A method and system for selecting a uniform and stable scene for spaceborne microwave radiation reference transfer

Abstract

This application relates to the field of microwave radiation reference technology, and particularly to a method and system for selecting uniform and stable scenes for spaceborne microwave radiation reference transfer. The method includes: based on brightness temperature observation data from a reference spaceborne microwave radiometer, performing spatial projection, temporal grouping, and atmospheric condition screening on candidate surface scenes; selecting a surface scene from the screened candidate surface scenes that meets preset conditions as the target surface scene for spaceborne microwave radiation reference transfer; wherein, the preset conditions characterize the spatial uniformity and temporal stability of the brightness temperature. The method and system for selecting uniform and stable scenes for spaceborne microwave radiation reference transfer provided by this invention can more clearly screen the reference scenes used for transfer, ensuring that the transferred scenes have spatial uniformity and temporal stability.

Description

Technical Field

[0001] This application relates to the field of microwave radiation reference technology, and in particular to a method and system for selecting a uniform and stable scene for spaceborne microwave radiation reference transfer. Background Technology

[0002] Microwave radiometric reference is a concept proposed for future continuous observations by spaceborne microwave radiometers requiring high accuracy, stability, and consistency. It involves using a microwave reference satellite and employing cross-calibration methods to transfer the reference radiation to other satellite payloads that require calibration. Cross-calibration effectively improves the consistency of brightness temperature observations across different instruments and can remove systematic brightness temperature observation errors from satellite instruments when providing long-term passive microwave remote sensing datasets.

[0003] A common method is the Simultaneous Nadir Overpass (SNOs), which involves selecting a high-precision reference payload, setting appropriate temporal and spatial matching criteria, and matching the observation data of two payloads. When the two payloads observe the same location at the nadir, their observed brightness temperatures are compared and calibrated. Due to orbital differences between satellites, traditional SNOs typically only consider the nadir, with most matching scenarios located at the poles. Furthermore, they focus more on the stability of the scenario over long periods rather than spatial uniformity.

[0004] Unlike traditional cross-calibration, the reference satellite is specifically designed for radiation reference transfer. Its satellite platform has high maneuverability, meaning that the orbit and observation geometry can be adjusted through the capabilities of the satellite platform. It is not limited to the nadir point and can match the observation geometry of the calibrated payload at the same time and place to achieve cross-calibration of the same observation geometry at the same time and place.

[0005] Therefore, it is necessary to more clearly select the reference scenarios used for transmission to ensure that the transmitted scenarios have spatial uniformity and temporal stability. Summary of the Invention

[0006] The purpose of this application is to overcome the above-mentioned defects of the prior art, and thus provide a method and system for selecting a uniform and stable scene for spaceborne microwave radiation reference transfer.

[0007] To address the aforementioned technical problems, the technical solution provided in this application offers a method for selecting uniform and stable scenes for spaceborne microwave radiation reference transfer. This method includes: based on brightness temperature observation data from a reference spaceborne microwave radiometer, performing spatial projection, temporal grouping, and atmospheric condition screening on candidate surface scenes; selecting a surface scene that meets preset conditions from the screened candidate surface scenes as the target surface scene for spaceborne microwave radiation reference transfer; wherein, the preset conditions are used to characterize the spatial uniformity and temporal stability of the brightness temperature.

[0008] As an improvement to the above method, the reference spaceborne microwave radiometer has the same detection channel as the transferred microwave radiometer. The accuracy and stability of the reference spaceborne microwave radiometer are higher than those of the transferred microwave radiometer. The brightness temperature observation data of the reference spaceborne microwave radiometer are brightness temperature data that have undergone consistency calibration, geolocation, and resampling processing.

[0009] As an improvement to the above method, the spatial projection specifically includes: projecting the brightness temperature observation data onto an equi-area scalable Earth grid based on the actual latitude and longitude coordinates corresponding to the brightness temperature observation data, so as to form standardized brightness temperature spatial distribution data; wherein, the grid size of the Earth grid is larger than the maximum pixel size of the reference spaceborne microwave radiometer.

[0010] As an improvement to the above method, the step of projecting the brightness temperature observation data onto an equi-area scalable Earth grid based on the actual latitude and longitude coordinates corresponding to the brightness temperature observation data specifically includes:

[0011] ;

[0012] ;

[0013] in, It is the row index of the Earth grid. It is a column index of the Earth grid. It is the Earth's radius. It is the grid size of the Earth grid. It is the auxiliary projection angle. These are the actual longitude coordinates of the brightness temperature observation data, and These are the actual latitude coordinates of the brightness temperature observation data. It is the central row index of the Earth grid. It is the central column index of the Earth grid.

[0014] As an improvement to the above method, the time grouping specifically includes: based on the orbital and scanning characteristics of the reference satellite microwave radiometer, dividing the brightness temperature observation data acquired on the same day into multiple consecutive time periods, so as to distinguish and process the brightness temperature observation data corresponding to different transit times, thereby avoiding the merging and calculation of brightness temperature observation data from different times.

[0015] As an improvement to the above method, the atmospheric conditions include preset clear sky conditions, which are used to eliminate brightness temperature observation data affected by rainfall or atmospheric liquid water. The preset clear sky conditions are determined by reanalysis of meteorological data or by the brightness temperature difference of different microwave channels. When using reanalysis of meteorological data to determine the preset clear sky conditions, the total amount of atmospheric liquid water is less than a preset threshold as the clear sky criterion. When using the brightness temperature difference of different microwave channels to determine the preset clear sky conditions, corresponding channel brightness temperature difference determination conditions are set for different land surface types. The land surface types include forests and oceans.

[0016] As an improvement to the above method, for the reanalysis meteorological data, when the total amount of liquid water is less than 0.2 g / m2, it is determined that the preset clear sky condition is met; for the brightness temperature difference of different microwave channels, when the surface type is forest, if TB19V - TB37V < 4.5K, it is determined that the preset clear sky condition is met, where TB19V is the brightness temperature data observed by the 19 GHz vertical polarization channel of the reference satellite microwave radiometer, TB37V is the brightness temperature data observed by the 37 GHz vertical polarization channel of the reference satellite microwave radiometer, and K represents Kelvin; when the surface type is ocean, if TB37V - TB37H > 50K, it is determined that the preset clear sky condition is met, where TB37H is the brightness temperature data observed by the 37 GHz horizontal polarization channel of the reference satellite microwave radiometer.

[0017] As an improvement to the above method, the preset conditions include: under single-pass conditions, the standard deviation of the brightness temperature data of each channel in the Earth grid is less than a first preset threshold, which is used to determine the spatial uniformity of brightness temperature.

[0018] As an improvement to the above method, the preset conditions further include: under multiple transit conditions, the standard deviation of the brightness temperature data of the same channel, which changes with the time of multiple transits, is less than a second preset threshold, which is used to determine the stability of the brightness temperature over time.

[0019] To achieve another objective of the present invention, the present invention also provides a uniform and stable scene selection system for spaceborne microwave radiation reference transfer, characterized in that it comprises:

[0020] The filtering module, based on brightness temperature observation data from a reference spaceborne microwave radiometer, is used to filter candidate surface scenes by spatial projection, temporal grouping, and atmospheric conditions; and

[0021] The selection module is used to select a surface scene that meets the preset conditions from the screened candidate surface scenes as the target surface scene for the transfer of spaceborne microwave radiation reference; wherein, the preset conditions are used to characterize the spatial uniformity and temporal stability of brightness temperature.

