Photosynthetic light-use efficiency of boreal forests derived from MODIS narrow-band reflectance data
Guillaume
Drolet, Centre d'Étude de la Forêt, Laval University, guillaume.drolet.1@ulaval.ca
(Presenting)
Elizabeth
M
Middleton, Biospheric Sciences Branch 614.4, NASA/GSFC, elizabeth.m.middleton@nasa.gov
Karl
F
Huemmrich, Joint Center for Earth Systems Technology-UMBC, karl.huemmrich@gsfc.nasa.gov
Forrest
G
Hall, Joint Center for Earth Systems Technology-UMBC, fghall@ltpmail.gsfc.nasa.gov
Hank
A.
Margolis, Centre d'Étude de la Forêt, Laval University, hank.margolis@sbf.ulaval.ca
Direct estimation of photosynthetic light-use efficiency (LUE) from space would be of significant benefit to LUE-based productivity models which use inputs from remote sensing to estimate terrestrial productivity. The Photochemical Reflectance Index (PRI) has shown promise in tracking LUE at the leaf- to small canopy levels, but its use at regional to global scales still remains a challenge. In this study, we used different formulations of PRI calculated from the MODIS ocean band centered at 531 nm and a set of alternative reference bands at 488, 551, and 678 nm to explore the relationship between PRI and LUE where LUE was measured at eight eddy covariance flux towers located in Saskatchewan, Canada.
We used one of the derived PRI-LUE models to create a 47,500 km2 regional LUE90a (90-minute average) map for three cover types in the study. The MODIS PRI-derived LUE90a map appeared to capture more realistic spatial heterogeneity of LUE across the landscape compared to a daily LUE map derived using the MODIS GPP (MOD17) algorithm. While our LUE map is only a snapshot of minimum regional LUE90a values, with appropriate gap-filling methods it could be used to improve regional-scale monitoring of GPP. Moreover, the strong relationship between midday and daily LUE on clear days (r2 = 0.93) indicates that instantaneous MODIS observations of LUE90a could be used to estimate daily LUE.
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