Method and system for measuring exhaust emission rate of ship in real time based on foundation DOAS

Abstract

The invention relates to the technical field of ship emission monitoring, in particular to a method and system for measuring the ship exhaust emission rate in real time based on a foundation DOAS. The technical scheme comprises the following steps: installing and correcting an instrument; real-time data acquisition and processing, and an optimal estimation method based on Monte Carlo radiation transmission model simulation. Spectral information and distribution information of smoke plume emitted by a ship are collected in real time, a discrete Gaussian smoke plume model is established and input into a Monte Carlo radiation transmission model, the radiation transmission process of the smoke plume in the atmosphere is reconstructed, radiance data in a spectrograph view field are simulated and compared with actually-collected spectral information, and the smoke plume emission performance is improved. The exhaust emission rate of the ship is deduced through an optimal estimation method, and the characteristics of rapid and flexible measurement of a passive DOAS instrument are fully exerted.

Description

Technical Field

[0001] The present invention relates to the technical field of ship emission monitoring, and in particular to a method and system for real-time measurement of ship exhaust emission rate based on ground-based DOAS. Background Art

[0002] Ship exhaust emissions are an increasingly serious environmental problem, mainly including harmful substances such as sulfur dioxide (SO2), nitrogen oxides (NOx), particulate matter (PM) and carbon dioxide (CO2). These pollutants not only lead to a decline in air quality, but also pose a threat to human health. Exhaust emissions from ships can even directly affect ocean water quality, endanger marine life and ecological balance. In addition, the increase in greenhouse gases has also contributed to global warming and affected climate change. Therefore, the shipping industry is facing increasingly stringent environmental regulations and urgently needs to adopt more environmentally friendly technologies and management measures to achieve sustainable development.

[0003] Until now, fuel compliance has been checked by inspection bodies, who enter ships at anchor, review the fuel logbook and fuel quality certificate and, if suspicion arises, take fuel samples for analysis in certified laboratories. Based on the results of these analyses, compliance can be verified and, if needed, legal action can be taken. However, these controls can only check a small number of ships.

[0004] For monitoring ship emissions, some simple but effective methods are to use on-site instruments to directly measure polluting trace gases. The current technologies for monitoring ship emissions are mainly divided into sniffer technology and optical principle technology. Sniffing technology is widely used to collect and analyze exhaust emissions transmitted by wind. This technology captures the gas components flowing in the environment through a series of sensors and instrument systems. The sniffer is usually located far away from the emission source in order to collect and analyze the components of the gas propagated by the wind. Some other scholars install sniffers on drones or airplanes, and the airborne platform enters the ship's smoke plume to collect exhaust gas. Sniffer technology is currently the most widely used and convenient type of equipment, with flexible installation and low cost. However, it is greatly affected by environmental conditions, and the exhaust gas emitted by ships must be transmitted to the instrument to be detected.

[0005] Optical principle technology is theoretically less affected by the environment and the measurement results are more reliable. Optical principle technology is generally divided into DOAS instruments, laser radar (LIDAR), ultraviolet cameras, etc. Lidar technology is an active optical method that emits short pulse lasers into the atmosphere. Differential absorption laser radar (DIAL) can measure the concentration of gases in the atmosphere. It is achieved by emitting two or more pulses of different wavelengths. The wavelengths are selected so that one wavelength is absorbed more strongly than the other by the gas to be measured. The distance information along the laser beam path is still available, so the instrument determines the concentration at a known location in the atmosphere. The ultraviolet camera is composed of an ultraviolet charge coupled array (CCD) and an ultraviolet lens. Taking SO2 detection as an example, SO2 will cause attenuation of the recorded light intensity in the camera field of view. By calibrating the camera with a gas chamber containing a known amount of SO2, the recorded light intensity can be directly related to the path concentration. The camera can sample quickly, so it can track features in the image and obtain wind speed and gas flux in the plume. The DOAS principle analyzes gas concentration by measuring the difference in gas absorption of light within a specific wavelength range. Since it was proposed in 1979, it has been widely used in remote sensing monitoring of atmospheric pollutants.

