The Moderate Resolution Imaging Spectroradiometer (MODIS) global land surface temperature (LST)/emissivity products supply daily, 8-day, and monthly global temperature and narrowband emissivity data. This article uses these products to calculate the surface long wave radiation of natural objects such as sand, soil, vegetation, etc., based on the Planck function and the Stefan-Boltzmann law. The results show that using the narrowband emissivity of a single band instead of the broadband emissivity results in large errors of up to 100 W m-2 of the calculated long wave radiation. A method to calculate broadband emissivity in the entire TIR spectral region from the narrowband emissivities of the MODIS bands (29, 31, and 32) in the thermal infrared region is proposed. Using the broadband emissivity, the surface long wave radiation could be calculated to an accuracy better than 6 W m-2 in the temperature region of 240--330 K, with a standard deviation of 1.22 W m-2, and a maximum error of 6.05 W m-2 (not considering the uncertainty associated with the MODIS LST/emissivity products themselves). The satellite estimated broadband emissivity was compared with 3-year (January 2001 to December 2003) ground-based measurements of emissivity at Gaize (32.30¿N, 84.06¿E, 4420 m) on the western Tibetan Plateau. The results show that the broadband emissivity calculated from MODIS narrowband emissivities by this method matches well the ground measurements, with a standard deviation of 0.0085 and a bias of 0.0015.