Toward Routine Mapping of Land-Surface Carbon, Water and Energy Fluxes at Field to Regional Scales
May 14, 2013 16:46:19
Description of Problem
In the absence of clouds, remotely sensed observations in the reflective solar and thermal infrared (TIR) domains have great utility for monitoring the terrestrial biosphere and vegetation dynamics at a range of spatial and temporal scales. The satellite signal in these wavebands is indirectly related to a variety of key biophysical and vegetation biochemical descriptors of the land surface that are needed for reliable assessments of land-surface carbon, water and energy fluxes.
Scientific Objectives and Approach
LAI or greenness data of some sort (e.g. NDVI) function as the primary remote sensing based control on vegetation dynamics in most current land surface models operating at local to global scales. Other important controls on vegetation processes are often treated less rigorously due to simplifying assumptions of the modeling systems or lack of suitable input data for an accurate spatio-temporal representation of the given parameter. The predictability of production efficiency models and coupled carbon, water and energy modeling systems, for instance, depend heavily on the setting of photosynthetic efficiency parameters, which are usually assigned fixed literature-based values for broad categories of vegetation environments. Chlorophyll content is being increasingly recognized as a key for quantifying photosynthetic efficiency and gross primary production of terrestrial vegetation. A key objective of this work is to research avenues for integrating remotely sensed leaf chlorophyll retrievals into coupled models of land-surface carbon, water and energy exchange.
We developed the REGularized canopy reFLECtance (REGFLEC) tool that integrates leaf optics, canopy reflectance, and atmospheric radiative transfer model components, facilitating direct use of at-sensor radiance observations in green, red, and near-infrared wavelengths for the retrieval of leaf chlorophyll and LAI at a range of spatial scales. Relative root-mean-square deviations for both variables were typically on the order of 10-15 % for agricultural regions in Maryland, Oklahoma and Texas. Results indicate significant potential for using remotely sensed leaf chlorophyll content for quantifying variability in photosynthetic efficiency across a heterogeneous corn field that was exposed to severe environmental stresses during the 2007 drought in Maryland, U.S.A. Maps of daily leaf chlorophyll, derived by fusing in-situ and image-based inferences, were well-correlated with temporal changes in nominal light-use-efficiency (LUE), which is used as a key input to a thermal-based two-source energy balance framework that implements a LUE-based model of stomatal conductance (TSEB_LUE) for coupling carbon and water fluxes. Comparison with flux tower eddy covariance observations demonstrated improved utility of TSEB_LUE to reproduce temporal patterns and magnitudes of carbon, water and energy exchange when using leaf chlorophyll to prescribe temporal changes in nominal LUE.
Refereed Journal Publications
Houborg, R., Anderson, M.C., Daughtry, C.S.T., Kustas, W.P., and Rodell, M. (2011). Using leaf chlorophyll to parameterize light-use-efficiency within a thermal-based carbon, water and energy exchange model. Remote Sensing Environ (in press).
Houborg, R., Anderson, M.C., Norman, J.M., Wilson, T., and Meyers, T., 2009: Intercomparison of a ‘bottom-up’ and ‘top-down’ modeling paradigm for estimating carbon and energy fluxes over a variety of vegetative regimes across the U.S. Agric. For. Meteorol., 149 (11), 1875-1895.
Houborg, R., and Anderson, M.C., 2009: Utility of an image-based canopy reflectance modeling tool for remote estimation of LAI and leaf chlorophyll content at regional scales. Journal of Applied Remote Sensing, 3(033529) 10.1117/1.3141522.
Houborg, R., M.C. Anderson, and C. Daughtry, 2009: Utility of an image-based canopy reflectance modeling tool for remote estimation of LAI and leaf chlorophyll content at the field scale. Remote Sensing of Environment, 113, 259-274.
Other Publications and Conferences
Houborg, R., Anderson, M.C., Kustas, W.P., & Rodell, M. (2010). Combining observations in the reflective solar and thermal domains for improved mapping of carbon, water and energy fluxes. Geoscience & Remote Sensing Symposium, IGARSS 2010, July 25 – 30, Hawaii, pp. 2648-2651.
Houborg, R., Anderson, M., Kustas, W.P., & Rodell, M. (2010). Combining Observations in the Reflective Solar and Thermal Domains for Improved Carbon and Energy Flux Estimation. Opportunities for Emerging Geospatial Technologies, ASPRS 2010, San Diego, 26-30 April.
Houborg, R., Anderson, M.C., Kustas, W.P., and Daughtry, C., 2009: A spatiotemporal analysis on the correlation of leaf chlorophyll with light-use-efficiencies across a heterogeneous corn field. Eos Trans. AGU, 90 (22), Jt. Assem. Suppl., Abstract H23B-11.
Houborg, R., Anderson, M.C., Daughtry, C., Kustas, W.P., Rodell, M., 2009: Combining observations in the reflective solar and thermal domains for estimating carbon and energy fluxes across a heterogeneous corn field. 2nd HyspIRI NASA Decadal Survey Mission Science Workshop, Pasadena, CA, 11-13 August, 2009.