Assessment of a photon recollision probability based forest reflectance model in European boreal and temperate forests

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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Remote Sensing of Environment, articlenumber 112804
We report a new version and an empirical evaluation of a forest reflectance model based on photon recollision probability (p). For the first time, a p-based approach to modeling forest reflectance was tested in a wide range of differently structured forests from different biomes. To parameterize the model, we measured forest canopy structure and spectral characteristics for 50 forest plots in four study sites spanning from boreal to temperate biomes in Europe (48°–62°N). We compared modeled forest reflectance spectra against airborne hyperspectral data at wavelengths of 450–2200 nm. Large overestimation occurred, especially in the near-infrared region, when the model was parameterized considering only leaves or needles as plant elements and assuming a Lambertian canopy. The model root mean square error (RMSE) was on average 80%, 80%, 54% for coniferous, broadleaved, and mixed forests, respectively. We suggest a new parameterization that takes into account the nadir to hemispherical reflectance ratio of the canopy and contribution of woody elements to the forest reflectance. We evaluated the new parameterization based on inversion of the model, which resulted in average RMSE of 20%, 15%, and 11% for coniferous, broadleaved, and mixed forests. The model requires only few structural parameters and the spectra of foliage, woody elements, and forest floor as input. It can be used in interpretation of multi- and hyperspectral remote sensing data, as well as in land surface and climate modeling. In general, our results also indicate that even though the foliage spectra are not dramatically different between coniferous and broadleaved forests, they can still explain a large part of reflectance differences between these forest types in the near-infrared, where sensitivity of the reflectance of dense forests to changes in the scattering properties of the foliage is high.
| openaire: EC/H2020/771049/EU//FREEDLES Funding Information: We would like to thank Tomáš Fabiánek for significant contributions in airborne data processing. Thanks also to Lukáš Fajmon, Petri Forsström, Karel Holouš, Mihkel Kaha, Bijay Karki, Lauri Korhonen, Nea Kuusinen, Andres Kuusk, Titta Majasalmi, Matti Mõttus, Ville Ranta, and the staff of Hyytiälä forestry field station for assistance and comments in various stages of field work, data processing, and interpretation. This study has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No 771049). The text reflects only the authors' view and the Agency is not responsible for any use that may be made of the information it contains. This study was also funded by the Academy of Finland grants BOREALITY (286390) and DIMEBO (323004). This study was also supported by the Ministry of Education, Youth and Sports of the Czech Republic within the CzeCOS program, grant number LM2018123 . Petr Lukeš acknowledges support by the project LTAUSA18154 awarded by the Ministry of Education, Youth and Sports of the Czech Republic. Jan Pisek acknowledges support by the Eesti Teadusagentuur (grant no. PUT1355). Publisher Copyright: © 2021 The Authors
Broadleaved, Coniferous, Forest, Hyperspectral, Leaf area index, Radiative transfer, Scattering, Spectra, Spectral invariants
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Hovi, A, Schraik, D, Hanuš, J, Homolová, L, Juola, J, Lang, M, Lukeš, P, Pisek, J & Rautiainen, M 2022, ' Assessment of a photon recollision probability based forest reflectance model in European boreal and temperate forests ', Remote Sensing of Environment, vol. 269, 112804 .