A Method for Detecting and Suppressing the Interference of the Moon on the Cold Sky Field of View of a Spaceborne Microwave Radiometer

Abstract

The present invention provides a method for detecting and suppressing the interference of the moon on the cold sky field of view of a spaceborne microwave radiometer. Compared with the prior art method in which all error sources are uniformly processed, resulting in a deviation in the observed brightness temperature and making it difficult to identify the lunar radiation with less interference, the method of the present invention can detect and accurately locate the interference of the lunar radiation on the cold sky field of view, and uses the method of sliding window weighted interpolation for higher-precision suppression processing. The abnormal observed brightness temperature with calibration errors is interpolated to complete the correction of the deviation of the observed brightness temperature, eliminating the influence of extraterrestrial celestial bodies on the spaceborne microwave radiometer.

Description

Technical Field

[0001] The present invention belongs to the field of satellite observation. Specifically, it relates to a method for detecting and suppressing the interference of the moon on the cold sky field of view of a spaceborne microwave radiometer. Background Art

[0002] The calibration of a spaceborne microwave radiometer is to first observe a precisely known high-temperature source body, receive the radiation signal, and obtain the high-temperature voltage value; then observe a low-temperature source body. Liquid nitrogen is used as the low-temperature source body during ground calibration, and the cold sky is directly observed through a cold sky mirror as the low-temperature source body in space to obtain the low-temperature voltage value. The two-point calibration method can be used to calculate the observed voltage value of the target scene, and then convert it into a brightness temperature value, which can be used for the inversion of various ocean dynamic environment parameters such as sea surface height, sea surface temperature, sea surface wind field, and water vapor content. These data can provide support for the early warning and forecasting of disastrous sea conditions, and provide strong support for ocean scientific research, ocean environmental protection, ocean resource development, and national defense construction.

[0003] The spaceborne microwave radiometer will be calibrated in a dark room before launch, but the calibration is carried out under ideal conditions without interference because it is not known before launch what error sources the spaceborne microwave radiometer will be interfered by and the degree of interference. After the spaceborne microwave radiometer is launched into orbit, it is necessary to detect and suppress the existing error interference sources.

[0004] When the spaceborne microwave radiometer operates in a polar orbit or a sun-synchronous orbit with an orbital altitude of 600 - 800 kilometers, it will be affected by extraterrestrial celestial bodies. The radiation brightness temperature of the moon appears in the cold sky field of view twice a month, once during the ascending orbit and once during the descending orbit. When the angle between the beam direction of the cold sky mirror and the moon is less than 2 degrees, the moon will interfere with the cold sky field of view, raising the brightness temperature observed by the cold sky mirror, resulting in calibration errors and deviations in the observed brightness temperature value of the scene.

[0005] Currently, few spaceborne microwave radiometers in orbit detect and suppress lunar interference. The existing interference suppression methods uniformly process the interference of extraterrestrial celestial bodies, the data jitter of the spaceborne microwave radiometer receiver itself, and the electromagnetic interference radiation brought by other devices, and eliminate the abnormal data. However, the interference of the moon on the cold sky field of view is small, and it will be ignored during the unified processing by the existing methods, resulting in a certain deviation in the observed brightness temperature of the target area and not meeting the application requirements. There is a need for a method for detecting and suppressing the interference of the moon on the cold sky field of view of a spaceborne microwave radiometer to eliminate the influence of extraterrestrial celestial bodies on the spaceborne microwave radiometer. Summary of the Invention

[0006] The technical problem solved by the present invention is as follows: In the current existing technologies, traditional interference suppression methods cannot detect and eliminate the interference of the moon on the cold sky field of view, resulting in a deviation between the observed brightness temperature of the target area and the actual brightness temperature. For this problem, a method for detecting and suppressing the interference of the moon on the cold sky field of view of a spaceborne microwave radiometer is proposed for the first time, which detects and suppresses the interference generated by the moon on the cold sky mirror and completes the correction of the observed brightness temperature deviation.

