All-sky total cloud cover detection method

Abstract

The invention discloses an all-sky total cloud cover detection method, and relates to the technical field of meteorology, and the method comprises the steps: based on the characteristic that the brightness temperature data in an atmosphere background state is greatly different from the brightness temperature data of cloud, under the characteristic that the atmosphere background state has continuity and does not suddenly change instantly, calculating the brightness temperature data of the cloud; performing data screening on observation data in a historical acquisition period in a clear sky state before a current detection moment, adding the data into a data processing pool, extracting historical minimum brightness temperature data in each elevation angle range in the data processing pool, and performing fitting to obtain an all-sky clear sky model; the method is used for representing the characteristics of brightness temperature data in an atmosphere background state at a current detection moment, and then the total cloud cover of the whole sky can be obtained according to the whole sky infrared brightness temperature data at the current detection moment in combination with a whole sky clear sky model. According to the method, the dependence on a large amount of historical data is reduced, the detection convenience and accuracy are high, and the application range is wide.

Description

Technical Field

[0001] The present application relates to the field of meteorological technology, and in particular to a method for detecting total cloud cover in the entire sky. Background Art

[0002] Clouds are the external manifestation of thermal and dynamic processes in the atmosphere, and are also an important part of the water cycle. Clouds play an important role in the balance of ground-atmosphere radiation, have a significant impact on climate patterns and weather forecasts, and are an important observation object in meteorological operations.

[0003] Infrared cloud meters are commonly used equipment for detecting cloud data in meteorological services. The total cloud cover in the whole sky is an important observation item of infrared cloud meters. When observing the total cloud cover in the whole sky of a region, the infrared cloud meter regularly uses a thermal infrared sensor (8-14μm) to collect infrared brightness temperature (Infrared Brightness Temperature, Tb) data of the whole sky, and collects the surrounding temperature and humidity environmental parameters at the same time. The atmospheric radiation transmission model is used to calculate the corresponding cloud base height (Cloud Base Height, CBH) based on the collected data, and then the number of cloud points N in the whole sky is calculated according to the definition of the local common cloud height observation range in "GB / T 35222-2017 Ground Meteorological Observation Specification Cloud". cloudy and the number of cloud-free sky points N clear , then follow N cloudy / (N cloudy +N clear ) to calculate the total cloud cover in the sky.

[0004] However, when infrared cloud meters measure the total cloud cover in a region, it is necessary to accumulate a sufficient amount of historical meteorological data in the region and then use the atmospheric radiation transfer model to express the atmospheric conditions of the region for one year with a mathematical model. However, the atmospheric radiation transfer model only supports six atmospheric models by default, namely tropical, mid-latitude summer, mid-latitude winter, subarctic summer, subarctic winter, and 1976 US standard atmosphere, which cannot well represent the atmospheric mode in most regions, resulting in large measurement errors. In addition, in the above-mentioned approach, the accumulated historical meteorological data can only be used to calculate the cloud base height when the data types and data volume are sufficient. Therefore, in actual operation, it is often necessary to accumulate historical meteorological data including ground temperature, ground humidity, sounding atmospheric temperature profile, sounding atmospheric humidity profile, sounding atmospheric pressure profile, etc. in the region in the past year. For field stations or newly built stations without historical meteorological data, it is impossible to complete the observation of the total cloud cover in the sky, and the scope of application is limited, or only historical meteorological data of nearby areas can be used, resulting in large measurement errors. Summary of the invention

[0005] In view of the above problems and technical requirements, this application proposes a method for detecting total cloud cover in the entire sky. The technical solution of this application is as follows:

[0006] A method for detecting total cloud cover in the entire sky, the method comprising:

[0007] Obtain observation data from a historical collection period in a clear sky state before the current detection time, the observation data at least including the full sky infrared brightness temperature data observed in the current historical collection period, and the atmospheric background state of the historical collection period is consistent with that of the current detection time;

[0008] Eliminate some abnormal infrared brightness temperature data in the observation data of the current historical collection period to obtain filtered infrared brightness temperature data;

[0009] Add the filtered infrared brightness temperature data of the historical collection period to the data processing pool;

[0010] The filtered infrared brightness temperature data in the data processing pool are grouped according to the acquisition angle range, and the minimum value of the infrared brightness temperature data under each elevation angle range is obtained as the historical minimum brightness temperature data under the current elevation angle range;

[0011] The full-sky clear sky model is obtained by fitting the historical minimum brightness temperature data of each elevation angle range in the data processing pool. The full-sky clear sky model indicates the clear sky threshold brightness temperature data T at each elevation angle θ in the full sky range. ref (θ);

[0012] The total cloud cover of the entire sky is obtained based on the infrared brightness temperature data of the entire sky at the current detection moment combined with the entire sky clear sky model.

