Fig. 1. Schematic of aerosol concentration distribution plane detection system

Fig. 2. Signal and histogram. (a) The original signal; (b) result of histogram equalization; (c) result of preprocessing; (d) histogram of the original signal; (e) histogram of Fig. 2(b); (f) histogram of Fig. 2(c)

Fig. 3. Flow chart of signal processing

Fig. 4. The original signal of aerosol flow field. (a)‒(e) Exhalation for 1 s, 15 s, 30 s, 50 s, 52 s; (f)‒(j) sedimentation for 1 s, 2 s, 6 s, 48 s, 60 s

Fig. 5. Processing results of aerosol flow field signal. (a) Preprocessed signal; (b) order assignment; (c) order squared assignment; (d) CLAHE

Fig. 6. Intensity transformation. (a) Order assignment; (b) order squared assignment

Fig. 7. Application of order squared assignment. (a) Signal with background noise; (b) result of order squared assignment applied on the signal in Fig. 7 (a)

Fig. 8. Results of order assignment applied on the signal in Fig.4. (a)‒(e) Exhalation for 1 s, 15 s, 30 s, 50 s, 52 s; (f)‒(j) sedimentation for 1 s, 2 s, 6 s, 48 s, 60 s

Fig. 9. Comparison of original signals and processed signals. (a)‒(d) Original signals ; (e)‒(h) processed signals

Fig. 10. Signal area and R_SB. (a) Schematic of signal areas; (b) R_SB of signal with different processing

Fig. 11. The R_SB of weak signals with different exhalation time processed by different processing