[0007] To achieve the above method objective, the present invention is implemented by adopting the following technical solutions: A method for detecting and suppressing the interference of the moon on the cold sky field of view of a spaceborne microwave radiometer, including:

[0008] Step 1: First, perform orbital simulation in the STK software, input the starting coordinates, starting time, and flight speeds in the X, Y, and Z directions of the spaceborne microwave radiometer, calculate the WGS-84 coordinates of the moon and the corresponding world time for each coordinate, select the interval of the coordinate data as 1 second, and store the moon coordinate data.

[0009] Step 2: Match the target area coordinate time observed by the spaceborne microwave radiometer with the corresponding moon coordinates, determine the starting time and ending time of the target area, and match the moon coordinates at the same time according to the starting time and ending time. If the time difference between the two is less than 10 seconds, it is considered a successful match, and the moon coordinates within this time period are selected.

[0010] Step 3: Interpolate the position vector and velocity vector of the spaceborne microwave radiometer. Since the detection head of the spaceborne microwave radiometer rotates about one circle every 3 - 4 seconds, the position vector and velocity vector are stored once every 3 - 4 seconds. Given the uniform flight speed of the satellite, the position vector and velocity vector of the spaceborne microwave radiometer can be interpolated to store a set of data every 1 second, and corrected to have the same interval as the moon coordinate data.

[0011] Step 4: Convert the beam axis vector of the cold sky mirror from the satellite body coordinate system to the satellite orbit coordinate system. Given from the satellite data that the observation angle of the cold sky mirror in the satellite body coordinate system is α and the scanning azimuth angle is Then the beam axis vector of the cold sky mirror in the satellite body coordinate system is expressed as:

[0012]

[0013] Z ben After conversion to the satellite orbit coordinate system, it is:

[0014] Z orb = M orb ·Z ben

[0015] Where M orbThe transformation matrix is used to transform the beam line-of-sight vector of the cold sky mirror in the satellite body coordinate system to the satellite orbit coordinate system, Z orb is the beam line-of-sight vector of the cold sky mirror in the satellite orbit coordinate system. The transformation matrix M orb is expressed as:

[0016]

[0017] where y, r, and p are the yaw angle, roll angle, and pitch angle respectively, and are the satellite attitude parameters.

[0018] Step 5: Transform the beam line-of-sight vector of the cold sky mirror from the satellite orbit coordinate system to the WGS-84 coordinate system. The coordinate transformation formula is:

[0019]

[0020] where, Z ecf represents the beam line-of-sight vector of the cold sky mirror in the WGS-84 coordinate system, and M ecf is the transformation matrix, specifically expressed as:

[0021]

[0022] where, correspond to the unit vectors of the X, Y, and Z axes in the WGS-84 coordinate system respectively.

[0023] Step 6: Obtain the satellite coordinates and lunar coordinates from the above steps. The lunar coordinates are P moont =(x moon , y moon , z moon ), and the satellite coordinates are P st =(x sat , y sat , z sat ). The pointing vector from the satellite coordinates P st to the lunar coordinates P moont is:

[0024] P moonsat =P moon -P st

[0025] The angle between the moon and the satellite is the angle between P moonsat and Z ecf :

[0026]

[0027] where Z ecf is the beam line-of-sight vector of the cold sky mirror obtained in Step 5, and θ moonIt is the angle between the moon and the beam axis vector of the cold sky mirror, that is, the moon angle.

[0028] Step 7: Detect whether the moon interferes with the cold sky field of view. Set the decision threshold σ = 2, and the detection method is to judge the moon angle θ obtained in step 6 moon Whether it is less than the decision threshold σ. When the moon angle θ moon Is less than the decision threshold σ, mark the observation data of the spaceborne microwave radiometer at this time as the data affected by the moon radiation, that is, the moon interferes with the cold sky field of view. There is a deviation in the observed brightness temperature at this moment, and the data at the current moment is identified. When the moon angle is greater than the decision threshold, it is considered that the moon radiation does not interfere with the cold sky field of view.

[0029] Step 8: Process the observation data of the spaceborne microwave radiometer affected by the moon radiation to suppress the interference caused by the moon to the cold sky field of view. When it is judged that there is an identification for the current data, perform sliding window weighted interpolation processing on the current data. Use the data of the 30 scan lines before and after for weighted smoothing. The closer the scan line is to the identified data at the current moment, the higher the weight value. After obtaining the weighted value, interpolate the data at this moment to the weighted value, and eliminate the observed data with deviations, completing the suppression of the interference of the moon to the cold sky field of view.

