If you are using ENVi 3.4 or more, an aster l1b image is already corrected in radiance. 1)Check in the data header info,if all tir bands have the proper wavelenght unit in micrometer. 2)Apply the TIR-Thermal atmosferic correction 3)Apply the EMISSIVITY NORMALIZATION or REFERENCE CHANNEL to extract emissivity and temperature I think is better study on a night image for geothermal exploration, or the combination between a day and a night image in order to calculate thermal inertia. If you are using ENVi 3.4 or more, an aster l1b image is already corrected in radiance. 1)Check in the data header info,if all tir bands have the proper wavelenght unit in micrometer. 2)Apply the TIR-Thermal atmosferic correction 3)Apply the EMISSIVITY NORMALIZATION or REFERENCE CHANNEL to extract emissivity and temperature I think is better study on a night image for geothermal exploration, or the combination between a day and a night image in order to calculate thermal inertia. If you are using ENVi 3.4 or more, an aster l1b image is already corrected in radiance. 1)Check the wavelenght unit in the data header info. All tir bands must have the proper wavelenght unit in micrometer. 2)Apply the TIR-Thermal atmosferic correction only to the 5 TIR bands. 3)Apply the EMISSIVITY NORMALIZATION or REFERENCE CHANNEL to extract emissivity and temperature Using ASTER in geothermal explorationI, it is better study on a night image, or the combination between a day and a night image, in order to calculate thermal inertia. Luca www.chartagena.com