[0006] DOAS instruments are divided into passive DOAS instruments and active DOAS instruments. Passive DOAS instruments rely on natural light sources as the illumination source for gas measurement, and are generally composed of an optical system and a detector. Active DOAS instruments, such as long-path DOAS (LP-DOAS), use active light sources, combining DOAS with lidar technology, illuminating the target area with an artificial laser light source, and measuring the reflection or scattering of the light signal to analyze the gas concentration. They are generally composed of lasers, reflectors, and detectors. Passive DOAS uses natural light sources and is affected by weather, but it is low-cost and suitable for large-scale monitoring. Active DOAS is not affected by weather, and its measurement accuracy is higher than that of passive DOAS.

[0007] The main purpose of applying DOAS instruments to ship emission regulation is to measure the emission rate of ship exhaust gas and determine whether the ship is in violation of regulations. Therefore, the identity of the ship must be identified and the results of the DOAS instrument measurement must be assigned to the specified ship. The current common ship identification technology is the Automatic Identification System (AIS). AIS is a system based on wireless communication between ships and between ships and shores, which is used to improve the safety of maritime traffic. AIS broadcasts its position, speed, heading and other information through equipment on the ship, and receives relevant data from other ships. On the other hand, the measurement of wind speed and direction is crucial for ship identification. The ship's plume is affected by natural wind transmission. The position of the ship's plume is generally the combined force of the relative wind generated by the ship's running speed and the real wind (natural wind).

[0008] For the monitoring of ship emissions during navigation, the existing monitoring methods cannot guarantee that the observation position is always at the chimney outlet of the ship. Therefore, the monitoring of the emission rate of a specific ship is often carried out by measuring the old smoke plume emitted by the ship and then combining it with the wind speed or Gaussian smoke plume model to estimate the emission rate at the chimney outlet.

[0009] From the above, the differential absorption spectroscopy (DOAS) technology has important value in ship exhaust monitoring. The non-contact monitoring method is suitable for real-time monitoring of ship emissions, especially in open waters and port environments. However, since ships are mobile emission sources and the exhaust gas emitted is usually a transparent and invisible target, it is difficult for DOAS instruments to determine the location of the observation target; at the same time, the measurement of ship exhaust emission rate is affected by factors such as the ship's own emission factors, fuel type, meteorological conditions (especially wind speed), background interference, and optical path uncertainty. Existing passive DOAS instruments are difficult to use in the field of ship exhaust measurement, and the advantages of DOAS instruments in real time and accuracy cannot be brought into play.

[0010] Therefore, we propose a method and system for real-time measurement of ship exhaust emission rate based on ground-based DOAS. Summary of the invention

[0011] The purpose of the present invention is to provide a ground-based DOAS observation system that combines an imaging spectrometer with a visual camera, an AIS receiver, and a meteorological sensor to collect the spectral information and distribution information of the smoke plume emitted by the ship in real time, establish a discrete Gaussian smoke plume model and input it into a Monte Carlo radiation transfer model, reconstruct the radiation transfer process of the smoke plume in the atmosphere, simulate the radiance data in the field of view of the spectrometer, and compare it with the actual collected spectral information, and infer the exhaust gas emission rate of the ship through the optimal estimation method.

[0012] On the one hand, the present invention proposes a method for real-time measurement of ship exhaust emission rate based on ground-based DOAS, comprising the following steps:

[0013] Installation and calibration of instruments, installation of optical lens, DOAS imaging spectrometer, visual camera, AIS receiver, matching of visual camera and spectrometer field of view and selection of observation line of sight;

[0014] Real-time data collection and processing, searching for the presence of pollutant emissions from the light intensity values ​​collected by the DOAS imaging spectrometer, aggregating the collected data and constructing the spatial distribution of the ship's emission plume;

[0015] Based on the optimal estimation method of Monte Carlo radiative transfer model simulation, the Gaussian plume model is added to the Monte Carlo radiative transfer model as an inhomogeneous medium, the collected radiance is simulated and compared with the actual collected radiance value, the source concentration parameters of the Gaussian plume are adjusted, and the actual emission concentration value is inferred.

