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Evaluation of global leaf area index and fraction of absorbed photosynthetically active radiation products over North America using Copernicus Ground Based Observations for Validation data

Evaluation of global leaf area index and fraction of absorbed photosynthetically active radiation products over North America using Copernicus Ground Based Observations for Validation data
Evaluation of global leaf area index and fraction of absorbed photosynthetically active radiation products over North America using Copernicus Ground Based Observations for Validation data
With a growing number of Earth observation (EO) products available through operational programmes such as the European Union’s Copernicus, there is increasing emphasis on product accuracy and uncertainty, necessitating evaluation against in situ reference measurements. Whilst existing reference datasets have proven a valuable resource, they incorporate little data with which products from recent EO instruments can be assessed. A reliance on individual field campaigns has also led to several inconsistencies, whilst limiting the extent to which temporal variations in EO product performance can be captured. Recently established environmental monitoring networks such as the National Ecological Observatory Network (NEON), which collect routine in situ measurements using standardised instruments and protocols, provide a promising opportunity in this respect. The Copernicus Ground Based Observations for Validation (GBOV) service was initiated in recognition of this fact. In the first component of the project, raw observations from existing networks have been collected and processed to provide reference data for a range of EO land products. In this study, we focus on leaf area index (LAI) and the fraction of absorbed photosynthetically active radiation (FAPAR). Raw digital hemispherical photography (DHP) from twenty NEON sites was processed to derive in situ reference measurements, which were then upscaled to provide high spatial resolution reference maps. Using these data, we assess the recently released Copernicus Global Land Service (CGLS) 300 m Version 1 (V1) products derived from PROBA-V, in addition to existing products derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Radiometer Suite (VIIRS). When evaluated against reference data, the CGLS 300 m V1 product demonstrated the best agreement (RMSD = 0.57 for LAI and 0.08 for FAPAR), followed by the Collection 6 VNP15A2H and MOD15A2H products (RMSD = 0.81 to 0.89 for LAI and 0.12 for FAPAR). Differing assumptions of the products and in situ reference measurements, which cause them to be sensitive to slightly different quantities, are thought to explain apparent biases over sparse vegetation and forest environments. To ensure their continued utility, future work should focus on updating the GBOV in situ reference measurements, implementing additional corrections, and improving their geographical representativeness.
Copernicus, FAPAR, GBOV, LAI, MODIS, PROBA-V, VIIRS, digital hemispherical photography, validation
0034-4257
1-22
Brown, Luke
3f3ee47e-ee1f-4a44-a223-36059b69ce92
Meier, Courtney
9b08ef14-ac47-4d1a-b2f1-a229bb940c29
Morris, Harry
d7b9d1e5-e105-40a3-9f5d-7c3e4531b32c
Pastor-Guzman, Julio
af286673-9f3f-44e9-9f2d-b367a2217c49
Bai, Gabriele
3f0dc99b-873c-4535-80e4-1e9af492b944
Lerebourg, Christophe
23ac5590-51eb-4104-a2b8-9dae3b487b59
Gobron, Nadine
19dfd40b-78e4-4067-be0b-ac8896dde032
Lanconelli, Christian
932b78e9-e5d4-414e-ad86-35bfeb9019c6
Clerici, Marco
3b1097db-25e6-41e2-bdbe-f0e0cfd96db9
Dash, Jadunandan
51468afb-3d56-4d3a-aace-736b63e9fac8
Brown, Luke
3f3ee47e-ee1f-4a44-a223-36059b69ce92
Meier, Courtney
9b08ef14-ac47-4d1a-b2f1-a229bb940c29
Morris, Harry
d7b9d1e5-e105-40a3-9f5d-7c3e4531b32c
Pastor-Guzman, Julio
af286673-9f3f-44e9-9f2d-b367a2217c49
Bai, Gabriele
3f0dc99b-873c-4535-80e4-1e9af492b944
Lerebourg, Christophe
23ac5590-51eb-4104-a2b8-9dae3b487b59
Gobron, Nadine
19dfd40b-78e4-4067-be0b-ac8896dde032
Lanconelli, Christian
932b78e9-e5d4-414e-ad86-35bfeb9019c6
Clerici, Marco
3b1097db-25e6-41e2-bdbe-f0e0cfd96db9
Dash, Jadunandan
51468afb-3d56-4d3a-aace-736b63e9fac8

