CN114252834A - Satellite-borne microwave radiometer external calibration method and device based on ocean target - Google Patents
Satellite-borne microwave radiometer external calibration method and device based on ocean target Download PDFInfo
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Abstract
The application provides a satellite-borne microwave radiometer external calibration method and device based on a marine target, wherein the method comprises the following steps: acquiring observation data of each channel of the satellite-borne microwave radiometer to be calibrated and sea data of forecast reanalysis data; determining a calibration reference target according to a preset calibration target selection condition, and determining a search brightness temperature range according to the calibration reference target; acquiring a matching data set matched with the searched brightness temperature range according to a preset time-space matching rule, observation data and sea data; filtering the matched data set to obtain a target data set; calculating simulated brightness temperature data corresponding to the target data set according to the target data set and a preset microwave radiation transmission calculation model; and performing coefficient fitting according to the target data set and the simulated brightness temperature data to obtain a calibration coefficient. Therefore, by the implementation of the embodiment, a wider data range can be selected, different ocean uniform targets are increased, the number of calibration samples is increased, and the calibration precision can be improved.
Description
Technical Field
The application relates to the field of satellite application, in particular to an external calibration method and device of a satellite-borne microwave radiometer based on a marine target.
Background
In the prior art, off-board calibration of a satellite-borne microwave radiometer is typically performed on a surface target using prognostic reanalysis data. Specifically, the technology utilizes a microwave radiation transmission model to calculate the simulated observation brightness temperature of the satellite-borne microwave radiometer under each frequency and polarization mode, and the simulated observation brightness temperature is compared with the brightness temperature actually observed by the satellite-borne microwave radiometer for analysis, so that the external scaling coefficient of the satellite-borne microwave radiometer is obtained. However, in practice, it is found that in the prior art, the sea surface targets under the conditions of a calm sea surface and a dry atmosphere are selected, so that only less data meeting the conditions are usually found, and the brightness and temperature values of the corresponding targets are low, so that the data coverage is not enough, the statistical error is large, the use difficulty is increased, and the calibration precision is low.
Disclosure of Invention
An object of the embodiments of the present application is to provide a satellite-borne microwave radiometer external calibration method and device based on a marine target, which can select a wider data range, increase different marine uniform targets, thereby increasing the number of calibration samples and further improving the calibration accuracy.
The embodiment of the application provides a satellite-borne microwave radiometer external calibration method based on a marine target in a first aspect, which comprises the following steps:
acquiring observation data of each channel of the satellite-borne microwave radiometer to be calibrated and sea data of forecast reanalysis data; the observation data comprise observation brightness temperature data and first time-space mark data corresponding to the observation brightness temperature data, and the sea gas data comprise sea gas parameters and second time-space mark data corresponding to the sea gas parameters;
determining a calibration reference target according to preset calibration target selection conditions, and determining a search brightness temperature range according to the calibration reference target;
acquiring a matching data set matched with the search brightness temperature range according to a preset time-space matching rule, the observation data and the sea data;
filtering the matched data set to obtain a target data set;
calculating simulated brightness temperature data corresponding to the target data set according to the target data set and a preset microwave radiation transmission calculation model;
performing coefficient fitting according to the target data set and the simulated brightness temperature data to obtain a calibration coefficient;
and carrying out external calibration on the observed brightness temperature data according to the calibration coefficient to obtain a calibration result.
Further, the step of determining a search brightness temperature range according to the scaled reference target includes:
acquiring preset parameters and observation parameters of each frequency band of the satellite-borne microwave radiometer to be calibrated;
determining a search brightness temperature range according to the calibration reference target, the preset parameters and the observation parameters; and the searched bright temperature range comprises a quiet sea surface bright temperature range and a dry atmosphere bright temperature range.
Further, the step of obtaining a matching data set matched with the search brightness temperature range according to a preset space-time matching rule, the observation data and the sea data comprises:
acquiring first initial matching data corresponding to the quiet sea surface bright temperature range from the observation data, and acquiring second initial matching data corresponding to the dry atmosphere bright temperature range from the observation data;
and performing multivariate data space-time matching on the first initial matching data according to a preset space-time matching rule to obtain first matching data, and performing multivariate data space-time matching on the second initial matching data according to the space-time matching rule to obtain second matching data.
Further, the step of filtering the matching data set to obtain a target data set includes:
verifying the matching data set under the assumed condition to obtain a first verification result, and deleting unqualified data verified in the matching data set according to the first verification result to obtain a first filtered data set;
performing gradient data verification on the first filtered data set to obtain a second verification result, and deleting unqualified data verified in the first filtered data set according to the second verification result to obtain a second filtered data set;
and performing offshore distance verification on the second filtered data set to obtain a third verification result, and deleting unqualified data verified in the second filtered data set according to the third verification result to obtain a target data set.
Further, the method further comprises:
calculating a fitting root mean square error and a fitting average absolute error according to the target data set, the simulated light temperature data and the calibration coefficient;
acquiring a sample coverage range and a sample histogram of the simulated brightness temperature data;
and performing coefficient evaluation on the scaling coefficient according to the fitting root mean square error, the fitting average absolute error, the sample coverage range and the sample histogram to obtain an evaluation result.
Further, the step of calculating a fitted root mean square error and a fitted mean absolute error according to the target data set, the simulated light temperature data and the scaling coefficient comprises:
acquiring a linear relation between the target data set and the simulated brightness temperature data;
calculating calibration brightness temperature data according to the linear relation, the simulated brightness temperature data and the calibration coefficient;
and calculating the fitting root mean square error and the fitting average absolute error of the calibration coefficient according to the calibration brightness temperature data and the simulated brightness temperature data.
The embodiment of the present application provides a calibration device outside satellite-borne microwave radiometer based on a marine target in a second aspect, which includes:
the acquisition unit is used for acquiring observation data of each channel of the satellite-borne microwave radiometer to be calibrated and marine gas data of forecast reanalysis data; the observation data comprise observation brightness temperature data and first time-space mark data corresponding to the observation brightness temperature data, and the sea gas data comprise sea gas parameters and second time-space mark data corresponding to the sea gas parameters;
the determining unit is used for determining a calibration reference target according to a preset calibration target selection condition and determining a search brightness temperature range according to the calibration reference target;
the acquisition unit is further used for acquiring a matching data set matched with the search brightness temperature range according to a preset space-time matching rule, the observation data and the sea air data;
the filtering unit is used for filtering the matched data set to obtain a target data set;
the calculation unit is used for calculating simulated brightness temperature data corresponding to the target data set according to the target data set and a preset microwave radiation transmission calculation model;
the fitting unit is used for performing coefficient fitting according to the target data set and the simulated brightness temperature data to obtain a calibration coefficient;
and the calibration unit is used for carrying out external calibration on the observed brightness temperature data according to the calibration coefficient to obtain a calibration result.
Further, the external calibration device for the marine target-based satellite-borne microwave radiometer further comprises:
the calculation unit is further configured to calculate a fitting root mean square error and a fitting average absolute error according to the target data set, the simulated light temperature data, and the scaling coefficient;
the acquisition unit is further used for acquiring a sample coverage range and a sample histogram of the simulated brightness temperature data;
and the evaluation unit is used for performing coefficient evaluation on the scaling coefficient according to the fitted root mean square error, the fitted average absolute error, the sample coverage range and the sample histogram to obtain an evaluation result.
A third aspect of the embodiments of the present application provides an electronic device, including a memory and a processor, where the memory is used to store a computer program, and the processor runs the computer program to make the electronic device execute the method for external calibration of a marine-target-based microwave radiometer according to any one of the first aspect of the embodiments of the present application.
A fourth aspect of the embodiments of the present application provides a computer-readable storage medium, which stores computer program instructions, where the computer program instructions, when read and executed by a processor, perform the method for external calibration of a microwave radiometer based on marine targets in any of the first aspects of the embodiments of the present application.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments of the present application will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and that those skilled in the art can also obtain other related drawings based on the drawings without inventive efforts.
Fig. 1 is a schematic flowchart of an external calibration method for a satellite-borne microwave radiometer based on a marine target according to an embodiment of the present application;
fig. 2 is a schematic structural diagram of an external calibration device of a satellite-borne microwave radiometer based on a marine target according to an embodiment of the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application.
The prior art has the following disadvantages:
(1) disadvantages in target selection: in the prior art, the sea surface targets under the conditions of a calm sea surface and a dry atmosphere are selected, so that the data meeting the conditions are less to find, the brightness temperature value of the target is lower, the data coverage is insufficient, the statistical error is increased, and the use difficulty is increased.
(2) Disadvantages in space-time matching: in the prior art, all data are adopted for space-time matching during matching, the matching efficiency is low, the matching rule is too simple, and only the conditions such as time, space distance and the like are judged, so that the matching efficiency is low and the precision is low.
(3) The disadvantages of quality control: in the prior art, only the most common method of 3 times standard deviation is used for removing the outlier, so that the outlier is difficult to be accurately removed, error statistic points exist, and the fitting precision of the calibration coefficient is reduced.
(4) The results confirmed the disadvantages: in the prior art, the quality of a calibration result is only determined according to the size of the root mean square error of the calibration coefficient fitting, and whether the calibration coefficient is suitable for subsequent application is difficult to determine practically, so that the uncertainty of the calibration coefficient is increased, and the application effect of calibration is reduced.
Aiming at the defects in the aspects, the method and the device can be used for correspondingly solving the problems, so that the precision of the obtained calibration coefficient is improved, and the result precision of subsequent calibration is improved.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures. Meanwhile, in the description of the present application, the terms "first", "second", and the like are used only for distinguishing the description, and are not to be construed as indicating or implying relative importance.
Example 1
Referring to fig. 1, fig. 1 is a schematic flow chart of a satellite-borne microwave radiometer external calibration method based on a marine target according to an embodiment of the present application. The satellite-borne microwave radiometer external calibration method based on the marine target comprises the following steps:
s101, obtaining observation data of each channel of the satellite-borne microwave radiometer to be calibrated and forecasting sea gas data of reanalysis data; the observation data comprise observation brightness temperature data and first time-space tag data corresponding to the observation brightness temperature data, and the sea air data comprise sea air parameters and second time-space tag data corresponding to the sea air parameters.
In the embodiment, the method can read the brightness temperature data of each channel observation quantity of the microwave radiometer to be calibrated, read the corresponding time and geographical latitude and longitude information, and read the marking information such as a quality control mark, a sea and land mark, a sea ice mark, a rainfall mark and the like; in addition, the sea air parameters of the re-analysis data are read, mainly sea surface temperature, sea surface wind U/V component, atmosphere water vapor and liquid water layering data and rainfall information, the quality control marks of the re-analysis data are read, and time and longitude and latitude information are read.
In this embodiment, the first time-space tag data is time and geographical latitude and longitude information corresponding to the observed brightness temperature data of each channel; the second spatiotemporal marker data is time and latitude information corresponding to the forecast reanalysis data.
S102, determining a calibration reference target according to a preset calibration target selection condition, and determining a search brightness temperature range according to the calibration reference target.
In this embodiment, search bright temperature range and the second bright temperature range of dry atmosphere of the first bright temperature range of the peaceful sea of the bright temperature range Wei.
As an optional implementation, the step of determining the search brightness temperature range according to the scaled reference target includes:
acquiring preset parameters and observation parameters of each frequency band of a satellite-borne microwave radiometer to be calibrated;
determining a search brightness temperature range according to the calibration reference target, the preset parameters and the observation parameters; the searched bright temperature range comprises a quiet sea surface bright temperature range and a dry atmosphere bright temperature range.
In this embodiment, the method first needs to select a uniform large-area sea surface as a calibration reference target, and uses the radiation transmission model to simulate and calculate the simulated brightness temperature data of the satellite-borne microwave radiometer in the sea area, and compares the simulated brightness temperature data with the actual observed brightness temperature data of the satellite-borne microwave radiometer in the sea area, and calculates to obtain the calibration coefficient.
In this embodiment, because the observation surface element of the satellite-borne microwave radiometer is large (generally larger than thirty kilometers), an area with a length and a width larger than the size of the observation surface element of the radiometer load is generally selected, and the radiation brightness temperature of the area is uniform, so that a stable reference calibration target can be obtained. The conditions for selecting the sea area (i.e. the preset target selection conditions) include the following aspects:
on the first hand, selecting a sea area under the conditions of calm sea and dry atmosphere, wherein the calm sea means the sea without wind, the temperature gradient of the sea is uniform if the temperature gradient is small, and the atmosphere is dry, which means the water vapor and liquid water content is small, the atmosphere mainly containing oxygen and nitrogen is approximately a uniform atmosphere interface, so that the combined target is a uniform target;
in addition, because the probability of occurrence of the average sea surface and the dry atmosphere is low, more data are needed to accumulate necessary fitting calculation samples, and therefore, comprehensively, more data samples with higher brightness temperature need to be selected.
In this embodiment, because waves reflected on land are overlapped to cause uneven sea surface, waves are required to be overlapped and broken in a non-offshore area with a low wind speed condition, data beyond fifty kilometers are generally required, the roughness of the sea surface is uniform at this time, and the sea surface can be approximately considered as a uniform sea surface as long as the sea surface temperature and the wind field are uniformly distributed, so that the selected condition is that the offshore distance is more than fifty kilometers, and the uniform sea surface is found when the gradient of the sea surface temperature and the wind field is small.
S103, acquiring a matching data set matched with the searched bright temperature range according to a preset space-time matching rule, observation data and sea data.
As an alternative implementation, the step of obtaining a matching data set matching the search brightness temperature range according to the preset spatio-temporal matching rule, the observation data and the sea data includes:
acquiring first initial matching data corresponding to a bright temperature range of a calm sea surface from the observation data, and acquiring second initial matching data corresponding to a bright temperature range of dry atmosphere from the observation data;
and performing multivariate data space-time matching on the first initial matching data according to a preset space-time matching rule to obtain first matching data, and performing multivariate data space-time matching on the second initial matching data according to the space-time matching rule to obtain second matching data.
In this embodiment, the step is configured to obtain first observed bright temperature data matched with the first bright temperature range and second observed bright temperature data matched with the second bright temperature range according to a preset space-time matching rule and the first space-time tag data.
Specifically, when the method develops the space-time matching in the step, in order to improve the efficiency, the space-time matching method is to use a cyclic algorithm to retrieve two or more types of data according to a fixed space-time condition. The method for improving the space-time matching efficiency mainly comprises the following steps: according to the possible brightness temperature range of the target, the data quantity of the satellite-borne microwave radiometer needing to be searched is reduced, so that the circulation times are greatly reduced, and the matching efficiency is improved; secondly, the matching precision needs to be improved, so that when the two uniform targets are matched, different space-time rules are adopted for matching according to the conditions of the two uniform targets, and the matching precision is improved.
For example, the method can calculate the target brightness temperature ranges of two conditions according to the model, search all observation brightness temperature data meeting the conditions by using the observation brightness temperature of the satellite-borne microwave radiometer according to the ranges, and simultaneously record the corresponding time and geographical position information and the like; then, aiming at the first uniform target occurrence condition, multi-source data space-time matching is carried out on the searched data, a matching rule is selected, the sea surface temperature is required to be uniform, therefore, sea temperature data which is closer in time and space as far as possible can be selected, data within one hour and within fifty kilometers of geographical interval are selected, and the distance between any two points A and B is as follows;
r is the radius of the earth, omega and
the radians of the two points in a WGS84 coordinate system are respectively equal to pi multiplied by longitude and latitude/180; secondly, aiming at conditions of occurrence of a second uniform target, multi-source data space-time matching is carried out on the searched data, a matching rule is selected, and the sea surface temperature and the wind field are required to be uniform at the same time, so that sea surface temperature and wind field data which are closer in time and space as much as possible can be selected, data within one hour of interval, data within fifty kilometers of sea surface temperature geographical interval and data within twenty five miles of wind field geographical interval are selected; therefore, the sea surface brightness temperature data searched by the model calculation is matched with the sea surface temperature, the sea surface wind vector, the atmospheric water vapor content, the cloud liquid water content, the rainfall rate and other data in the reanalysis data. Meanwhile, it is also noted that the condition for the second uniform target to appear also includes a non-offshore area, so that firstly, according to the land-sea mark and sea ice mark information in the satellite-borne microwave radiometer, the data of the land and sea ice appearing cannot be matched, and the offshore distance between the matching point and the land shore line is calculated, and the minimum distance, namely the offshore distance of the matching point is found. The result of the offshore distance is used for quality control. Finally, calculating the gradient of data around the matching point during matching, calculating the gradient of the sea surface temperature and the gradient of the bright temperature according to the occurrence condition of the target during matching the target in the first condition, and calculating the gradients in the vertical direction and the horizontal direction; when the target in the second situation is matched, the gradients of sea surface temperature, wind speed, wind direction, atmospheric temperature, humidity and brightness temperature are calculated according to the occurrence conditions of the target, and the gradients in the vertical direction and the horizontal direction are calculated. The gradient settlement results are used for quality control.
And S104, filtering the matched data set to obtain a target data set.
As an optional implementation, the step of filtering the matching data set to obtain the target data set includes:
verifying the matching data set under the assumed condition to obtain a first verification result, and deleting unqualified data verified in the matching data set according to the first verification result to obtain a first filtered data set;
performing gradient data verification on the first filtered data set to obtain a second verification result, and deleting unqualified data verified in the first filtered data set according to the second verification result to obtain a second filtered data set;
and performing offshore distance verification on the second filtered data set to obtain a third verification result, and deleting unqualified data verified in the second filtered data set according to the third verification result to obtain a target data set.
In this embodiment, the method may perform high-precision quality control by verifying conditions of occurrence of a uniform target, a data gradient, and a triple standard deviation to obtain an accurate matching sample set for subsequent calibration coefficient calculation, and the specific steps may be as follows:
firstly, verifying assumed conditions in a matched data set, verifying whether input conditions of model calculation in the first step of space-time matching are met, and adding a certain error range during verification. Firstly, under the conditions of a calm sea surface and a dry atmosphere, verifying whether the wind speed is 0-5 m/s, the atmospheric water vapor is 0-20 mm and the liquid water is 0-0.05 mm in the matched sea gas parameters in the reanalysis data set; and secondly, verifying whether the wind speed is 0-9 m/s, whether the atmospheric water vapor is 0-80 mm, whether the liquid water content is 0-0.1 mm and the rainfall rate is 0mm/h in the matched sea air parameters in the reanalysis data set under the conditions of non-calm sea surface and clear air atmosphere. Verifying unqualified data deletion;
secondly, verifying according to the gradient data, and selecting a data set with smaller gradients in the vertical direction and the horizontal direction from the gradient data calculated in the second step of space-time matching, wherein the brightness temperature gradient is less than 0.5K, the sea surface temperature gradient is less than 0.3 ℃, the wind speed gradient is less than 1m/s, the wind direction gradient is less than 15 degrees, the atmospheric temperature gradient is less than 1 degree, the humidity gradient is less than 15 percent, and unsatisfactory data are removed;
thirdly, verifying according to the offshore distance, and eliminating unsatisfied data with larger offshore distance requirement of at least fifty kilometers when verifying the second type of data;
fourthly, inputting the matched sea gas parameters into the target brightness temperature simulation model, calculating a brightness temperature simulation value of the matched target, and calculating a standard deviation of the simulated brightness temperature and the observed brightness temperature, wherein the formula is as follows:
and eliminating the data with the standard deviation larger than 3 times, wherein the formula is as follows:
ΔTBi≥3ΔTBSTD。
and S105, calculating simulated brightness temperature data corresponding to the target data set according to the target data set and a preset microwave radiation transmission calculation model.
In the embodiment, the brightness temperature ranges of the calm sea and the dry atmosphere are calculated through a microwave radiation transmission calculation model, when the brightness temperatures of the calm sea and the dry atmosphere are simulated, the set sea temperature range is generally [ -2-33 ℃), the wind speed is set to be 0m/s, and the contents of atmospheric water vapor and liquid water are set to be 0 mm; when the rough sea surface brightness temperature is simulated, the set sea surface temperature range is generally [ -2-33 ℃), the wind speed is set to be [ 0-7 m/s ], the atmospheric water vapor [ 0-80 mm ] and the liquid water content are set to be [ 0-0.1 mm ], and the rainfall rate is 0 mm/h. And observing ground incident angle, frequency and polarization information according to each frequency band of the satellite-borne microwave radiometer, calculating actual brightness temperature ranges under a calm sea surface and dry atmosphere, searching brightness temperature of each channel according to the ranges, and verifying whether the brightness temperature ranges are within the condition range by combining reanalyzed sea surface temperature, sea surface wind speed, atmospheric water vapor, cloud liquid water and rainfall data during matching.
The calculation of the radiant brightness temperature of a sea surface target of the satellite-borne microwave radiometer is generally expressed as the following formula:
TB＝TBU+τ(e×SST+(1-e)×(TBD+τ×TBC))；
here, the atmospheric upward radiation TBUExpressed as:
atmospheric downlink radiation TBDExpressed as:
the transmittance τ is expressed as:
cosmic background radiation is represented as:
TBC＝2.69+0.003625f；
e is the sea surface emissivity, SST is the sea surface physical temperature, where TBUExpressed as ascending atmospheric radiation, TBDIs the descending atmospheric radiation, τ is the transmission rate of the total path from the surface to the top of the atmosphere, TBCThe radiation of the cold air background is basically a constant, at the moment, under a calm sea surface, the calculation e does not need to consider the emissivity change caused by roughness, and does not need to consider the influence of foam emission superposed on the sea surface, so that the calculation e can be simplified as follows:
e＝(1-R)；
r is the emissivity of the calm sea surface, which can be calculated according to the Fresnel reflectivity formula, and the reflectivity for horizontal and vertical polarization is respectively expressed as
The method can calculate the observed brightness temperature of the satellite-borne microwave radiometer on the calm sea surface, and when calculating the rough sea surface, the rough sea surface radiation brightness temperature comprises two parts: light temperature under completely calm sea and light temperature increase due to rough and excessive sea:
in general, the reflectivity of a rough sea surface is defined as: all incident energy scattered from the sea surface received at frequency f and in a particular direction. Therefore, the luminance temperature of a rough sea surface can be expressed as:
in the formula (I), the compound is shown in the specification,
and
i-polarization to i-polarization, i-polarization to j-polarization bistatic scattering coefficients, respectively, which are related to the dielectric constant of the seawater and the state of the sea surface. Theta0,
The observation direction is bright temperature; thetas,
Is the scattering direction.
And S106, performing coefficient fitting according to the target data set and the simulated brightness temperature data to obtain a calibration coefficient.
In this embodiment, when the observed bright temperature and the simulated bright temperature are subjected to coefficient fitting, a linear rule is followed, so that a least square method is adopted to perform parameter fitting, and the known linear relationship is as follows:
TBobs＝a×TBsim+b；
wherein TBobsIndicating the observed light temperature, TBsimRepresenting the simulated light temperature, a and b are the slope and intercept of this linear equation, i.e., the coefficients of the scale obtained by fitting such that
Minimum, where m is the number of samples fitted, σKIs the fitted residual.
As an optional implementation manner, after step S106, the method further includes:
calculating a fitting root mean square error and a fitting average absolute error according to the target data set, the simulated brightness temperature data and the calibration coefficient;
acquiring a sample coverage range and a sample histogram of simulated brightness temperature data;
and performing coefficient evaluation on the scaling coefficient according to the fitted root mean square error, the fitted average absolute error, the sample coverage range and the sample histogram to obtain an evaluation result.
As a further alternative, the step of calculating a fitted root mean square error and a fitted mean absolute error from the target data set, the simulated light temperature data and the scaling coefficients comprises:
acquiring a linear relation between a target data set and simulated brightness temperature data;
calculating the calibration brightness temperature data according to the linear relation, the simulation brightness temperature data and the calibration coefficient;
and calculating the fitting root mean square error and the fitting average absolute error of the calibration coefficient according to the calibration brightness temperature data and the simulated brightness temperature data.
In this embodiment, after obtaining the scaling factor, the method may bring the scaling factor into TBobs＝a×TBsim+ b, the calibrated TB is calculatedobs. The fitted root mean square error and the mean absolute error can be calculated by the following equations:
and S107, carrying out external calibration on the observed brightness temperature data according to the calibration coefficient to obtain a calibration result.
