1. College of Geo-exploration Science and Technology, Jilin University, Changchun 130026, China;
2. China Railway Design Corporation, Tianjin 130062, China;
3. First Activity Station, Xi'an Satellite Control Center, Weinan 714000, Shaanxi, China

To study the directionality of radiation emitted by high temperature targets in short wave infrared, a multi-angle observation physical model is established. The burning bamboo charcoal is used as a small-surface high temperature target, and the radiance of the high temperature targets is observed and analyzed from multi-angle by an ASD Field3 spectrometer under darkroom conditions. The observation data of multiple angles cannot be acquired simultaneously using only one spectrometer, and the temperature of the high temperature target changes significantly when observed at different angles. In this paper, a custom cooling model is used to calculate the reference radiance of multi-angle observations, and a concept -radiance ratio (multi-angle radiance/reference radiance) is proposed to eliminate the effect of high temperature target cooling. The results show that the accuracy of the cooling model is extremely high. The directionality of high-temperature targets can be well characterized by the concept of radiance ratio in short wave infrared radiation. High-precision fitting of the radiance ratio with angle can be achieved by a cosine function and a Fourier series.