A land surface index, defined as the difference of microwave land surface emissivity at 19 and 37 GHz, is calculated for a heavily forested area in north central Massachusetts. The microwave emissivity difference index (MEDI) is estimated from satellite SSM/I measurements at the defined wavelengths and used to estimate land surface turbulent fluxes. Narrowband visible and infrared measurements and broadband solar radiation observations are used in the MEDI retrievals and turbulent flux estimations. The collocated land surface turbulent and radiative fluxes were found empirically to be linked together by the MEDI values. The vertical component of the MEDI is statistically sensitive to the evapotranspiration (ET) fraction with a correlation coefficient (R) greater than 0.75. The products of MEDI and input energy (solar shortwave and photosynthetically-active radiation) are also statistically significantly correlated with ET (R=0.5) and CO2 uptake flux (R=0.79), respectively.