Brown, Luke, Meier, Courtney, Morris, Harry, Pastor-Guzman, Julio, Bai, Gabriele, Lerebourg, Christophe, Gobron, Nadine, Lanconelli, Christian, Clerici, Marco and Dash, Jadunandan (2020) Evaluation of global leaf area index and fraction of absorbed photosynthetically active radiation products over North America using Copernicus Ground Based Observations for Validation data. Remote Sensing of Environment, 274, 1-22, [111935]. (doi:10.1016/j.rse.2020.111935).

Record type: Article

Abstract

With a growing number of Earth observation (EO) products available through operational programmes such as the European Union’s Copernicus, there is increasing emphasis on product accuracy and uncertainty, necessitating evaluation against in situ reference measurements. Whilst existing reference datasets have proven a valuable resource, they incorporate little data with which products from recent EO instruments can be assessed. A reliance on individual field campaigns has also led to several inconsistencies, whilst limiting the extent to which temporal variations in EO product performance can be captured. Recently established environmental monitoring networks such as the National Ecological Observatory Network (NEON), which collect routine in situ measurements using standardised instruments and protocols, provide a promising opportunity in this respect. The Copernicus Ground Based Observations for Validation (GBOV) service was initiated in recognition of this fact. In the first component of the project, raw observations from existing networks have been collected and processed to provide reference data for a range of EO land products. In this study, we focus on leaf area index (LAI) and the fraction of absorbed photosynthetically active radiation (FAPAR). Raw digital hemispherical photography (DHP) from twenty NEON sites was processed to derive in situ reference measurements, which were then upscaled to provide high spatial resolution reference maps. Using these data, we assess the recently released Copernicus Global Land Service (CGLS) 300 m Version 1 (V1) products derived from PROBA-V, in addition to existing products derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Radiometer Suite (VIIRS). When evaluated against reference data, the CGLS 300 m V1 product demonstrated the best agreement (RMSD = 0.57 for LAI and 0.08 for FAPAR), followed by the Collection 6 VNP15A2H and MOD15A2H products (RMSD = 0.81 to 0.89 for LAI and 0.12 for FAPAR). Differing assumptions of the products and in situ reference measurements, which cause them to be sensitive to slightly different quantities, are thought to explain apparent biases over sparse vegetation and forest environments. To ensure their continued utility, future work should focus on updating the GBOV in situ reference measurements, implementing additional corrections, and improving their geographical representativeness.

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Accepted/In Press date: 30 May 2020
e-pub ahead of print date: 23 June 2020
Published date: 15 September 2020
Keywords: Copernicus, FAPAR, GBOV, LAI, MODIS, PROBA-V, VIIRS, digital hemispherical photography, validation

Identifiers

Local EPrints ID: 441862
URI: http://eprints.soton.ac.uk/id/eprint/441862
ISSN: 0034-4257
PURE UUID: 1487e3f1-6f83-4629-9473-fd6dfeb52440
ORCID for Luke Brown: ORCID iD orcid.org/0000-0003-4807-9056
ORCID for Jadunandan Dash: ORCID iD orcid.org/0000-0002-5444-2109

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Date deposited: 30 Jun 2020 16:37
Last modified: 28 Apr 2022 02:21

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Contributors

Author: Luke Brown ORCID iD
Author: Courtney Meier
Author: Harry Morris
Author: Julio Pastor-Guzman
Author: Gabriele Bai
Author: Christophe Lerebourg
Author: Nadine Gobron
Author: Christian Lanconelli
Author: Marco Clerici
Author: Jadunandan Dash ORCID iD

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