Fig. 1. Schematic diagram of smoke plume taken by SO₂ camera

Fig. 2. Simple diagram of neural network

Fig. 3. Flow chart of SO₂ emission rate

Fig. 4. SO₂ concentration inversion. (a) 310 nm optical density image; (b) 330 nm optical density image;(c) calibration curve; (d) SO₂ concentration image

Fig. 5. Original optical flow image (including plume cross-section for emission rate inversion)

Fig. 6. Speed of cross correlation method, Farneback optical flow and neural network optical flow method

Fig. 7. Emission rate retrieval of cross correlation method, Farneback optical flow and neural network optical flow method

Fig. 8. SO₂ emission rate of edge plume cross-section

Fig. 9. Mean SO₂ emission rates (a) and errors (b) for plume cross-sections in columns 1243-1343