[0013] A further technical solution is that the method for detecting total cloud cover in the entire sky further includes:

[0014] Initialize integer parameter i=1;

[0015] Obtain the observation data of the i-th historical collection period most recent before the current detection time;

[0016] Add the filtered infrared brightness temperature data of the i-th historical collection period to the data processing pool;

[0017] When it is detected that the historical minimum brightness temperature data at each elevation angle range in the data processing pool meets the brightness temperature data quality control condition under the clear sky state, the step of fitting the historical minimum brightness temperature data at each elevation angle range in the data processing pool to obtain a full-sky clear sky model is executed;

[0018] When it is detected that the historical minimum brightness temperature data under each elevation angle range in the data processing pool does not meet the brightness temperature data quality control conditions under the clear sky state, set i=i+1 and execute again the step of obtaining the observation data of the most recent i-th historical collection period before the current detection moment.

[0019] Its further technical solution is to detect whether the historical minimum brightness temperature data at each elevation angle range in the data processing pool meets the brightness temperature data quality control conditions under clear sky conditions, including:

[0020] When the temperature difference between the historical minimum brightness temperature data in each elevation angle range and the ground temperature reaches the second temperature difference threshold, it is determined that the quality control conditions of the brightness temperature data under the clear sky state are met; otherwise, it is determined that the quality control conditions of the brightness temperature data under the clear sky state are not met; wherein the ground temperature is the temperature at the historical observation time of the historical minimum brightness temperature data in the elevation angle range corresponding to the zenith direction.

[0021] A further technical solution is that the observation data of any i-th historical collection period also includes the surface temperature data in the current historical collection period, and the filtered infrared brightness temperature data of the i-th historical collection period includes:

[0022] Determine the sun position in the i-th historical collection period according to the time of the i-th historical collection period combined with the longitude and latitude;

[0023] The infrared brightness temperature data in the predetermined area around the sun position are removed from the all-sky infrared brightness temperature data of the observation data of the i-th historical collection period, and the infrared brightness temperature data whose temperature difference with the surface temperature data reaches the first temperature difference threshold are removed to obtain the filtered infrared brightness temperature data of the i-th historical collection period.

[0024] Its further technical solution is to fit the historical minimum brightness temperature data of each elevation angle range to obtain a full sky clear sky model including:

[0025] The clear sky brightness temperature reference curve is obtained by fitting the historical minimum brightness temperature data in each elevation angle range. The clear sky brightness temperature reference curve indicates the clear sky reference brightness temperature data T at each elevation angle θ in the whole sky range. b (θ);

[0026] Calculate the clear sky reference brightness temperature data T at each elevation angle θ b (θ) and threshold temperature T th The sum is taken as the clear sky threshold brightness temperature data T at the current elevation angle θ ref (θ) = T b (θ)+T th , and obtain the full sky clear sky model.

[0027] A further technical solution is to obtain a clear sky brightness temperature reference curve by fitting the historical minimum brightness temperature data in each elevation angle range, including:

[0028] Using the historical minimum brightness temperature data T in the elevation range where the first reference elevation angle θ1 is located min (θ1), and the historical minimum brightness temperature data T in the elevation range where the second reference elevation angle θ2 is located min (θ2), according to T min (θ)=a×sec(θ)+b for curve fitting; where sec(θ) is the rate of change of infrared brightness temperature data with elevation angle θ, and a and b are curve fitting parameters respectively;

[0029] According to the fitted curve, T at each elevation angle θ in the whole sky range min (θ) to obtain the clear sky reference brightness temperature data T at each elevation angle θ b (θ).

