CN108318871B - Cold air calibration correction method for satellite-borne microwave radiometer - Google Patents

Abstract

A calibration and correction method, especially a cold-space calibration and correction method for a spaceborne microwave radiometer, by using the cold-air observation data in the ocean area to fit the cold-air observation count value that only changes with the temperature of the receiver. The cold space observation count value of each scanning period affected by the contribution of the earth's side lobe radiation is calibrated to obtain the cold space calibration brightness temperature correction value, and then use the cold space calibration brightness temperature correction value, the original cold space observation count value, and the original heat source. The observation count value and the heat source brightness temperature are used to calibrate the scene observation count value, which corrects the calibration error caused by the cold air brightness temperature error and improves the calibration accuracy.

Description

A cold space calibration correction method for spaceborne microwave radiometer

technical field

The invention relates to a cold space calibration and correction method for a space-borne microwave radiometer, belonging to the field of microwave remote sensing.

Background technique

At present, in the calibration module of the microwave radiometer ground data processing system, the cold air brightness temperature usually adopts the standard 2.73K radiation brightness temperature. However, since the cold space observation is realized by the antenna pointing to the cosmic cold space background, the earth radiation with higher radiation brightness temperature enters the cold space observation field of view from the direction of the side lobe of the cold space observation antenna pattern, resulting in the actual received brightness temperature of the radiometer is higher than The cold air nominal radiant brightness temperature of 2.73K. If the cold air radiation brightness temperature of 2.73K is directly used for calibration, it will directly bring about the calibration error of the target brightness temperature, which will lead to the inversion error of the marine environmental parameters and reduce the accuracy of the data processing results. When correcting the brightness temperature of the cold space calibration in each scanning period, it is necessary to first project some side lobes of the antenna pattern to the earth, and then weighted summation of the pattern data projected to each point on the earth and the corresponding earth radiation brightness temperature, Thus, the radiant brightness temperature contribution of the Earth region can be calculated. However, this method needs to complete the projection of the sidelobe of the cold-space observation antenna to the ground in each scanning period, which requires a large amount of computation and is difficult to meet the needs of efficient data processing.

SUMMARY OF THE INVENTION

The technical problem solved by the invention is: overcoming the deficiencies of the prior art, and providing a cold space calibration correction method for a spaceborne microwave radiometer. The cold space observation count value affected by the contribution of the earth's sidelobe radiation is calibrated to obtain the cold space calibration brightness temperature correction value, and then the scene observation count value is calculated by using the cold space brightness temperature correction value and the original heat source observation count value. The calibration is carried out, the calibration error caused by the cold air brightness temperature error is corrected, and the calibration accuracy is improved.

The technical solution steps of the inventive method are as follows:

S1, use the microwave radiometer to observe the target, obtain the original cold air observation count value, the original heat source observation count value, the heat source brightness temperature and the original scene observation count value, and calculate the sub-satellite point at The average count value of cold air observations in the ocean area and the land area; then combined with the original heat source observation count value and the original scene observation count value, the average brightness temperature of the scene in the ocean area and the land area are calculated respectively. The average brightness temperature of the scene in the area, the average count value of the cold air observations at the sub-satellite point in the ocean area and the land area, and the average gain of the microwave radiometer system calculate the earth scale factor. The proportional coefficient of the earth area in the whole cold space antenna pattern when the observation is calibrated;

S2, fit the relationship between the original cold sky observation count value of the sub-satellite point located in the ocean area and the latitude of the sub-satellite point, and then combine the latitude of the sub-satellite point in each scanning period of the microwave radiometer to calculate the cold sky observation in each scanning period. count value;

S3, according to the earth scale factor and the average value of the global ocean area brightness temperature simulation value, calculate the ocean area cold air brightness temperature correction value;

S4, the original cold air observation count value is calibrated according to the cold air observation count value, the cold air brightness temperature correction value of the ocean region, the original heat source observation count value and the heat source brightness temperature in each scanning period, to obtain the cold air calibration Brightness temperature correction value;

S5, the original scene observation count value is calibrated according to the cold air calibration brightness temperature correction value, the original cold air observation count value, the original heat source observation count value and the heat source brightness temperature to obtain a scene brightness temperature correction value.

