Atmospheric aerosol laser radar device capable of synchronously outputting distinguishable components in multiple polarization states

Abstract

The invention discloses a multi-polarization-state atmospheric aerosol laser radar device capable of synchronously outputting distinguishable components. The multi-polarization-state atmospheric aerosol laser radar device is provided with a laser transmitting module, an echo signal receiving module and a signal processing module. The laser emission module accurately distributes laser energy through a spectroscope, and a polarization state modulation module is utilized to synchronously generate various polarization state light beams (horizontal, vertical, 45-degree linear polarized light and right-handed circular polarized light), so that synchronous output of the multi-polarization state light beams is realized, and the problems of time delay and measurement errors caused by traditional time-sharing modulation are solved. The echo signal receiving module adopts a plurality of parallel independent telescope systems, receives back scattering signals in different polarization states at the same time, generates a Mueller matrix in combination with the signal processing module, and accurately calculates the components of the aerosol. Compared with the prior art, by means of accurate energy light splitting and synchronous modulation, the stability and the real-time performance of the detection system are remarkably improved, angle errors are eliminated, and the time resolution and the measurement precision are improved.

Description

Technical Field

[0001] The present invention relates to the field of air pollution monitoring technology in the field of environmental monitoring equipment, and in particular to an atmospheric aerosol laser radar device capable of synchronously outputting resolvable components in multiple polarization states. Background Art

[0002] The composition of atmospheric aerosols is complex, and different aerosol components have different effects on human health and the environment. Therefore, accurate monitoring of aerosol composition is crucial in environmental science, meteorological monitoring, and pollution control. As a non-contact detection method, lidar has been widely used in the detection of atmospheric aerosols. Its basic principle is to use lasers to interact with aerosol particles in the atmosphere and analyze the physical and chemical properties of aerosols by detecting backscattered signals.

[0003] Existing lidar technology usually obtains aerosol composition information by emitting polarized lasers and detecting and analyzing the scattered signals after the lasers interact with aerosols. The traditional technical route relies on the time-sharing output of laser beams with different polarization states, such as gradually changing the polarization state of the laser by rotating lenses or other mechanical devices. Although this method can detect signals with different polarization states, there are obvious problems in practical applications: 1. Time delay: Since lasers in different polarization states need to be emitted in different time periods, there is a time delay when light beams in different polarization states interact with the atmosphere. This delay makes the detection results susceptible to the influence of instantaneous changes in the environment in a complex or rapidly changing atmospheric environment, thereby reducing the accuracy and real-time performance of the measurement.

[0004] 2. Mechanical error: Time-sharing adjustment usually relies on mechanical devices such as rotating lenses. Such devices are prone to mechanical wear or adjustment errors during long-term use, resulting in angular errors in the output polarization state, which in turn affects the accuracy of the polarization state and reduces the ability to accurately analyze aerosol components.

[0005] 3. Low data acquisition resolution: Since the polarization states need to be adjusted and transmitted one by one, the time resolution of the entire data acquisition is low, making it difficult to respond quickly to sudden environmental events. Especially in scenarios that require high-frequency monitoring, the system response is delayed, affecting detection efficiency.

[0006] In order to solve the above problems, the industry has tried to use multiple lasers and multiple receiving systems for synchronous detection. However, this method not only makes the system structure complex and bulky, but also significantly increases the cost. In addition, the coordination and synchronous operation between multiple systems also face technical challenges, and the final detection accuracy cannot be fully guaranteed.