[0030] The advantages of the present invention compared with the prior art are:

[0031] The present invention provides a method for detecting and suppressing the interference of the moon to the cold sky field of view of a spaceborne microwave radiometer. Compared with the prior art method of uniformly processing all error sources, resulting in a deviation in the observed brightness temperature and making it difficult to identify the moon radiation with relatively small interference, the method of the present invention can detect and accurately locate the interference of the moon radiation to the cold sky field of view, and adopt the method of sliding window weighted interpolation for higher-precision suppression processing, interpolate the abnormal observed brightness temperature with calibration errors, and complete the correction of the deviation of the observed brightness temperature. Eliminate the influence of extraterrestrial celestial bodies on the spaceborne microwave radiometer. Description of the Drawings

[0032] Figure 1 It is a block diagram of the composition of the spaceborne microwave radiometer system;

[0033] Figure 2 It is a diagram of the change of the angle between the moon and the beam axis vector of the cold sky mirror in the present invention;

[0034] Figure 3 It is a flowchart of the interference detection and suppression method provided by the present invention;

[0035] Figure 4 It is a flowchart of the conversion of the geolocation coordinate system of the spaceborne microwave radiometer in the present invention;

[0036] Figure 5It is a diagram of the abnormal observation voltage value where the cold sky field of view of the spaceborne microwave radiometer is interfered by the moon;

[0037] Figure 6 It is a diagram of the observed voltage value after detecting interference and removing abnormal values. Specific implementation mode

[0038] The present invention will be further described below with reference to the accompanying drawings.

[0039] As Figure 1 shown, it is a block diagram of the composition of the spaceborne microwave radiometer system. The cold sky mirror is fixed, the scanning mechanism drives the antenna and the feed array to rotate, the feed array is placed below the cold sky mirror, and every time it rotates one circle, it will reflect the cold sky signal into the feed array through the cold sky mirror, and then convert it into brightness temperature through the information collector for calibration. The cold sky mirror receives the cold sky signal in space, generally 2.73K, as a low temperature source, and jointly completes two-point calibration with the hot calibration source. When the spaceborne microwave radiometer is flying in space, the direction of the beam axis vector of the cold sky mirror is constantly changing. When the angle between the moon and the beam axis vector of the cold sky mirror, that is, the moon angle, is less than the set threshold, the brightness temperature radiation of the moon will enter the cold sky mirror, resulting in the brightness temperature of the low temperature source being higher than the actual value, thus bringing calibration deviation. Here, the threshold is set to 2 degrees. The change of the moon angle with the scanning line is as Figure 2 shown. Figure 2 In the figure, the abscissa represents the number of scanning lines in the observation direction within a month, and the ordinate is the moon angle. It can be seen that there are two situations where the moon angle is less than the set threshold within a month, which appear respectively in the satellite ascending orbit and descending orbit states.

[0040] To solve the above problem that the brightness temperature of the moon radiation enters the cold sky mirror, thus raising the brightness temperature of the low temperature source and causing calibration deviation, the present invention proposes a method for detecting and suppressing the interference of the moon on the cold sky field of view of a spaceborne microwave radiometer, Figure 3 which is the working flow chart of the method of the present invention. The specific steps are as follows:

[0041] Step 1, first, the coordinates of the moon in the WGS-84 coordinate system need to be obtained. Through STK software for orbit simulation, input the starting coordinates and starting velocities of the satellite in the X, Y, and Z directions that need to be calculated, establish the WGS-84 coordinates P st of the spaceborne microwave radiometer and the corresponding orbit data. The time interval between the coordinates and the time is 1 second. Add the extraterrestrial celestial body moon, select the moment synchronized with the spaceborne microwave radiometer, and export the coordinates P moont of the moon in the WGS-84 coordinate system and the corresponding moment data;

