RADIOMETRIC AND EQUIVALENT ISOTHERMAL SURFACE TEMPERATURES

The analytical solution for the heat flux from an anisothermal canopy developed from K theory by Brutsaert and Sugita [1996] (hereinafter re ferred to as B&S) has been extended to provide a parameterization of t he difference between the radiometric and the equivalent isothermal su rface temperature. The latter is the isothermal temperature at which a canopy would give the correct sensible heat flux if the sensible heat roughness length z(0h) was given its theoretical, isothermal value de rived by B&S. A parameterization of the canopy temperature seen by a r adiometer is developed which incorporates the same foliage temperature profile as that used by B&S. From this the weighting fraction (i.e., the fraction of canopy top versus canopy bottom temperature ''seen'' b y the radiometer) can be derived, as can an equation for the view zeni th angle at which the radiometric and equivalent isothermal surface te mperatures are the same. Field data indicate that multiangle radiometr ic surface temperatures alone cannot determine the three unknowns desc ribing the foliage temperature profile. Several strategies to overcome this problem are outlined. The parameterization may eventually help t o interpret remotely sensed infrared surface temperatures and to impro ve estimates of sensible heat flux and evapotranspiration, but compreh ensive field testing is still needed.