[0007] Therefore, how to achieve synchronous output of multi-polarization lasers, eliminate time delay and mechanical errors, and improve the real-time and accuracy of atmospheric aerosol detection has become a technical problem to be solved by the present invention. Summary of the invention

[0008] The technical problem solved by the present invention is to provide an atmospheric aerosol lidar device with multi-polarization state synchronous output of resolvable components in response to the defects existing in the above-mentioned prior art, so as to solve the problems of time delay, mechanical error and low data acquisition resolution of the atmospheric aerosol detection system proposed in the above-mentioned background technology.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: An atmospheric aerosol laser radar device with multi-polarization state synchronous output and resolvable components, the device comprises a laser emission module, an echo signal receiving module and a signal processing module, the laser emission module comprises: Laser, used for emitting laser light; A plurality of beam splitters, used to split the laser into multiple beams, and split the beams according to a specific ratio, wherein the specific beam splitting ratio refers to 1:3, 1:2 and / or 1:1; A polarization state modulation module is located on the path of each split laser beam and is used to modulate different polarization states, including horizontal linear polarization, vertical linear polarization, 45° linear polarization and right-hand circular polarization; wherein the multiple laser beams are synchronously output and enter the atmosphere to interact with aerosol particles; The echo signal receiving module includes a plurality of independent receiving systems, each receiving system includes a telescope for receiving backscattered signals of different polarization states and sending them to the signal processing module; The signal processing module generates a Mueller matrix to analyze the polarization change characteristics after the lasers with different polarization states interact with the aerosol, thereby determining the components of the aerosol.

[0010] As a further solution of the present invention, the laser is a pulsed laser or a continuous laser, and the laser wavelength outputted by the laser is within the absorption band of the aerosol to be measured.

[0011] As a further solution of the present invention, the spectroscope accurately splits light according to the energy ratio. The reflectivity and transmittance ratio of lens No. 2 to the laser output wavelength is 1:3, lens No. 3 is 1:2, and lens No. 4 is 1:1, so as to ensure the consistency of the intensity of multiple laser beams.

[0012] As a further solution of the present invention, the polarization state modulation module includes a combination of two half-wave plates and a quarter-wave plate, which is used to generate horizontal linear polarization, vertical linear polarization, 45° linear polarization and right-hand circular polarization.

[0013] As a further solution of the present invention, the echo signal receiving module includes four Cassegrain telescopes, which are respectively used to receive backscattered signals from lasers of different polarization states in the atmosphere and convert the optical signals into electrical signals through photoelectric converters.

[0014] As a further solution of the present invention, each Cassegrain telescope of the echo signal receiving module extracts only the polarization state signal corresponding to it through a spectroscopic device, including one of horizontal linear polarization, vertical linear polarization, 45° linear polarization and right-hand circular polarization.

[0015] As a further solution of the present invention, the signal processing module includes a detector and a high-speed acquisition card, which is used to synchronously receive and process polarization state signals provided by four receiving systems, generate and calculate the corresponding Mueller matrix; the signal processing module solves the bidirectional attenuation characteristics D, polarization characteristics P, phase delay characteristics R and depolarization characteristics Δ of the atmospheric aerosol according to the generated Mueller matrix, and then determines the main components of the atmospheric aerosol.

[0016] As a further solution of the present invention, the Mueller matrix generated by the signal processing module is M0, and M0 is calculated by Stokes vectors S1, S2, S3, and S4, and the calculation formula is: Here, the Stokes vector is defined as: As a further solution of the present invention, the signal processing module solves the particle interaction matrix A of the aerosol, and the calculation formula is: Among them, M1 is the Stokes vector calculated based on the image received by the CCD, and the aerosol component matrix A is solved by the following formula: As a further solution of the present invention, the calculation results of the aerosol component matrix A can further solve the bidirectional attenuation characteristics D, polarization characteristics P, phase delay characteristics R and depolarization characteristics Δ of the aerosol, and compare these characteristics with the data in the aerosol sample library to determine the composition and content of the aerosol in the atmosphere.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. Synchronous output of multiple polarization states to eliminate time delay: Polarization state modulation in traditional lidar systems relies on time-sharing adjustment, which results in time delay when polarized light beams interact with atmospheric aerosols, thereby introducing measurement errors. The present invention achieves synchronous output of multiple polarization state light beams, allowing all polarization state lasers to interact with aerosols at the same time, eliminating the inaccuracy caused by time differences, ensuring the real-time and consistency of detection data, and has significant advantages, especially in complex and rapidly changing environments.