[0030] A further technical solution is that the clear sky reference brightness temperature data T at any elevation angle θ b (θ) is: T determined based on the fitted curve min The smaller value between (θ) and the historical minimum brightness temperature data in the elevation angle range where the elevation angle θ lies.

[0031] Its further technical solution is that the first reference elevation angle θ1 = 30°, the second reference elevation angle θ2 = 30°, sec(30°) = 2sec(90°), and the curve fitting parameter a = T min (30°)-T min (90°), b = 2 × T min (90°)-T min (30°).

[0032] A further technical solution is to determine the threshold temperature T th include:

[0033] Determine the maximum measurement error in the cloud height observation range, and take the product of the maximum measurement error and the adiabatic lapse rate of the moist atmosphere as the threshold temperature T th .

[0034] Its further technical solution is to obtain the total cloud cover of the whole sky based on the infrared brightness temperature data of the whole sky at the current detection time combined with the clear sky model of the whole sky, including:

[0035] For any detection point in the whole sky, when the infrared brightness temperature data of the detection point at the current detection time is greater than the clear sky threshold brightness temperature data at the elevation angle where the detection point is located, the detection point is determined to be a cloud point, otherwise the detection point is determined to be a cloudless sky point;

[0036] The total cloud amount in the sky is calculated based on the number of cloud points and the number of cloud-free sky points in the entire sky.

[0037] The beneficial technical effects of this application are:

[0038] The present application discloses a method for detecting the total cloud cover of the whole sky. The method is based on the fact that the brightness temperature data under the atmospheric background state is greatly different from the brightness temperature data of the cloud. Under the characteristic that the atmospheric background state is continuous and will not change suddenly, the observation data of the historical acquisition period of the neighbors at the current detection time under the clear sky state is used to fit the whole sky clear sky model, which is used to characterize the characteristics of the brightness temperature data under the atmospheric background state at the current detection time. Thus, the total cloud cover of the whole sky can be detected according to the infrared brightness temperature data of the whole sky at the current detection time combined with the whole sky clear sky model. The method avoids the defect of the existing method that only the atmospheric radiation transmission model can be used to analyze limited patterns, which is conducive to improving the detection accuracy. In addition, the method does not need to accumulate a large amount of local sounding data and temperature and humidity historical data, reduces the dependence on long-term historical data, and is easy to implement. It is also conducive to expanding the scope of application, so that the method has high detection convenience and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a method flow chart of a method for detecting total cloud cover in the entire sky in one embodiment of the present application.

[0040] Figure 2 It is a schematic diagram of the curves of the clear sky reference brightness temperature data and the clear sky threshold brightness temperature data at different elevation angles obtained in an example.

[0041] Figure 3 It is a flow chart of a method for fitting a full-sky clear sky model in one embodiment of the present application. DETAILED DESCRIPTION

[0042] The specific implementation of the present application is further described below in conjunction with the accompanying drawings.

[0043] This application discloses a method for detecting total cloud cover in the entire sky. Please refer to Figure 1 The flowchart shown in the figure shows that the method for detecting the total cloud cover in the whole sky can be performed by an infrared cloud meter. The method for detecting the total cloud cover in the whole sky includes:

[0044] Step 1, obtain the observation data of the historical collection period before the current detection time under the clear sky state. The clear sky state referred to in this application refers to the meteorological state in which at least part of the sky is not covered by clouds and is in the atmospheric background state, including the common sunny weather state and the sunny and cloudy weather state.

[0045] The observation data of a historical collection period at least includes the all-sky infrared brightness temperature data observed in the current historical collection period. The all-sky infrared brightness temperature data includes the infrared brightness temperature data of any detection point within the entire sky, and each detection point has its own corresponding azimuth and elevation angle.

[0046] The full sky range referred to in this application generally includes the sky range from the horizon to 90° elevation and 360° azimuth in the pitch direction, and the direction close to 90° elevation is defined as the zenith direction. However, in actual applications, due to the interference and obstruction of near-surface objects, it is actually difficult for infrared cloud meters to completely cover detection from the horizon. According to the first item of Article 14 of the "Regulations on the Protection of Meteorological Facilities and Meteorological Detection Environment": It is prohibited to build buildings and structures with a height exceeding 1 / 8 of the distance from the observation field within the 800-meter detection environmental protection range around the observation field. Through conversion, it can be known that the full sky range that complies with this regulation includes the sky range from 7.125° elevation to 90° elevation and 360° azimuth in the pitch direction. Taking into account that there are many objects near the surface that will affect the observation, the general industry definition of the full sky range includes the sky range from 15° elevation to 90° elevation and 360° azimuth in the pitch direction.

