 |
| Titel |
Retrieval of the photochemical reflectance index for assessing xanthophyll cycle activity: a comparison of near-surface optical sensors |
| VerfasserIn |
A. Harris, J. A. Gamon, G. Z. Pastorello, C. Y. S. Wong |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 22 ; Nr. 11, no. 22 (2014-11-21), S.6277-6292 |
| Datensatznummer |
250117682
|
| Publikation (Nr.) |
 copernicus.org/bg-11-6277-2014.pdf |
|
|
|
|
|
| Zusammenfassung |
| Unattended optical sensors are increasingly being deployed on eddy covariance
flux towers and are often used to complement existing vegetation and
micrometeorological measurements to enable assessment of biophysical states
and biogeochemical processes over a range of spatial scales. Of particular
interest are sensors that can measure the photochemical reflectance index
(PRI), which can provide information pertaining to leaf pigments and
photosynthetic activity. This interest has facilitated the production of a
new range of lower-cost multispectral sensors specifically designed to
measure temporal changes in the PRI signal. However, little is known about
the characteristics (spectral, radiometric and temporal) of many of these PRI
sensors, making it difficult to compare data obtained from these sensors
across time, geographical locations and instruments. Furthermore, direct
testing of the capability of these sensors to actually detect the conversion
of the xanthophyll cycle, which is the original biological basis of the PRI
diurnal signal, is largely absent, often resulting in an unclear
interpretation of the signal, particularly given the wide range of factors
now known to influence PRI. Through a series of experiments, we assess the
sensitivity of one of the leading brands of PRI sensor (Skye SKR 1800) to
changes in vegetation photosynthetic activity in response to changing
irradiance. We compare the results with those obtained using a more expensive
industry-standard visible to near-infrared hyperspectral spectrometer
(PP Systems UniSpec) and determine the radiometric compatibility of
measurements made by the different instruments. Results suggest that the SKR
1800 instrument is able to track rapid (seconds to minutes) and more gradual
diurnal changes in photosynthetic activity associated with xanthophyll cycle
pigment conversion. Measurements obtained from both the high and lower cost
instrument were significantly linearly correlated but were subject to a large
systematic bias, illustrating that differences in instrument configuration
(e.g. spectral response functions and band positions) can have a large impact
on the PRI measurement values obtained. Despite differences in absolute PRI
values, significant correlations were observed between the canopy PRI derived
from both the SKR 1800 and the UniSpec instruments, and the epoxidation state
of the xanthophyll cycle (r2 = 0.46 p < 0.05 and r2 = 0.76 p <
0.01, respectively). However, the dynamic range of the SKR 1800 PRI signal
was often lower than more expensive instruments and thus the lower cost
multispectral instrument may be less sensitive to pigment dynamics related to
photosynthetic activity. Based on our findings, we make a series of
recommendations for the effective use of such sensors under field conditions
and advocate that sensors should be fully characterized prior to their field
deployment. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|