[0018] 2. Precise beam splitting and polarization modulation to improve detection stability: The present invention ensures balanced energy output of each polarization state beam through precise ratio control of the beam splitter (1:3, 1:2 and 1:1 beam splitting ratio) and optimized design of the polarization modulation module. This precise energy distribution and modulation significantly reduces the detection deviation caused by uneven beam energy in traditional solutions, and improves the stability and accuracy of aerosol component detection.

[0019] 3. Multi-channel parallel reception to improve data processing efficiency: The echo signal receiving module of the present invention uses multiple independent telescopes to receive backscattered signals of different polarization states in parallel. Compared with the traditional single-channel serial receiving system, the present invention shortens the signal acquisition and analysis time through multi-channel parallel processing, improves the system's time resolution, and enables the device to maintain high detection efficiency and accuracy under complex meteorological conditions.

[0020] 4. Eliminate mechanical rotation and reduce error sources: Traditional technologies rely on lens rotation to adjust the polarization state, which easily introduces mechanical errors and reduces detection accuracy. The present invention completely eliminates the mechanical rotation device through the design of synchronous modulation of the polarization state, avoids angle errors, greatly improves the stability and reliability of the system, and reduces the complexity and maintenance cost of the equipment.

[0021] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0023] Figure 1 It is a system architecture diagram of the present invention. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] See also Figure 1 In an embodiment of the present invention, an atmospheric aerosol laser radar device with multi-polarization state synchronous output of resolvable components includes a laser emission module, an echo signal receiving module and a signal processing module, wherein the laser emission module includes: a laser for emitting laser light; a plurality of spectroscopes for dividing the laser light into multiple beams and splitting the light according to a specific ratio, wherein the specific splitting ratio refers to 1:3, 1:2 and / or 1:1; The polarization state modulation module is located on the path of each split laser beam and is used to modulate different polarization states, including horizontal linear polarization, vertical linear polarization, 45° linear polarization and right-hand circular polarization. The multiple laser beams are synchronously output and enter the atmosphere to interact with aerosol particles. The echo signal receiving module includes multiple independent receiving systems, each receiving system includes a telescope for receiving backscattered signals of different polarization states and sending them to the signal processing module. The signal processing module generates the Mueller matrix and analyzes the polarization change characteristics after the interaction between lasers of different polarization states and aerosols, thereby determining the composition of the aerosol. The laser is a pulsed laser or a continuous laser, and the laser wavelength it outputs is within the absorption band of the aerosol to be measured.

[0026] The beam splitter accurately splits light according to the energy ratio. The reflectivity and transmittance ratio of lens No. 2 to the laser output wavelength is 1:3, lens No. 3 is 1:2, and lens No. 4 is 1:1, to ensure consistent intensity of multiple laser beams.

[0027] The polarization modulation module includes a combination of two half-wave plates and a quarter-wave plate, which is used to generate horizontal linear polarization, vertical linear polarization, 45° linear polarization and right-hand circular polarization. The echo signal receiving module includes four Cassegrain telescopes, which are used to receive backscattered signals from lasers of different polarization states in the atmosphere and convert the optical signals into electrical signals through photoelectric converters.

[0028] Each Cassegrain telescope of the echo signal receiving module only extracts the polarization state signal corresponding to it through the spectroscopic device, including one of horizontal linear polarization, vertical linear polarization, 45° linear polarization and right-hand circular polarization. The signal processing module includes a detector and a high-speed acquisition card, which is used to synchronously receive and process the polarization state signals provided by the four receiving systems, generate and calculate the corresponding Mueller matrix. The signal processing module solves the bidirectional attenuation characteristic D, polarization characteristic P, phase delay characteristic R and depolarization characteristic Δ of the atmospheric aerosol according to the generated Mueller matrix, and then determines the main components of the atmospheric aerosol. The synchronous output and reception design of multi-polarization state laser improves the real-time and accuracy of the measurement by eliminating the time delay between each polarization state beam. The device can be installed at a fixed ground-based site or used for cruise monitoring, and is suitable for real-time monitoring of complex atmospheric environments.

