HR: 1340h
AN: H23E-1669    [Abstracts]
TI: Tower Based Measurements of Bio-indicators Over the Growing Season at a Mature Douglas-fir Coniferous Forest
AU: * Cheng, Y
EM: ybcheng@ucdavis.edu
AF: NASA Goddard Space Flight Center, Code 614.4, Biospheric Sciences Branch, Earth Systems Science Building, Greenbelt, MD 20771, United States
AU: Hilker, T
EM: thilker@interchange.ubc.ca
AF: Faculty of Forest Resources Management, University of British Columbia, 2424 Main Mall, Vancouver, BC V6T 1Z4, Canada
AU: Middleton, E M
EM: Elizabeth.M.Middleton@nasa.gov
AF: NASA Goddard Space Flight Center, Code 614.4, Biospheric Sciences Branch, Earth Systems Science Building, Greenbelt, MD 20771, United States
AU: Coops, N C
EM: nicholas.coops@ubc.ca
AF: Faculty of Forest Resources Management, University of British Columbia, 2424 Main Mall, Vancouver, BC V6T 1Z4, Canada
AU: Black, T A
EM: andrew.black@ubc.ca
AF: Faculty of Land and Food Systems, University of British Columbia, 2357 Main Mall, Vancouver, BC V6T 1Z4, Canada
AU: Krishnan, P
EM: Praveena.Krishnan@ubc.ca
AF: Faculty of Land and Food Systems, University of British Columbia, 2357 Main Mall, Vancouver, BC V6T 1Z4, Canada
AB: The use of remotely sensed measurements collected by satellite, aircraft, and ground instruments to improve our understanding of ecological and hydrological processes were successfully demonstrated through the First International Satellite Land Surface Climatology (ISLSCP) Field Experiment [FIFE] and the BOReal Ecosystem- Atmosphere Study [BOREAS]. Following the concept of FIFE and BOREAS, we analyzed hyperspectral reflectance measurements collected at a coastal forest in British Columbia, Canada through the 2006 growing season. Diurnal and seasonal dynamics of the Photochemical Reflectance Index (PRI), a normalized difference spectral band-ratio index based on the xanthophyll signal at 531 nm which expresses protective responses to high light stress, were studied. This index has been shown to correlate with photosynthetic light use efficiency (LUE), an essential variable to model carbon uptake efficiency by plants. The measurements were collected from an automated system mounted on a flux tower under different sun and view geometries and atmospheric conditions through the 2006 growing season. Canopy structure was modeled using Light Detection and Ranging (LiDAR) technology, from which the sunlit and shaded canopy fractions were calculated as a function of incoming photosynthetically active radiation (PAR). These automated directional observations allowed us to: 1) investigate diurnal and seasonal changes of the PRI under different sky conditions; 2) compare the PRI with tower-based micro-meteorological measurements; and 3) separately investigate the PRI dynamics for sunlit and shaded partitions of the canopy which differ in response to their light environments. The data were categorized into six different groups based on two sky conditions (sunny and cloudy) and three illumination conditions (sunlit, shaded and intermediate). PRI showed a clear correlation with the LiDAR-based shadow fraction estimates. In April, the commencement of the growing season, clear diurnal dynamics of the PRI were observed for the sunlit foliage subset which showed lower (more negative) PRI values and a more dramatic change with sun altitude than shaded leaves. This was expected since leaves exposed to direct sunlight in their natural environment are likely under higher light stress. Consequently, diurnal changes of PRI and the differences among foliage groups were less obvious on overcast days because of limited direct irradiance. In August, when water availability was at its lowest of the year, the PRI exhibited relatively constant values throughout the day but with clear distinguishable values among the three leaf groups on sunny days. For other tower based measurements, PAR and GEP both showed clear seasonal patterns. Better estimates of the actual PAR intensity illuminating the sunlit and shaded canopy fractions were retrieved using the shadow fraction to reduce the above-canopy PAR. A clear seasonal pattern emerged for this revised PAR that distinguished among the groups and was also used to estimate LUE for the leaf groups. The correlation between PRI and LUE was confirmed. From these results, better understandings of the dynamics of carbon exchange bio-indicators that can be derived from directional hyperspectral reflectance measurements were demonstrated. Keywords: PRI, photosynthesis, PAR, GEP, LUE
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 1818 Evapotranspiration
DE: 1843 Land/atmosphere interactions (1218, 1631, 3322)
DE: 1878 Water/energy interactions (0495)
SC: Hydrology [H]
MN: 2007 Fall Meeting