A method and system for detecting sea fog

Abstract

The present invention discloses a sea fog detection method and system, which relates to the field of sea fog detection. By means of various cloud and fog simulation models, the reflectance and brightness temperature of each spectral channel included therein are obtained under various cloud and fog simulation environments, so as to design criterion conditions corresponding to each set cloud and fog type. After the cloud top phase state corresponding to the target ocean area is discriminated, according to the reflectance of the first channel, the second channel and the third channel in the primary data, the set cloud and fog type corresponding to the target ocean area is obtained by using the single-layer water cloud criterion condition, the single-layer sea fog criterion condition, the single-layer ice cloud criterion condition, the upper-layer ice cloud and lower-layer water cloud criterion condition and the upper-layer ice cloud and lower-layer sea fog criterion condition. It breaks through the limitation that it is impossible to effectively detect low-level sea fog or water cloud when blocked by ice clouds, and realizes the detection of low-level water cloud and sea fog under ice clouds.

Description

Technical Field

[0001] The present invention relates to the field of sea fog detection, and particularly to a sea fog detection method and system. Background Art

[0002] Sea fog is a weather phenomenon in the lower atmosphere of the ocean or coastal areas, where a large number of water droplets or ice crystals are generated due to water vapor condensation, resulting in a horizontal visibility of less than 1 km in the atmosphere. It will have a serious impact on maritime traffic, operations, production activities, etc. Therefore, monitoring and forecasting the generation, development, and influence range of sea fog, and providing a basis for relevant departments to implement scientific regulation and management, have important practical significance for disaster prevention and mitigation. Since there are only a few or even no stations on the ocean, and there is a lack of effective observation means, it is difficult to meet the operational application of sea fog monitoring. The geostationary satellite spectral imager has a wide field of view and can achieve continuous detection within the ocean area, providing powerful observational data for quantitative research on the generation and dissipation characteristics and influence range of sea fog. However, the satellite imager can only passively receive the solar short-wave radiation reflected by the target and the long-wave radiation emitted by the earth, and has great limitations in the detection ability of the atmospheric vertical structure. For example, when high clouds exist above the sea fog, the signals will interfere with each other, affecting the accuracy of sea fog detection. Therefore, the current sea fog detection method based on satellite imager is only applicable to single-layer cloud and fog. If there are clouds covering the fog area, the detection result is judged as a cloud area, and the sea fog blocked by the clouds cannot be identified. Therefore, there are the following defects in the current sea fog detection technology based on satellite remote sensing: when high clouds exist, sea fog detection cannot be carried out. However, in all cloud systems in the real atmosphere, the proportion of high clouds (ice clouds) exceeds 40%, and the judgment of whether there are water clouds or sea fog below the ice clouds has always been a difficult point in the field of satellite remote sensing. Summary of the Invention

[0003] In order to solve the problem that the accuracy of sea fog detection is affected when high clouds exist above the sea fog, the present invention proposes a sea fog detection method, including the steps of:

[0004] S1: Obtain satellite data in a real cloud and fog environment through a satellite imager. The satellite data includes longitude and latitude data. Obtain the primary data and cloud detection data corresponding to the target ocean area in the satellite data through the longitude and latitude data. The primary data includes the reflectance of the first channel, the second channel, and the third channel, and the brightness temperature of the fourth channel and the fifth channel. The first channel is the visible light channel with a central wavelength of 0.64 μm, the second channel is the near-infrared channel with a central wavelength of 1.6 μm, the third channel is the near-infrared channel with a central wavelength of 2.25 μm, the fourth channel is the long-wave infrared channel with a central wavelength of 8.5 μm, and the fifth channel is the long-wave infrared channel with a central wavelength of 11 μm;

[0005] S2: Based on radiative transfer simulation, establish cloud simulation models corresponding to each set cloud type, which are used to simulate the real cloud environment detected by the satellite imager under each set cloud type, so as to obtain the cloud simulation environment corresponding to each set cloud type; the set cloud types include: single-layer water cloud, single-layer sea fog, single-layer ice cloud, upper-layer ice cloud and lower-layer water cloud, and upper-layer ice cloud and lower-layer sea fog; each cloud simulation model includes each spectral channel in the first-level data.

[0006] S3: Through each cloud simulation model, obtain the reflectance and brightness temperature of each spectral channel included therein under each cloud simulation environment.

[0007] S4: Design criterion conditions corresponding to each set cloud type based on the reflectance and brightness temperature of each spectral channel under each cloud simulation environment. The criterion conditions include: water phase criterion condition, single-layer water cloud criterion condition, single-layer sea fog criterion condition, ice phase criterion condition, single-layer ice cloud criterion condition, upper-layer ice cloud and lower-layer water cloud criterion condition, and upper-layer ice cloud and lower-layer sea fog criterion condition.

[0008] S5: Through the first-level data and cloud detection data corresponding to the target ocean area in the real cloud environment, use the criterion conditions to obtain the set cloud type corresponding to the target ocean area. The obtaining method includes:

[0009] S51: According to the brightness temperature of the fourth channel and the fifth channel in the first-level data, use the water phase criterion condition and the ice phase criterion condition to obtain the cloud top phase corresponding to the target ocean area. The cloud top phase is the water phase or the ice phase.

[0010] S52: When the cloud top phase is the water phase, according to the reflectance of the first channel and the second channel in the first-level data, use the single-layer water cloud criterion condition and the single-layer sea fog criterion condition to obtain the set cloud type corresponding to the target ocean area.

[0011] S53: When the cloud top phase is the ice phase, according to the reflectance of the first channel, the second channel and the third channel in the first-level data, use the single-layer ice cloud criterion condition, the upper-layer ice cloud and lower-layer water cloud criterion condition, and the upper-layer ice cloud and lower-layer sea fog criterion condition to obtain the set cloud type corresponding to the target ocean area.

