canopy chlorophyll content (CCC). The process involves quantifying the uncertainties associated with individual in situ reference measurements and incorporating these uncertainties within the upscaling procedure (as well as those associated with the high-spatial-resolution imagery used for upscaling). The framework was demonstrated in two field campaigns covering agricultural crops (Las Tiesas–Barrax, Spain) and deciduous broadleaf forest (Wytham Woods, UK). Providing high-spatial-resolution reference maps with per-pixel uncertainty estimates, the framework is applicable to a range of other bio-geophysical variables including leaf area index (LAI), the fraction of vegetation cover (FCOVER), and canopy water content (CWC). The proposed procedures will facilitate conformity testing of moderate spatial resolution vegetation bio-geophysical products in future validation exercises.

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remotesensing-13-03194
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Accepted/In Press date: 9 August 2021
Published date: 12 August 2021
Additional Information: Funding Information: Funding: This study has been undertaken using data from “Fiducial Reference Measurements for Vegetation—Phase 1” (FRM4VEG—Phase 1), which was funded by the European Commission and managed by the European Space Agency under the Copernicus programme. Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
Keywords: CCC, FAPAR, FRM, Upscaling, Validation

Identifiers

Local EPrints ID: 450920
URI: http://eprints.soton.ac.uk/id/eprint/450920
ISSN: 2072-4292
PURE UUID: 2755dfcc-45cf-4c68-8b30-40c0048b441e
ORCID for Luke Brown: ORCID iD orcid.org/0000-0003-4807-9056
ORCID for Jadunandan Dash: ORCID iD orcid.org/0000-0002-5444-2109

Catalogue record

Date deposited: 20 Aug 2021 16:38
Last modified: 18 Apr 2024 01:52

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Contributors

Author: Luke Brown ORCID iD
Author: Fernando Camacho
Author: Vicente García-Santos
Author: Niall Origo
Author: Beatriz Fuster
Author: Harry Morris
Author: Julio Pastor-Guzman
Author: Jorge Sánchez-Zapero
Author: Rosalinda Morrone
Author: James Ryder
Author: Joanne Nightingale
Author: Valentina Boccia
Author: Jadunandan Dash ORCID iD

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