Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) is a Japanese sensor proposed to NASA EOS-am platform and Thermal Infrared Radiometer (TIR) is one of subsystems. ASTER TIR and Thermal Infrared Multispectral Scanner (TIMS), NASA/JPL airborne sensor, are unique because of their capabilities of multispectral and high spatial resolution observation of the earth surface in thermal infrared region.<BR>In this parer, the applicability of the split window technique to TIMS data was discussed. The split window technique is a surface temperature estimation technique widely applied to AVHRR data for global sea surface temperature retrieval.<BR>First, the effects of approximations used in this technique were examined. After that, computer simulations using LOWTRAN7 with several model atmospheres were carried out to investigate linear relations between surface and observed temperatures. These results indicate that TIMS Ch. 1 and 3, and 5 and 6 combinations are suitable for the split window application compared with other combinations.<BR>A technique to determine coefficients of the split window equation which fits local atmospheric conditions was also proposed. This technique uses one base model atmosphere and several different relative humidity profiles in the simulations, and the equation can correct effects of local variations of water vapor content from the base atmosphere. Linear relations between simulated temperatures were significantly improved because atmospheres used in the simulations were identical except their humidity profiles. As a result, it can be said that the split window technique is applicable to TIMS Ch. 1/3 and 5/6 combinations within. these simulation conditions.<BR>These split window equations were experimentally applied to TIMS data acquired over jasper Ridge, California. Though the atmosphere at jasper Ridge had less water vapor than Midlatitude Summer (MLS) model, the split window equations based on MLS model were able to correct the effects of this atmosphere properly. The effects of spectral variation of surface brightness temperature on the split window application were also found.