[0012] Further, in step S4, designing the criterion conditions corresponding to each set cloud type based on the reflectance and brightness temperature of each spectral channel under each cloud simulation environment includes:

[0013] By performing sensitivity analysis on the reflectance of the first channel, the second channel, and the third channel under each cloud simulation environment, obtain the difference characteristics of the reflectance of each spectral channel between each cloud simulation environment. The obtaining method of the difference characteristics is:

[0014] Based on the particle characteristics that the effective particle radius of water clouds is between 10 and 20 microns and the effective particle radius of sea fog is between 3 and 5 microns, and obtained from the reflectance of each spectral channel in each cloud and fog simulation environment during the simulation process:

[0015] When both the optical thickness and the effective particle radius are less than the corresponding set lower limit values, the reflectance difference between the first channel and the second channel is less than 0. When both the optical thickness and the effective particle radius are greater than the corresponding set upper limit values, the characteristic that the reflectance difference is greater than or equal to 0 is obtained:

[0016] The difference characteristic that the reflectance difference between the first channel and the second channel corresponding to water cloud particles is greater than or equal to the threshold value, and the reflectance difference between the first channel and the second channel corresponding to sea fog particles is less than the threshold value, where the threshold value is equal to 0;

[0017] The difference characteristics obtained during the simulation process also include: the difference characteristics of the reflectance of each spectral channel between the single-layer ice cloud, the upper-layer ice cloud and the lower-layer water cloud, and the cloud and fog simulation environments corresponding to the upper-layer ice cloud and the lower-layer sea fog;

[0018] Set the single-layer water cloud criterion condition and the single-layer sea fog criterion condition through the difference characteristics corresponding to water cloud particles and sea fog particles;

[0019] Adjust the threshold value in the difference characteristics corresponding to water cloud particles and sea fog particles, and set the single-layer ice cloud criterion condition, the upper-layer ice cloud and the lower-layer water cloud criterion condition, and the upper-layer ice cloud and the lower-layer sea fog criterion condition through the difference characteristics of the reflectance of each spectral channel between the single-layer ice cloud, the upper-layer ice cloud and the lower-layer water cloud, and the cloud and fog simulation environments corresponding to the upper-layer ice cloud and the lower-layer sea fog.

[0020] Further, the data types of the cloud detection data include: cloud, possible cloud, clear sky, and possible clear sky.

[0021] Further, in step S5, before step S51, it also includes:

[0022] S50: Determine whether the data type of the cloud detection data is "cloud" or "possible cloud". If so, enter step S51.

[0023] Further, the water phase criterion condition is: the brightness temperature corresponding to the fifth channel is greater than the first preset value, and the difference between the brightness temperatures corresponding to the fourth channel and the fifth channel is less than or equal to the second preset value;

[0024] The ice phase criterion condition is: the brightness temperature corresponding to the fifth channel is less than or equal to the first preset value, or the difference between the brightness temperatures corresponding to the fourth channel and the fifth channel is greater than or equal to the third preset value; the third preset value is greater than the second preset value.

[0025] Further, the single-layer water cloud criterion is: the difference between the reflectances corresponding to the first channel and the second channel is greater than or equal to zero;

[0026] The single-layer sea fog criterion is: the difference between the reflectances corresponding to the first channel and the second channel is less than zero;

[0027] The single-layer ice cloud criterion is: the difference between the reflectances corresponding to the second channel and the third channel is greater than a fourth preset value.

[0028] Further,

[0029] The upper-layer ice cloud and lower-layer water cloud criterion is: the difference between the reflectances corresponding to the second channel and the third channel is less than or equal to the fourth preset value; and, the difference between the reflectances corresponding to the first channel and the second channel is greater than or equal to a fifth preset value;

[0030] The upper-layer ice cloud and lower-layer sea fog criterion is: the difference between the reflectances corresponding to the second channel and the third channel is less than or equal to the fourth preset value; and, the difference between the reflectances corresponding to the first channel and the second channel is less than the fifth preset value.

[0031] Further, the first preset value, the second preset value, the third preset value, the fourth preset value, and the fifth preset value are, in sequence: 238K, -1K, 0.5K, 0.04, 0.08.

[0032] The present invention also provides a sea fog detection system, including:

[0033] A real data acquisition module, configured to acquire satellite data in a real cloud and fog environment through a satellite imager. The satellite data includes longitude and latitude data. Through the longitude and latitude data, the primary data and cloud detection data corresponding to the target ocean area in the satellite data are acquired. The primary data includes the reflectances of the first channel, the second channel, and the third channel, as well as the brightness temperatures of the fourth channel and the fifth channel. The first channel is a visible light channel with a central wavelength of 0.64 μm, the second channel is a near-infrared channel with a central wavelength of 1.6 μm, the third channel is a near-infrared channel with a central wavelength of 2.25 μm, the fourth channel is a long-wave infrared channel with a central wavelength of 8.5 μm, and the fifth channel is a long-wave infrared channel with a central wavelength of 11 μm;

[0034] A model establishment module, configured to establish a cloud and fog simulation model corresponding to each set cloud and fog type based on radiative transfer simulation to simulate the real cloud and fog environment detected by the satellite imager under each set cloud and fog type, so as to obtain a cloud and fog simulation environment corresponding to each set cloud and fog type. The set cloud and fog types include: single-layer water cloud, single-layer sea fog, single-layer ice cloud, upper-layer ice cloud and lower-layer water cloud, and upper-layer ice cloud and lower-layer sea fog. The cloud and fog simulation model includes each spectral channel in the primary data;

