Karl
Fred
Huemmrich, UMBC, karl.f.huemmrich@nasa.gov
(Presenting)
Lawrence
Corp, SSAI, lcorp@hydrolab.ars.usda.gov
Andrew
Russ, USDA ARS, andrew.russ@ars.usda.gov
Elizabeth
M.
Middleton, NASA, elizabeth.m.middleton@nasa.gov
William
Kustas, USDA ARS, bill.kustas@ars.usda.gov
John
Prueger, USDA ARS, john.prueger@ars.usda.gov
Yen-Ben
Cheng, NASA, ybcheng@ucdavis.edu
Understanding global carbon cycle dynamics requires accurate determination of spatial and temporal distribution of photosynthetic CO2 uptake by vegetation. Remote sensing observations can provide data for this type of analysis as inputs to a light use efficiency model. These models describe gross ecosystem production (GEP) as the product of a photosynthetic efficiency term and absorbed photosynthetically active radiation (APAR). Light use efficiency (LUE) changes over time in response to environmental factors such as soil moisture, air temperature, and vapor pressure deficit. Stress conditions result in photosynthetic down-regulation of LUE and cause changes in the apparent spectral reflectance of leaves. We examine how narrow band vegetation indexes detect spectral changes and relate LUE over the course of a day and through the growing season. In a corn field in Beltsville, MD, carbon flux measurements were made at a flux tower using eddy covariance techniques. On six days during the 2007 growing season hyperspectral reflectance measurements were collected at hourly intervals along a 300-foot transect. LUE was determined at the time of the reflectance measurements from flux tower data. A number of spectral indices have been shown to be related to leaf characteristics including: the status of the xanthophyll cycle solar induced fluorescence leaf water content and concentrations of pigments such as chlorophyll, carotenoids, and anthocyanins. LUE values were compared with the indices examining relationships within a day and through the growing season. A number of indices provide good estimates of both diurnal and seasonal LUE. This methodology provides a nondestructive, repeatable, direct comparison between ecosystem carbon fluxes and spectral reflectance at scales relevant to remote sensing, developing approaches that can be used to monitor vegetation physiological status in future satellite missions.
NASA Carbon Cycle & Ecosystems Active Awards Represented by this Poster: