Ground-based millimeter wave cloud radar data verification method and system

Abstract

The invention relates to a verification method and system for ground-based millimeter wave cloud radar data, and belongs to the technical field of meteorological analysis. The method comprises the following steps: establishing a clear sky echo identification and filtering method, and generating ground-based millimeter wave cloud radar base data after quality control; classifying the ground-based millimeter wave cloud radar base data after quality control into cloud data and rainfall data; the Cloud Sat satellite and the ground-based millimeter wave cloud radar after quality control have reflectivity factor matching and evaluation in cloud data; and matching and evaluating reflectivity factors in GPM satellite and quality-controlled ground-based millimeter wave cloud radar rainfall data. According to the invention, a ground-based millimeter wave cloud radar quality control and classification method is established, a high-quality refined ground-based millimeter wave cloud radar database can be generated, and a good basis is provided for ground-based millimeter wave cloud radar data application; a matching and evaluation method of spaceborne radar and ground-based millimeter wave cloud radar reflectivity factors under different conditions is established, and reference is provided for ground-based millimeter wave cloud radar calibration correction and satellite-ground radar combined application.

Description

Technical Field

[0001] This invention relates to the field of meteorological analysis technology, and in particular to a method and system for verifying ground-based millimeter-wave cloud radar data. Background Technology

[0002] Cloud precipitation plays a crucial role in regional and global energy exchange, radiation balance, and climate change. Ground-based millimeter-wave cloud radar, with its excellent penetration and high sensitivity to cloud precipitation particles, is currently an important detection method for obtaining the three-dimensional characteristics of cloud precipitation. However, as operating time increases, ground-based millimeter-wave cloud radar observation data may become offset, necessitating periodic verification. Furthermore, the data from ground-based millimeter-wave cloud radar itself may have quality issues; therefore, quality control is required before conducting verification to minimize verification errors caused by data source quality.

[0003] Existing ground-based millimeter-wave radar verification technologies mostly verify ground-based millimeter-wave cloud radar data directly, neglecting the measurement differences of ground-based millimeter-wave cloud radar for different objects, such as differences in cloud and precipitation measurements. Radar echoes attenuate rapidly during precipitation, and the inherent data quality issues of ground-based millimeter-wave cloud radar itself are also ignored. For example, if low-level clear-sky echoes are not filtered out, it will affect the accuracy of low-cloud identification by ground-based millimeter-wave cloud radar, thus affecting data quality. These factors introduce uncertainty into the verification results of ground-based millimeter-wave cloud radar observation data, increasing errors. Furthermore, existing verification studies of ground-based millimeter-wave cloud radar are mostly limited to single radars and cannot be uniformly applied to global radar networks. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for verifying ground-based millimeter-wave cloud radar data. This involves establishing a quality control and classification algorithm for ground-based millimeter-wave cloud radar, generating a high-quality and refined ground-based millimeter-wave cloud radar database, and reducing verification errors. For the obtained quality-controlled and classified data (cloud data and precipitation data), globally observable satellites are used. The cloud profiler radar (CloudSat CPR) and precipitation radar (GPM DPR) onboard these satellites are matched with the cloud and precipitation profile data to generate optimal matching samples. Based on these optimal matching samples, evaluation indicators are used to accurately verify and evaluate the detection capability of the ground-based millimeter-wave cloud radar globally.

[0005] To achieve the above objectives, the present invention provides the following solution: A method for verifying ground-based millimeter-wave cloud radar data, the verification method comprising: Acquire base data from ground-based millimeter-wave cloud radar; The basic data of the ground-based millimeter-wave cloud radar is processed using clear-sky echo identification and filtering algorithms to obtain the quality-controlled basic data of the ground-based millimeter-wave cloud radar. The baseline data of the ground-based millimeter-wave cloud radar after quality control are identified and classified to obtain cloud data and precipitation data; Verify the cloud data and evaluate the detection capability of the ground-based millimeter-wave cloud radar in cloud conditions; The precipitation data was verified to assess the detection capability of the ground-based millimeter-wave cloud radar under precipitation conditions.

[0006] Optionally, the step of processing the basic data of the ground-based millimeter-wave cloud radar using clear-sky echo identification and filtering algorithms to obtain the quality-controlled basic data of the ground-based millimeter-wave cloud radar specifically includes: The parameters for obtaining the basic data of the ground-based millimeter-wave cloud radar include: reflectivity factor, radial velocity, and depolarization ratio; Within a first altitude range, the number of points with a reflectivity factor greater than -25 dBZ and the number of points with a non-nullable reflectivity factor are counted. It is then determined whether the number of points with a reflectivity factor greater than -25 dBZ and the number of points with a non-nullable reflectivity factor satisfy a first judgment condition. If the first judgment condition is satisfied, the base data of the corresponding ground-based millimeter-wave cloud radar is determined to be rainfall data or low cloud data. If the first judgment condition is not satisfied, clear-sky echo judgment is performed on the base data of the corresponding ground-based millimeter-wave cloud radar. The first judgment condition is that the number of points with a reflectivity factor greater than -25 dBZ is greater than 20 and the number of points with a non-nullable reflectivity factor is greater than 25. Preferably, the first altitude is 1 km. The reflectivity factor threshold, radial velocity threshold, and depolarization ratio threshold of the basic data of the ground-based millimeter-wave cloud radar below the second altitude are set. The reflectivity factor threshold and the radial velocity threshold are used to perform segmented identification of different altitude layers and full-altitude layer identification. The depolarization ratio threshold is used to perform full-altitude layer identification, identify clear-sky echoes, and remove the corresponding clear-sky echo points. The second altitude is greater than the first altitude. Preferably, the second altitude is 3 km. Isolated point filtering is performed on the base data of the ground-based millimeter-wave cloud radar after removing clear-sky echo points. The filtered data, together with the rainfall data or the low cloud data, constitutes the quality-controlled base data of the ground-based millimeter-wave cloud radar.