[0047] The duration of a historical collection period can be customized, and a historical collection period can contain all-sky infrared brightness temperature data of multiple historical observation times. The duration and observation frequency of a specific historical collection period can be customized. For example, in an example, a historical collection period is set to cover a 24-hour duration, and observations are made every 10 minutes in a historical collection period, then a historical collection period includes all-sky infrared brightness temperature data of 144 historical observation times.

[0048] Step 2: Remove the abnormal infrared brightness temperature data in the observation data of the historical collection period to obtain the filtered infrared brightness temperature data. Due to the influence of the sun and the observation noise, there will be some abnormal data in the observed infrared brightness temperature data. In order to avoid the influence of these abnormal data on the subsequent detection process, data screening is first performed.

[0049] In addition to the infrared brightness temperature data of the entire sky, the observation data of the current historical collection period also includes the surface temperature data of the current historical collection period. The infrared brightness temperature data of any detection point in the observation data of the current historical collection period is subtracted from the surface temperature data. Under normal circumstances, the temperature difference between the two should be less than the first temperature difference threshold. Therefore, the abnormal noise points that reach the first temperature difference threshold need to be removed. The first temperature threshold is generally set to 70°C. In addition, the infrared brightness temperature data at the direct sunlight position will also have a large error due to the influence of the sun, so it also needs to be removed.

[0050] Based on the above considerations, the sun position in the ith historical collection period is first determined according to the time of the ith historical collection period combined with the longitude and latitude of the location of the infrared cloud meter. This step can be implemented using existing methods and will not be repeated here. Then, the infrared brightness temperature data in the predetermined area around the sun position is removed from the full-sky infrared brightness temperature data of the observation data of the ith historical collection period, and the infrared brightness temperature data whose temperature difference with the surface temperature data reaches the first temperature difference threshold is removed to obtain the filtered infrared brightness temperature data. The range of the predetermined area around the sun position can be customized. For example, in one example, the predetermined area around the sun position is set to cover the range of ±5° elevation angle and ±5° azimuth angle of the sun position.

[0051] Step 3: Add the filtered infrared brightness temperature data of the historical collection period to the data processing pool.

[0052] Step 4, grouping the filtered infrared brightness temperature data in the data processing pool according to the collection angle range, and obtaining the minimum value of the infrared brightness temperature data under each elevation range as the historical minimum brightness temperature data under the current elevation range. Each elevation range can be customized. Generally, the full elevation range of the entire sky range is divided according to the required elevation resolution, such as the elevation resolution of the infrared nephelometer itself, or according to the common 2.25°. When a historical collection period contains observation data from multiple historical observation times, this step combines the filtered infrared brightness temperature data of the current historical collection period at multiple historical observation times to obtain the historical minimum brightness temperature data under each elevation range.

[0053] Step 5: Fit the full-sky clear sky model based on the historical minimum brightness temperature data of each elevation angle range in the data processing pool. The fitted full-sky clear sky model indicates the clear sky threshold brightness temperature data T at each elevation angle θ in the full sky range. ref (θ) is used to characterize the brightness temperature data of the atmospheric background state at each elevation angle θ.

[0054] The core design concept of this application is: in the atmospheric background state, the 8-14μ thermal radiation received by the ground comes from cosmic radiation, solar radiation, thermal radiation emitted by the atmosphere during transmission due to solar radiation heating, and thermal radiation scattered and refracted by the ground. At the same time, 8-14μ is also called the atmospheric window area. The atmosphere has little influence on this section, and cosmic radiation and solar radiation (in the direction not directly shining on the sun) are also very small, so the infrared brightness temperature data (infrared radiation) in the atmospheric background state is also very small. Clouds can be considered as objects entering in the atmospheric background state. Since they are generally within 10 kilometers from the ground, the infrared thermal radiation of clouds is greatly affected by the atmospheric temperature. At this time, the infrared thermal radiation of clouds must be higher than the atmospheric background, that is, the infrared brightness temperature data of clouds must be greater than the infrared brightness temperature data in the atmospheric background state. Therefore, it is only necessary to characterize the infrared brightness temperature data in the atmospheric background state at the current detection time, and the difference between the atmospheric background state and the infrared brightness temperature data of clouds can be used to distinguish clouds.