[0016] Optionally, the DOAS imaging spectrometer is an ultraviolet DOAS imaging spectrometer with a wavelength band of 300nm to 400nm.

[0017] Optionally, the optical lens adopts a rectangular field of view of 5.5°×5.5°, and transmits the optical signal to the slit of the DOAS imaging spectrometer via an optical fiber.

[0018] Optionally, the field of view of the visual camera is 60°×30°.

[0019] Optionally, the light intensity values ​​collected by the DOAS imaging spectrometer are inverted to retrieve whether there are pollutant emissions from passing ships by inverting the concentration changes in the time dimension, and the spectral data corresponding to the peak concentration is converted into radiance data collected by the DOAS imaging spectrometer through radiation calibration.

[0020] Optionally, the spectral data is inverted automatically using the QDOAS tool, and the reference spectrum selects the zenith spectrum when no ship passes. After inversion, each piece of spectral data generates 49 concentration values ​​corresponding to 49 optical fibers. The concentration values ​​at different times constitute a concentration change curve in the time dimension, and the concentration curve in the time dimension is low-pass filtered to extract its peak change, and at the same time, the peak change below the gas concentration detection line of the DOAS imaging spectrometer is eliminated.

[0021] Optionally, there are 49 optical fibers, which are arranged as 7×7 at the optical lens end and 1×49 at the slit end. The optical fibers transpose the two-dimensional spatial image in the optical lens into a one-dimensional spatial image collected by the DOAS imaging spectrometer.

[0022] Optionally, the image position captured by the visual camera includes the position of the ship chimney. The effective height of the smoke plume emitted by the ship is related to the height of the chimney and the initial vertical velocity of the smoke plume. The calculation formula is as follows:

[0023]

[0024] Among them, h eff is the effective height of the plume, h stack is the chimney height, is the initial vertical velocity of the plume, and g is the acceleration due to gravity.

[0025] Optionally, the calculation formula of the Gaussian plume model is as follows:

[0026]

[0027] In the formula, C(x, y, z) represents the pollutant concentration at a distance of x meters downwind, y meters horizontally, and z meters in height from the emission source, Q is the emission rate of the emission source, and σ yis the lateral diffusion coefficient, σ z is the longitudinal diffusion coefficient, U is the wind speed at the emission height H, and H is the effective height of the emission source.

[0028] On the other hand, the present invention proposes a system for real-time measurement of ship exhaust emission rate based on ground-based DOAS, using the above-mentioned method, the system includes an industrial computer for controlling and processing data of each subsystem, and is characterized in that it also includes:

[0029] An optical lens and a DOAS imaging spectrometer connected to the optical lens, wherein the optical lens collects spectral information of the target and transmits it to an imaging circuit in the DOAS imaging spectrometer, and transmits the received optical signal to the industrial computer;

[0030] A visible camera mounted on a rotating pan / tilt head is used to identify the ship's position, collect information about the ship's appearance, and determine the field of view of the DOAS imaging spectrometer;

[0031] AIS receiver, which receives AIS data broadcast by nearby ships through an antenna;

[0032] Meteorological data system, obtains data related to wind direction, wind speed, temperature and air pressure in the observation area.

[0033] In summary, the present application includes at least one of the following beneficial technical effects:

[0034] The present invention proposes a ground-based DOAS observation system that combines an imaging spectrometer with a visual camera, an AIS receiver, and a meteorological sensor, collects the spectral information and distribution information of the smoke plume emitted by the ship in real time, establishes a discrete Gaussian smoke plume model and inputs it into a Monte Carlo radiation transmission model, reconstructs the radiation transmission process of the smoke plume in the atmosphere, simulates the radiance data in the spectrometer field of view, and compares it with the actual collected spectral information, and infers the exhaust gas emission rate of the ship through the optimal estimation method. The present invention is not affected by the optical path when calculating the ship emission rate, and gives full play to the fast and flexible measurement characteristics of the passive DOAS instrument.

