Abstract
The SO2 discharged by ships causes serious pollution to the atmosphere. Therefore, the International Maritime Organization has set strict requirements on the sulfur content of marine fuel. For the first time, this study investigates the optimal detection wavelength based on the imaging technology to realize an accurate monitoring of the SO2 concentration in ship exhaust. First, a simulation analysis model of the optimal imaging detection (SAMID) wavelength of the SO2 concentration in ship exhaust is proposed and analyzed in this study. Next, a bench experiment is designed. The values and the range of the gas concentration values required for the simulation are obtained. Finally, based on the principle of minimum error, the optimal detection wavelengths of the single- and the dual-wavelength imaging detection technologies are determined as 287 nm and 297 nm and 298 nm, respectively. During the SO2 concentration retrieval, the minimum values of the root mean squared error, the mean absolute error, and the mean absolute percentage error of the single- and the dual-wavelengths are 563.14 molecules/cm3, 445.11 molecules/cm3, and 347.22% and 0.62 molecules/cm3, 0.49 molecules/cm3, and 0.85%, respectively. The simulation analysis results provide a theoretical basis for the future hardware development of an optical remote sensing system based on the imaging detection technology.
Highlights
Since the beginning of the 20th century, the impact of ship emissions on the atmosphere has continued to increase as coal-fired ships started to replace sailing vessels
I=1 where I0 is the initial light intensity; I is the light intensity received by the optical system after extinction of the absorbing gas; L is the optical path length; λ is the light source spectrum wavelength; cso2 is the SO2 concentration; σso2 (λ) is the SO2 absorption cross-section corresponding to the wavelength; ci is the concentration of the other absorbing gases, except SO2 ; σi (λ) is the absorption cross-section of the other absorbing gases; and n is the number of the other types of absorbing gases. ln[I0 (λ)/I(λ)] is denoted by D(λ), which defines the optical thickness of the absorbed gas
The root mean square error (RMSE), the mean absolute error (MAE), and the mean absolute percentage error (MAPE) in different detection wavelengths were arranged in order from small to large according to the single-wavelength simulation analysis data obtained from SAMID
Summary
Since the beginning of the 20th century, the impact of ship emissions on the atmosphere has continued to increase as coal-fired ships started to replace sailing vessels. SO2 produces acid rain when it meets with rain in the atmosphere. This hugely affects the air and the ecological environment and damages human health. Law enforcement personnel mainly adopted the supervision method of sampling and inspection on board to detect the sulfur content of berthing ships and effectively monitor and control marine fuel quality. This approach is time consuming and laborious and cannot realize supervision of ships in the sea. The methods of measuring the SO2 concentration in ship exhaust and calculating the sulfur content of fuel according to the SO2 concentration are gradually being adopted
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