In this embodiment, in the prior art, the quality of the calibration result is determined only according to the magnitude of the root mean square error fitted by the calibration coefficient, generally, the root mean square error and the average absolute error of all data are calculated, and it is difficult to determine whether the calibration coefficient is suitable for subsequent application only through these two indexes, which increases the uncertainty of the calibration coefficient and reduces the application effect of the calibration. The method adopts the root mean square error and the average absolute error of the sample, and also calculates the coverage range and the histogram distribution of the sample for judgment, whether the coverage range is wider or not is judged, the histogram distribution is reasonable, and the coverage range is judged as follows:
TBRange＝[TBmin,sim,TBmax,sim]；
if the range is closer to the maximum and minimum value ranges calculated by the uniform sea surface target brightness temperature model, that is, the sample distribution is wider, the sample coverage is better, and the calculated scaling coefficient is more suitable for subsequent applications. If the sample coverage is poor and the phase difference is generally more than 3K, the data amount is not enough, and the method is usually adopted to increase the sample amount, read more data for matching and recalculate the scaling coefficient.
By implementing the implementation mode, the technical problems in the prior art can be correspondingly solved, specifically:
(1) aiming at the defects of the prior art, the method selects a wider data range, increases different ocean uniform targets, increases the number of calibration samples and further improves the precision and the application effect;
(2) aiming at the defect of low space-time matching efficiency in the prior art, the method utilizes the brightness-temperature analog value of the uniform sea surface target to search and reduce the matching data volume, thereby improving the matching efficiency;
(3) aiming at the defect of single space-time matching rule in the prior art, the method provides matching rules of different uniform ocean targets, and improves matching precision;
(4) aiming at the defect of simple quality control judgment conditions in the prior art, the method adds the methods of the offshore distance, the data gradient and the like, eliminates invalid data in the matching result by verifying whether the data of the matching result meets the initial assumed conditions, and improves the calibration precision.
(5) The method aims at the defect that the selection index is unreasonable in result analysis in the prior art, the index of data sample coverage is selected, and the rationality judgment of the calibration result is realized.
In the embodiment of the present application, the execution subject of the method may be a computing device such as a computer and a server, and is not limited in this embodiment.
In this embodiment, an execution subject of the method may also be an intelligent device such as a smart phone and a tablet computer, which is not limited in this embodiment.
It can be seen that, by implementing the external calibration method for the satellite-borne microwave radiometer based on the marine target described in this embodiment, firstly, the brightness temperature data of the satellite-borne microwave radiometer to be calibrated and the ocean parameter of the mode forecast data can be respectively read, and the time, the geographic position, the mark and other data of the satellite-borne microwave radiometer to be calibrated and the ocean parameter of the mode forecast data can be read; then calculating the range of the brightness temperature according to the condition of the uniform target; matching to obtain data sets of the searched brightness temperature range and the searched space-time matching rule; after eliminating invalid data and wild values, obtaining a quality-controlled matching data set; based on the data after quality control, obtaining model calculation brightness temperature corresponding to the actual observation brightness temperature through forward model calculation; and then, obtaining the slope and intercept of the calibration straight line by using a least square fitting method, thereby determining an accurate calibration coefficient.
Example 2
Referring to fig. 2, fig. 2 is a schematic structural diagram of an external calibration device of a satellite-borne microwave radiometer based on a marine target according to an embodiment of the present application. As shown in fig. 2, the external calibration device of the satellite-borne microwave radiometer based on the marine target comprises:
the acquisition unit 210 is configured to acquire observation data of each channel of the satellite-borne microwave radiometer to be calibrated and marine gas data of forecast reanalysis data; the observation data comprise observation brightness temperature data and first time-space tag data corresponding to the observation brightness temperature data, and the sea air data comprise sea air parameters and second time-space tag data corresponding to the sea air parameters;
a determining unit 220, configured to determine a calibration reference target according to a preset calibration target selection condition, and determine a search brightness temperature range according to the calibration reference target;
the obtaining unit 210 is further configured to obtain a matching data set matching the searched bright temperature range according to a preset space-time matching rule, observation data and sea data;
the filtering unit 230 is configured to filter the matching data set to obtain a target data set;
the calculating unit 240 is configured to calculate simulated brightness temperature data corresponding to the target data set according to the target data set and a preset microwave radiation transmission calculation model;
the fitting unit 250 is used for performing coefficient fitting according to the target data set and the simulated brightness temperature data to obtain a calibration coefficient;
and the calibration unit 260 is used for performing external calibration on the observed brightness temperature data according to the calibration coefficient to obtain a calibration result.
As an alternative embodiment, the determining unit 220 includes:
the second obtaining subunit 221 is configured to obtain preset parameters and observation parameters of each frequency band of the satellite-borne microwave radiometer to be calibrated;
a determining subunit 222, configured to determine a search brightness temperature range according to the calibration reference target, the preset parameter, and the observation parameter; the searched bright temperature range comprises a quiet sea surface bright temperature range and a dry atmosphere bright temperature range.
