Fig. 1. (a) Schematic diagram of long-range point target detection; (b) Working principle of infrared spectral system

Fig. 2. (a) Variation of number of wavebands with mean deviations of equivalent temperature and true value ; (b) Variation of number of wavebands with mean deviations of equivalent area and true value

Fig. 3. Long wave (8–12 μm). (a) Variation of equivalent temperature standard deviation with wave band number and SNR; (b) Variation of equivalent area standard deviation with wave band number and SNR

Fig. 4. Mid wave (3–5 μm) and long wave (8–12 μm). (a) Variation of equivalent temperature standard deviation with wave band number and SNR; (b) Variation of equivalent area standard deviation with wave band number and SNR

Fig. 5. Inconsistency of signal-to-noise ratio between mid wave and long wave. (a) Variation of equivalent temperature standard deviation with wave band number and SNR of mid wave; (b)Variation of equivalent area standard deviation with wave band number and SNR of long wave

Fig. 6. Inconsistency of wave band number between mid wave and long wave. (a) Variation of equivalent temperature standard deviation with wave band number; (b) Variation of equivalent area standard deviation with wave band number

Fig. 7. Variation of photon flux density of atmospheric background with field angle for (a) Mid wave; (b) Long wave

Fig. 8. For a target with temperature of 300 K and area of 20 m². (a) Standard deviation of equivalent temperature varies with distance; (b) Standard deviation of equivalent area varies with distance

Fig. 9. For a target with distance of 2 000 km and area of 20 m². (a) Standard deviation of equivalent temperature varies with target’s temperature; (b) Standard deviation of equivalent area varies with target’s temperature

Fig. 10. For a target with distance of 2 000 km and temperature of 300 K. (a) Standard deviation of equivalent temperature varies with target’s area; (b) Standard deviation of equivalent area varies with target’s area