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Calibration and characterisation of four chlorophyll meters and transmittance spectroscopy for non-destructive estimation of forest leaf chlorophyll concentration

Calibration and characterisation of four chlorophyll meters and transmittance spectroscopy for non-destructive estimation of forest leaf chlorophyll concentration
Calibration and characterisation of four chlorophyll meters and transmittance spectroscopy for non-destructive estimation of forest leaf chlorophyll concentration

Chlorophyll meters enable efficient and non-destructive estimation of leaf chlorophyll concentration (LCC), but require calibration against destructively-determined values to provide an absolute quantity that is comparable between different studies and species. Well-established instruments can provide accurate LCC estimates, but the performance of recent low-cost devices is less clear. Questions also remain over the choice of generic or species-specific calibration functions. Additionally, little attention has been paid to transmittance spectroscopy, which offers substantially increased spectral sampling, as a potential alternative. We investigated the well-established Konica Minolta SPAD-502+ and Opti-Sciences CCM-200 instruments and the low-cost atLEAF CHL PLUS and PhotosynQ MultispeQ V1.0 devices for non-destructive estimation of forest LCC. We calibrated each chlorophyll meter against destructively-determined LCC values for eight temperate deciduous broadleaf forest species, and characterised relationships between the different instruments. We also assessed whether transmittance spectroscopy could provide improved accuracy. All investigated chlorophyll meters demonstrated similarly strong relationships with destructively-determined LCC, indicating that once calibrated, even the low-cost devices represent a suitable choice for non-destructive forest LCC estimation. With the exception of oak, chlorophyll meter – LCC relationships were consistent between species, indicating that for these species, a generic calibration function may be suitable depending on required accuracy. Specifically, LCC values provided by the generic calibration functions fell within the prediction uncertainties of species-specific calibration functions for most considered species. The generic calibration functions explained between 2% and 16% less variation in LCC than the species-specific calibration functions, resulting in a mean increase in RMSE (NRMSE) of just 0.01 g m −2 to 0.02 g m −2 (2% to 5%). Transmittance spectroscopy was able to provide improved performance over the chlorophyll meters, indicating that they may miss some relevant spectral information at blue and green wavelengths. However, this improved performance comes at the expense of reduced practicality in the field.

CCI, CCM-200, Chlorophyll, MultispeQ, SPAD, atLEAF
0168-1923
Brown, Luke
3f3ee47e-ee1f-4a44-a223-36059b69ce92
Williams, Owen
83e2f0cc-b4fa-4366-abef-7f9968febad3
Dash, Jadunandan
51468afb-3d56-4d3a-aace-736b63e9fac8
Brown, Luke
3f3ee47e-ee1f-4a44-a223-36059b69ce92
Williams, Owen
83e2f0cc-b4fa-4366-abef-7f9968febad3
Dash, Jadunandan
51468afb-3d56-4d3a-aace-736b63e9fac8

Brown, Luke, Williams, Owen and Dash, Jadunandan (2022) Calibration and characterisation of four chlorophyll meters and transmittance spectroscopy for non-destructive estimation of forest leaf chlorophyll concentration. Agricultural and Forest Meteorology, 323, [109059]. (doi:10.1016/j.agrformet.2022.109059).

Record type: Article

Abstract

Chlorophyll meters enable efficient and non-destructive estimation of leaf chlorophyll concentration (LCC), but require calibration against destructively-determined values to provide an absolute quantity that is comparable between different studies and species. Well-established instruments can provide accurate LCC estimates, but the performance of recent low-cost devices is less clear. Questions also remain over the choice of generic or species-specific calibration functions. Additionally, little attention has been paid to transmittance spectroscopy, which offers substantially increased spectral sampling, as a potential alternative. We investigated the well-established Konica Minolta SPAD-502+ and Opti-Sciences CCM-200 instruments and the low-cost atLEAF CHL PLUS and PhotosynQ MultispeQ V1.0 devices for non-destructive estimation of forest LCC. We calibrated each chlorophyll meter against destructively-determined LCC values for eight temperate deciduous broadleaf forest species, and characterised relationships between the different instruments. We also assessed whether transmittance spectroscopy could provide improved accuracy. All investigated chlorophyll meters demonstrated similarly strong relationships with destructively-determined LCC, indicating that once calibrated, even the low-cost devices represent a suitable choice for non-destructive forest LCC estimation. With the exception of oak, chlorophyll meter – LCC relationships were consistent between species, indicating that for these species, a generic calibration function may be suitable depending on required accuracy. Specifically, LCC values provided by the generic calibration functions fell within the prediction uncertainties of species-specific calibration functions for most considered species. The generic calibration functions explained between 2% and 16% less variation in LCC than the species-specific calibration functions, resulting in a mean increase in RMSE (NRMSE) of just 0.01 g m −2 to 0.02 g m −2 (2% to 5%). Transmittance spectroscopy was able to provide improved performance over the chlorophyll meters, indicating that they may miss some relevant spectral information at blue and green wavelengths. However, this improved performance comes at the expense of reduced practicality in the field.

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Accepted/In Press date: 13 June 2022
e-pub ahead of print date: 24 June 2022
Published date: 15 August 2022
Additional Information: Funding Information: The authors thank the two anonymous reviewers for their constructive comments, which helped to substantially improve the manuscript. This study has been undertaken using data from “Fiducial Reference Measurements for Vegetation – Phase 2” (FRM4VEG – Phase 2), which was funded by the European Space Agency. The authors thank the Natural Environment Research Council (NERC) Field Spectroscopy Facility (FSF) for supplying equipment and training that enabled a pilot study leading to this work. Funding Information: The authors thank the two anonymous reviewers for their constructive comments, which helped to substantially improve the manuscript. This study has been undertaken using data from “Fiducial Reference Measurements for Vegetation – Phase 2” (FRM4VEG – Phase 2), which was funded by the European Space Agency . The authors thank the Natural Environment Research Council (NERC) Field Spectroscopy Facility (FSF) for supplying equipment and training that enabled a pilot study leading to this work. Publisher Copyright: © 2022 The Author(s)
Keywords: CCI, CCM-200, Chlorophyll, MultispeQ, SPAD, atLEAF

Identifiers

Local EPrints ID: 467917
URI: http://eprints.soton.ac.uk/id/eprint/467917
ISSN: 0168-1923
PURE UUID: 69cdd833-5537-4852-9178-d4cb03450fbc
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: 25 Jul 2022 16:46
Last modified: 31 Jan 2023 02:55

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Contributors

Author: Luke Brown ORCID iD
Author: Owen Williams
Author: Jadunandan Dash ORCID iD

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