The calculation method of the earth scale factor f _CsE described in S1 is:

为微波辐射计系统平均增益，且

为热源观测平均计数值，

为冷空观测平均计数值，

为热源平均亮温，T_C0为冷空标称辐射亮温，所述冷空标称辐射亮温T_C0为2.73K；

为星下点位于陆地区域时的冷空观测平均计数值，

为陆地区域场景亮温平均值，

为星下点位于海洋区域时冷空观测平均计数值，

为海洋区域场景亮温平均值。in,

is the average gain of the microwave radiometer system, and

is the observed mean count value for the heat source,

is the average count value of cold air observations,

is the average brightness temperature of the heat source, T _C0 is the nominal radiant brightness temperature of the cold air, and the nominal radiant brightness temperature of the cold air, T _C0 , is 2.73K;

is the average count value of cold sky observations when the sub-satellite point is located in the land area,

is the average brightness temperature of the scene in the land area,

is the average count value of cold sky observations when the subsatellite point is located in the ocean area,

It is the average brightness temperature of the marine area scene.

Further, the relationship between the scene observation count value and the scene brightness temperature is:

C_H为原始热源观测计数值，C_C为原始冷空观测计数值，T_H为热源亮温，u为地面试验室测得的通道非线性系数。Among them, _CS is the scene observation count value,

_CH is the observed count value of the original heat source, C _C is the original cold air observation count value, _TH is the brightness temperature of the heat source, and u is the channel nonlinear coefficient measured by the ground laboratory.

其中，

为全球海洋区域亮温模拟值的平均值。Further, the calculation method of the cold air brightness temperature correction value T _C0cor in the ocean area in the S3 is:

in,

is the average value of the simulated brightness temperature in the global ocean area.

其中，

C_C,Sat为每个扫描周期内冷空观测计数值。Further, the calculation method of the cold air calibration brightness temperature correction value T _Ccor in the S4 is:

in,

C _{C, Sat} is the count value of cold air observations in each scan period.

Further, the calculation method of the scene brightness temperature correction value in the S5 is wherein,

The advantages of the method of the present invention compared with the prior art are:

(1) The traditional cold-space calibration brightness temperature correction uses the cold-space correction scale factor and the earth's radiation brightness temperature to simply multiply the cold-space correction brightness temperature, but it cannot accurately correct the cold-space antenna pattern. Sidelobes include both ocean and land conditions The cold air calibration brightness temperature error below. The invention can overcome the deficiency of the traditional correction method, accurately correct the cold air brightness temperature error in the case where the side lobe of the cold air antenna pattern contains both the ocean and the land, and further improves the overall data processing accuracy.

(2) In the traditional cold-space calibration brightness temperature correction method, in order to obtain the accurate earth radiation brightness temperature, it is necessary to project the side lobes of the cold-space antenna pattern to the earth and integrate the radiation brightness temperature of each point on the earth, and the data processing efficiency is low. The invention does not need to calculate the contribution of the earth radiation to the calibration temperature of the cold space by the method of integration in each scanning period, and only needs to calibrate the actual cold space observation count value based on the fitting data to realize the calibration of the brightness temperature of the cold space. Accurate correction avoids a large number of projection calculations while ensuring the accuracy of data processing results, improving the efficiency of data processing.

(3) The cold air calibration brightness temperature correction method in the present invention is simple in principle, simple and feasible to implement in the correction calculation process, convenient for implementation in the ground data processing system, and can further improve the accuracy of the ground system data processing results.

Description of drawings

Figure 1 is a block diagram of the calibration principle of the microwave radiometer;

FIG. 2 is a flow chart of the implementation of the method of the present invention.

Detailed ways

The spaceborne microwave radiometer performs remote sensing measurement of marine environmental parameters such as sea surface temperature, wind speed, atmospheric liquid water content and atmospheric water vapor content by passively receiving sea surface microwave radiation signals. The spaceborne microwave radiometer realizes continuous scanning and observation of ocean targets through periodic rotation of the antenna. In each scanning period, the microwave radiometer observes the scene, heat source and cold air in turn. The heat source is realized by a microwave absorber that is precisely temperature-controlled at a constant temperature, and the cold space is realized by an antenna whose beam points to the background of the cold space of the universe. In each scan cycle, the system calibration parameters can be determined by observing the heat source and cold air combined with the ground test parameters, and then the scene observation count value is converted into brightness temperature, as shown in Figure 1.

In the spaceborne microwave radiometer ground data processing system, it is necessary to use the radiometer on-orbit original heat source observation count value, original cold space observation count value, heat source brightness temperature, cold source radiation brightness temperature and nonlinear coefficient to observe the scene in the same scanning period. The count value is calibrated to obtain the scene observation brightness temperature:

_CH and C _C are the original heat source observation count value and the original cold air observation count value, respectively, T _H0 and T _C0 are the heat source and cold source radiation brightness temperature, C _S is the scene observation count value, and u is measured in the ground laboratory. The nonlinear coefficient of .

