Fig. 1. Geometric definition of bidirectional reflection distribution function

Fig. 2. Space angle definition of observation direction

Fig. 3. Reflectance envelope of light source perpendicular to wall surface

Fig. 4. Block diagram of wall reflection brightness measurement system

Fig. 5. Beam shaping

Fig. 6. Schematic diagram of wall reflection brightness light path

Fig. 7. RNN architecture

Fig. 8. LSTM node model

Fig. 9. Bi-LSTM network model

Fig. 10. Regression band and atmospheric window

Fig. 11. Luminance regression network structure

Fig. 12. Loss of RMSE during training

Fig. 13. Calibrate blackbody brightness and emissivity. (a) Radiance curve; (b) Emissivity curve

Fig. 14. Wall reflection radiance measurement experimental system. (a) Reflected radiation source; (b) MR170 radiometer

Fig. 15. Brightness curve measured in the direction of observation angle =35°. (a) 3-5 μm; (b) 8-14 μm 观测角度 =35°方向测量所得亮度曲线。 (a) 3~5 μm；(b) 8~14 μm

Fig. 16. Measurement results of each observation angle (3-5 μm). (a) Luminance regression curve; (b) BRDF curve

Fig. 17. Measurement results of each observation angle (8-14 μm). (a) Luminance regression curve; (b) BRDF curve