As an optional implementation, the obtaining unit 210 includes:
a first obtaining subunit 211, configured to obtain, from the observation data, first initial matching data corresponding to a light temperature range of a calm sea surface, and obtain, from the observation data, second initial matching data corresponding to a light temperature range of a dry atmosphere;
the matching subunit 212 is configured to perform multivariate data space-time matching on the first initial matching data according to a preset space-time matching rule to obtain first matching data, and perform multivariate data space-time matching on the second initial matching data according to a space-time matching rule to obtain second matching data.
As an alternative embodiment, the filtering unit 230 includes:
the first deleting subunit 231 is configured to verify the assumed conditions of the matching data set to obtain a first verification result, and delete the data that is not verified in the matching data set according to the first verification result to obtain a first filtered data set;
the second deleting subunit 232 is configured to perform gradient data verification on the first filtered data set to obtain a second verification result, and delete data that is not qualified in the verification in the first filtered data set according to the second verification result to obtain a second filtered data set;
and a third deleting subunit 233, configured to perform offshore distance verification on the second filtered data set to obtain a third verification result, and delete the data that is not qualified in verification in the second filtered data set according to the third verification result to obtain the target data set.
As an optional implementation manner, the external calibration device of the satellite-borne microwave radiometer based on the marine target further comprises:
the calculating unit 240 is further configured to calculate a fitting root mean square error and a fitting average absolute error according to the target data set, the simulated brightness temperature data, and the calibration coefficient;
the obtaining unit 210 is further configured to obtain a sample coverage range and a sample histogram of the simulated brightness temperature data;
and the evaluation unit 270 is configured to perform coefficient evaluation on the scaling coefficient according to the fitted root mean square error, the fitted average absolute error, the sample coverage range, and the sample histogram to obtain an evaluation result.
As an alternative embodiment, the computing unit 240 includes:
a third obtaining subunit 241, configured to obtain a linear relationship between the target data set and the simulated brightness temperature data;
a calculating subunit 242, configured to calculate scaled brightness temperature data according to the linear relationship, the simulated brightness temperature data, and the scaling coefficient;
the calculating subunit 242 is further configured to calculate a fitting root mean square error and a fitting average absolute error of the scaling coefficient according to the scaled brightness temperature data and the simulated brightness temperature data.
In the embodiment of the present application, for the explanation of the external calibration device of the satellite-borne microwave radiometer based on the marine target, reference may be made to the description in embodiment 1, and further details are not repeated in this embodiment.
It can be seen that, by implementing the external calibration device of the satellite-borne microwave radiometer based on the marine target described in this embodiment, an accurate calibration coefficient can be obtained, and an accurate external calibration operation can be performed according to the calibration coefficient.
The embodiment of the application provides electronic equipment, which comprises a memory and a processor, wherein the memory is used for storing a computer program, and the processor runs the computer program to enable the electronic equipment to execute the off-site calibration method of the marine target-based satellite-borne microwave radiometer in the embodiment 1 of the application.
The embodiment of the present application provides a computer-readable storage medium, which stores computer program instructions, and when the computer program instructions are read and executed by a processor, the method for performing the off-site calibration of the microwave radiometer based on marine targets in embodiment 1 of the present application is performed.
In the embodiments provided in the present application, it should be understood that the disclosed apparatus and method can be implemented in other ways. The apparatus embodiments described above are merely illustrative, and for example, the flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of apparatus, methods and computer program products according to various embodiments of the present application. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.
In addition, functional modules in the embodiments of the present application may be integrated together to form an independent part, or each module may exist separately, or two or more modules may be integrated to form an independent part.
The functions, if implemented in the form of software functional modules and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present application or portions thereof that substantially contribute to the prior art may be embodied in the form of a software product stored in a storage medium and including instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
The above description is only an example of the present application and is not intended to limit the scope of the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application. It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.
The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present application, and shall be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
Claims (10)
1. An external calibration method of a satellite-borne microwave radiometer based on a marine target is characterized by comprising the following steps:
acquiring observation data of each channel of the satellite-borne microwave radiometer to be calibrated and sea data of forecast reanalysis data; the observation data comprise observation brightness temperature data and first time-space mark data corresponding to the observation brightness temperature data, and the sea gas data comprise sea gas parameters and second time-space mark data corresponding to the sea gas parameters;
determining a calibration reference target according to preset calibration target selection conditions, and determining a search brightness temperature range according to the calibration reference target;
acquiring a matching data set matched with the search brightness temperature range according to a preset time-space matching rule, the observation data and the sea data;
filtering the matched data set to obtain a target data set;
calculating simulated brightness temperature data corresponding to the target data set according to the target data set and a preset microwave radiation transmission calculation model;
performing coefficient fitting according to the target data set and the simulated brightness temperature data to obtain a calibration coefficient;
and carrying out external calibration on the observed brightness temperature data according to the calibration coefficient to obtain a calibration result.
