1. Date of download: 6/21/2016 Copyright © 2016 SPIE. All rights reserved. The realization of “grid translation method.” The original grid is 4×4 and the moving distance of each time is 1/3 side length of the cell. Figure Legend: From: Mapping of methane spatial distribution around biogas plant with an open-path tunable diode absorption spectroscopy scanning system Opt. Eng. 2013;52(2):026203-026203. doi:10.1117/1.OE.52.2.026203

2. Date of download: 6/21/2016 Copyright © 2016 SPIE. All rights reserved. The structure of the experimental site. Figure Legend: From: Mapping of methane spatial distribution around biogas plant with an open-path tunable diode absorption spectroscopy scanning system Opt. Eng. 2013;52(2):026203-026203. doi:10.1117/1.OE.52.2.026203

3. Date of download: 6/21/2016 Copyright © 2016 SPIE. All rights reserved. The structure of the optical path used in methane detection (a) The optical rays used in MLEM scanning, (b) The optical rays used in SBFM scanning. Figure Legend: From: Mapping of methane spatial distribution around biogas plant with an open-path tunable diode absorption spectroscopy scanning system Opt. Eng. 2013;52(2):026203-026203. doi:10.1117/1.OE.52.2.026203

4. Date of download: 6/21/2016 Copyright © 2016 SPIE. All rights reserved. The reconstruction maps of methane mixing ratio obtained by the MLEM algorithm. Figure Legend: From: Mapping of methane spatial distribution around biogas plant with an open-path tunable diode absorption spectroscopy scanning system Opt. Eng. 2013;52(2):026203-026203. doi:10.1117/1.OE.52.2.026203

5. Date of download: 6/21/2016 Copyright © 2016 SPIE. All rights reserved. The reconstruction maps of methane mixing ratio obtained by the SBFM algorithm. Figure Legend: From: Mapping of methane spatial distribution around biogas plant with an open-path tunable diode absorption spectroscopy scanning system Opt. Eng. 2013;52(2):026203-026203. doi:10.1117/1.OE.52.2.026203