[0055] The present application uses the observation data of the historical collection period under the clear sky state to fit the full sky clear sky model, and the full sky clear sky model is used to characterize the brightness temperature data of the atmospheric background state during the historical collection period. Therefore, the atmospheric background state and clouds can be distinguished using the clear sky threshold brightness temperature data indicated by the full sky clear sky model. Since the atmospheric background state is continuous and does not suddenly change, when the historical collection period used to fit the full sky clear sky model is close in time to the current detection moment, it can be considered that the atmospheric background state of the historical collection period is consistent with the atmospheric background state of the current detection moment within the error range, so the full sky clear sky model that characterizes the atmospheric background state of the historical collection period can be used to characterize the atmospheric background state of the current detection moment.

[0056] In order to meet this requirement, the time difference between the historical collection period and the current detection time for fitting the full sky clear sky model in this application does not exceed the time difference threshold, and the time difference threshold is the continuous length of time during which the atmospheric background state remains unchanged by meteorological data statistics, thereby ensuring that the atmospheric background state of the historical collection period is consistent with that of the current detection time. For example, according to the actual meteorological data statistics, it is generally believed that the atmospheric background state within 7 days remains basically unchanged, so the time difference threshold is set to 7 days, that is, 168 hours. When the similarity of the atmospheric background state within the error allowable range reaches the predetermined requirement, it can be considered that the atmospheric background state remains consistent.

[0057] In order to fit the obtained full sky clear sky model, the following steps are included:

[0058] (1) First, a continuous clear sky brightness temperature reference curve is obtained by fitting the historical minimum brightness temperature data of each discrete elevation angle range. The clear sky brightness temperature reference curve obtained here is a continuous curve, indicating the clear sky reference brightness temperature data T at each elevation angle θ in the entire sky range. b(θ).

[0059] According to the distribution of historical minimum brightness temperature data with elevation angle observed by ground-based observations, the distribution of historical minimum brightness temperature data under atmospheric background conditions satisfies T min (θ) = a×sec(θ) + b, then first use the historical minimum brightness temperature data T in the elevation range where the first reference elevation angle θ1 is located min (θ1), and the historical minimum brightness temperature data T in the elevation range where the second reference elevation angle θ2 is located min (θ2), according to T min (θ)=a×sec(θ)+b for curve fitting. Among them, sec(θ) is the rate of change of infrared brightness temperature data with elevation angle θ, and a and b are curve fitting parameters respectively. In order to ensure the accuracy of fitting, the first reference elevation angle θ1 and the second reference elevation angle θ2 used reach a predetermined elevation angle difference to avoid the fitting error caused by the closeness of the two reference elevation angles. In order to reduce the fitting error and facilitate calculation, in one embodiment, the first reference elevation angle θ1=30° and the second reference elevation angle θ2=90°. At this time, since sec(30°)=2sec(90°), the curve fitting parameters can be quickly calculated according to the following formula: a=T min (30°)-T min (90°), b = 2 × T min (90°)-T min (30°). In addition, the infrared radiation transmission at an elevation angle of 90° is the shortest, and the historical minimum brightness temperature data here is the smallest, which is conducive to obtaining an accurate distribution curve of the historical minimum brightness temperature data.

[0060] Then, according to the T at each elevation angle θ in the whole sky range indicated by the fitted curve, min (θ) can get the clear sky reference brightness temperature data T at each elevation angle θ b (θ), specifically: clear sky reference brightness temperature data T at any elevation angle θ b (θ) is the T at the elevation angle θ determined according to the fitted curve min The smaller value between (θ) and the measured historical minimum brightness temperature data within the elevation angle range where the elevation angle θ is located.