[0029] Embodiment 1: In the urban air quality monitoring system, real-time monitoring of aerosol composition in the atmosphere plays a vital role in assessing pollution sources and predicting changes in air quality. Traditional aerosol monitoring equipment usually relies on time-sharing adjustment of laser emission systems in different polarization states, and calculates the composition of aerosols by receiving scattered light. However, this system encounters the following problems in practical applications: due to the time-sharing emission of lasers in different polarization states, the time delay of detection data leads to inaccurate detection results in complex and rapidly changing atmospheric environments. Especially during peak hours in the morning and evening, industrial emissions and traffic pollutants spread rapidly, and high-frequency and high-precision detection systems are required at this time. However, the low time resolution and large mechanical rotation errors of traditional equipment make it difficult to meet the needs of real-time monitoring.

[0030] In order to solve this problem, the present invention proposes an atmospheric aerosol lidar device with multi-polarization state synchronous output of distinguishable components. The device realizes the synchronous output of four different polarization state light beams (horizontal linear polarization, vertical linear polarization, 45° linear polarization and right-hand circular polarization) through a precisely designed laser emission module, and ensures the energy balance of each light beam. In specific applications, at urban air quality monitoring sites, the device emits these multi-polarization state lasers into the atmosphere, interacts with aerosol particles, and generates backscattered signals. These backscattered signals are synchronously received by a multi-channel receiving system, which includes four Cassegrain telescopes, each of which corresponds to the receiving task of a polarization state light beam.

[0031] Due to the time-sharing transmission and reception of traditional equipment, the detection results of different polarization states cannot reflect the atmospheric conditions in the same time period. In contrast, the synchronous multi-polarization state transmission and reception of the present device solves the time delay problem, making the detection results more immediate and accurate in a rapidly changing environment. For example, when a heavy truck is driving in a city, the particulate matter it emits instantly will diffuse rapidly with the airflow. If the monitoring equipment cannot respond to these changes in real time, the detection data may have lagged behind. The device of the present invention uses synchronous transmission and reception, so that each set of polarization state signals is acquired at almost the same time, thereby being able to capture these instantaneous changes more accurately.

[0032] In addition, the present device avoids the problem of decreased polarization state accuracy caused by rotation errors in traditional devices by eliminating the design of mechanically rotating the lens. The mechanical rotation of traditional devices requires repeated angle adjustment, which can easily introduce mechanical wear or angle deviation. Especially during long-term monitoring, these errors will continue to accumulate, resulting in detection data deviations. Through synchronous polarization state modulation, the present invention not only reduces the error source, but also simplifies the equipment structure and reduces maintenance costs. For example, in long-term pollution monitoring, the equipment usually needs to work continuously for a long time, and any failure of mechanical components will cause data inaccuracy. The present invention can maintain stable detection performance during long-term operation through a design without mechanical rotation.

[0033] In terms of signal processing, the signal processing module in the device generates a Mueller matrix through synchronously received multi-channel polarization backscattered signals, and compares it with the known atmospheric aerosol component library to accurately solve the main aerosol components in the atmosphere. In specific applications, this technology can quickly analyze the composition changes of major pollutants in the air, such as sulfates, nitrates, carbonaceous particles, etc., to help decision makers understand the real-time emissions of pollution sources. For example, in an industrial area, when a factory emits a large amount of harmful aerosols instantaneously, the device of the present invention can capture the source of pollution within a few seconds and feedback the pollutant composition, thereby providing a scientific basis for rapid decision-making. This real-time monitoring capability provides strong technical support for emergency response to air pollution.

[0034] Through the above technical solutions, the present invention has demonstrated significant technical progress in the application of complex atmospheric environments. Compared with existing technologies, the proposed device not only improves the real-time and accuracy of detection, but also greatly simplifies the equipment structure and reduces maintenance and operating costs. Especially in response to sudden environmental pollution incidents, it can quickly capture and analyze aerosol components in the atmosphere, providing an effective means for environmental protection and air quality monitoring.