[0035] The smoke plume model emitted by the ship is further defined in the Monte Carlo radiation transfer model, and the real instrument parameters are simulated to simulate the radiance under actual observation conditions. The emission rate of the pollutant gas from the ship is inferred by comparing it with the actual observation value through the optimal estimation method. This method can be applied to experimental scenarios under various observation conditions, avoiding the measurement error caused by the uncertainty of the integral path, and is suitable for more flexible experimental optical path design. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic diagram of a system for real-time measurement of ship exhaust emission rate based on ground-based DOAS according to the present invention;

[0037] Figure 2 This is a flow chart of the present invention for real-time monitoring of the emission rate of pollutant gases from ships;

[0038] Figure 3 Schematic diagram of the relationship between the field of view of the optical lens and the field of view of the DOAS imaging spectrometer;

[0039] Figure 4 It is a schematic diagram of the field of view correction process and results;

[0040] Figure 5 This is a diagram of the peak matching process in real-time data acquisition and processing;

[0041] Figure 6 This is a schematic diagram of the smoke plume orientation;

[0042] Figure 7 Flowchart for setting specific parameters in the MCARaTs tool. DETAILED DESCRIPTION

[0043] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0044] The components of the embodiments of the present invention generally described and shown in the drawings herein may be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention.

[0045] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0046] like Figure 1As shown, the system proposed by the present invention for real-time measurement of ship exhaust emission rate based on ground-based DOAS is mainly composed of an industrial computer, a DOAS imaging spectrometer, an optical lens, a visual camera, a pan-tilt, an AIS receiver, a meteorological data system and related supporting software. The industrial computer completes the control and data processing of each subsystem; the DOAS imaging spectrometer is connected to an optical lens through an optical fiber to complete the spectral information collection of the target, and the imaging circuit in the DOAS imaging spectrometer transmits the optical signal received by the detector to the industrial computer. In practical applications, the DOAS imaging spectrometer used in the present invention is an ultraviolet DOAS imaging spectrometer with a wavelength of 300nm to 400nm, which is used to invert the NO2 and SO2 concentration information in ship emissions; the visual camera is used to identify the position of the ship, collect the ship's appearance information and determine the field of view of the DOAS imaging spectrometer; the visual camera and the optical lens are fixedly installed on the pan-tilt, and the rotation of the pan-tilt drives the change of the optical lens's line of sight to complete the adjustment of the system's optical path.

[0047] In the practical application of the present invention, the field of view of the visible camera is 60°×30°, and the field of view of the optical lens is 5.5°×5.5°; the AIS receiver receives AIS data broadcast by nearby ships through an antenna; the meteorological data system obtains data such as wind direction, wind speed, temperature, and air pressure in the observation area. In practical applications, data can be obtained through the API provided by the online meteorological model or from the local meteorological station.

[0048] The flow chart of this system for real-time monitoring of ship pollutant gas emission rate is as follows Figure 2 As shown. The overall test process can be divided into three parts: instrument installation and calibration, real-time data acquisition and processing, and optimal estimation method based on Monte Carlo radiation transfer model simulation. The installation and calibration part of the instrument mainly completes the matching of the visible camera and the spectrometer field of view and the selection of the observation line of sight of this system, which is carried out before the field experiment begins. Real-time data acquisition and processing mainly retrieves whether there is pollutant gas emission from the light intensity value collected by the DOAS imaging spectrometer, summarizes the collected data and constructs the spatial distribution of the ship's emission plume. The optimal estimation method based on Monte Carlo radiation transfer model simulation mainly adds the Gaussian plume model as a non-uniform medium to the Monte Carlo radiation transfer model to simulate the radiance collected by this system and compares it with the actual collected radiance value, adjusts the source concentration parameters of the Gaussian plume, and infers the actual emission concentration value.