[0061] 2. Calculate the clear sky reference brightness temperature data T at each elevation angle θ b (θ) and threshold temperature T th The sum is taken as the clear sky threshold brightness temperature data T at the current elevation angle θ ref (θ) = T b (θ)+T th , we get the full sky clear model. Here the threshold temperature T thThe setting of directly affects the final clear sky threshold brightness temperature data and determines the threshold temperature T th The method is: determine the maximum measurement error of the cloud height observation range, and use the product of the maximum measurement error and the adiabatic lapse rate of the moist atmosphere as the threshold temperature T th .

[0062] According to the definition of cloud height observation range in GB / T 35222-2017 Ground Meteorological Observation Specification Cloud, the range from the ground to 10km in the sky (the upper limit of cirrus cloud observation) is defined as the cloud height observation range, while the cloud height error in the Laser Ceilometer Observation Specification (Trial) is ±20% when it is greater than 1km. Combining the above two specifications, it can be seen that the cloud height observation range is 10km in the sky, and its maximum measurement error is 10km*20%=2km, and the adiabatic lapse rate of humid atmosphere is 6.5℃ / km, so the two are multiplied to get the threshold temperature threshold T th In one example, the clear sky reference brightness temperature data T at each elevation angle θ is obtained. b (θ), and the clear sky threshold brightness temperature data T at each elevation angle θ ref (θ) Figure 2 shown.

[0063] Step 6, obtain the infrared brightness temperature data of the whole sky at the current detection time, and obtain the total cloud cover of the whole sky based on the infrared brightness temperature data of the whole sky at the current detection time combined with the clear sky model of the whole sky. For any detection point within the whole sky, when the infrared brightness temperature data of the detection point at the current detection time is greater than the clear sky threshold brightness temperature data at the elevation angle of the detection point, it is determined that the detection point belongs to a cloud point, otherwise it is determined that the detection point belongs to a cloudless sky point. Then, according to the general calculation formula for the total cloud cover of the whole sky, the total cloud cover of the whole sky can be calculated according to the number of cloud points and the number of cloudless sky points within the whole sky.

[0064] As mentioned above, this application needs to use the observation data of the historical collection period in the clear sky state that is consistent with the atmospheric background state at the current detection time to fit the full sky clear sky model. However, in fact, during the operation of the infrared cloud meter, the infrared cloud meter will obtain observation data at each observation time and save it. When it is necessary to fit the full sky clear sky model at the current detection time, it is difficult to directly locate the required historical collection period from all the saved observation data. Therefore, in actual implementation, the full sky clear sky model is fitted by cyclic detection, including the following steps, please refer to Figure 3 The flowchart shown:

[0065] (1) Initialize the integer parameter i=1 and initialize the data processing pool to be empty.

[0066] (2) Obtain the observation data of the i-th historical collection period most recent before the current detection time.

[0067] (3) The filtered infrared brightness temperature data of the i-th historical collection period are added to the data processing pool. The data processing pool is a space for data processing and contains the filtered infrared brightness temperature data of each previous historical collection period.

[0068] (4) The observation data of the i-th historical collection period are screened through the above step 2, and the historical minimum brightness temperature data under each elevation angle range in the data processing pool are obtained through steps 3 and 4.

[0069] (5) Check whether the historical minimum brightness temperature data at each elevation angle range in the data processing pool meets the brightness temperature data quality control conditions under clear sky conditions.

[0070] According to the conclusion of the existing atmospheric radiation transmission model: in clear and cloudless weather, the infrared brightness temperature of the sky is very low, and the infrared brightness temperature from the zenith to the elevation angle of 30° is 30 to 40°C lower than the surface temperature. Considering the low visibility, when the temperature difference between the historical minimum brightness temperature data from the zenith to the elevation angle of 30° and the ground temperature reaches the second temperature difference threshold, it is determined that the brightness temperature data quality control conditions under the clear sky state are met, otherwise it is determined that the brightness temperature data quality control conditions under the clear sky state are not met. Among them, the ground temperature is the temperature at the historical observation time of the historical minimum brightness temperature data under the elevation angle range corresponding to the zenith direction. The second temperature difference threshold is set based on experience, generally set to 30°C.

[0071] (6) When it is detected that the historical minimum brightness temperature data at each elevation angle range in the data processing pool meets the brightness temperature data quality control conditions under the clear sky state, the full-sky clear sky model is fitted according to the method in step 5 above.

