TAILIEUCHUNG - Air Pollution Part 13

Tham khảo tài liệu 'air pollution part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Air quality monitoring using CCD CMOS devices 293 out using data collected by a webcam K. L. Low 2007 and Penang Bridge CCTV system. K. L. Low 2006 2007 2007 2. Methodology In this study a modification was made to the model developed by Ahmad and Hashim 1997 . Skylight is an indirect radiation which occurs when the radiation from the sun being scattered by elements within the air pollutant column. It is not a direct radiation which is dominated by pixels on the reference surface. Figure 2 shows electromagnetic radiation path propagating from the sun towards the digital camera penetrating through the air pollutant column Source Modified after Ahmad and Hashim 1997 . PIXEL Wall Of A Building Radiation Reflected Or Scattered Incoming Radiation From The Sun CCTV Camera Atmospheric Pollutant Column And Direct Towards IP Camera Atmosphere Suspended Particular Matter I Carbon Monoxide PM10 CO Colour Paper I Wall Of A Building As A Know Reference 0 m Distance 200 m Fig. 2. The skylight parameter model Source Modified after Ahmad and Hashim 1997 294 Air Pollution The modified model is described by Rs - Rr Ra 5 where Rs reflectance recorded by IP camera sensor Rr reflectance from the known reference and Ra reflectance from atmospheric scattering. Algorithm Model The atmospheric reflectance due to molecule Rr is given by Liu et al. 1996 Rr - TrPr 0 4PsPy 6 where Tr Aerosol optical thickness Molecule Pr 0 Rayleigh scattering phase function pv Cosine of viewing angle and qs Cosine of solar zenith angle. We assume that the atmospheric reflectance due to particle Ra is also linear with the Ta King et al. 1999 and Fukushima et al. 2000 . This assumption is valid because Liu et al. 1996 also found the linear relationship between both aerosol and molecule scattering. R - TP Q 7 4AsA where Ta Aerosol optical thickness aerosol and Pa 0 Aerosol scattering phase function. Atmospheric reflectance is the sum of the particle reflectance and molecule reflectance Ratm Vermote et al. 1997