[0049] Specifically, due to the existence of assembly errors, the field of view calibration is first performed after the instrument is installed to ensure that the field of view of the DOAS imaging spectrometer is accurately positioned in the field of view of the visual camera, to help select the observation area of ​​the DOAS imaging spectrometer, and to provide a reliable basis for subsequent data processing and the establishment of a forward transmission model. The optical lens used in the present invention is a 5.5°×5.5° rectangular field of view. The optical signal is transmitted to the slit of the imaging spectrometer through an optical fiber. There are 49 optical fibers, which are arranged as 7×7 at the optical lens end and 1×49 at the slit end. Figure 3 As shown, the optical fiber transposes the two-dimensional spatial image in the optical lens into a one-dimensional spatial image collected by the DOAS imaging spectrometer. The specific method of field of view correction is to use the instrument to observe a specific target pattern or a target with obvious light and dark distribution characteristics, select the light intensity value of a single wavelength from the one-dimensional spatial image collected by the spectrometer and reconstruct the two-dimensional image to form a low-resolution pattern of 7×7 pixels, and then convert the image collected by the visible camera into a grayscale image, use a rectangle with a range of 5.5°×5.5° and divided into 7×7 grids to reduce the resolution in the collected visible camera grayscale image and compare it with the low-resolution pattern collected by the DOAS imaging spectrometer, and finally determine the exact position of the DOAS imaging spectrometer in the field of view of the visible camera. The field of view correction process and results are shown in Figure 4 As shown, Figure (a) is an image captured by a visible camera, in which the white rectangular box indicates the approximate position of the DOAS imaging spectrometer in the visible camera. Figure (b) is a down-scaled image captured by the visible camera, and Figure (c) is a two-dimensional spatial image captured by the DOAS imaging spectrometer. Compare (b) with (c) to determine the position of the DOAS imaging spectrometer field of view in the visible camera field of view.

[0050] The selection of the observation line of sight of this system is determined by the experimental plan. This system determines whether the passing ship has emitted polluted gases by detecting whether there is an instantaneous peak change in the concentration of the target gas when the ship passes. Therefore, the observation line of sight always stays at the position where the ship's smoke plume passes in advance, so that this system can retrieve the peak value from the background concentration of the detected gas. After field correction, the line of sight of the instrument is controlled by the pan-tilt. The general instrument line of sight is perpendicular to the ship's heading. When measuring in inland rivers and ports, the instrument is installed on both sides and the line of sight is perpendicular to the river. In order to make the instrument line of sight pass through the ship's emission plume as much as possible, this system adjusts the pan-tilt pitch angle according to the ship's navigation information received in the AIS receiver. Therefore, the size and position information of the ship in the received AIS information are critical. This system pre-adjusts the line of sight to the top of the ship passing.

[0051] After the line of sight is adjusted, the system starts to collect and analyze data. The light intensity data generated by the DOAS imaging spectrometer is mainly used to retrieve whether the passing ships have pollution emissions through the concentration changes in the time dimension after inversion, and the spectral data corresponding to the peak concentration is converted into radiance data collected by the instrument through radiation calibration. The specific process is as follows: The spectral data is automatically inverted using the QDOAS tool, and the reference spectrum selects the zenith spectrum when no ship passes by. After inversion, each spectral data generates 49 concentration values ​​corresponding to 49 optical fibers. The concentration values ​​at different times constitute the concentration change curve in the time dimension. Due to the existence of inversion errors, the background value of the concentration (when no ship passes) is always fluctuating. Therefore, for the concentration curve in the time dimension, low-pass filtering is used to extract its peak changes, and at the same time, the peak changes below the instrument's gas concentration detection line are eliminated. The process is as follows: Figure 5 shown.

[0052] When the ship passes by and an effective peak concentration appears, the original spectral data collected by the DOAS imaging spectrometer at this moment is matched with the relevant data collected by other parts of the system for subsequent plume modeling and concentration calculation. Among them, the image position collected by the visual camera mainly provides the position of the ship's chimney. The effective height of the ship's exhaust plume is related to the height of the chimney and the initial vertical velocity of the plume, which is calculated as follows:

[0053]

[0054] Among them, h eff is the effective height of the plume, h stack is the chimney height, is the initial vertical velocity of the plume, and g is the acceleration due to gravity.

[0055] The size and propagation direction of the smoke plume are determined by the ship speed and direction provided by the AIS data and the wind speed and direction provided by the meteorological data, such as Figure 6 shown.