[0035] A simulation data acquisition module, configured to obtain the reflectance and brightness temperature of each spectral channel included therein under each cloud simulation environment through each cloud simulation model;

[0036] A criterion condition setting module, configured to design the criterion conditions corresponding to each set cloud type through the reflectance and brightness temperature of each spectral channel under each cloud simulation environment, where the criterion conditions include: water phase state criterion condition, single-layer water cloud criterion condition, single-layer sea fog criterion condition, ice phase state criterion condition, single-layer ice cloud criterion condition, upper-layer ice cloud and lower-layer water cloud criterion condition, and upper-layer ice cloud and lower-layer sea fog criterion condition;

[0037] A detection module, configured to obtain the set cloud type corresponding to the target ocean area by using the criterion conditions through the primary data and cloud detection data corresponding to the target ocean area in the real cloud environment, specifically including:

[0038] A cloud top phase state detection unit, configured to obtain the cloud top phase state corresponding to the target ocean area by using the water phase state criterion condition and the ice phase state criterion condition according to the brightness temperature of the fourth channel and the fifth channel in the primary data, where the cloud top phase state is a water phase state or an ice phase state;

[0039] A first detection unit, configured to, when the cloud top phase state is a water phase state, obtain the set cloud type corresponding to the target ocean area by using the single-layer water cloud criterion condition and the single-layer sea fog criterion condition according to the reflectance of the first channel and the second channel in the primary data;

[0040] A second detection unit, configured to, when the cloud top phase state is an ice phase state, obtain the set cloud type corresponding to the target ocean area by using the single-layer ice cloud criterion condition, the upper-layer ice cloud and lower-layer water cloud criterion condition, and the upper-layer ice cloud and lower-layer sea fog criterion condition according to the reflectance of the first channel, the second channel, and the third channel in the primary data.

[0041] Compared with the prior art, the present invention has at least the following beneficial effects:

[0042] (1) Through each cloud simulation model, the present invention obtains the reflectance and brightness temperature of each spectral channel included therein under each cloud simulation environment to design the criterion conditions corresponding to each set cloud type, and after determining the cloud top phase state corresponding to the target ocean area, according to the reflectance of the first channel, the second channel, and the third channel in the primary data, uses the single-layer water cloud criterion condition, the single-layer sea fog criterion condition, the single-layer ice cloud criterion condition, the upper-layer ice cloud and lower-layer water cloud criterion condition, and the upper-layer ice cloud and lower-layer sea fog criterion condition to obtain the set cloud type corresponding to the target ocean area, which breaks through the limitation that it is impossible to effectively detect the low-layer sea fog or water cloud when blocked by ice clouds, realizes the detection of the low-layer water cloud and sea fog under the ice cloud, improves the technical level of the satellite imager in sea fog monitoring, and provides more accurate and efficient sea fog detection results for future business applications;

[0043] (2) The present invention conducts sensitivity analysis on the reflectance of the first channel, the second channel, and the third channel in each cloud and fog simulation environment to obtain the difference characteristics of the reflectance of each spectral channel between each cloud and fog simulation environment. The single-layer water cloud criterion condition and the single-layer sea fog criterion condition are set according to the corresponding difference characteristics of water cloud particles and sea fog particles; the threshold value in the corresponding difference characteristics of water cloud particles and sea fog particles is adjusted, and the single-layer ice cloud criterion condition, the upper ice cloud and lower water cloud criterion condition, and the upper ice cloud and lower sea fog criterion condition are set according to the difference characteristics of the reflectance of each spectral channel between the corresponding cloud and fog simulation environments of single-layer ice cloud, upper ice cloud and lower water cloud, and upper ice cloud and lower sea fog. By simulating the real cloud and fog environment corresponding to each set cloud and fog type and performing data analysis on the reflectance of each spectral channel obtained during the simulation process, the criterion conditions corresponding to each set cloud and fog type are designed, realizing the identification of low-level water cloud and sea fog below the ice cloud and solving the problem that sea fog or water cloud detection cannot be performed when there are clouds at high altitudes in the present invention. Description of the Drawings

[0044] Figure 1 It is a flowchart of a sea fog detection method;

[0045] Figure 2 It is a module diagram of a sea fog detection system. Detailed Embodiments

[0046] The following are specific embodiments of the present invention in combination with the drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0047] Embodiment 1

[0048] In order to realize the detection of low-level water cloud and sea fog below the ice cloud and improve the technical level of satellite imagers in sea fog monitoring, as Figure 1 shown, the present invention proposes a sea fog detection method, including the steps:

[0049] S1: Obtain satellite data in a real cloud and fog environment through a satellite imager. The satellite data includes latitude and longitude data. Based on the latitude and longitude data, obtain the primary data and cloud detection data corresponding to the target ocean area in the satellite data (that is, match the corresponding primary data and cloud detection data according to the geographical location of the target ocean area). The primary data includes the reflectance of the first channel, the second channel, and the third channel, as well as the brightness temperature of the fourth channel and the fifth channel. The first channel is a visible light channel with a central wavelength of 0.64 microns, the second channel is a near-infrared channel with a central wavelength of 1.6 microns, the third channel is a near-infrared channel with a central wavelength of 2.25 microns, the fourth channel is a long-wave infrared channel with a central wavelength of 8.5 microns, and the fifth channel is a long-wave infrared channel with a central wavelength of 11 microns.

[0050] It should be noted that before the primary data and cloud detection data are used in the following steps, invalid values therein are also excluded.