[0022] The advantages of this application are as follows: Traditional SNOs methods only consider acquiring matching data in limited areas such as polar regions where nadir points coincide; alternative calibration methods have large matching time differences, necessitating consideration of long-term scenario stability; and existing cross-calibration methods require the introduction of radiative transfer models. These methods are suitable for current in-orbit satellites but not for reference satellites. For future reference satellites with platform maneuverability and active pointing capabilities, more cross-calibration opportunities and scenarios need to be considered, and it is not sufficient to only consider nadir point coincidence or introduce model uncertainties. This method primarily relies on the spatial uniformity of in-orbit satellite observation data. Through global gridding and spatiotemporal uniformity quantification calculations (using the standard deviation of regional brightness temperature), it quantitatively selects scenarios that can achieve direct cross-transfer of reference radiation. Within the microwave reference satellite system, it actively constructs high-quality transfer links, avoids introducing model uncertainties, and achieves synchronous reference transfer, thus combining the advantages of SNOs methods and traditional cross-calibration methods. Attached Figure Description

[0023] Figure 1 A flowchart illustrating a method for selecting a uniform and stable scene for transferring a spaceborne microwave radiation reference, provided in an embodiment of this application. Detailed Implementation

[0024] The technical solutions provided in this application are further illustrated below with reference to the embodiments.

[0025] Example 1

[0026] The method for selecting a uniform and stable scene for spaceborne microwave radiation reference transfer provided in this embodiment selects an internationally recognized, high-precision, and high-stability microwave remote sensing payload with the same detection channel. For example, the Global Precipitation Measurement Microwave Imager (GMI) on the Global Precipitation Measurement Core Observation Platform (GPMCO) in the United States is used as the reference payload. The L1C-R (Level 1C-R) brightness temperature data of the GMI, which has been uniformly calibrated, geolocated, and resampled, is used. The scheme is as follows:

[0027] (1) First, select an appropriate projection grid size based on the spatial pixel size of the reference payload, and project its brightness temperature onto an equal-area scalable Earth grid (EASE) to divide the regional data for scenarios such as forests, oceans, and deserts;

[0028] (2) Since different satellites have different orbits, their transit time and revisit time are also different, and the swath width of the payload scan is different. Generally, there will be 2 to 3 opportunities to observe the same scene in a day. It is necessary to distinguish the time when the scene is observed in the same day to avoid calculating the data of repeated observations at different times together.

[0029] (3) Since atmospheric conditions such as rainfall can significantly affect the microwave radiation brightness temperature of a scene, the selection of a scene is mainly based on data under clear sky conditions. Therefore, it is necessary to select clear sky conditions by using auxiliary data or physical relationships between different channels, and then calculate the brightness temperature variation characteristics within the EASE grid, ensuring that there are enough observation points;

[0030] (4) By comparing with the known load system sensitivity, the brightness temperature change of the scene radiation itself with spatial variation is determined by the scene data during a single transit.

[0031] (5) Use data from multiple transits to determine the brightness temperature changes caused by the changes in scene radiation over time;

[0032] (6) Finally, select the most ideal transmission scenario based on the transmission accuracy requirements.

[0033] like Figure 1 As shown, the specific processing flow is as follows:

[0034] (1) Read the L1C-R brightness temperature data from GMI;

[0035] (2) Select the corresponding EASE grid area according to the size of the load cell. The grid should be larger than the maximum cell size. For example, the maximum cell size of GMI is 32.1km×19.4km, so a 50km grid should be selected.

[0036] (3) Project the data onto the EASE grid. Given the latitude and longitude coordinates of the observation point, its position in the EASE standard grid can be calculated using the following formula:

[0037]

[0038]

[0039] in, It is the row index of the EASE grid. It is the column index of the EASE grid. It is the Earth's radius (6371.228 km). It is the EASE standard grid size. It is the auxiliary projection angle (usually 30°). It is the actual longitude coordinates of the observed brightness temperature data, and These are the actual latitude coordinates of the observed brightness temperature data. It is the center row index of the EASE projection map. It is the center column index of the EASE projection graph.

[0040] Different projection methods and different resolutions result in different standard grids. and For parameters, the equal area projection of a cylinder is generally selected.

[0041] (4) Divide the daily observations into 4 time periods at 6-hour intervals. The specific division depends on the orbit and scanning characteristics of the reference payload.

[0042] (5) Clear sky scene screening can be done by using ERA5 reanalysis data or by judging the brightness temperature difference of different channels. ERA5 (European Centre for Medium-Range Weather Forecasts Reanalysis 5) is a global meteorological reanalysis dataset that includes various meteorological parameters such as total atmospheric liquid water.