[0056] The smoke plume model is approximated by the Gaussian smoke plume model. The calculation formula of the standard three-dimensional Gaussian smoke plume model is as follows:

[0057]

[0058] In the formula, C(x, y, z) represents the pollutant concentration at a distance of x meters downwind, y meters horizontally, and z meters in height from the emission source, Q is the emission rate of the emission source, and σ y is the lateral diffusion coefficient, σ z is the longitudinal diffusion coefficient, U is the wind speed at the emission height H, and H is the effective height of the emission source.

[0059] In reality, the shape of Gaussian plumes is affected by atmospheric stability and can be divided into looping plumes, coning plumes, fanning plumes, lofting plumes, trapped plumes, and fumigation plumes. The level of atmospheric stability is related to meteorological factors such as wind speed, temperature, and pressure.

[0060] After the three-dimensional Gaussian plume model is established, the relationship between the emission rate of the emission source and the concentration at any spatial position of the plume can be obtained. This relationship is continuous. In order to further serve as the input of numerical simulation, the Gaussian plume model is discretized. The size of the spatial grid is related to the spatial grid scale defined by the Monte Carlo radiation transfer model. In the present invention, the MCARaTs tool is used as the Monte Carlo radiation transfer model as a solution tool, and the minimum grid is defined as 1×1×1 meter.

[0061] In the optimal estimation method based on the Monte Carlo radiative transfer model simulation, a three-dimensional grid scene close to the actual observation conditions is established, the gas absorption coefficient is set according to the space-concentration relationship in the discretized Gaussian plume model, and then the instrument perspective is simulated to obtain the observed radiance, which is compared with the actual observed radiance, and the emission source concentration of the Gaussian plume model is further adjusted to infer the actual emission concentration of the ship. The specific parameter setting process in the MCARaTs tool of the present invention is as follows: Figure 7 shown.

[0062] The parameters related to the Monte Carlo radiation transfer model mainly include the phase function related to the calculation, the order of photon scattering, etc., atmospheric parameters, surface reflection parameters, and radiance simulation parameters, among which the most core is the atmospheric parameter setting. In the MCARaTs software, the atmosphere is divided into three-dimensional grids, and each layer is regarded as a homogeneous layer. Parameters such as temperature, pressure, extinction coefficient, and gas absorption coefficient are set for each layer. At the same time, a three-dimensional extinction coefficient and a gas absorption coefficient scaling function are provided to modify the homogeneous layer into a non-homogeneous layer to simulate the actual atmospheric state. In the present invention, the scaling factor of the gas absorption coefficient is set according to the space-concentration relationship in the established discrete Gaussian plume model to simulate the plume emitted by the ship. The surface reflection parameters can simulate the actual reflection parameters of the channel and the ground combination. The position parameters of the light source and radiance calculation are set according to the actual observation time and the instrument design parameters to simulate the radiance data under the actual observation conditions.

[0063] After the Monte Carlo radiation transfer model simulates the radiance, the spectral data collected by the spectrometer under this observation condition is converted into radiance data through a radiation calibration experiment. The radiation calibration experiment is usually completed in advance and the relationship between the radiance and the light intensity value of the same instrument is determined. The simulated radiance and the actual measured radiance are compared using the optimal estimation method, and the gas absorption coefficient scaling factor of the smoke plume in the radiation transfer model is adjusted to minimize the error between the simulated radiance and the actual measured radiance, and infer the concentration distribution information of the actual smoke plume. The emission rate of the polluted gas is then obtained based on the established Gaussian smoke plume model.

[0064] The above specific embodiments are only several optional embodiments of the present invention. Based on the technical solutions of the present invention and the relevant inspirations of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A method for real-time measurement of ship exhaust emission rate based on ground-based DOAS, characterized in that: The following steps are involved: Installation and calibration of instruments, installation of optical lens, DOAS imaging spectrometer, visual camera, AIS receiver, matching of visual camera and spectrometer field of view and selection of observation line of sight; Real-time data collection and processing, searching for the presence of pollutant emissions from the light intensity values ​​collected by the DOAS imaging spectrometer, aggregating the collected data and constructing the spatial distribution of the ship's emission plume; Based on the optimal estimation method of Monte Carlo radiative transfer model simulation, the Gaussian plume model is added to the Monte Carlo radiative transfer model as an inhomogeneous medium, the collected radiance is simulated and compared with the actual collected radiance value, the source concentration parameters of the Gaussian plume are adjusted, and the actual emission concentration value is inferred.