[0051] S2: Based on radiative transfer simulation, use an accurate forward radiative transfer model to establish cloud and fog simulation models corresponding to each set cloud and fog type, which are used to simulate the real cloud and fog environment detected by the satellite imager under each set cloud and fog type, so as to obtain the cloud and fog simulation environment corresponding to each set cloud and fog type. The set cloud and fog types include: single-layer water cloud, single-layer sea fog, single-layer ice cloud, upper-layer ice cloud and lower-layer water cloud, and upper-layer ice cloud and lower-layer sea fog. Each cloud and fog simulation model includes each spectral channel (the first channel, the second channel, the third channel, the fourth channel, and the fifth channel) in the primary data.

[0052] Specifically, in the cloud and fog simulation environment, ice cloud particles are aggregates composed of solid cylinders with a rough surface, and water cloud and sea fog particles are spherical with relatively regular shapes. The parameters of ice cloud, water cloud, and sea fog are set as follows in turn: the thickness of ice cloud and water cloud is 1 km, the thickness of sea fog is 0.5 km, and the heights are 10 km, 2 km, and 0.5 km respectively. The range of the effective particle radius of ice cloud, water cloud, and sea fog is set to 0 - 70 microns, 0 - 70 microns, and 0 - 10 microns respectively, and the optical thickness range is 0 - 40 for all.

[0053] S3: Through each cloud and fog simulation model, obtain the reflectance and brightness temperature of each spectral channel included therein under each cloud and fog simulation environment.

[0054] S4: Design criterion conditions corresponding to each set cloud and fog type through the reflectance and brightness temperature of each spectral channel under each cloud and fog simulation environment. The criterion conditions include: water phase criterion condition, single-layer water cloud criterion condition, single-layer sea fog criterion condition, ice phase criterion condition, single-layer ice cloud criterion condition, upper-layer ice cloud and lower-layer water cloud criterion condition, and upper-layer ice cloud and lower-layer sea fog criterion condition.

[0055] Specifically, according to the reflectance in each cloud and fog simulation environment, the difference characteristics of the reflectance of each spectral channel between each cloud and fog simulation environment are obtained, and the criterion conditions corresponding to each set cloud and fog type are designed based on the difference characteristics.

[0056] It should be noted that the purpose of simulating the cloud and fog environments of five set cloud and fog types, namely single-layer water cloud, single-layer sea fog, single-layer ice cloud, upper ice cloud and lower water cloud, and upper ice cloud and lower sea fog, is to conduct a sensitivity analysis on the reflectance of the first channel, the second channel, and the third channel in each cloud and fog simulation environment, so as to obtain the difference characteristics of the reflectance of each spectral channel between each set cloud and fog type. Specifically, both water cloud and sea fog are composed of liquid water, and their main difference lies in the particle size. The effective particle radius of water cloud is mainly between 10 and 20 microns, while the effective particle radius of sea fog is mostly 3 to 5 microns. The difference characteristics of the channel reflectance shown by the simulation results are as follows: when the optical thickness and the effective particle radius are small (both less than the corresponding set lower limit values), the difference in reflectance between the first channel and the second channel is less than 0, while when the optical thickness and the effective particle radius are large (both greater than the corresponding set upper limit values), the difference in reflectance is greater than 0. Therefore, for most water cloud particles, the difference in reflectance between the first channel and the second channel is greater than 0, while for sea fog particles, the difference in reflectance between the first channel and the second channel is less than 0. Based on the difference characteristics of the channel reflectance, the identification of water cloud and sea fog can be achieved. For ice cloud, the reflectance of most ice cloud particles in the first channel is greater than that in the second channel (if the cloud top phase state is judged to be the ice phase state and the difference in reflectance corresponding to the second channel and the third channel is greater than 0.04, it is indicated as a single-layer ice cloud). When there is an upper ice cloud blocking and there is a lower water cloud or sea fog, the characteristics of the lower water cloud or sea fog will be interfered. When the upper ice cloud layer is thick (exceeding the set value), the signal received by the satellite imager mainly comes from the ice cloud, and the reflectance of each channel shows the characteristics of the ice cloud; but when the optical thickness of the upper ice cloud is thin (the optical thickness is less than 7.5), the signal received by the satellite imager shows both some ice cloud characteristics and some water cloud or sea fog characteristics. Combining the above difference characteristics of the channel reflectance of water cloud and sea fog, by adjusting the thresholds corresponding to the first channel and the second channel (the fifth preset value in this embodiment), the water cloud and the sea fog can be distinguished.

[0057] In step S4, the criterion conditions corresponding to each set cloud and fog type are designed through the reflectance and brightness temperature of each spectral channel in each cloud and fog simulation environment, including:

[0058] By conducting a sensitivity analysis on the reflectance of the first channel, the second channel, and the third channel in each cloud and fog simulation environment, the difference characteristics of the reflectance of each spectral channel between each cloud and fog simulation environment are obtained. The method for obtaining the difference characteristics is:

[0059] Based on the particle characteristics that the effective particle radius of water cloud is between 10 and 20 microns and the effective particle radius of sea fog is between 3 and 5 microns, and obtained from the reflectance through each spectral channel in each cloud and fog simulation environment during the simulation process:

[0060] When both the optical thickness and the effective particle radius are less than the corresponding set lower limit values, the difference in reflectance between the first channel and the second channel is less than 0. When both the optical thickness and the effective particle radius are greater than the corresponding set upper limit values, the characteristic that the difference in reflectance is greater than or equal to 0 is obtained:

[0061] The difference in reflectance between the first channel and the second channel corresponding to water cloud particles is greater than or equal to the threshold value, and the difference in reflectance between the first channel and the second channel corresponding to sea fog particles is less than the threshold value. The threshold value is equal to 0;

[0062] The difference characteristics obtained during the simulation process also include: the difference characteristics of the reflectance of each spectral channel between the simulated cloud and fog environments corresponding to single-layer ice cloud, upper-layer ice cloud and lower-layer water cloud, and upper-layer ice cloud and lower-layer sea fog;

[0063] Set the criterion conditions for single-layer water cloud and single-layer sea fog through the difference characteristics corresponding to water cloud particles and sea fog particles;

[0064] Adjust the threshold value in the difference characteristics corresponding to water cloud particles and sea fog particles, and set the criterion conditions for single-layer ice cloud, upper-layer ice cloud and lower-layer water cloud, and upper-layer ice cloud and lower-layer sea fog through the difference characteristics of the reflectance of each spectral channel between the simulated cloud and fog environments corresponding to single-layer ice cloud, upper-layer ice cloud and lower-layer water cloud, and upper-layer ice cloud and lower-layer sea fog.

