Application of Radiometric Surface Temperature for Surface Energy Balance Estimation: John Monteith's Contributions.

Over 25 years ago, Huband and Monteith paper’s investigating the radiative surface temperature and the surface energy balance of a wheat canopy, highlighted the key issues in computing fluxes with radiometric surface temperature.  These included the relationship between radiometric and aerodynamic surface temperature and the accuracy of radiometric surface temperature observations.  Almost 10 years later, John Norman and co-authors proposed a thermal-based land surface modeling strategy that treated the energy exchange and kinetic temperatures of the soil and vegetated components in a unique “Two-Source Energy Balance (TSEB) modeling approach.  The TSEB formulation addresses key factors affecting the convective and radiative exchange within the soil-canopy-atmosphere system, focusing on the relationship between radiometric and aerodynamic temperature.   This modeling approach came at a time when thermal-based techniques for large scale land surface flux and evapotranspiration (ET) estimation was generally considered unreliable and not viable for operational remote sensing applications.  The TSEB model has been and continues to be evaluated over a wide variety of landscapes and is shown to be fairly robust. In addition, the TSEB land surface scheme has been incorporated within in the Atmosphere Land EXchange Inverse/Disaggregation ALEXI ( ALEXI/DisALEXI ) modeling system, designed for operational applications at local to continental scales using multi-scale thermal imagery.  The ability of the TSEB to partition ET into evaporation and transpiration components provides additional hydrologic information about the moisture status of the soil and canopy system, and about the vertical distribution of moisture in the soil profile (surface layer vs. root zone).  The accuracy of this partitioning has not been thoroughly evaluated, however, recent studies under highly advective conditions suggest the original parameterization for canopy transpiration used in TSEB based on Priestley-Taylor should be replaced by the Penman-Monteith  formulation for more reliable partitioning between soil evaporation and canopy transpiration  components. This strategy for utilizing radiometric surface temperature in land surface modeling has invigorated many in the research and operational remote sensing communities to reconsider the utility of thermal infrared remote sensing for monitoring land surface fluxes from local to regional scales.