[0007] Optionally, the step of identifying and classifying the baseline data of the quality-controlled ground-based millimeter-wave cloud radar to obtain cloud data and precipitation data specifically includes: The parameters of the basic data of the ground-based millimeter-wave cloud radar after quality control are obtained, including: reflectivity factor, signal-to-noise ratio, Doppler velocity and vertical velocity; the average value of the melting layer height during the passage of CloudSat satellite is obtained; The signal-to-noise ratio data is subjected to Gaussian filtering to remove non-cloud data from the ground-based millimeter-wave cloud radar; The influence of wind speed is removed using the Doppler velocity, and it is determined whether the reflectivity factor and the vertical velocity meet the second judgment condition. If the second judgment condition is met, the base data of the corresponding ground-based millimeter-wave cloud radar is the first precipitation data. The second judgment condition is that the average value of the reflectivity factor is greater than 10 dBZ and the vertical velocity is less than -3 m / s per unit time. Preferably, the unit time is 1 minute. The average melting layer height during the CloudSat satellite's transit is used as the melting layer height for the ground-based millimeter-wave cloud radar, and data points below this melting layer height are identified. It is then determined whether the reflectivity factor meets a third condition. If the third condition is met, the corresponding baseline data from the ground-based millimeter-wave cloud radar is used as the second precipitation data. The third condition is that the baseline data from ground-based millimeter-wave cloud radars with a reflectivity factor greater than -10 dBZ exceeds 10% of the data points. The set of the first precipitation data and the second precipitation data is used as the precipitation data, and the rest is the cloud data.

[0008] Optionally, verifying the cloud data and evaluating the ground-based millimeter-wave cloud radar's ability to detect cloud conditions specifically includes: Obtain the reflectance factor of CloudSat satellite data and the cloud data; Match the reflectance factors of the CloudSat satellite data and the cloud-covered data to generate matching samples; Preprocess the matching samples to generate the optimal matching sample; Calculate the evaluation index of the optimal matching sample for the cloud-covered conditions; The difference between the reflectivity factors of CloudSat satellite and ground-based millimeter-wave cloud radar is quantified based on the evaluation indicators to assess the detection capability of ground-based millimeter-wave cloud radar in cloud conditions.

[0009] Optionally, the preprocessing includes: Eliminate matched samples with a reflectance factor below -29 dBZ; Remove matching samples below the first height; Non-cloud samples and precipitation samples from CloudSat satellites were removed.

[0010] Optionally, verifying the precipitation data and evaluating the detection capability of the ground-based millimeter-wave cloud radar under precipitation conditions specifically includes: Obtain the reflectance factor of GPM satellite data and the precipitation data; Match the reflectance factors of the GPM satellite data and the precipitation data to generate matching samples; Preprocess the matching samples to generate the optimal matching sample; Calculate the evaluation index of the optimal matching sample for the precipitation conditions; The difference between the reflectivity factors of GPM satellite and ground-based millimeter-wave cloud radar is quantified based on the evaluation indicators to assess the detection capability of ground-based millimeter-wave cloud radar for precipitation.

[0011] Optionally, the preprocessing includes: Select the matching samples in the GPM satellite data where the qualityFlag parameter is 0; Eliminate matching samples whose altitude is below the altitude represented by the binClutterFreeBottom parameter in the GPM satellite data; Eliminate matching samples at altitudes above the third altitude; preferably, the third altitude is 15km.

[0012] Optional evaluation metrics include correlation coefficient, root mean square error, and mean deviation.

[0013] This invention provides a verification system for ground-based millimeter-wave cloud radar data, used to implement the aforementioned verification method for ground-based millimeter-wave cloud radar data; the verification system includes: The data acquisition module is used to acquire base data from ground-based millimeter-wave cloud radar. The quality control module is used to process the base data of the ground-based millimeter-wave cloud radar using clear-sky echo identification and filtering algorithms to obtain the base data of the ground-based millimeter-wave cloud radar after quality control. The identification and classification module is used to identify and classify the base data of the quality-controlled ground-based millimeter-wave cloud radar to obtain cloud data and precipitation data. A cloud data verification module is used to verify the cloud data and evaluate the detection capability of the ground-based millimeter-wave cloud radar in cloud conditions. The precipitation data verification module is used to verify the precipitation data and evaluate the detection capability of the ground-based millimeter-wave cloud radar under precipitation conditions.