[0065] The criterion condition for the water phase state is: the brightness temperature corresponding to the fifth channel is greater than the first preset value (238K), and the difference in brightness temperature between the fourth channel and the fifth channel is less than or equal to the second preset value (-1K);

[0066] The criterion condition for the ice phase state is: the brightness temperature corresponding to the fifth channel is less than or equal to the first preset value (238K), or the difference in brightness temperature between the fourth channel and the fifth channel is greater than or equal to the third preset value (0.5K); the third preset value (0.5K) is greater than the second preset value (-1K).

[0067] The criterion condition for single-layer water cloud is: the difference in reflectance between the first channel and the second channel is greater than or equal to zero;

[0068] The criterion condition for single-layer sea fog is: the difference in reflectance between the first channel and the second channel is less than zero;

[0069] The criterion condition for single-layer ice cloud is: the difference in reflectance between the second channel and the third channel is greater than the fourth preset value (0.04).

[0070] The criterion conditions for the upper ice cloud and lower water cloud are as follows: the difference in reflectance corresponding to the second channel and the third channel is less than or equal to a fourth preset value (0.04); and, the difference in reflectance corresponding to the first channel and the second channel is greater than or equal to a fifth preset value (0.08).

[0071] The criterion conditions for the upper ice cloud and lower sea fog are as follows: the difference in reflectance corresponding to the second channel and the third channel is less than or equal to a fourth preset value (0.04); and, the difference in reflectance corresponding to the first channel and the second channel is less than a fifth preset value (0.08).

[0072] The first preset value, the second preset value, the third preset value, the fourth preset value, and the fifth preset value are 238K, -1K, 0.5K, 0.04, and 0.08 in sequence.

[0073] S5: Using the primary data and cloud detection data corresponding to the target ocean area in a real cloud and fog environment, obtain the set cloud and fog types corresponding to the target ocean area by using the criterion conditions; the data types of the cloud detection data include: cloud, possible cloud, clear sky, and possible clear sky.

[0074] The method for obtaining the set cloud and fog types corresponding to the target ocean area by using the criterion conditions includes the steps: S50: Determine whether the data type of the cloud detection data is "cloud" or "possible cloud", if so, enter step S51.

[0075] It should be noted that the cloud top phase refers to the phase of the top of the cloud. If it is the "water phase", it may be a single-layer water cloud or a single-layer sea fog; if it is the "ice phase", the uppermost part is an ice cloud, and there may be a water cloud or sea fog below.

[0076] S51: According to the brightness temperatures of the fourth channel and the fifth channel in the primary data, use the water phase criterion conditions and the ice phase criterion conditions to obtain the cloud top phase corresponding to the target ocean area, and the cloud top phase is the water phase or the ice phase.

[0077] S52: When the cloud top phase is the water phase, according to the reflectances of the first channel and the second channel in the primary data, use the single-layer water cloud criterion conditions and the single-layer sea fog criterion conditions to obtain the set cloud and fog types corresponding to the target ocean area.

[0078] S53: When the cloud top phase is the ice phase, according to the reflectances of the first channel, the second channel, and the third channel in the primary data, use the single-layer ice cloud criterion conditions, the upper ice cloud and lower water cloud criterion conditions, and the upper ice cloud and lower sea fog criterion conditions to obtain the set cloud and fog types corresponding to the target ocean area.

[0079] After obtaining the set cloud types corresponding to the target ocean area using the sea fog detection method in the present invention, the present invention further includes obtaining satellite lidar detection data for the target ocean area to verify the accuracy of the detection results of the present invention, so as to demonstrate the applicability of this method in different ocean areas and cloud conditions.

[0080] The present invention performs sensitivity analysis on the reflectivities of the first channel, the second channel, and the third channel in each cloud simulation environment to obtain the difference characteristics of the reflectivities of each spectral channel between each cloud simulation environment. The single-layer water cloud criterion condition and the single-layer sea fog criterion condition are set according to the difference characteristics corresponding to the water cloud particles and the sea fog particles; the thresholds in the difference characteristics corresponding to the water cloud particles and the sea fog particles are adjusted, and the single-layer ice cloud criterion condition, the upper ice cloud lower water cloud criterion condition, and the upper ice cloud lower sea fog criterion condition are set according to the difference characteristics of the reflectivities of each spectral channel between the cloud simulation environments corresponding to the single-layer ice cloud, the upper ice cloud lower water cloud, and the upper ice cloud lower sea fog. It simulates the real cloud environment corresponding to each set cloud type and performs data analysis on the reflectivities of each spectral channel obtained during the simulation process to design the criterion conditions corresponding to each set cloud type. It realizes the identification of low-level water clouds and sea fogs under the ice cloud, and solves the problem that sea fog or water cloud detection cannot be performed when there are clouds at high altitudes in the present invention.