2. The off-board calibration method for microwave radiometers based on marine targets of claim 1, wherein said step of determining a search bright temperature range from said calibration reference targets comprises:
acquiring preset parameters and observation parameters of each frequency band of the satellite-borne microwave radiometer to be calibrated;
determining a search brightness temperature range according to the calibration reference target, the preset parameters and the observation parameters; and the searched bright temperature range comprises a quiet sea surface bright temperature range and a dry atmosphere bright temperature range.
3. The off-board calibration method for microwave radiometers based on marine targets as claimed in claim 2, wherein said step of obtaining a matching data set matching said searched bright temperature range according to a preset space-time matching rule, said observation data and said sea data comprises:
acquiring first initial matching data corresponding to the quiet sea surface bright temperature range from the observation data, and acquiring second initial matching data corresponding to the dry atmosphere bright temperature range from the observation data;
and performing multivariate data space-time matching on the first initial matching data according to a preset space-time matching rule to obtain first matching data, and performing multivariate data space-time matching on the second initial matching data according to the space-time matching rule to obtain second matching data.
4. The off-board calibration method for microwave radiometers based on marine targets of claim 1, wherein said step of filtering said matching data set to obtain a target data set comprises:
verifying the matching data set under the assumed condition to obtain a first verification result, and deleting unqualified data verified in the matching data set according to the first verification result to obtain a first filtered data set;
performing gradient data verification on the first filtered data set to obtain a second verification result, and deleting unqualified data verified in the first filtered data set according to the second verification result to obtain a second filtered data set;
and performing offshore distance verification on the second filtered data set to obtain a third verification result, and deleting unqualified data verified in the second filtered data set according to the third verification result to obtain a target data set.
5. The off-board calibration method for marine target based microwave radiometer according to claim 1, further comprising:
calculating a fitting root mean square error and a fitting average absolute error according to the target data set, the simulated light temperature data and the calibration coefficient;
acquiring a sample coverage range and a sample histogram of the simulated brightness temperature data;
and performing coefficient evaluation on the scaling coefficient according to the fitting root mean square error, the fitting average absolute error, the sample coverage range and the sample histogram to obtain an evaluation result.
6. The off-site calibration method for marine target based microwave radiometer according to claim 5, wherein said step of calculating a fitted root mean square error and a fitted mean absolute error based on said target data set, said simulated light temperature data and said calibration coefficients comprises:
acquiring a linear relation between the target data set and the simulated brightness temperature data;
calculating calibration brightness temperature data according to the linear relation, the simulated brightness temperature data and the calibration coefficient;
and calculating the fitting root mean square error and the fitting average absolute error of the calibration coefficient according to the calibration brightness temperature data and the simulated brightness temperature data.
7. An off-board calibration device for a satellite-borne microwave radiometer based on a marine target, which is characterized by comprising:
the acquisition unit is used for acquiring observation data of each channel of the satellite-borne microwave radiometer to be calibrated and marine gas data of forecast reanalysis data; the observation data comprise observation brightness temperature data and first time-space mark data corresponding to the observation brightness temperature data, and the sea gas data comprise sea gas parameters and second time-space mark data corresponding to the sea gas parameters;
the determining unit is used for determining a calibration reference target according to a preset calibration target selection condition and determining a search brightness temperature range according to the calibration reference target;
the acquisition unit is further used for acquiring a matching data set matched with the search brightness temperature range according to a preset space-time matching rule, the observation data and the sea air data;
the filtering unit is used for filtering the matched data set to obtain a target data set;
the calculation unit is used for calculating simulated brightness temperature data corresponding to the target data set according to the target data set and a preset microwave radiation transmission calculation model;
the fitting unit is used for performing coefficient fitting according to the target data set and the simulated brightness temperature data to obtain a calibration coefficient;
and the calibration unit is used for carrying out external calibration on the observed brightness temperature data according to the calibration coefficient to obtain a calibration result.
8. The off-board marine target-based microwave radiometer calibration device according to claim 7, further comprising:
the calculation unit is further configured to calculate a fitting root mean square error and a fitting average absolute error according to the target data set, the simulated light temperature data, and the scaling coefficient;
the acquisition unit is further used for acquiring a sample coverage range and a sample histogram of the simulated brightness temperature data;
and the evaluation unit is used for performing coefficient evaluation on the scaling coefficient according to the fitted root mean square error, the fitted average absolute error, the sample coverage range and the sample histogram to obtain an evaluation result.
9. An electronic device, characterized in that the electronic device comprises a memory for storing a computer program and a processor for executing the computer program to cause the electronic device to perform the off-board microwave radiometer calibration method according to any of claims 1-6.
10. A readable storage medium, wherein computer program instructions are stored in the readable storage medium, and when the computer program instructions are read and executed by a processor, the method for external calibration of ocean target based microwave radiometer according to any of claims 1 to 6 is performed.
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