[0035] Embodiment 2: The present invention provides an accurate real-time monitoring method for atmospheric aerosol monitoring in industrial parks. The system is composed of a laser emission module, an echo signal receiving module, a signal processing module and a spectroscopic module, and can quickly and accurately analyze the components of aerosol.

[0036] See also Figure 1 The laser emission module includes a laser (1), a beam splitter (2.3.4), a total reflector (5) and a polarization state generator (6.7.8.9). The laser (1) can be a pulsed or continuous laser, with an output wavelength within the atmospheric aerosol absorption band and a polarization state of vertical or horizontal polarization. The beam splitter (2.3.4) splits the output beam of the laser into four beams according to the ratios of 1:3, 1:2 and 1:1, and after being modulated by the polarization state generator (6.7.8.9), it outputs horizontal linear polarization, vertical linear polarization, 45° linear polarization and right-hand circular polarization.

[0037] The four beams of light emitted by the laser are adjusted by the beam splitter and then emitted into the atmosphere at the same time, interacting with the aerosols in the atmosphere to generate backscattered signals. The polarization state of each beam of light is modulated into a specific polarization state by a pre-set polarization adjustment module to ensure that the polarization states of the four beams can be output and received synchronously.

[0038] The echo signal receiving module is composed of four Cassegrain telescopes (10.11.12.13), each of which is responsible for receiving backscattered signals of a specific polarization state. The telescopes extract horizontal linear polarization, vertical linear polarization, 45° linear polarization and right-hand circular polarization respectively through high-reflection mirrors (14.15.16.17) and spectrometers (22.23.24.25). The pinhole diaphragm (18.19.20.21) is used to adjust the optical path of the receiving light beam, and the CCD of the image acquisition module (26.27.28.29) is used to collect and image the signals of each polarization state in real time.

[0039] The signal acquisition module (30) is responsible for converting and high-speed acquisition of the received photoelectric signals. The design of the entire system ensures the synchronous emission and reception of the four polarization state light beams, thereby ensuring that the system can still accurately and real-time capture aerosol components in a rapidly changing atmospheric environment.

[0040] The system composition and cascade relationship of each module are as follows: The laser emission module divides the laser output beam into four beams through the beam splitter (2.3.4), and each beam is modulated by the polarization adjustment module (6.7.8.9) to produce different polarization states. Since the distance between the laser and the beam splitter is very short (less than 0.5m), the time difference can be ignored to ensure the synchronous emission of the four beams. The echo signal is received by the Cassegrain telescope (10.11.12.13) and then enters the signal processing module. Each receiving system extracts its specific polarization state signal, which is recorded by the CCD imaging device and then transmitted to the signal acquisition module for photoelectric signal conversion and data acquisition.

[0041] The four polarization states of the light beams emitted by the laser emission end can be represented by Stokes vectors S1, S2, S3, and S4 respectively, and the generated Mueller matrix M0 is: The Stokes vector is defined as follows: When the light beam passes through the aerosol in the atmosphere, the particle action matrix is ​​A, and the relationship is: Where M1 is the Stokes vector matrix of the scattered signal calculated by the receiving system based on the image received by the CCD. By solving A, the composition of the aerosol can be determined by the following formula: By comparing the change patterns of the elements of matrix A and combining them with the pre-established aerosol component sample library, the system can accurately determine the aerosol composition in the atmosphere. This technology demonstrates significant real-time performance and accuracy under complex and rapidly changing atmospheric conditions, providing a reliable solution for air pollution monitoring.