[0072] (7) When it is detected that the historical minimum brightness temperature data under each elevation angle range in the data processing pool does not meet the brightness temperature data quality control conditions under the clear sky state, i=i+1 is set and the step of obtaining the observation data of the i-th historical collection period most recently before the current detection time is executed again, that is, the observation data of the previous historical collection period is continued to be detected until the time difference between the i-th historical collection period and the current detection time reaches the time difference threshold. At this time, it is considered that there is a difference between the atmospheric background state of the i-th historical collection period and the current detection time. For example, the atmosphere is affected by the aerosol process (high-altitude dust, water vapor, etc.). At this time, the atmospheric background state before and after the aerosol impact is quite different. It is not suitable to continue to traverse the historical collection period further ago. Then, the full-sky clear sky model obtained by the previous fitting can be used to analyze the total cloud cover of the whole sky. However, according to the results of actual meteorological statistical data, there will always be several historical collection periods in the clear sky state in the historical time period when the time difference with the current detection time reaches the time difference threshold, and there will basically be no clear sky state. Therefore, before the time difference between the i-th historical collection period and the current detection time reaches the time difference threshold, the historical collection period in the clear sky state can basically be traversed to fit the full sky clear sky model. Through the above traversal order from near to far from the current detection time, the observation data of the historical collection period closest to the current detection time and in the clear sky state can be traversed to fit the full sky clear sky model of the current detection time, which can improve the accuracy of the full sky clear sky model.

[0073] In theory, the historical collection period can be customized according to actual needs, and the denser the historical collection period is, the more conducive it is to improving the accuracy of the fitted all-sky clear sky model, thereby improving the accuracy of the total cloud amount detected in the sky. However, if the time interval of the historical collection period is short, the density of the historical collection period is high. Considering the limited computing power of the infrared cloud meter itself, this will lead to an increase in computing power and processing time. Therefore, considering the detection accuracy and detection efficiency, one historical collection period is generally taken as one day.

[0074] The above is only a preferred embodiment of the present application, and the present application is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present application should be considered to be included in the protection scope of the present application.

Claims

1. A method for detecting total cloud cover in the entire sky, characterized in that: The whole sky total cloud amount detection method comprises: Obtain observation data of a historical collection period in a clear sky state before the current detection time, wherein the observation data at least includes all-sky infrared brightness temperature data observed in the current historical collection period, and the historical collection period is consistent with the atmospheric background state at the current detection time; Eliminate some abnormal infrared brightness temperature data in the observation data of the historical collection period to obtain filtered infrared brightness temperature data; Adding the filtered infrared brightness temperature data of the historical collection period to a data processing pool; The filtered infrared brightness temperature data in the data processing pool are grouped according to the acquisition angle range, and the minimum value of the infrared brightness temperature data under each elevation angle range is obtained as the historical minimum brightness temperature data under the current elevation angle range; The full sky clear sky model is obtained by fitting the historical minimum brightness temperature data of each elevation angle range in the data processing pool, and the full sky clear sky model indicates the clear sky threshold brightness temperature data T at each elevation angle θ in the full sky range. ref (θ); The total cloud cover of the entire sky is obtained based on the infrared brightness temperature data of the entire sky at the current detection moment in combination with the entire sky clear sky model.

2. The method for detecting total cloud cover in the whole sky according to claim 1, characterized in that: The whole sky total cloud amount detection method also includes: Initialize integer parameter i=1; Obtain the observation data of the i-th historical collection period most recent before the current detection time; Add the filtered infrared brightness temperature data of the i-th historical collection period to the data processing pool; When it is detected that the historical minimum brightness temperature data at each elevation angle range in the data processing pool meets the brightness temperature data quality control condition under the clear sky state, the step of fitting the historical minimum brightness temperature data at each elevation angle range in the data processing pool to obtain the full sky clear sky model is executed; When it is detected that the historical minimum brightness temperature data under each elevation angle range in the data processing pool does not meet the brightness temperature data quality control conditions under the clear sky state, set i=i+1 and execute the step of obtaining the observation data of the most recent i-th historical collection period before the current detection moment again.

