Fig. 1. Test optical path diagram

Fig. 2. Doppler frequency shift diagram of absorption spectrum signal

Fig. 3. Flow field discretization

Fig. 4. Beams projection arrangement

Fig. 5. Reconstruction result under 15 dB. (a1) Original spectral absorption coefficient field; (a2) reconstructed spectral absorption coefficient field; (a3) relative error distribution of spectral absorption coefficient field; (b1) original velocity field; (b2) reconstructed velocity field; (b3) relative error distribution of velocity field

Fig. 6. Variation of $E_u$ with SNR

Fig. 7. Reconstruction results under different velocity distribution gradients. (a1)‒(a3) Reconstruction results; (b1)‒(b3) error distribution

Fig. 8. Variation of $E_u$ with Gaussian standard deviation of velocity distribution

Fig. 9. Reconstruction results of bimodal velocity field. (a1) Original bimodal spectral absorption coefficient field; (a2) reconstructed spectral absorption coefficient field; (a3) error distribution of bimodal spectral absorption coefficient field; (b1) original bimodal velocity field; (b2) reconstructed velocity field; (b3) error distribution of velocity field

Fig. 10. Reconstruction results of different annular velocity fields. (a1)‒(a3) Reconstructed annular velocity field; (b1)‒(b3) reconstruction error distribution

Fig. 11. Beam arrangement patterns. (a) 3-group pattern; (b) 4-group pattern; (c) 5-group pattern

Fig. 12. Variation of $E_u$ with beam number under different beam arrangement patterns