At present, in the calibration module of the microwave radiometer ground data processing system, the cold air brightness temperature usually adopts the standard 2.73K radiation brightness temperature. However, because the cold space is realized by the antenna pointing to the cosmic cold space background, the earth radiation with higher radiation brightness temperature enters the cold space observation field from the side lobe direction of the cold space observation antenna pattern, resulting in the actual received brightness temperature of the radiometer higher than 2.73 The cold air nominal radiant brightness temperature of K is:

表示地球辐射亮温分布，

表示冷空观测天线方向图，SL表示天线方向图副瓣中地球所占立体角区域，ML表示除地球所占立体角区域外天线方向图其它指向冷空的立体角区域，T_C0为2.73K。in

represents the distribution of the Earth's radiant brightness temperature,

Indicates the antenna pattern for cold space observation, SL represents the solid angle area occupied by the earth in the side lobe of the antenna pattern, ML represents the solid angle area of the antenna pattern pointing to the cold air except the solid angle area occupied by the earth, and T _C0 is 2.73K .

Because the Earth's radiant brightness temperature is usually high, T' _C0 is greater than T _C0 . If the cold air radiation brightness temperature of 2.73K is directly used for calibration, it will directly bring about the calibration error of the target brightness temperature, which will lead to the inversion error of the marine environmental parameters and reduce the accuracy of the data processing results.

The method steps of the present invention are shown in Figure 2, and the details are as follows:

(1) Calculate the earth scale factor

The earth scale factor indicates the scale factor of the earth area in the whole cold space observation antenna pattern when the microwave radiometer performs the cold space calibration observation. The scale factor can be calculated using on-orbit measured data.

a) Use the cold air nominal brightness temperature T _C0 (2.73K), the heat source observation count value _CH , the cold air observation count value C _C , the heat source brightness temperature _TH and the channel nonlinear coefficient u to perform the scene observation count value C _S . Calibration is performed to obtain the scene brightness temperature estimate T′ _B .

冷源观测平均计数值

和热源平均亮温

计算得到辐射计系统平均增益

b) Using the cold air nominal radiant brightness temperature T _C0 and the observed average count value of the heat source

Average counts of cold source observations

and the average brightness temperature of the heat source

Calculate the average gain of the radiometer system

对应的海洋观测亮温平均值为

星下点位于陆地区域时的冷空观测平均计数值为

对应陆地观测亮温平均值为

c) When the sub-satellite point is located in the ocean area, the average count of cold sky observations is set to be

The corresponding average value of ocean observation brightness temperature is

When the sub-satellite point is located in the land area, the average count of cold sky observations is

The corresponding average brightness temperature of land observations is

和

可以计算出地球比例因子f_CsE。d) according to

and

The earth scale factor f _CsE can be calculated.

(2) Fitting of cold air observation count values

When the temperature of the heat source is relatively stable, the relationship between the channel gain (temperature) of the microwave radiometer and the latitude of the sub-satellite point can be deduced according to the variation of the observed count value of the heat source with the latitude of the sub-satellite point. Fit the cold sky observation count value of all sub-satellite points located in the ocean area in each orbit with the latitude variation relationship of the sub-satellite point, and fit the variation relationship of the cold source observation count value with the sub-satellite point latitude θ:

C _C = F(θ) (4-8)

(3) Calculation of cold air observation count value

When the microwave radiometer conducts cold sky observations in any scanning period, set the latitude of the corresponding sub-satellite point to be θ _Sat , then according to the relationship between the fitted cold sky observation count value and the sub-satellite point latitude θ (4-8 ), it can be deduced that the cold air observation count value of each scanning period is:

C _C,Sat =F(θ _Sar ) (4-9)

(4) Brightness temperature correction of cold air in ocean areas

According to the earth scale factor f _CsE calculated in Equation (4-7), the corrected brightness temperature of cold air when the sub-satellite point is located in the ocean area can be calculated:

为基于全球海洋区域模式亮温数据计算出的平均值。所述全球海洋区域模式亮温(brightness temperature computed from RTM)为将全球海洋环境参数如海面温度、海面风速、大气液态水含量、大气水蒸气和海水盐度等参数作为输入，代入现有的辐射传输模型函数RTM(Radiative Transfer Model)计算得到海面模式亮温。然后通过对海面模式亮温进行统计平均即可得到均值

Average value calculated based on global ocean area model brightness temperature data. The global ocean region model brightness temperature (brightness temperature computed from RTM) is to take global ocean environment parameters such as sea surface temperature, sea surface wind speed, atmospheric liquid water content, atmospheric water vapor and seawater salinity as input, and substitute existing radiation The transfer model function RTM (Radiative Transfer Model) calculates the brightness temperature of the sea surface model. Then, the mean value can be obtained by statistically averaging the brightness temperature of the sea surface model.