[0043] For ERA5, the clear sky condition is a total liquid water content of less than 0.2 g / m³. 2 For channel combinations, the following conditions apply:

[0044] Forest area: TB 19V -TB 37V <4.5K; TB 19V To reference the brightness temperature data observed by the 19 GHz vertical polarization channel of the spaceborne microwave radiometer, TB 37V K represents Kelvin, referring to the brightness temperature data observed in the 37 GHz vertical polarization channel of the spaceborne microwave radiometer;

[0045] Ocean area: TB 37V -TB 37H >50K; of which, TB 37H For reference, the brightness temperature data observed by the 37 GHz horizontal polarization channel of the spaceborne microwave radiometer;

[0046] (6) Calculate the standard deviation of the brightness temperature of each channel within each EASE grid;

[0047] (7) Select a region with a relatively uniform brightness temperature standard deviation as the reference transfer scenario. The selection of uniformity is related to the reference load. The system sensitivity is slightly greater than the reference load. For example, for the GMI instrument, the brightness temperature standard deviation is required to be no more than 1K.

[0048] Example 2

[0049] This embodiment provides a uniform and stable scene selection system for spaceborne microwave radiation reference transfer, used to implement the uniform and stable scene selection method for spaceborne microwave radiation reference transfer in Embodiment 1, including:

[0050] The filtering module, based on brightness temperature observation data from a reference spaceborne microwave radiometer, is used to filter candidate surface scenes by spatial projection, temporal grouping, and atmospheric conditions; and

[0051] The selection module is used to select a surface scene that meets the preset conditions from the screened candidate surface scenes as the target surface scene for the transfer of spaceborne microwave radiation reference; wherein, the preset conditions are used to characterize the spatial uniformity and temporal stability of brightness temperature.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for selecting a uniform and stable scene for spaceborne microwave radiation reference transfer, comprising: Based on the brightness temperature observation data of the reference spaceborne microwave radiometer, the candidate surface scenes are spatially projected, time-grouped and screened by atmospheric conditions. From the screened candidate surface scenes, the surface scenes that meet the preset conditions are selected as the target surface scenes for the transfer of spaceborne microwave radiation reference. The preset conditions are used to characterize the spatial uniformity and temporal stability of brightness temperature. The reference satellite-borne microwave radiometer has the same detection channel as the transferred microwave radiometer. The accuracy and stability of the reference satellite-borne microwave radiometer are higher than those of the transferred microwave radiometer. The brightness temperature observation data of the reference satellite-borne microwave radiometer are brightness temperature data that have undergone consistency calibration, geolocation and resampling processing. The spatial projection specifically includes: projecting the brightness temperature observation data onto an equidistant, scalable Earth grid based on the actual latitude and longitude coordinates corresponding to the brightness temperature observation data, so as to form standardized brightness temperature spatial distribution data; wherein, the grid size of the Earth grid is larger than the maximum pixel size of the reference spaceborne microwave radiometer; The step of projecting the brightness temperature observation data onto a scalable, equal-area Earth grid based on the actual latitude and longitude coordinates corresponding to the brightness temperature observation data specifically includes: ； ； in, It is the row index of the Earth grid. It is a column index of the Earth grid. It is the Earth's radius. It is the grid size of the Earth grid. It is the auxiliary projection angle. These are the actual longitude coordinates of the brightness temperature observation data, and These are the actual latitude coordinates of the brightness temperature observation data. It is the central row index of the Earth grid. It is the central column index of the Earth grid.

2. The method for selecting a uniform and stable scene for spaceborne microwave radiation reference transfer according to claim 1, characterized in that, The time grouping specifically includes: based on the orbital and scanning characteristics of the reference satellite microwave radiometer, dividing the brightness temperature observation data acquired on the same day into multiple consecutive time periods, so as to distinguish and process the brightness temperature observation data corresponding to different transit times, thereby avoiding the merging and calculation of brightness temperature observation data from different times.