[0042] Step 2, select the moon coordinate data P within the matching time according to the start and end times of the target area moontSelect the coordinates of the target area to be detected and the corresponding time. Match the start time and end time of the detected target area with the time of the exported moon. If the time difference between the two is less than 10 seconds, it is considered a successful match, and the lunar coordinate data for this time period is selected;

[0043] Step 3: Align the position vector and velocity vector of the spaceborne microwave radiometer with the length of the lunar coordinate data. It is necessary to interpolate the position vector and velocity vector of the spaceborne microwave radiometer. As Figure 1 It can be seen that the scanning mechanism drives the antenna and the feed array to rotate, and it takes 3-4 seconds to rotate one circle. During this one circle, the spaceborne microwave radiometer observes the target area and receives the cold sky signal reflected by the cold sky mirror as the low-temperature calibration source, and the feed array receives the radiation brightness temperature of the hot calibration source as the high-temperature calibration source. After the satellite rotates one circle, it stores the position vector and velocity vector of the satellite. Therefore, the interval of each group of values is 3-4 seconds. Since the data interval of the lunar coordinates is 1 second and the satellite flies at a constant speed, the position vector and velocity vector of the spaceborne microwave radiometer can be interpolated at equal intervals and stored as a group of data every 1 second;

[0044] Step 4: Since the beam axis vector of the cold sky mirror is in the satellite body coordinate system and the lunar coordinates are defined in the WGS-84 coordinate system, it is necessary to convert the beam axis vector. As Figure 4 shown, it is the satellite coordinate system conversion flow chart. First, convert the beam axis vector from the satellite body coordinate system to the satellite orbit coordinate system, which is completed by the satellite attitude rotation matrix. Given that the observation angle of the cold sky mirror in the satellite body coordinate system is α and the scanning azimuth angle is then the beam axis vector of the cold sky mirror in the satellite body coordinate system is expressed as:

[0045]

[0046] Then, through the satellite attitude rotation matrix, convert Z ben to the satellite orbit coordinate system:

[0047] Z orb = M orb ·Z ben

[0048] where M orb is the satellite attitude rotation matrix used to convert the beam axis vector of the cold sky mirror from the satellite body coordinate system to the satellite orbit coordinate system, and Z orb is the beam axis vector of the cold sky mirror in the satellite orbit coordinate system.

[0049] Let the yaw angle, roll angle and pitch angle of the satellite be y, r, p respectively, which are the satellite attitude parameters. Then the corresponding rotation matrices are respectively expressed as:

[0050]

[0051]

[0052]

[0053] The satellite attitude rotation matrix from the orbital coordinate system to the satellite coordinate system is:

[0054] M orb = P(R·Y)

[0055] Step 5: Convert the cold sky mirror beam line-of-sight vector in the satellite orbital coordinate system to the cold sky mirror beam line-of-sight vector in the WGS-84 coordinate system. The coordinate transformation formula is:

[0056]

[0057] where Z ecf represents the cold sky mirror beam line-of-sight vector in the WGS-84 coordinate system, and M ecf is the position-velocity vector rotation matrix, which is specifically expressed as:

[0058]

[0059] where correspond to the unit vectors of the X, Y, and Z axes in the WGS-84 coordinate system respectively, as follows:

[0060]

[0061] where is the satellite position vector in the WGS-84 coordinate system, and r is the modulus of the position vector; is the satellite velocity vector, and v is the modulus of the velocity vector.

[0062] Step 6: Obtain the satellite coordinates and the lunar coordinates from the above steps. The lunar coordinates are P moont =(x moon , y moon , z moon ), and the satellite coordinates are P st =(x sat , y sat , z sat ). The pointing vector from the satellite coordinates P st to the lunar coordinates P moont is:

[0063] P moonsat = P moon - P st

[0064] The angle between the moon and the satellite is Pmoonsat and Z ecf The included angle between

[0065]

[0066] where Z ecf is the cold sky mirror beam boresight vector in the WGS - 84 coordinate system obtained in step 5, and θ moon is the included angle between the moon and the cold sky mirror beam boresight vector, that is, the moon angle.

