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Tracking diurnal variation in photosynthetic down-regulation using low cost spectroscopic instrumentation.

van Leeuwen M, Kremens RL, van Aardt J - Sensors (Basel) (2015)

Bottom Line: The results demonstrate an excellent performance against a calibration standard (R2 = 0.9999) and at low light conditions.Radiance measurements over vegetation demonstrate a reversible reduction in green reflectance that was, however, seen in both the reference and signal wavebands.Effects of light quality, bidirectional scattering effects, and possible sensor artifacts on PRI are discussed.

View Article: PubMed Central - PubMed

Affiliation: Rochester Institute of Technology, Chester F. Carlson Center for Imaging Science, 54 Lomb Memorial Drive, Rochester, NY 14623, USA. vanleeuwen@cis.rit.edu.

ABSTRACT
Photosynthetic light-use efficiency (LUE) has gained wide interest as an input to modeling forest gross primary productivity (GPP). The photochemical reflectance index (PRI) has been identified as a principle means to inform LUE-based models, using airborne and satellite-based observations of canopy reflectance. More recently, low-cost electronics have become available with the potential to provide for dense in situ time-series measurements of PRI. A recent design makes use of interference filters to record light transmission within narrow wavebands. Uncertainty remains as to the dynamic range of these sensors and performance under low light conditions, the placement of the reference band, and methodology for reflectance calibration. This paper presents a low-cost sensor design and is tested in a laboratory set-up, as well in the field. The results demonstrate an excellent performance against a calibration standard (R2 = 0.9999) and at low light conditions. Radiance measurements over vegetation demonstrate a reversible reduction in green reflectance that was, however, seen in both the reference and signal wavebands. Time-series field measurements of PRI in a Douglas-fir canopy showed a weak correlation with eddy-covariance-derived LUE and a significant decline in PRI over the season. Effects of light quality, bidirectional scattering effects, and possible sensor artifacts on PRI are discussed.

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Change of the photochemical reflectance index (PRI) over time. Two largest discrepancies between observations and model fit represent days with lengthy periods of low-light conditions in mornings that caused visible noise in PRI data. R2 = 0.8 would have been achieved by selecting a shorter time span, e.g., 10 a.m. to 2 p.m.
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sensors-15-10616-f011: Change of the photochemical reflectance index (PRI) over time. Two largest discrepancies between observations and model fit represent days with lengthy periods of low-light conditions in mornings that caused visible noise in PRI data. R2 = 0.8 would have been achieved by selecting a shorter time span, e.g., 10 a.m. to 2 p.m.

Mentions: In addition to correlations between LUE and PRI, trends in PRI over time were examined and exhibited a strong linear decrease in PRI over the period March to July (R2 = 0.6), shown in Figure 11. The two largest errors in the model fit were caused by days with a prolonged period of low-light conditions and for these days some visible noise was observed in the PRI data. Restricting the time-of-day selection between 10 a.m. and 2 p.m. improved the model fit to R2 = 0.8 (data not shown). The decrease in PRI is likely linked to phenological changes, including chlorophyll:carotenoid ratio changes [13] and growth, as well as changes in irradiation quality and sun angle effects that could not be further examined using the collected data sets.


Tracking diurnal variation in photosynthetic down-regulation using low cost spectroscopic instrumentation.

van Leeuwen M, Kremens RL, van Aardt J - Sensors (Basel) (2015)

Change of the photochemical reflectance index (PRI) over time. Two largest discrepancies between observations and model fit represent days with lengthy periods of low-light conditions in mornings that caused visible noise in PRI data. R2 = 0.8 would have been achieved by selecting a shorter time span, e.g., 10 a.m. to 2 p.m.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4481939&req=5

sensors-15-10616-f011: Change of the photochemical reflectance index (PRI) over time. Two largest discrepancies between observations and model fit represent days with lengthy periods of low-light conditions in mornings that caused visible noise in PRI data. R2 = 0.8 would have been achieved by selecting a shorter time span, e.g., 10 a.m. to 2 p.m.
Mentions: In addition to correlations between LUE and PRI, trends in PRI over time were examined and exhibited a strong linear decrease in PRI over the period March to July (R2 = 0.6), shown in Figure 11. The two largest errors in the model fit were caused by days with a prolonged period of low-light conditions and for these days some visible noise was observed in the PRI data. Restricting the time-of-day selection between 10 a.m. and 2 p.m. improved the model fit to R2 = 0.8 (data not shown). The decrease in PRI is likely linked to phenological changes, including chlorophyll:carotenoid ratio changes [13] and growth, as well as changes in irradiation quality and sun angle effects that could not be further examined using the collected data sets.

Bottom Line: The results demonstrate an excellent performance against a calibration standard (R2 = 0.9999) and at low light conditions.Radiance measurements over vegetation demonstrate a reversible reduction in green reflectance that was, however, seen in both the reference and signal wavebands.Effects of light quality, bidirectional scattering effects, and possible sensor artifacts on PRI are discussed.

View Article: PubMed Central - PubMed

Affiliation: Rochester Institute of Technology, Chester F. Carlson Center for Imaging Science, 54 Lomb Memorial Drive, Rochester, NY 14623, USA. vanleeuwen@cis.rit.edu.

ABSTRACT
Photosynthetic light-use efficiency (LUE) has gained wide interest as an input to modeling forest gross primary productivity (GPP). The photochemical reflectance index (PRI) has been identified as a principle means to inform LUE-based models, using airborne and satellite-based observations of canopy reflectance. More recently, low-cost electronics have become available with the potential to provide for dense in situ time-series measurements of PRI. A recent design makes use of interference filters to record light transmission within narrow wavebands. Uncertainty remains as to the dynamic range of these sensors and performance under low light conditions, the placement of the reference band, and methodology for reflectance calibration. This paper presents a low-cost sensor design and is tested in a laboratory set-up, as well in the field. The results demonstrate an excellent performance against a calibration standard (R2 = 0.9999) and at low light conditions. Radiance measurements over vegetation demonstrate a reversible reduction in green reflectance that was, however, seen in both the reference and signal wavebands. Time-series field measurements of PRI in a Douglas-fir canopy showed a weak correlation with eddy-covariance-derived LUE and a significant decline in PRI over the season. Effects of light quality, bidirectional scattering effects, and possible sensor artifacts on PRI are discussed.

Show MeSH
Related in: MedlinePlus