3. The method for selecting a uniform and stable scene for spaceborne microwave radiation reference transfer according to claim 1, characterized in that, The atmospheric conditions include preset clear sky conditions, which are used to exclude brightness temperature observation data affected by rainfall or atmospheric liquid water; the preset clear sky conditions are determined by reanalysis of meteorological data or by differences in brightness temperature across different microwave channels; wherein... When using reanalysis meteorological data to determine the pre-set clear sky conditions, the total amount of atmospheric liquid water is less than the pre-set threshold as the criterion for clear sky. When using the brightness temperature difference of different microwave channels to determine preset clear sky conditions, corresponding channel brightness temperature difference determination conditions are set for different surface types; the surface types include forests and oceans.

4. The method for selecting a uniform and stable scene for spaceborne microwave radiation reference transfer according to claim 3, characterized in that, For the reanalysis meteorological data, when the total liquid water content is less than 0.2 g / m², it is determined that the preset clear sky conditions are met; for the brightness temperature difference of different microwave channels, when the surface type is forest, it meets the TB standard. 19V -TB 37V If the temperature is less than 4.5K, it is considered to meet the preset clear sky conditions, where TB 19V To reference the brightness temperature data observed by the 19 GHz vertical polarization channel of the spaceborne microwave radiometer, TB 37V To reference the brightness temperature data observed in the 37 GHz vertical polarization channel of the spaceborne microwave radiometer, K represents Kelvin; when the surface type is ocean, it satisfies TB 37V -TB 37H If the value is greater than 50K, it is determined that the preset clear sky condition is met, where TB 37H Brightness temperature data was obtained from the 37 GHz horizontal polarization channel of the spaceborne microwave radiometer for reference.

5. The method for selecting a uniform and stable scene for spaceborne microwave radiation reference transfer according to claim 1, characterized in that, The preset conditions include: under single-pass conditions, the standard deviation of brightness temperature data of each channel in the Earth grid is less than a first preset threshold, which is used to determine the spatial uniformity of brightness temperature.

6. The method for selecting a uniform and stable scene for spaceborne microwave radiation reference transfer according to claim 5, characterized in that, The preset conditions also include: under multiple transit conditions, the standard deviation of the brightness temperature data of the same channel, which changes with the time of multiple transits, is less than a second preset threshold, which is used to determine the stability of brightness temperature over time.

7. A uniform and stable scene selection system for spaceborne microwave radiation reference transfer, characterized in that, include: The screening module, based on brightness temperature observation data from a reference satellite-borne microwave radiometer, is used to screen candidate surface scenes by spatial projection, temporal grouping, and atmospheric conditions. and The selection module is used to select a surface scene that meets the preset conditions from the screened candidate surface scenes, and use it as the target surface scene for the transfer of the spaceborne microwave radiation reference; wherein, the preset conditions are used to characterize the spatial uniformity and temporal stability of the brightness temperature. The reference satellite-borne microwave radiometer has the same detection channel as the transferred microwave radiometer. The accuracy and stability of the reference satellite-borne microwave radiometer are higher than those of the transferred microwave radiometer. The brightness temperature observation data of the reference satellite-borne microwave radiometer are brightness temperature data that have undergone consistency calibration, geolocation and resampling processing. The spatial projection specifically includes: projecting the brightness temperature observation data onto an equidistant, scalable Earth grid based on the actual latitude and longitude coordinates corresponding to the brightness temperature observation data, so as to form standardized brightness temperature spatial distribution data; wherein, the grid size of the Earth grid is larger than the maximum pixel size of the reference spaceborne microwave radiometer; The step of projecting the brightness temperature observation data onto a scalable, equal-area Earth grid based on the actual latitude and longitude coordinates corresponding to the brightness temperature observation data specifically includes: ； ； in, It is the row index of the Earth grid. It is a column index of the Earth grid. It is the Earth's radius. It is the grid size of the Earth grid. It is the auxiliary projection angle. These are the actual longitude coordinates of the brightness temperature observation data, and These are the actual latitude coordinates of the brightness temperature observation data. It is the central row index of the Earth grid. It is the central column index of the Earth grid.

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