[0014] Optionally, the cloud data verification module includes: The first data acquisition unit is used to acquire CloudSat satellite data and the reflectivity factor of the cloud data; The first matching unit is used to match the reflectance factors of the CloudSat satellite data and the cloud data to generate matching samples. The first preprocessing unit is used to preprocess the matching samples to generate the optimal matching samples; The first calculation unit is used to calculate the evaluation index of the optimal matching sample for the cloud-covered situation. The first evaluation unit is used to quantify the difference between the reflectivity factors of CloudSat satellite and ground-based millimeter-wave cloud radar according to the evaluation index, thereby evaluating the detection capability of ground-based millimeter-wave cloud radar in the presence of clouds. The precipitation data verification module includes: The second data acquisition unit is used to acquire the reflectance factor of GPM satellite data and the precipitation data; The second matching unit is used to match the reflectance factors of the GPM satellite data and the precipitation data to generate matching samples. The second preprocessing unit is used to preprocess the matching samples to generate the optimal matching samples; The second calculation unit is used to calculate the evaluation index of the optimal matching sample of the precipitation situation; The second evaluation unit is used to quantify the difference in reflectivity factors between the GPM satellite and the ground-based millimeter-wave cloud radar according to the evaluation indicators, thereby evaluating the ground-based millimeter-wave cloud radar's ability to detect precipitation.

[0015] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects: The present invention establishes a quality control (clear-sky echo filtering) and classification method for ground-based millimeter-wave cloud radar, which can generate a high-quality and refined ground-based millimeter-wave cloud radar database, providing a good foundation for the application of ground-based millimeter-wave cloud radar data; The present invention establishes a matching and evaluation method for reflectivity factors of spaceborne radar (cloud profiler radar, CloudSat CPR and precipitation radar, GPM DPR) and ground-based millimeter-wave cloud radar under different conditions, and gives the differences between the two, providing a reference for the calibration and correction of ground-based millimeter-wave cloud radar and the joint application of spaceborne and ground-based radar. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A flowchart illustrating the verification method for ground-based millimeter-wave cloud radar data provided in this embodiment of the invention; Figure 2 Flowchart of the clear-sky echo quality control method for low-level segmented threshold method of ground-based millimeter-wave cloud radar provided in an embodiment of the present invention; Figure 3 A schematic diagram of a ground-based millimeter-wave cloud radar data verification system provided in an embodiment of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] The terms "first," "second," "third," etc. (if present) in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the objects described in this way can be used interchangeably where appropriate. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0020] In this invention, the accompanying drawings and embodiments used to describe the principles of the invention are for illustrative purposes only and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that the principles of the invention can be implemented in any suitably arranged system. Exemplary embodiments will be described in detail, examples of which are illustrated in the accompanying drawings.

[0021] The terminology used in this specification is for describing particular embodiments only and is not intended to represent the concept of the invention. Unless the context clearly distinguishes them, singular expressions encompass plural expressions. In this specification, it should be understood that terms such as “comprising,” “having,” and “containing” are intended to describe the possibility of the presence of the features, numbers, steps, actions, or combinations thereof disclosed in this specification, and are not intended to exclude the possibility of the presence or addition of one or more other features, numbers, steps, actions, or combinations thereof.

[0022] This invention establishes, on the one hand, a quality control (clear-sky echo filtering) and classification method for ground-based millimeter-wave cloud radar, which can generate a high-quality and refined ground-based millimeter-wave cloud radar database, providing a good foundation for the application of ground-based millimeter-wave cloud radar data; on the other hand, it establishes a matching and evaluation method for reflectivity factors of spaceborne radar (cloud profiler radar, CloudSat CPR and precipitation radar, GPM DPR) and ground-based millimeter-wave cloud radar under different conditions, and gives the differences between the two, providing a reference for the calibration and correction of ground-based millimeter-wave cloud radar and the joint application of spaceborne and ground-based radar.

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Ground-based millimeter-wave cloud radar data source: The baseline data used were from a Ka-band ground-based millimeter-wave cloud radar deployed by the my country Meteorological Administration. The baseline data parameters included reflectivity factor, radial velocity, spectral width, signal-to-noise ratio, and depolarization ratio. The ground-based millimeter-wave cloud radar was used for vertical zenith observations, with a range (vertical) resolution of 30 m, 639 data points, a detection altitude greater than 19 km, a temporal resolution of 5 s, a reflectivity factor measurement range of -40 to 30 dBZ, a radial velocity measurement range of ±15 m / s, and a spectral width measurement range of 0 to 15 m / s.

[0025] CloudSat satellite data source: The CloudSat satellite carries a cloud profiling radar (CPR), which operates at a frequency of 94 GHz, has a vertical resolution of 240 m, and a minimum detection signal of <-29 dBZ. The radar reflectivity factor, cloud feature products, and data quality parameters from CloudSat's 2B-GROPROF product, and melting layer height data from the 2C-PRE-CIP-COLUMN.P1 product, were used.

