H23E-1667 

Monitoring Stand Level Photosynthesis from Spectral Reflectance

* Hilker, T (thilker@interchange.ubc.ca), University of British Columbia, 2424 Main Mall, Vancouver, BC V6T 1Z4, Canada Coops, N C), University of British Columbia, 2424 Main Mall, Vancouver, BC V6T 1Z4, Canada Hall, F G), University of Maryland, Joint Center for Earth Systems Technology, GSFC, Code 614.4, Greenbelt, MD 20771, United States Black, A T), University of British Columbia, 2357 Main Mall, Vancouver, BC V6T 1Z4, Canada Krishnan, P), University of British Columbia, 2357 Main Mall, Vancouver, BC V6T 1Z4, Canada Chen, B), University of British Columbia, 2357 Main Mall, Vancouver, BC V6T 1Z4, Canada Wulder, M A), Canadian Forest Service (PFC), 506 West Burnside Road, Victoria, BC V8Z 1M5, Canada Nesic, Z), University of British Columbia, 2357 Main Mall, Vancouver, BC V6T 1Z4, Canada Huemmrich, K F), University of Maryland, Joint Center for Earth Systems Technology, GSFC, Code 614.4, Greenbelt, MD 20771, United States Middleton, E M), NASA GSFC, Code 614.4, Biospheric Sciences Branch Earth Systems Science Building, Room G319, Greenbelt, MD 20771, United States Margolis, H A), Universite Laval, Pavillon Abitibi-Price, Québec, QC G1K 7P4, Canada Drolet, G), Universite Laval, Pavillon Abitibi-Price, Québec, QC G1K 7P4, Canada Cheng, Y), University of California, One Shields Avenue, Davis, CA 95616, United States

Global determination and monitoring of gross primary production (GPP) is a critical component of climate change research. On local scales, GPP can be assessed from measuring CO2 exchange above the plant canopy using tower-based eddy covariance (EC) systems. The limited footprint inherent to this method however, restricts observations to relatively few discrete areas making continuous predictions of global CO2 fluxes challenging. Recently, the advent of high resolution optical remote sensing devices has offered new possibilities to address some of the scaling issues related to GPP using approaches based on spectral reflectance. One key component for inferring GPP from remote sensing is the efficiency (e) with which plants can convert absorbed photosynthetically active radiation into biomass. Whilst recent years have seen progress determining e at the leaf level using the photochemical reflectance index PRI, little is known about the temporal and spatial requirements for upscaling PRI. For instance, satellite observations of canopy reflectance are subject to view and illumination geometry effects induced by the bi-directional reflectance distribution function (BRDF) of canopies that can confound the desired signal; however little is known about interactions between these effects and PRI. Further areas of research include dependencies of PRI on canopy structure, understorey and species composition. One potential way to investigate these requirements is using automated tower-based remote sensing platforms, facilitating spectral observations of the canopy with high spatial, temporal, and spectral resolution. The experimental setup presented herein features an automated spectral radiometer (AMSPEC) with a motor-driven probe allowing observations in a nearly full circle around the tower. Year round data are sampled every 5 sec., a full rotation is completed within 15 min. The spatial similarity to the flux-footprint allows direct comparisons with EC and micro-meteorological measurements, facilitating the investigation of interactions between meteorology and canopy reflectance. The wide range of illumination and viewing geometries permits comprehensive modeling of the BRDF under different physiological and atmospheric conditions. Diurnal and seasonal effects can be assessed from differences in year-round reflectance measurements and dependencies on canopy structure are derived using airborne Laser-scanning to relate PRI to canopy volume and canopy shadow fractions. Spatial dependencies are further assessed comparing EC and radiometer footprint using a meteorologically based modeling approach. Results from analytical study and reflectance observations demonstrate that PRI is useful for tracking diurnal and seasonal changes in canopy light use efficiency. Permanently established canopy reflectance measurements are vital components of ongoing research aiming at upscaling PRI based estimates of e to landscape, regional and global scales. Instruments like AMSPEC can help understanding physiological cycles of vegetation and serve as calibration tool for the broader band spectral observations available from satellite data. Ultimately, a comprehensive understanding of correlations between variations in e and PRI can help determining GPP from space.

H23E-1668 

Estimating Transpiration Of Temperate Deciduous Forest In Korea Using Sap Flow Measurements And Eco-hydrological Model

* JUNG, E (jungey@snu.ac.kr), Seoul National University, Graduate school of Environmental Studies, 82 dong, San 56-1, Sillim 9-dong, Gwanak-gu, Seoul, 151-019, Korea, Republic of Lee, B (puplebr@kangwon.ac.kr), Kangwon National University, Hyoja 2-dong, Gangwon-do, Chuncheon, 200-092, Korea, Republic of Kim, E (drummer76@empal.com), Seoul National University, Graduate school of Environmental Studies, 82 dong, San 56-1, Sillim 9-dong, Gwanak-gu, Seoul, 151-019, Korea, Republic of Lee, D (dwlee@snu.ac.kr), Seoul National University, Graduate school of Environmental Studies, 82 dong, San 56-1, Sillim 9-dong, Gwanak-gu, Seoul, 151-019, Korea, Republic of Kang, S), Kangwon National University, Hyoja 2-dong, Gangwon-do, Chuncheon, 200-092, Korea, Republic of Lim, J), Korea Forest Research institute, 57, Hoegi-dong, Dongdaemun-gu, Seoul, 130-872, Korea, Republic of Kim, J), Yonsei University, Sinchon-dong, Seodaemun-gu, Seoul, 120-749, Korea, Republic of

In forests, vegetation is a major factor in the hydrological cycle. Even though the studies of transpiration has been developed, transpiration in trees is still difficult to measure under natural conditions due to canopy heterogeneity, topography, and large size of trees of forest stands. In this study, transpiration was measured by using sap flow measurement, Thermal Diccipation Probe (TDP), first proposed by Granier (1985) in Gwangneung Research Forest, Pocheon-gun, Gyeonggi-do. Average estimated stand transpiration from measuring sap flow was 1.31mm/day (Maximum value : 2.31mm/day) in May and June. We compared this average stand transpiration with the simulated transpiration by eco-hydrological model, RHESSys (Regional Hydrologic Ecological Simulation System). As a result, we found simulated transpiration was highly overestimated. Thus, sap flow measurement has been underestimated transpiration relatively. This difference is possibly caused by scaling up the value from point to tree and stand level.