3. The method for detecting total cloud cover in the whole sky according to claim 2, characterized in that: Check whether the historical minimum brightness temperature data at each elevation angle in the data processing pool meets the brightness temperature data quality control conditions under clear sky conditions, including: When the temperature difference between the historical minimum brightness temperature data in each elevation angle range and the ground temperature reaches the second temperature difference threshold, it is determined that the quality control conditions of the brightness temperature data under the clear sky state are met; otherwise, it is determined that the quality control conditions of the brightness temperature data under the clear sky state are not met; wherein the ground temperature is the temperature at the historical observation time of the historical minimum brightness temperature data in the elevation angle range corresponding to the zenith direction.

4. The method for detecting total cloud cover in the whole sky according to claim 2, characterized in that: The observation data of any i-th historical collection period also includes the surface temperature data in the current historical collection period. The filtered infrared brightness temperature data of the i-th historical collection period includes: Determine the sun position in the i-th historical collection period according to the time of the i-th historical collection period combined with the longitude and latitude; The infrared brightness temperature data in the predetermined area around the sun position are removed from the all-sky infrared brightness temperature data of the observation data of the i-th historical collection period, and the infrared brightness temperature data whose temperature difference with the surface temperature data reaches the first temperature difference threshold are removed to obtain the filtered infrared brightness temperature data of the i-th historical collection period.

5. The method for detecting total cloud cover in the whole sky according to claim 1, characterized in that: The full sky clear sky model obtained by fitting the historical minimum brightness temperature data in each elevation angle range includes: The clear sky brightness temperature reference curve is obtained by fitting the historical minimum brightness temperature data of each elevation angle range. The clear sky brightness temperature reference curve indicates the clear sky reference brightness temperature data T at each elevation angle θ in the whole sky range. b (θ); Calculate the clear sky reference brightness temperature data T at each elevation angle θ b (θ) and threshold temperature T th The sum is taken as the clear sky threshold brightness temperature data T at the current elevation angle θ ref (θ) = T b (θ)+T th , and obtain the full-sky clear sky model.

6. The method for detecting total cloud cover in the whole sky according to claim 5, characterized in that: The clear sky brightness temperature reference curves obtained by fitting the historical minimum brightness temperature data in each elevation angle range include: Using the historical minimum brightness temperature data T in the elevation range where the first reference elevation angle θ1 is located min (θ1), and the historical minimum brightness temperature data T in the elevation range where the second reference elevation angle θ2 is located min (θ2), according to T min (θ)=a×sec(θ)+b for curve fitting; where sec(θ) is the rate of change of infrared brightness temperature data with elevation angle θ, and a and b are curve fitting parameters respectively; According to the fitted curve, T at each elevation angle θ in the whole sky range min (θ) to obtain the clear sky reference brightness temperature data T at each elevation angle θ b (θ).

7. The method for detecting total cloud cover in the whole sky according to claim 6, characterized in that: Clear sky reference brightness temperature data T at any elevation angle θ b (θ) is: T determined based on the fitted curve min (θ) and the smaller value between the historical minimum brightness temperature data in the elevation angle range within which the elevation angle θ is located.

8. The method for detecting total cloud cover in the whole sky according to claim 6, characterized in that: The first reference elevation angle θ1 = 30°, the second reference elevation angle θ2 = 90°, sec(30°) = 2sec(90°), and the curve fitting parameter a = T min (30°)-T min (90°), b = 2 × T min (90°)-T min (30°).

9. The method for detecting total cloud cover in the whole sky according to claim 5, characterized in that: Determine the threshold temperature T th include: Determine the maximum measurement error in the cloud height observation range, and take the product of the maximum measurement error and the adiabatic lapse rate of the moist atmosphere as the threshold temperature T th .

10. The method for detecting total cloud cover in the whole sky according to claim 1, characterized in that: The total cloud cover of the whole sky is obtained based on the infrared brightness temperature data of the whole sky at the current detection time and the whole sky clear sky model, including: For any detection point in the whole sky, when the infrared brightness temperature data of the detection point at the current detection time is greater than the clear sky threshold brightness temperature data at the elevation angle where the detection point is located, the detection point is determined to be a cloud point, otherwise the detection point is determined to be a cloudless sky point; The total cloud amount in the sky is calculated based on the number of cloud points and the number of cloud-free sky points in the entire sky.

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