Airborne thermal scanner is capable of obtaining terrestrial temperature distribution with high resolution and efficiency. One of the essential parameters is signal to noise ratio （SNR）

which determines the final quality of thermal image. There are several factors such as emissivity

temperature

and scanning angle

which contribute to the SNR and in this paper

their influences on SNR have been theoretically analyzed and approaches of enhancing the SNR have been supplied. By using Gauss-Laguerre approximation method

the contributions of temperature

emissivity and scanning angle to the SNR have been studied and their mathematical expressions are presented. The theoretical estimation indicates that the emissivity has the highest influence on SNR and the scanning angle has the least one. The influence of scanning angle tends to lower the SNR and the value varies with angles. Laboratory measurement has been made

and the discrepancy between the theoretically computed and measured values of SNR is within the permissive error scope

considering the difference between conditions and that utilized to simulate.