[0042] In the present invention, unless otherwise clearly stipulated and limited, the terms "installation", "setting", "connection", "fixation", "screw-on" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, ordinary technicians in this field can understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0043] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. An atmospheric aerosol laser radar device with multi-polarization state synchronous output of resolvable components, characterized in that: The device comprises a laser emission module, an echo signal receiving module and a signal processing module, wherein the laser emission module comprises: Laser, used for emitting laser light; A plurality of beam splitters, used to split the laser into multiple beams, and split the beams according to a specific ratio, wherein the specific beam splitting ratio refers to 1:3, 1:2 and / or 1:1; A polarization state modulation module is located on the path of each split laser beam and is used to modulate different polarization states, including horizontal linear polarization, vertical linear polarization, 45° linear polarization and right-hand circular polarization; wherein the multiple laser beams are synchronously output and enter the atmosphere to interact with aerosol particles; The echo signal receiving module includes a plurality of independent receiving systems, each receiving system includes a telescope for receiving backscattered signals of different polarization states and sending them to the signal processing module; The signal processing module generates a Mueller matrix to analyze the polarization change characteristics after the lasers with different polarization states interact with the aerosol, thereby determining the components of the aerosol.

2. The atmospheric aerosol laser radar device with multi-polarization state synchronous output of resolvable components according to claim 1, characterized in that: The laser is a pulsed laser or a continuous laser, and the laser wavelength outputted by the laser is within the absorption band of the aerosol to be measured.

3. The atmospheric aerosol laser radar device with multi-polarization state synchronous output of resolvable components according to claim 1, characterized in that: The spectroscope precisely splits light according to the energy ratio. The reflectivity and transmittance ratio of lens No. 2 to the laser output wavelength is 1:3, lens No. 3 is 1:2, and lens No. 4 is 1:1, so as to ensure the consistency of the intensity of multiple laser beams.

4. The atmospheric aerosol laser radar device with multi-polarization state synchronous output of resolvable components according to claim 1, characterized in that: The polarization state modulation module includes a combination of two half-wave plates and a quarter-wave plate, which is used to generate horizontal linear polarization, vertical linear polarization, 45° linear polarization and right-hand circular polarization.

5. The atmospheric aerosol laser radar device with multi-polarization state synchronous output of resolvable components according to claim 1, characterized in that: The echo signal receiving module includes four Cassegrain telescopes, which are respectively used to receive backscattered signals from lasers of different polarization states in the atmosphere and convert the optical signals into electrical signals through a photoelectric converter.

6. The atmospheric aerosol laser radar device with multi-polarization state synchronous output of resolvable components according to claim 1, characterized in that: Each Cassegrain telescope of the echo signal receiving module extracts only the polarization state signal corresponding thereto through the spectroscopic device, including one of horizontal linear polarization, vertical linear polarization, 45° linear polarization and right-hand circular polarization.

7. The atmospheric aerosol laser radar device with multi-polarization state synchronous output of resolvable components according to claim 1, characterized in that: The signal processing module includes a detector and a high-speed acquisition card, which are used to synchronously receive and process polarization state signals provided by four receiving systems, generate and calculate the corresponding Mueller matrix; the signal processing module solves the bidirectional attenuation characteristic D, polarization characteristic P, phase delay characteristic R and depolarization characteristic Δ of the atmospheric aerosol according to the generated Mueller matrix, and then determines the main components of the atmospheric aerosol.

8. The atmospheric aerosol laser radar device with multi-polarization state synchronous output of resolvable components according to claim 1, characterized in that: The Mueller matrix generated by the signal processing module is M0, which is calculated by Stokes vectors S1, S2, S3, and S4. The calculation formula is: Here, the Stokes vector is defined as: 。 9. The atmospheric aerosol laser radar device with multi-polarization state synchronous output of resolvable components according to claim 8, characterized in that: The signal processing module solves the particle action matrix A of the aerosol, and its calculation formula is: Among them, M1 is the Stokes vector calculated based on the image received by the CCD, and the aerosol component matrix A is solved by the following formula: 。 10. The atmospheric aerosol laser radar device with multi-polarization state synchronous output of resolvable components according to claim 9, characterized in that: The calculation results of the aerosol component matrix A can further solve the bidirectional attenuation characteristics D, polarization characteristics P, phase delay characteristics R and depolarization characteristics Δ of the aerosol, and compare these characteristics with the data in the aerosol sample library to determine the composition and content of the aerosol in the atmosphere.

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