[0026] GPM satellite data source: The system employs a dual-frequency precipitation radar (DPR) based on the Global Precipitation Satellite (GPM), operating in both Ka and Ku bands. It has a temporal resolution of approximately 90 minutes, a nadir distance of 5 km, a vertical resolution of 125 m, and a detection altitude of 22 km. The minimum detection signal for the Ka band is 12 dBZ, and for the Ku band, it is 18 dBZ. The attenuation-corrected radar reflectivity factor and bright band height parameters are also presented in the 2AKa product using the GPM DPR.

[0027] like Figure 1 As shown, the verification methods for ground-based millimeter-wave cloud radar data include: Acquire base data from ground-based millimeter-wave cloud radar; The baseline data of the ground-based millimeter-wave cloud radar was processed using clear-sky echo identification and filtering algorithms to obtain the baseline data of the ground-based millimeter-wave cloud radar after quality control. The baseline data of the ground-based millimeter-wave cloud radar after quality control are identified and classified to obtain cloud data and precipitation data; Verify cloud data and evaluate the detection capability of ground-based millimeter-wave cloud radar in cloud conditions; Verify precipitation data and assess the detection capabilities of ground-based millimeter-wave cloud radar under precipitation conditions.

[0028] The baseline data of the ground-based millimeter-wave cloud radar was processed using clear-sky echo identification and filtering algorithms. The resulting quality-controlled baseline data specifically includes: The parameters for acquiring the basic data of ground-based millimeter-wave cloud radar include: reflectivity factor, radial velocity, and depolarization ratio; Within the first altitude range, count the number of points with a reflectivity factor greater than -25 dBZ and the number of points with a non-nullable reflectivity factor; determine whether the number of points with a reflectivity factor greater than -25 dBZ and the number of points with a non-nullable reflectivity factor meet the first judgment condition; if the first judgment condition is met, determine that the base data of the corresponding ground-based millimeter-wave cloud radar is rainfall data or low cloud data; if the first judgment condition is not met, perform clear sky echo judgment on the base data of the corresponding ground-based millimeter-wave cloud radar; wherein, the first judgment condition is that the number of points with a reflectivity factor greater than -25 dBZ is greater than 20 and the number of points with a non-nullable reflectivity factor is greater than 25. The reflectivity factor threshold, radial velocity threshold, and depolarization ratio threshold of the basic data of the ground-based millimeter-wave cloud radar below the second altitude are set. The reflectivity factor threshold and radial velocity threshold are used to perform segmented identification of different altitude layers and full-altitude layer identification. The depolarization ratio threshold is used to perform full-altitude layer identification, identify clear-sky echoes, and remove the corresponding clear-sky echo points. The second altitude is greater than the first altitude. Preferably, the second altitude is 3 km. Isolated points are filtered out from the baseline data of the ground-based millimeter-wave cloud radar after removing clear-sky echo points. The filtered data is then combined with rainfall data or low cloud data to form the baseline data of the ground-based millimeter-wave cloud radar after quality control.

[0029] Figure 2 The flowchart of the clear-sky echo quality control method based on the low-level segmented threshold method of ground-based millimeter-wave cloud radar is shown, which specifically includes: Acquire reflectivity factor Z, radial velocity V, and depolarization ratio LDR of ground-based millimeter-wave cloud radar data; Count the number of points with Z > -25dB within 1km, and the number of points with non-empty Z values; if the number of points is greater than 20 and the non-empty value is greater than 25, it is considered rain or low clouds and is not filtered out; otherwise, it is considered as clear sky echo. Clear-sky echo identification: First, determine the distance database at an altitude of 3km. Below the distance database, segmented identification at different altitude levels and full-altitude layer identification are performed by setting Z threshold and V threshold, and full-altitude layer identification is performed by setting LDR threshold, thereby identifying clear-sky echoes; Remove identified clear-sky echo points; Isolated points are filtered out from the data that excludes clear-sky echo points. Scattered clutter points are removed by sliding through 5×5 and 5×1 windows in areas below 3km. In areas below 3km, 5×5 windows C and 5×1 windows S are cyclically set according to time and altitude. The number of non-empty points in the two windows, count_C and count_S, are calculated respectively. If count_C < 9, or (count_S < 4 & count_C < 12), it is considered a scattered clutter point and is filtered out.

[0030] The above threshold parameter settings are based on empirical statistics. By comparing and evaluating the quality control effects of multiple cases, the threshold parameters of the quality control algorithm can be dynamically adjusted to obtain the best quality control results.

[0031] The baseline data of the ground-based millimeter-wave cloud radar after quality control is divided into cloud data and precipitation data, thereby generating a high-quality and refined ground-based millimeter-wave cloud radar database.