(5) Cold air calibration brightness temperature correction

Using the cold air observation count value C _C,Sat , the cold air brightness temperature correction value T _C0cor in the ocean area, the original heat source observation count value _CH and the heat source brightness temperature _TH derived in each scanning period, the original cold air temperature in each scanning period is calculated. The empty observation count value C _C is calibrated to obtain the cold air observation brightness temperature correction value T _Ccor .

(6) Scene observation brightness temperature calibration

Using the original cold air observation count value C _C , formula (4-15) cold air correction brightness temperature value T _Ccor , the heat source observation count value _CH , the heat source brightness temperature _TH and the channel nonlinear coefficient in each scanning period The scene observation count value C _S of the scanning period is re-scaled to obtain the scene brightness temperature correction value after the cold air brightness temperature is corrected and the scene count value is calibrated again.

The content not described in detail in the specification of the present invention belongs to the well-known technology of those skilled in the art.

Claims (6)

1. a cold space calibration correction method for a space-borne microwave radiometer, is characterized in that: comprise the steps: S1, use the microwave radiometer to observe the target, obtain the original cold air observation count value, the original heat source observation count value, the heat source brightness temperature and the original scene observation count value, and calculate the sub-satellite point at The average count value of cold air observations in the ocean area and the land area; then combined with the original heat source observation count value and the original scene observation count value, the average brightness temperature of the scene in the ocean area and the land area are calculated respectively. The average brightness temperature of the scene in the area, the average count value of the cold air observations at the sub-satellite point in the ocean area and the land area, and the average gain of the microwave radiometer system calculate the earth scale factor. The proportional coefficient of the earth area in the whole cold space antenna pattern when the observation is calibrated; S2, fit the relationship between the original cold sky observation count value of the sub-satellite point located in the ocean area and the latitude of the sub-satellite point, and then combine the latitude of the sub-satellite point in each scanning period of the microwave radiometer to calculate the cold sky observation in each scanning period. count value; S3, according to the earth scale factor and the average value of the global ocean area brightness temperature simulation value, calculate the ocean area cold air brightness temperature correction value; S4, the original cold air observation count value is calibrated according to the cold air observation count value, the cold air brightness temperature correction value of the ocean region, the original heat source observation count value and the heat source brightness temperature in each scanning period, to obtain the cold air calibration Brightness temperature correction value; S5, the original scene observation count value is calibrated according to the cold air calibration brightness temperature correction value, the original cold air observation count value, the original heat source observation count value and the heat source brightness temperature to obtain a scene brightness temperature correction value. 2. the cold space calibration correction method of spaceborne microwave radiometer according to claim 1, is characterized in that: the calculation method of earth scale factor f _CsE described in S1 is:

in,

is the average gain of the microwave radiometer system, and

is the observed mean count value for the heat source,

is the average count value of cold air observations,

is the average brightness temperature of the heat source, T _C0 is the nominal radiant brightness temperature of the cold air, and the nominal radiant brightness temperature of the cold air, T _C0 , is 2.73K;

is the average count value of cold sky observations when the sub-satellite point is located in the land area,

is the average brightness temperature of the land area scene,

is the average count value of cold sky observations when the subsatellite point is located in the ocean area,

It is the average brightness temperature of the marine area scene. 3. The cold-space calibration correction method of the spaceborne microwave radiometer according to claim 2, wherein the relational expression between the scene observation count value and the scene brightness temperature is:

Among them, _CS is the scene observation count value,

_CH is the observed count value of the original heat source, C _C is the original cold air observation count value, _TH is the brightness temperature of the heat source, and u is the channel nonlinear coefficient measured by the ground laboratory. 4. The cold space calibration correction method of spaceborne microwave radiometer according to claim 2 is characterized in that: the calculation method of the cold space brightness temperature correction value T _C0cor of the ocean area in the described S3 is:

in,

is the average value of the simulated brightness temperature in the global ocean area. 5. The cold space calibration correction method for spaceborne microwave radiometer according to claim 3, is characterized in that: the calculation method of cold space calibration brightness temperature correction value T _Ccor in the described S4 is:

in,

C _{C, Sat} is the count value of cold air observations in each scanning period, and T _C0cor is the correction value of the cold air brightness temperature in the ocean area. 6. The cold space calibration correction method of the spaceborne microwave radiometer according to claim 5, characterized in that: the scene brightness temperature correction value in the S5

The calculation method is

in,

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