The split window (SW) method is a technique for estimating surface temperature by the linear combination of the brightness temperatures measured from a satellite in two considered spectral channels in the thermal infrared window. The multi-channel (MC) method is an extension of the SW method; it uses the brightness temperatures measured in two or more channels for the estimation. The extended multi-channel (EMC) method is an extension of the MC method; its objective variable is not surface temperature, but the upward brightness temperature at surface level in each channel.<BR>In the case of applying these methods to land observations, the error based on the uncertainty of surface emissivity should be considered. We, therefore, researched the relationship between the error and the uncertainty of emissivity using the simulation data for NOAA12 AVHRR (channel 4 and 5) and EOS-AM1 ASTER (channel 10 to 14) under global conditions. The main results are as follows:<BR>1) The error of the SW method increases linearly with the uncertainty of emissivity. This result validates the Becker's error formula.<BR>2) The error based on the uncertainty of emissivity is significantly reduced by optimizing the equation to the uncertainty of emissivity using various emissivity data. And it is also reduced by increasing the number of channels and determining the equation with the emissivity data from spectral library.<BR>3) The error of the EMC method based on the uncertainty of emissivity depends on the channel, and converges as the uncertainty of emissivity increases.<BR>4) In no consideration of emissivity, the RMS error of the MC method is 0.8K for both AVHRR and ASTER. In the case that the domain of emissivity is from 0.98 to unity, the error is 1.0K for AVHRR and 0.7K for<BR>ASTER. And in the case that the domain of emissivity is from 0.95 to unity, the error is 1.5K for AVHRR and 1.0K for ASTER. For this domain, the RMS error of the EMC method for each channel is from 1.2 to 1.5K for AVHRR and from 0.9 to 1.1K for ASTER.