[0032] The baseline data from the quality-controlled ground-based millimeter-wave cloud radar are identified and classified to obtain cloud data and precipitation data, specifically including: The parameters of the basic data obtained after quality control of the ground-based millimeter-wave cloud radar include: reflectivity factor, signal-to-noise ratio, Doppler velocity, and vertical velocity; the average value of the melting layer height during the CloudSat satellite's passage is obtained. Gaussian filtering was applied to the signal-to-noise ratio data to remove non-cloud data from the ground-based millimeter-wave cloud radar. The influence of wind speed is removed by using Doppler velocity, and it is determined whether the reflectivity factor and vertical velocity meet the second judgment condition. If the second judgment condition is met, the base data of the corresponding ground-based millimeter-wave cloud radar is the first precipitation data. The second judgment condition is that the average reflectivity factor is greater than 10 dBZ and the vertical velocity is less than -3 m / s per unit time. Preferably, the unit time is 1 minute. The average melting layer height during CloudSat satellite transit is used as the melting layer height for ground-based millimeter-wave cloud radar, and data points below the melting layer height are identified. The reflectivity factor is then used to determine if it meets the third criterion. If the third criterion is met, the corresponding baseline data from the ground-based millimeter-wave cloud radar is used as the second precipitation data. The third criterion is that the baseline data from ground-based millimeter-wave cloud radar with a reflectivity factor greater than -10 dBZ exceeds 10% of the data points. The set of the first and second precipitation data is used as the precipitation data, and the rest is the cloud data.

[0033] By matching the reflectivity factors of CloudSat satellite data and ground-based millimeter-wave cloud radar data in the cloud area through spatial matching, temporal matching, altitude matching, and numerical matching, matching samples are generated. The matching samples are then preprocessed to generate the optimal matching sample. Evaluation indicators are calculated to quantify the difference between the reflectivity factors of CloudSat satellite data and ground-based millimeter-wave cloud radar data, and the detection capability of ground-based millimeter-wave cloud radar in the cloud area is tested and evaluated.

[0034] CloudSat satellite and ground-based millimeter-wave cloud radar reflectivity factor matching: Spatial matching: The grid size within a 200km radius before and after the ground-based millimeter-wave cloud radar is selected as the CloudSat satellite overpass area. If the CloudSat satellite passes over the area, it is considered to be spatially matched with the ground-based millimeter-wave cloud radar.

[0035] Time matching: The intermediate time of CloudSat satellite transit ±60 minutes is selected as the time range of ground-based millimeter-wave cloud radar data. Ground-based millimeter-wave cloud radar data within this time range are used for satellite-to-ground matching.

[0036] High-altitude matching: Ground-based millimeter-wave cloud radar and CloudSat satellite data need to be processed to the same altitude for comparison. The ground-based millimeter-wave cloud radar data (vertical resolution 30m) is linearly averaged to the CloudSat satellite data (vertical resolution 240m).

[0037] Numerical matching: Ground-based millimeter-wave cloud radar and CloudSat satellite observation frequencies are different. Taking the Ka-band of the cloud radar as an example, the Ka observation values ​​are converted to data at a 94GHz frequency (CloudSat observation frequency): Z 94GHz =Z 35GHz -10 -16.8251 (Z 35GHz +100) 8.4923 Z 35GHz Z 94GHz These are the reflectivity factors of Ka-band ground-based millimeter-wave cloud radar and CloudSat, respectively.

[0038] Preprocess the matching samples, and sequentially filter to generate the optimal matching samples: Matching samples with reflectivity factors below -29dBZ from CloudSat satellite and ground-based millimeter-wave cloud radar were removed. Eliminate matching samples below 1km altitude to reduce the impact of CloudSat satellite detection blind spots; Remove non-cloud and precipitation samples from CloudSat satellites. Remove non-cloud samples from CloudSat by removing reflectivity factors with cloudmask=0. Remove samples from CloudSat where precipitation is present. If the proportion of data points with reflectivity factors greater than -10dBZ below the melt layer height is greater than 35%, then precipitation is considered to exist and these samples need to be removed.

[0039] Based on the optimal matching samples under cloud cover conditions, evaluation indicators for CloudSat and ground-based millimeter-wave cloud radar are calculated for different months, different sites, and different altitudes. The differences in reflectivity factors between CloudSat and ground-based millimeter-wave cloud radar are quantified based on these evaluation indicators to assess the detection capability of ground-based millimeter-wave cloud radar under cloud cover conditions. Simultaneously, the profile differences of reflectivity factors between CloudSat and ground-based millimeter-wave cloud radar are compared across different months and different sites.

[0040] The evaluation metrics are correlation coefficient (CC), root mean square error (RMSE), and mean bias (BIAS).

[0041] Where N is the number of matched samples, and i is the sequence number of the matched sample. The average value of the (CloudSat) reflectance factor of the satellites used to match the sample is... , The average value of the ground-based millimeter-wave cloud radar reflectivity factor for matching samples is: .

[0042] The reflectivity factors of precipitation data from GPM satellite and ground-based millimeter-wave cloud radar are matched using spatial matching, temporal matching, altitude matching, and numerical matching to generate matching samples. The matching samples are then preprocessed to generate the optimal matching sample. Evaluation indicators are calculated to quantify the difference between the reflectivity factors of GPM satellite and ground-based millimeter-wave cloud radar, and the detection capability of ground-based millimeter-wave cloud radar under precipitation conditions is verified and evaluated.