H23E-1669 

Tower Based Measurements of Bio-indicators Over the Growing Season at a Mature Douglas-fir Coniferous Forest

* Cheng, Y (ybcheng@ucdavis.edu), NASA Goddard Space Flight Center, Code 614.4, Biospheric Sciences Branch, Earth Systems Science Building, Greenbelt, MD 20771, United States Hilker, T (thilker@interchange.ubc.ca), Faculty of Forest Resources Management, University of British Columbia, 2424 Main Mall, Vancouver, BC V6T 1Z4, Canada Middleton, E M (Elizabeth.M.Middleton@nasa.gov), NASA Goddard Space Flight Center, Code 614.4, Biospheric Sciences Branch, Earth Systems Science Building, Greenbelt, MD 20771, United States Coops, N C (nicholas.coops@ubc.ca), Faculty of Forest Resources Management, University of British Columbia, 2424 Main Mall, Vancouver, BC V6T 1Z4, Canada Black, T A (andrew.black@ubc.ca), Faculty of Land and Food Systems, University of British Columbia, 2357 Main Mall, Vancouver, BC V6T 1Z4, Canada Krishnan, P (Praveena.Krishnan@ubc.ca), Faculty of Land and Food Systems, University of British Columbia, 2357 Main Mall, Vancouver, BC V6T 1Z4, Canada

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

H23E-1670 

Land Surface Skin Temperature and Its Variations from FIFE and Beyond

Dickinson, R E (robted@eas.gatech.edu), Georgia Institute of Technology, Georgia Institute of Technology Earth & Atmospheric Sciences 311 Ferst Drive, Atlanta, GA 30332, United States * Jin, M (mjin@atmos.umd.edu), University of Maryland, College Park, Department of Atmospheric and Oceanic Science University of Maryland, Collage Park, College ParkMD, MD 20742, United States

Land surface skin temperature is the radiometric temperature measured by thermal infrared radiometer. The difference between this variable and the conventional surface air temperature measured by WMO weather station reveals the properties of soil moisture, land cover, and boundary layer conditions. Using FIFE and other field measurements together with satellite retrievals, we examined the skin temperature diurnal, seasonal, and interannual variations, and try to understand the mechanisms responsible for such variations. Furthermore, our understanding helps to validate and improve land surface model simulations on skin temperature. In this presentation, we will show how FIFE contributes significantly to our understanding on land surface skin temperature, and the historical growth of our knowledge on this variable.

H23E-1671 

Estimation of vegetated land surface properties in BOREAS area using daily MAIAC-based MODIS images

* Zhang, Q (qingyuan@umbc.edu), GEST,UMBC, UMBC, Baltimore, MD 21228, Hall, F (fghall@ltpmail.gsfc.nasa.gov), JECT,UMBC, UMBC, Baltimore, MD 21228, Wang, Y (ywang@pop900.gsfc.nasa.gov), GEST,UMBC, UMBC, Baltimore, MD 21228, Lyapustin, A (alyapust@pop900.gsfc.nasa.gov), GEST,UMBC, UMBC, Baltimore, MD 21228,

We recently developed a framework to estimate vegetated land surface properties in BOREAS area. The properties include leaf area index (LAI), leaf chlorophyll content, leaf water, leaf dry matter, the fraction of photosynthetically active radiation (PAR) absorbed by chlorophyll (FAPARchl) of a canopy, light use efficiency (LUE), gross primary productivity (GPP) and phenology. We used daily MODerate resolution Imaging Spectroradiometer (MODIS) image produced through an advanced atmospheric correction algorithm, i.e., the Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm. MAIAC uses gridded MODIS multitemporal images to mask clouds and simultaneously retrieve atmospheric aerosol and surface bi- directional reflectance. Conceptually, only PAR absorbed by chlorophyll is used for photosynthesis, and therefore, there is a need to quantify FAPARchl. A coupled leaf-canopy radiative transfer model (PROPSECT+SAIL2, PROSAIL-2) with daily MODIS data as input was inverted with a Markov Chain Monte Carlo (MCMC) method (the Metropolis algorithm), which provides posterior distributions of retrieved variables. We ran the PROSAIL-2 model for ten sites in BOREAS area. Our study shows that it is important to make sure the input data of the PROSAIL-2 model are covering same target area. One way is to scale up the MODIS acquisitions. The leaf optics changes during plant growing season and should not be assumed as constants for a whole growing season. We found that biogeochemical models that use fraction of PAR absorbed by canopy (FAPARcanopy) and fraction of PAR absorbed by leaf (FAPARleaf) in estimating gross and net primary production are likely to overestimate the amount of PAR used in photosynthesis process, which represents one large source of error and uncertainty of estimation of productivity. This study also investigated the potential of using MODIS ocean band reflectance to estimate LUE over the ten sites. We may use only meteorological PAR and MODIS images to estimate GPP.

Author(s) (2007), Title, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract #####-##.