2. According to claim 1, a method for real-time measurement of ship exhaust emission rate based on ground-based DOAS is characterized in that: The DOAS imaging spectrometer is an ultraviolet DOAS imaging spectrometer with a wavelength range of 300nm to 400nm.

3. The method for real-time measurement of ship exhaust emission rate based on ground-based DOAS according to claim 1 is characterized in that: The optical lens adopts a rectangular field of view of 5.5°×5.5°, and transmits the optical signal to the slit of the DOAS imaging spectrometer through an optical fiber.

4. The method for real-time measurement of ship exhaust emission rate based on ground-based DOAS according to claim 1 is characterized in that: The field of view of the visual camera is 60°×30°.

5. The method for real-time measurement of ship exhaust emission rate based on ground-based DOAS according to claim 1 is characterized in that: The light intensity values ​​collected by the DOAS imaging spectrometer are used to retrieve whether the passing ships have pollutant emissions by inverting the concentration changes in the time dimension, and the spectral data corresponding to the peak concentration is converted into radiance data collected by the DOAS imaging spectrometer through radiation calibration.

6. The method for real-time measurement of ship exhaust emission rate based on ground-based DOAS according to claim 5 is characterized in that: The spectral data is inverted automatically using the QDOAS tool, and the zenith spectrum when no ship passes is selected as the reference spectrum. After inversion, each spectral data generates 49 concentration values ​​corresponding to 49 optical fibers. The concentration values ​​at different times constitute a concentration change curve in the time dimension. The concentration curve in the time dimension is low-pass filtered to extract its peak change, and at the same time, the peak change below the gas concentration detection line of the DOAS imaging spectrometer is eliminated.

7. The method for real-time measurement of ship exhaust emission rate based on ground-based DOAS according to claim 6 is characterized in that: There are 49 optical fibers, which are arranged as 7×7 at the optical lens end and 1×49 at the slit end. The optical fibers transpose the two-dimensional spatial image in the optical lens into a one-dimensional spatial image collected by the DOAS imaging spectrometer.

8. The method for real-time measurement of ship exhaust emission rate based on ground-based DOAS according to claim 1 is characterized in that: The image position collected by the visual camera includes the position of the ship chimney. The effective height of the smoke plume emitted by the ship is related to the height of the chimney and the initial vertical velocity of the smoke plume. The calculation formula is as follows: Among them, h eff is the effective height of the plume, h stack is the chimney height, is the initial vertical velocity of the plume, and g is the acceleration due to gravity.

9. The method for real-time measurement of ship exhaust emission rate based on ground-based DOAS according to claim 8 is characterized in that: The calculation formula of the Gaussian plume model is as follows: In the formula, C(x, y, z) represents the pollutant concentration at a distance of x meters downwind, y meters horizontally, and z meters in height from the emission source, Q is the emission rate of the emission source, and σ y is the lateral diffusion coefficient, σ z is the longitudinal diffusion coefficient, U is the wind speed at the emission height H, and H is the effective height of the emission source.

10. A system for real-time measurement of ship exhaust emission rate based on ground-based DOAS, using the method according to any one of claims 1 to 9, wherein the system includes an industrial computer for controlling and processing data of each subsystem, characterized in that: Also includes: An optical lens and a DOAS imaging spectrometer connected to the optical lens, wherein the optical lens collects spectral information of the target and transmits it to an imaging circuit in the DOAS imaging spectrometer, and transmits the received optical signal to the industrial computer; A visible camera mounted on a rotating pan / tilt head is used to identify the ship's position, collect information about the ship's appearance, and determine the field of view of the DOAS imaging spectrometer; AIS receiver, which receives AIS data broadcast by nearby ships through an antenna; Meteorological data system, obtains data related to wind direction, wind speed, temperature and air pressure in the observation area.

Images