[0043] GPM satellite and ground-based millimeter-wave cloud radar reflectivity factor matching Spatial matching: Referring to the GPM satellite's nadir point of 5km, a circle with a radius of 2.5km centered on the ground-based millimeter-wave cloud radar is selected as the GPM satellite's overpass area. If the GPM satellite passes over the area, it is considered to be spatially matched with the ground-based millimeter-wave cloud radar.

[0044] Time matching: Combining meteorological wind speed data, the time required for the precipitation system to move 5km is calculated (assumed to be 2t). The ground-based millimeter-wave cloud radar profile within ±t of the midpoint of the GPM transit time is then selected for satellite-to-ground matching. The ground-based millimeter-wave cloud radar profile data within this time range are then averaged over time to form the profile for spatiotemporal synchronization of satellite-to-ground matching.

[0045] Height matching: The ground-based millimeter-wave cloud radar and GPM satellite data need to be processed to the same altitude for comparison. The ground-based millimeter-wave cloud radar data (vertical resolution 30m) is interpolated to the GPM satellite data at a vertical resolution of 125m.

[0046] Numerical matching: Taking Ka-band ground-based millimeter-wave cloud radar as an example, the satellite and ground data frequencies are consistent, and no frequency conversion is required.

[0047] Preprocess the matching samples, and sequentially filter to generate the optimal matching samples: Select matching samples with excellent overall quality in GPM data products, i.e., qualityFlag parameter = 0 in GPM; Eliminate matching samples with low-level clutter interference, that is, eliminate matching samples whose height is below the height represented by the binClutterFreeBottom parameter in GPM.

[0048] Matching samples affected by attenuation at high altitudes were removed. Ground-based millimeter-wave cloud radar experiences attenuation at high altitudes, so matching samples above 15km were removed.

[0049] Based on the optimal matching sample of precipitation conditions, the evaluation indexes of GPM and ground-based millimeter-wave cloud radar at different altitudes, with different precipitation intensities, types, and phases are calculated. The difference between the reflectivity factors of GPM and ground-based millimeter-wave cloud radar is quantified according to the indexes, thereby evaluating the detection capability of ground-based millimeter-wave cloud radar for precipitation conditions.

[0050] Precipitation intensity is classified into three types: weak, moderate, and strong. Based on the reflectance factor value of GPM, reflectance factor Z < 30 dBZ indicates weak precipitation, 30 dBZ ≤ Z < 45 dBZ indicates moderate precipitation, and Z ≥ 45 dBZ indicates strong precipitation.

[0051] Precipitation types are divided into two categories: stratified and convective. According to the typePrecip parameter of GPM, 10,000,000 ≤ typePrecip < 20,000,000 is stratified precipitation, and 20,000,000 ≤ typePrecip < 30,000,000 is convective precipitation.

[0052] Precipitation phases are classified into three types: liquid particles below the bright band, ice-water mixed layer within the bright band, and ice particles above the bright band. Based on the heightBB parameter of GPM, the area below heightBB-750m is liquid particles below the bright band, the area between heightBB-750m and heightBB+750m is ice-water mixed layer within the bright band, and the area above heightBB+750m is ice particles above the bright band.

[0053] The evaluation metrics are correlation coefficient (CC), root mean square error (RMSE), and mean bias (BIAS).

[0054] Where N is the number of matched samples, and i is the sequence number of the matched sample. The average value of the (GPM) reflectance factor of the satellites used to match the sample is: , The average value of the ground-based millimeter-wave cloud radar reflectivity factor for matching samples is: .

[0055] This invention establishes a quality control (clear-sky echo filtering) and classification method for ground-based millimeter-wave cloud radar, which can generate a high-quality and refined ground-based millimeter-wave cloud radar database, providing a good foundation for the application of ground-based millimeter-wave cloud radar data. It also establishes matching and evaluation methods for reflectivity factors of spaceborne radar (CloudSat CPR, GPM DPR) and ground-based millimeter-wave cloud radar under different conditions, and gives the differences between the two, providing a reference for the calibration and correction of ground-based millimeter-wave cloud radar and the joint application of spaceborne and ground-based radar.

[0056] Figure 3 This is a schematic diagram of a ground-based millimeter-wave cloud radar data verification system provided in an embodiment of the present invention. The system includes: a data acquisition module, a quality control module, an identification and classification module, a cloud data verification module, and a precipitation data verification module.

[0057] The data acquisition module is used to acquire the base data of the ground-based millimeter-wave cloud radar.

[0058] The quality control module is used to process the base data of ground-based millimeter-wave cloud radar using clear-sky echo identification and filtering algorithms to obtain the base data of ground-based millimeter-wave cloud radar after quality control.

[0059] The identification and classification module is used to identify and classify the baseline data of the ground-based millimeter-wave cloud radar after quality control, and obtain cloud data and precipitation data.

[0060] The cloud data verification module is used to verify cloud data and evaluate the detection capability of ground-based millimeter-wave cloud radar in cloud conditions.

[0061] The precipitation data verification module is used to verify precipitation data and evaluate the detection capability of ground-based millimeter-wave cloud radar under precipitation conditions.

[0062] The cloud data verification module includes: a first data acquisition unit, a first matching unit, a first preprocessing unit, a first calculation unit, and a first evaluation unit.

