A thermal-based remote sensing technique for routine mapping of land-surface carbon, water and energy fluxes from field to regional scales M.C. Anderson a, ⁎, J.M. Norman b , W.P. Kustas a , R. Houborg a , P.J. Starks c , N. Agam a a USDA-ARS, Hydrology and Remote Sensing Lab, Bldg. 007, BARC-West, Beltsville, MD 20705, United States b Department of Soil Science, University of Wisconsin, Madison, WI, 53706, United States c USDA-ARS, Grazinglands Research Laboratory, El Reno, OK 73036, United States abstract article info Article history: Received 1 August 2007 Received in revised form 11 July 2008 Accepted 13 July 2008 Keywords: Carbon assimilation Evapotranspiration Thermal remote sensing Surface energy balance Soil respiration Robust yet simple remote sensing methodologies for mapping instantaneous land-surface fluxes of water, energy and CO 2 exchange within a coupled framework add significant value to large-scale monitoring networks like FLUXNET, facilitating upscaling of tower flux observations to address questions of regional carbon cycling and water availability. This study investigates the implementation of an analytical, light-use efficiency (LUE) based model of canopy resistance within a Two-Source Energy Balance (TSEB) scheme driven primarily by thermal remote sensing inputs. The LUE model computes coupled canopy-scale carbon assimilation and transpiration fluxes, and replaces a Priestley–Taylor (PT) based transpiration estimate used in the original form of the TSEB model. In turn, the thermal remote sensing data provide valuable diagnostic information about the sub-surface moisture status, obviating the need for precipitation input data and prognostic modeling of the soil water balance. Both the LUE and PT forms of the model are compared with eddy covariance tower measurements acquired in rangeland near El Reno, OK. The LUE method resulted in improved partitioning of the surface energy budget, capturing effects of midday stomatal closure in response to increased vapor pressure deficit and reducing errors in half-hourly flux predictions from 16 to 12%. The spatial distribution of CO 2 flux was mapped over the El Reno study area using data from an airborne thermal imaging system and compared to fluxes measured by an aircraft flying a transect over rangeland, riparian areas, and harvested winter wheat. Soil respiration contributions to the net carbon flux were modeled spatially using remotely sensed estimates of soil surface temperature, soil moisture, and leaf area index. Modeled carbon and water fluxes from this heterogeneous landscape compared well in magnitude and spatial pattern to the aircraft fluxes. The thermal inputs proved to be valuable in modifying the effective LUE from a nominal species-dependent value. The model associates cooler canopy temperatures with enhanced transpiration, indicating higher canopy conductance and carbon assimilation rates. The surface energy balance constraint in this modeling approach provides a useful and physically intuitive mechanism for incorporating subtle signatures of soil moisture deficiencies and reduced stomatal aperture, manifest in the thermal band signal, into the coupled carbon and water flux estimates. Published by Elsevier Inc. 1. Introduction Given the physical interconnections between the land-surface water, energy and carbon cycles, and the importance of understanding and quantifying these cycles as they apply to issues of climate change and water availability, there is benefit to developing robust yet simple remote sensing models that will simulate regional fluxes of latent and sensible heat and CO 2 exchange within a unified, self-consistent framework. Remote sensing models provide the spatial context for upscaling point flux measurements from large-scale tower networks like FLUXNET to assessments of the carbon and water budgets at the continental scale. In the remote sensing community, models of evapotranspiration and carbon flux have tended to evolve indepen- dently, using very different physical constraints and modeling approaches (e.g., energy balance vs. biogeochemical cycling). How- ever, because CO 2 and water exchanges at the leaf surface are jointly controlled by stomatal aperture, these fluxes can be well correlated in space and time at the landscape scale and such natural correlations are best reproduced by a coupled modeling approach. Furthermore, the additional constraints required to model the bulk canopy resistance and assimilation flux have the potential for improving estimates of ET from surface energy balance models, provided the required meteorological inputs and model parameters can be specified with adequate accuracy. The benefits of coupled modeling systems have been realized in many studies at the plant to canopy scales where biochemical models Remote Sensing of Environment 112 (2008) 4227–4241 ⁎ Corresponding author. Bldg 007, Rm 104 BARC-West, 10300 Baltimore Ave, Beltsville, MD 20705, United States. Tel.: +1 301 504 6616; fax: +1 301 505 8931. E-mail address: martha.anderson@ars.usda.gov (M.C. Anderson). 0034-4257/$ – see front matter. Published by Elsevier Inc. doi:10.1016/j.rse.2008.07.009 Contents lists available at ScienceDirect Remote Sensing of Environment journal homepage: www.elsevier.com/locate/rse