[0081] Embodiment 2

[0082] As Figure 2 shown, the present invention also proposes a sea fog detection system, including:

[0083] A real data acquisition module, configured to obtain satellite data in a real cloud environment through a satellite imager. The satellite data includes longitude and latitude data, and the primary data and cloud detection data corresponding to the target ocean area in the satellite data are obtained through the longitude and latitude data. The primary data includes the reflectivities of the first channel, the second channel, and the third channel, as well as the brightness temperatures of the fourth channel and the fifth channel; the first channel is a visible light channel with a central wavelength of 0.64 microns, the second channel is a near-infrared channel with a central wavelength of 1.6 microns, the third channel is a near-infrared channel with a central wavelength of 2.25 microns, the fourth channel is a long-wave infrared channel with a central wavelength of 8.5 microns, and the fifth channel is a long-wave infrared channel with a central wavelength of 11 microns;

[0084] A model establishment module, which is used to establish cloud simulation models corresponding to each set cloud type based on radiative transfer simulation, and is used to simulate the real cloud environment detected by a satellite imager under each set cloud type to obtain a cloud simulation environment corresponding to each set cloud type; the set cloud types include: single-layer water cloud, single-layer sea fog, single-layer ice cloud, upper-layer ice cloud and lower-layer water cloud, and upper-layer ice cloud and lower-layer sea fog; each cloud simulation model includes each spectral channel in the first-level data.

[0085] A simulation data acquisition module, which is used to obtain the reflectance and brightness temperature of each spectral channel included in it in each cloud simulation environment through each cloud simulation model.

[0086] A criterion condition setting module, which is used to design criterion conditions corresponding to each set cloud type through the reflectance and brightness temperature of each spectral channel in each cloud simulation environment. The criterion conditions include: water phase criterion condition, single-layer water cloud criterion condition, single-layer sea fog criterion condition, ice phase criterion condition, single-layer ice cloud criterion condition, upper-layer ice cloud and lower-layer water cloud criterion condition, and upper-layer ice cloud and lower-layer sea fog criterion condition.

[0087] A detection module, which is used to obtain the set cloud type corresponding to the target ocean area by using the criterion conditions through the first-level data and cloud detection data corresponding to the target ocean area in the real cloud environment, specifically including:

[0088] A cloud top phase detection unit, which is used to obtain the cloud top phase corresponding to the target ocean area by using the water phase criterion condition and the ice phase criterion condition according to the brightness temperature of the fourth channel and the fifth channel in the first-level data. The cloud top phase is a water phase or an ice phase.

[0089] A first detection unit, which is used to obtain the set cloud type corresponding to the target ocean area by using the single-layer water cloud criterion condition and the single-layer sea fog criterion condition according to the reflectance of the first channel and the second channel in the first-level data when the cloud top phase is a water phase.

[0090] A second detection unit, which is used to obtain the set cloud type corresponding to the target ocean area by using the single-layer ice cloud criterion condition, the upper-layer ice cloud and lower-layer water cloud criterion condition, and the upper-layer ice cloud and lower-layer sea fog criterion condition according to the reflectance of the first channel, the second channel and the third channel in the first-level data when the cloud top phase is an ice phase.

[0091] Through various cloud and fog simulation models, the present invention obtains the reflectivity and brightness temperature of each spectral channel included therein under various cloud and fog simulation environments, so as to design the criterion conditions corresponding to each set cloud and fog type. After determining the cloud top phase state corresponding to the target ocean area, according to the reflectivities of the first channel, the second channel and the third channel in the primary data, the set cloud and fog type corresponding to the target ocean area is obtained by using the single-layer water cloud criterion condition, the single-layer sea fog criterion condition, the single-layer ice cloud criterion condition, the upper-layer ice cloud and lower-layer water cloud criterion condition, and the upper-layer ice cloud and lower-layer sea fog criterion condition. It breaks through the limitation that it is impossible to effectively detect low-level sea fog or water cloud when blocked by ice cloud, realizes the detection of low-level water cloud and sea fog under ice cloud, improves the technical level of satellite imager in sea fog monitoring, and provides more accurate and efficient sea fog detection results for future business applications.

[0092] It should be noted that all directional indications (such as up, down, left, right, front, back...) in the embodiments of the present invention are only used to explain the relative position relationship and movement conditions between various components in a specific posture (as shown in the attached drawings). If the specific posture changes, the directional indications will also change accordingly.

[0093] In addition, in the present invention, descriptions such as "first", "second", "one", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0094] In the present invention, unless otherwise clearly specified and defined, terms such as "connection" and "fixation" should be understood in a broad sense. For example, "fixation" may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and may be the internal connection of two components or the interaction relationship between two components, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0095] In addition, the technical solutions between various embodiments of the present invention can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