[0063] The first data acquisition unit is used to acquire the reflectivity factor of CloudSat satellite data and cloud data.

[0064] The first matching unit is used to match the reflectance factors of CloudSat satellite data and cloud-covered data to generate matching samples.

[0065] The first preprocessing unit is used to preprocess the matching samples to generate the optimal matching sample.

[0066] The first computing unit is used to calculate the evaluation metrics for the optimal matching sample in the case of clouds.

[0067] The first evaluation unit is used to quantify the difference in reflectivity factors between CloudSat satellite and ground-based millimeter-wave cloud radar according to evaluation indicators, thereby evaluating the ground-based millimeter-wave cloud radar's ability to detect cloud conditions.

[0068] The precipitation data verification module includes: a second data acquisition unit, a second matching unit, a second preprocessing unit, a second calculation unit, and a second evaluation unit.

[0069] The second data acquisition unit is used to acquire the reflectance factor of GPM satellite data and precipitation data.

[0070] The second matching unit is used to match the reflectance factors of GPM satellite data and precipitation data to generate matching samples.

[0071] The second preprocessing unit is used to preprocess the matching samples to generate the optimal matching sample.

[0072] The second calculation unit is used to calculate the evaluation index of the optimal matching sample of precipitation conditions.

[0073] The second evaluation unit is used to quantify the difference in reflectivity factors between the GPM satellite and the ground-based millimeter-wave cloud radar according to evaluation indicators, thereby evaluating the ground-based millimeter-wave cloud radar's ability to detect precipitation.

[0074] The system disclosed in the embodiments is described in a relatively simple manner because it corresponds to the method disclosed in the embodiments. For relevant details, please refer to the method section.

[0075] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for verifying ground-based millimeter-wave cloud radar data, characterized in that, The verification method includes: Acquire base data from ground-based millimeter-wave cloud radar; The basic data of the ground-based millimeter-wave cloud radar is processed using clear-sky echo identification and filtering algorithms to obtain the quality-controlled basic data of the ground-based millimeter-wave cloud radar. The baseline data of the ground-based millimeter-wave cloud radar after quality control are identified and classified to obtain cloud data and precipitation data; Verify the cloud data and evaluate the detection capability of the ground-based millimeter-wave cloud radar in cloud conditions; The precipitation data was verified to assess the detection capability of the ground-based millimeter-wave cloud radar under precipitation conditions.

2. The method for verifying ground-based millimeter-wave cloud radar data according to claim 1, characterized in that, The process of using clear-sky echo identification and filtering algorithms to process the base data of the ground-based millimeter-wave cloud radar to obtain quality-controlled base data specifically includes: The parameters for obtaining the basic data of the ground-based millimeter-wave cloud radar include: reflectivity factor, radial velocity, and depolarization ratio; Within a first altitude range, the number of points with a reflectivity factor greater than -25 dBZ and the number of points with a non-nullable reflectivity factor are counted. It is then determined whether the number of points with a reflectivity factor greater than -25 dBZ and the number of points with a non-nullable reflectivity factor satisfy a first judgment condition. If the first judgment condition is satisfied, the base data of the corresponding ground-based millimeter-wave cloud radar is determined to be rainfall data or low cloud data. If the first judgment condition is not satisfied, clear-sky echo judgment is performed on the base data of the corresponding ground-based millimeter-wave cloud radar. The first judgment condition is that the number of points with a reflectivity factor greater than -25 dBZ is greater than 20 and the number of points with a non-nullable reflectivity factor is greater than 25. The reflectivity factor threshold, radial velocity threshold, and depolarization ratio threshold of the basic data of the ground-based millimeter-wave cloud radar below the second altitude are set. The reflectivity factor threshold and the radial velocity threshold are used to perform segmented identification of different altitude layers and full-altitude layer identification. The depolarization ratio threshold is used to perform full-altitude layer identification, identify clear-sky echoes, and remove the corresponding clear-sky echo points. Wherein, the second altitude is greater than the first altitude. Isolated point filtering is performed on the base data of the ground-based millimeter-wave cloud radar after removing clear-sky echo points. The filtered data, together with the rainfall data or the low cloud data, constitutes the quality-controlled base data of the ground-based millimeter-wave cloud radar.

3. The method for verifying ground-based millimeter-wave cloud radar data according to claim 1, characterized in that, The process of identifying and classifying the baseline data from the quality-controlled ground-based millimeter-wave cloud radar to obtain cloud data and precipitation data specifically includes: The parameters of the basic data of the ground-based millimeter-wave cloud radar after quality control are obtained, including: reflectivity factor, signal-to-noise ratio, Doppler velocity and vertical velocity; the average value of the melting layer height during the passage of CloudSat satellite is obtained; The signal-to-noise ratio data is subjected to Gaussian filtering to remove non-cloud data from the ground-based millimeter-wave cloud radar; The influence of wind speed is removed using the Doppler velocity, and it is determined whether the reflectivity factor and the vertical velocity meet the second judgment condition; if the second judgment condition is met, the base data of the corresponding ground-based millimeter-wave cloud radar is the first precipitation data; wherein, the second judgment condition is that the average value of the reflectivity factor per unit time is greater than 10 dBZ and the vertical velocity is less than -3 m / s; The average melting layer height during the CloudSat satellite's transit is used as the melting layer height for the ground-based millimeter-wave cloud radar, and data points below this melting layer height are identified. It is then determined whether the reflectivity factor meets a third condition. If the third condition is met, the corresponding baseline data from the ground-based millimeter-wave cloud radar is used as the second precipitation data. The third condition is that the baseline data from ground-based millimeter-wave cloud radars with a reflectivity factor greater than -10 dBZ exceeds 10% of the data points. The set of the first precipitation data and the second precipitation data is used as the precipitation data, and the rest is the cloud data.

