Submitted to: American Society for Photogrammetry and Remote Sensing Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 12, 2010
Publication Date: April 26, 2010
Citation: Houborg, R., Anderson, M.C., Kustas, W.P. 2010. Combining observations in the reflective solar and thermal domains for improved carbon and energy flux estimation. In: Proceedings of the American Society for Photogrammetry and Remote Sensing Proceedings, April 26-30, 2010, San Diego, California. Available: http://www.asprs.org/publications/proceedings/sandiego2010/.
This study investigates the utility of integrating remotely sensed estimates of leaf chlorophyll (Cab) into a therma-based Two-Source Energy Balance (TSEB) model that estimates land-surface CO2 and energy fluxes using an analytical, light-use-efficiency (LUE) based model of canopy resistance. The LUE model component computes canopy-scale carbon assimilation and transpiration fluxes and incorporates LUE modifications from a nominal(species-dependent) value (LUEn) in response to variations in environmental conditions. However LUEn needs adjustment on a daily timescale to accommodate changes in plant physiological condition and nutrient status. Day to day variations in LUEn were assessed for a corn crop field in Maryland U.S.A. through model calibration with CO2 flux tower observations. The optimized daily LUEn values were then compared to estimates of Cab integrated from gridded maps of chlorophyll content weighted over the tower flux source area. The time-continuous maps of daily Cab over the study field were generated by fusing in-situ measurements with retrievals generated with an integrated radiative transfer modeling tool using at-sensor radiances in green, red and near-infrared wavelengths acquired with an aircraft imaging system. The resultant daily changes in Cab within the tower flux source area exhibited a curvilinear relationship with corresponding changes in daily calibrated LUEn values derived from the tower flux data, and hourly water, energy and carbon flux estimation accuracies from TSEB were significantly improved when using Cab for delineating spatio-temporal variations in LUEn. The applicability of the established relationship between LUEn and Cab is currently being tested for an agricultural area near Bushland, Texas using a combination of reflective and thermal satellite imagery from SPOT, Landsat and ASTER.