Claims

1. A sea fog detection method, characterized in that, Including the steps: S1: Obtain satellite data in a real cloud environment through a satellite imager. The satellite data includes latitude and longitude data. Obtain the primary data and cloud detection data corresponding to the target ocean area in the satellite data through the latitude and longitude data. The primary data includes the reflectance of the first channel, the second channel, and the third channel, as well as the brightness temperature of the fourth channel and the fifth channel. The first channel is the visible light channel with a central wavelength of 0.64 μm, the second channel is the near-infrared channel with a central wavelength of 1.6 μm, the third channel is the near-infrared channel with a central wavelength of 2.25 μm, the fourth channel is the long-wave infrared channel with a central wavelength of 8.5 μm, and the fifth channel is the long-wave infrared channel with a central wavelength of 11 μm. S2: Based on radiative transfer simulation, establish cloud simulation models corresponding to each set cloud type, which are used to simulate the real cloud environment detected by the satellite imager under each set cloud type to obtain the cloud simulation environment corresponding to each set cloud type. The each set cloud type includes: single-layer water cloud, single-layer sea fog, single-layer ice cloud, upper-layer ice cloud and lower-layer water cloud, and upper-layer ice cloud and lower-layer sea fog. Each cloud simulation model includes each spectral channel in the primary data. S4: Through each cloud simulation model, obtain the reflectance and brightness temperature of each spectral channel included in it under each cloud simulation environment. S4: Design the criterion conditions corresponding to each set cloud type through the reflectance and brightness temperature of each spectral channel under each cloud simulation environment. The criterion conditions include: water phase criterion condition, single-layer water cloud criterion condition, single-layer sea fog criterion condition, ice phase criterion condition, single-layer ice cloud criterion condition, upper-layer ice cloud and lower-layer water cloud criterion condition, and upper-layer ice cloud and lower-layer sea fog criterion condition. In step S4, designing the criterion conditions corresponding to each set cloud type through the reflectance and brightness temperature of each spectral channel under each cloud simulation environment includes: By performing sensitivity analysis on the reflectance of the first channel, the second channel, and the third channel under each cloud simulation environment, obtain the difference characteristics of the reflectance of each spectral channel between each cloud simulation environment. The method for obtaining the difference characteristics is: Based on the particle characteristics that the effective particle radius of water cloud is between 10 and 20 μm and the effective particle radius of sea fog is between 3 and 5 μm, and during the simulation process, obtained from the reflectance of each spectral channel under each cloud simulation environment: When both the optical thickness and the effective particle radius are less than the corresponding set lower limit value, the reflectance difference between the first channel and the second channel is less than 0. When both the optical thickness and the effective particle radius are greater than the corresponding set upper limit value, the reflectance difference is greater than or equal to 0. The characteristic is obtained: The difference characteristic that the reflectance difference between the first channel and the second channel corresponding to water cloud particles is greater than or equal to the threshold value, and the reflectance difference between the first channel and the second channel corresponding to sea fog particles is less than the threshold value. The threshold value is equal to 0. The difference characteristics obtained during the simulation process also include the difference characteristics of the reflectance of each spectral channel between the cloud simulation environments corresponding to single-layer ice cloud, upper-layer ice cloud and lower-layer water cloud, and upper-layer ice cloud and lower-layer sea fog. Set the single-layer water cloud criterion condition and the single-layer sea fog criterion condition according to the corresponding difference characteristics between water cloud particles and sea fog particles; Adjust the threshold value in the corresponding difference characteristics between water cloud particles and sea fog particles, and set the single-layer ice cloud criterion condition, the upper-layer ice cloud and lower-layer water cloud criterion condition, and the upper-layer ice cloud and lower-layer sea fog criterion condition according to the difference characteristics of the reflectance of each spectral channel between the single-layer ice cloud, the upper-layer ice cloud and lower-layer water cloud, and the corresponding cloud and fog simulation environment of the upper-layer ice cloud and lower-layer sea fog; S5: Through the primary data and cloud detection data corresponding to the target ocean area in the real cloud and fog environment, obtain the set cloud and fog types corresponding to the target ocean area by using the criterion conditions. The obtaining method includes: S51: According to the brightness temperatures of the fourth channel and the fifth channel in the primary data, use the water phase criterion condition and the ice phase criterion condition to obtain the cloud top phase corresponding to the target ocean area. The cloud top phase is the water phase or the ice phase; S52: When the cloud top phase is the water phase, according to the reflectances of the first channel and the second channel in the primary data, use the single-layer water cloud criterion condition and the single-layer sea fog criterion condition to obtain the set cloud and fog types corresponding to the target ocean area; S53: When the cloud top phase is the ice phase, according to the reflectances of the first channel, the second channel and the third channel in the primary data, use the single-layer ice cloud criterion condition, the upper-layer ice cloud and lower-layer water cloud criterion condition, and the upper-layer ice cloud and lower-layer sea fog criterion condition to obtain the set cloud and fog types corresponding to the target ocean area.

2. The sea fog detection method according to claim 1, wherein The data types of the cloud detection data include: cloud, possible cloud, clear sky, and possible clear sky.

3. The method for detecting sea fog according to claim 2, wherein, In the step S5, before the step S51, it further includes: S50: Judge whether the data type of the cloud detection data is "cloud" or "possible cloud". If so, enter the step S51.

4. A sea fog detection method according to claim 1, wherein The water phase criterion condition is: the brightness temperature corresponding to the fifth channel is greater than the first preset value, and the difference between the brightness temperatures corresponding to the fourth channel and the fifth channel is less than or equal to the second preset value; The ice phase criterion condition is: the brightness temperature corresponding to the fifth channel is less than or equal to the first preset value, or the difference between the brightness temperatures corresponding to the fourth channel and the fifth channel is greater than or equal to the third preset value; the third preset value is greater than the second preset value.

5. A sea fog detection method according to claim 4, wherein The single-layer water cloud criterion condition is: the difference between the reflectances corresponding to the first channel and the second channel is greater than or equal to zero; The single-layer sea fog criterion condition is: the difference between the reflectances corresponding to the first channel and the second channel is less than zero; The single-layer ice cloud criterion condition is: the difference between the reflectances corresponding to the second channel and the third channel is greater than the fourth preset value.

6. A sea fog detection method according to claim 5, wherein The upper-layer ice cloud and lower-layer water cloud criterion condition is: the difference between the reflectances corresponding to the second channel and the third channel is less than or equal to the fourth preset value; and, the difference between the reflectances corresponding to the first channel and the second channel is greater than or equal to the fifth preset value; The criterion conditions for upper-layer ice clouds and lower-layer sea fog are as follows: the difference in reflectance corresponding to the second channel and the third channel is less than or equal to a fourth preset value; and the difference in reflectance corresponding to the first channel and the second channel is less than a fifth preset value.