4. The method for verifying ground-based millimeter-wave cloud radar data according to claim 1, characterized in that, The verification of the cloud data and the evaluation of the ground-based millimeter-wave cloud radar's ability to detect cloud conditions specifically include: Obtain the reflectance factor of CloudSat satellite data and the cloud data; Match the reflectance factors of the CloudSat satellite data and the cloud-covered data to generate matching samples; Preprocess the matching samples to generate the optimal matching samples; Calculate the evaluation index of the optimal matching sample under the cloud cover condition; The difference between the reflectivity factors of CloudSat satellite and ground-based millimeter-wave cloud radar is quantified based on the evaluation indicators to assess the detection capability of ground-based millimeter-wave cloud radar in cloud conditions.

5. The method for verifying ground-based millimeter-wave cloud radar data according to claim 4, characterized in that, The preprocessing includes: Eliminate matched samples with a reflectance factor below -29 dBZ; Remove matching samples below the first height; Non-cloud samples and precipitation samples from CloudSat satellites were removed.

6. The method for verifying ground-based millimeter-wave cloud radar data according to claim 1, characterized in that, The verification of the precipitation data and the evaluation of the ground-based millimeter-wave cloud radar's detection capability under precipitation conditions specifically include: Obtain the reflectance factor of GPM satellite data and the precipitation data; Match the reflectance factors of the GPM satellite data and the precipitation data to generate matching samples; Preprocess the matching samples to generate the optimal matching samples; Calculate the evaluation index of the optimal matching sample for the precipitation conditions; The difference between the reflectivity factors of GPM satellite and ground-based millimeter-wave cloud radar is quantified based on the evaluation indicators to assess the detection capability of ground-based millimeter-wave cloud radar for precipitation.

7. The method for verifying ground-based millimeter-wave cloud radar data according to claim 6, characterized in that, The preprocessing includes: Select the matching samples in the GPM satellite data where the qualityFlag parameter is 0; Eliminate matching samples whose altitude is below the altitude represented by the binClutterFreeBottom parameter in the GPM satellite data; Remove matching samples with a height of 3 or higher.

8. The method for verifying ground-based millimeter-wave cloud radar data according to claim 4 or 6, characterized in that, The evaluation metrics include correlation coefficient, root mean square error, and mean deviation.

9. A verification system for ground-based millimeter-wave cloud radar data, characterized in that, The verification system includes: The data acquisition module is used to acquire base data from ground-based millimeter-wave cloud radar. The quality control module is used to process the base data of the ground-based millimeter-wave cloud radar using clear-sky echo identification and filtering algorithms to obtain the base data of the ground-based millimeter-wave cloud radar after quality control. The identification and classification module is used to identify and classify the base data of the quality-controlled ground-based millimeter-wave cloud radar to obtain cloud data and precipitation data. A cloud data verification module is used to verify the cloud data and evaluate the detection capability of the ground-based millimeter-wave cloud radar in cloud conditions. The precipitation data verification module is used to verify the precipitation data and evaluate the detection capability of the ground-based millimeter-wave cloud radar under precipitation conditions.

10. The verification system for ground-based millimeter-wave cloud radar data according to claim 9, characterized in that, The cloud data verification module includes: The first data acquisition unit is used to acquire CloudSat satellite data and the reflectivity factor of the cloud data; The first matching unit is used to match the reflectance factors of the CloudSat satellite data and the cloud data to generate matching samples. The first preprocessing unit is used to preprocess the matching samples to generate the optimal matching samples; The first computing unit is used for the evaluation metrics of the optimal matching sample in cloud conditions. The first evaluation unit is used to quantify the difference between the reflectivity factors of CloudSat satellite and ground-based millimeter-wave cloud radar according to the evaluation index, thereby evaluating the detection capability of ground-based millimeter-wave cloud radar in the presence of clouds. The precipitation data verification module includes: The second data acquisition unit is used to acquire the reflectance factor of GPM satellite data and the precipitation data; The second matching unit is used to match the reflectance factors of the GPM satellite data and the precipitation data to generate matching samples. The second preprocessing unit is used to preprocess the matching samples to generate the optimal matching samples; The second calculation unit is used to calculate the evaluation index of the optimal matching sample of the precipitation conditions; The second evaluation unit is used to quantify the difference in reflectivity factors between the GPM satellite and the ground-based millimeter-wave cloud radar according to the evaluation indicators, thereby evaluating the ground-based millimeter-wave cloud radar's ability to detect precipitation.

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