RT Journal Article
T1 Assessing scale-wise similarity of curves with a thick pen: As illustrated through comparisons of spectral irradiance
A1 Robson, Thomas Matthew
A1 Jach, Agnieszka Ewelina
A1 Grané Chávez, Aurea
AB Forest canopies create dynamic light environments in their understorey, where spectral composition changes among patterns of shade and sunflecks, and through the seasons with canopy phenology and sun angle. Plants use spectral composition as a cue to adjust their growth strategy for optimal resource use. Quantifying the ever-changing nature of the understorey light environment is technically challenging with respect to data collection. Thus, to capture the simultaneous variation occurring in multiple regions of the solar spectrum, we recorded spectral irradiance from forest understoreys over the wavelength range 300-800 nm using an array spectroradiometer. It is also methodologically challenging to analyze solar spectra because of their multi-scale nature and multivariate lay-out. To compare spectra, we therefore used a novel method termed thick pen transform (TPT), which is simple and visually interpretable. This enabled us to show that sunlight position in the forest understorey (i.e., shade, semi-shade, or sunfleck) was the most important factor in determining shape similarity of spectral irradiance. Likewise, the contributions of stand identity and time of year could be distinguished. Spectra from sunflecks were consistently the most similar, irrespective of differences in global irradiance. On average, the degree of cross-dependence increased with increasing scale, sometimes shifting from negative (dissimilar) to positive (similar) values. We conclude that the interplay of sunlight position, stand identity, and date cannot be ignored when quantifying and comparing spectral composition in forest understoreys. Technological advances mean that array spectroradiometers, which can record spectra contiguously over very short time intervals, are being widely adopted, not only to measure irradiance under pollution, clouds, atmospheric changes, and in biological systems, but also spectral changes at small scales in the photonics industry. We consider that TPT is an appl
SN 2045-7758
YR 2018
FD 2018-10-01
LK https://hdl.handle.net/10016/39011
UL https://hdl.handle.net/10016/39011
LA eng
NO TMR was supported by Academy of Finland project through the funding decisions # 266523 and # 304519. AJ and AG were partially supported by project MTM2014-56535-R of the Spanish Ministry of Economy and Competitiveness. We thank Lammi Biological Research Station of the University of Helsinki, Research Coordinator John Loehr and Director Janne Sundell, for logistical and practical support.
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RD 17 jul. 2024