7. A sea fog detection method according to claim 6, characterized in that, The first preset value, the second preset value, the third preset value, the fourth preset value, and the fifth preset value are, in sequence: 238K, -1K, 0.5K, 0.04, 0.

08.

8. A sea fog detection system, characterized in that, It includes: A real data acquisition module, which is used to acquire satellite data in a real cloud and fog environment through a satellite imager. The satellite data includes latitude and longitude data. Through the latitude and longitude data, the primary data and cloud detection data corresponding to the target ocean area in the satellite data are acquired. The primary data includes the reflectance of the first channel, the second channel, and the third channel, as well as the brightness temperature of the fourth channel and the fifth channel. The first channel is a visible light channel with a central wavelength of 0.64 micrometers, the second channel is a near-infrared channel with a central wavelength of 1.6 micrometers, the third channel is a near-infrared channel with a central wavelength of 2.25 micrometers, the fourth channel is a long-wave infrared channel with a central wavelength of 8.5 micrometers, and the fifth channel is a long-wave infrared channel with a central wavelength of 11 micrometers. A model establishment module, which is used to establish cloud and fog simulation models corresponding to each set cloud and fog type based on radiative transfer simulation to simulate the real cloud and fog environment detected by the satellite imager under each set cloud and fog type, so as to obtain the cloud and fog simulation environment corresponding to each set cloud and fog type. The set cloud and fog types include: single-layer water cloud, single-layer sea fog, single-layer ice cloud, upper-layer ice cloud and lower-layer water cloud, and upper-layer ice cloud and lower-layer sea fog. Each cloud and fog simulation model includes each spectral channel in the primary data. A simulated data acquisition module, which is used to obtain the reflectance and brightness temperature of each spectral channel included in it under each cloud and fog simulation environment through each cloud and fog simulation model. A criterion condition setting module, which is used to design criterion conditions corresponding to each set cloud and fog type through the reflectance and brightness temperature of each spectral channel under each cloud and fog simulation environment. The criterion conditions include: water phase criterion conditions, single-layer water cloud criterion conditions, single-layer sea fog criterion conditions, ice phase criterion conditions, single-layer ice cloud criterion conditions, upper-layer ice cloud and lower-layer water cloud criterion conditions, and upper-layer ice cloud and lower-layer sea fog criterion conditions. In the criterion condition setting module, designing the criterion conditions corresponding to each set cloud and fog type through the reflectance and brightness temperature of each spectral channel under each cloud and fog simulation environment includes: By performing sensitivity analysis on the reflectance of the first channel, the second channel, and the third channel under each cloud and fog simulation environment, the difference characteristics of the reflectance of each spectral channel between each cloud and fog simulation environment are obtained. The method for obtaining the difference characteristics is: Based on the particle characteristics that the effective particle radius of water clouds is between 10 and 20 micrometers and the effective particle radius of sea fog is between 3 and 5 micrometers, and during the simulation process, obtained from the reflectance of each spectral channel under each cloud and fog simulation environment: When both the optical thickness and the effective particle radius are less than the corresponding set lower limit values, the difference in reflectance between the first channel and the second channel is less than 0. When both the optical thickness and the effective particle radius are greater than the corresponding set upper limit values, the characteristic that the difference in reflectance is greater than or equal to 0 is obtained: The difference characteristic that the difference in reflectance between the first channel and the second channel corresponding to water cloud particles is greater than or equal to the threshold value, and the difference in reflectance between the first channel and the second channel corresponding to sea fog particles is less than the threshold value, where the threshold value is equal to 0; The difference characteristics obtained during the simulation also include: the difference characteristics of the reflectance of each spectral channel between the simulated cloud and fog environments corresponding to single-layer ice clouds, upper-layer ice clouds and lower-layer water clouds, and upper-layer ice clouds and lower-layer sea fogs; Set the single-layer water cloud criterion condition and the single-layer sea fog criterion condition according to the difference characteristics corresponding to water cloud particles and sea fog particles; Adjust the threshold value in the difference characteristics corresponding to water cloud particles and sea fog particles, and set the single-layer ice cloud criterion condition, the upper-layer ice cloud and lower-layer water cloud criterion condition, and the upper-layer ice cloud and lower-layer sea fog criterion condition according to the difference characteristics of the reflectance of each spectral channel between the simulated cloud and fog environments corresponding to single-layer ice clouds, upper-layer ice clouds and lower-layer water clouds, and upper-layer ice clouds and lower-layer sea fogs; A detection module, which is used to obtain the set cloud and fog type corresponding to the target ocean area by using the criterion condition through the primary data and cloud detection data corresponding to the target ocean area in the real cloud and fog environment, specifically including: A cloud top phase detection unit, which is used to obtain the cloud top phase corresponding to the target ocean area according to the brightness temperatures of the fourth channel and the fifth channel in the primary data by using the water phase criterion condition and the ice phase criterion condition, and the cloud top phase is the water phase or the ice phase; A first detection unit, which is used to obtain the set cloud and fog type corresponding to the target ocean area according to the reflectances of the first channel and the second channel in the primary data by using the single-layer water cloud criterion condition and the single-layer sea fog criterion condition when the cloud top phase is the water phase; A second detection unit, which is used to obtain the set cloud and fog type corresponding to the target ocean area according to the reflectances of the first channel, the second channel and the third channel in the primary data by using the single-layer ice cloud criterion condition, the upper-layer ice cloud and lower-layer water cloud criterion condition, and the upper-layer ice cloud and lower-layer sea fog criterion condition when the cloud top phase is the ice phase.

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