[0067] Step 7, detect whether the moon interferes with the cold sky field of view. Set the decision threshold σ = 2, and the detection method is to judge whether the moon angle θ moon obtained in step 6 is less than the decision threshold. When the decision criterion is:

[0068] θ moon < σ

[0069] That is, when the moon angle is less than the decision threshold, mark the observed data of the spaceborne microwave radiometer at this time as the data affected by the moon radiation, that is, the moon interferes with the cold sky field of view, and there is a deviation in the observed brightness temperature at this moment. Identify and interpolate the data at the current moment. When the decision criterion is:

[0070] θ moon > σ

[0071] When the moon angle is greater than the decision threshold, it is considered that the moon radiation does not interfere with the cold sky field of view and no processing is required.

[0072] Step 8, process the observed data of the spaceborne microwave radiometer affected by the moon radiation to suppress the interference of the moon on the cold sky field of view. When it is judged that there is an identification for the current data, perform sliding window weighted interpolation processing on the current data. The processing method is:

[0073]

[0074] where w(j scan ) is the j scan th scan line, C c (j scan ) is the cold sky observation count value, 2N c +1 is the number of scan lines used for smoothing, and N c takes 30, that is, use the data of the 30 scan lines before and after for weighted smoothing. The weight coefficient of the jth scan line among the 2N + 1 triangular weight coefficients before and after is:

[0075]

[0076] In the above formula, the weight of the scan line closer to the current identification data is higher. After obtaining the weighted value, the data at this moment is interpolated into the weighted value, and the observation data with deviations is eliminated, completing the suppression of the interference of the moon on the cold sky field of view, thereby correcting the deviation of the observed brightness temperature caused by the interference of the spaceborne microwave radiometer.

[0077] Figure 5 and Figure 6 The abscissa is the number of scan lines, and the ordinate is the observed voltage value of the cold sky field of view. Figure 5 In [reference], the observed voltage value of the cold sky field of view is invaded by the lunar brightness temperature, resulting in an increase in the observed voltage value, thereby bringing a deviation in the observed brightness temperature. Figure 6 After adopting the method of the present invention, the interference of the moon on the observed voltage value of the cold sky field of view is suppressed, the outliers are eliminated and interpolated, thereby correcting the deviation of the observed brightness temperature.

[0078] The parts not detailed in the present invention belong to the well-known technologies in the art.

Claims

1. A method for detecting and suppressing the interference of the moon on the cold sky field of view of a spaceborne microwave radiometer, characterized in that Including: Conduct orbit simulation, input the starting coordinates, starting time of the spaceborne microwave radiometer, and flight velocities in the X, Y, and Z directions, calculate the WGS-84 coordinates of the moon and the world time corresponding to each coordinate, and store the lunar coordinate data; Match the coordinate moments of the target area observed by the spaceborne microwave radiometer with the corresponding lunar coordinates, determine the starting moment and ending moment of the target area, and match the lunar coordinates at the same moment according to the starting moment and ending moment, and select the lunar coordinates within this time period; Interpolate the position vector and velocity vector of the spaceborne microwave radiometer; Convert the beam boresight vector of the cold space mirror from the satellite body coordinate system to the satellite orbit coordinate system; Convert the beam boresight vector of the cold space mirror from the satellite orbit coordinate system to the WGS-84 coordinate system; The satellite coordinates and the lunar coordinates are calculated, and the lunar angle θ is calculated based on the satellite coordinates and the lunar coordinates moon ; The lunar angle θ moon has the following calculation formula: Lunar angle θ moon is the included angle between the moon and the beam optical axis vector of the cold air mirror: Among them, the lunar coordinate P moont =(x moon , y moon , z moon ), and the satellite coordinate P st =(x sat , y sat , z sat ); From the satellite coordinate P st to the lunar coordinate P moont of the pointing vector P moonsat = P moont - P st ; Detect whether the moon interferes with the cold space field of view, including: Set the decision threshold σ and judge the lunar angle θ moon to determine whether it is less than the decision threshold σ: When the lunar angle θ moon is less than the decision threshold, it is considered that the moon interferes with the cold sky field of view. At this moment, there is a deviation in the observed brightness temperature, and the data at the current moment is marked; When the lunar angle θ moon is greater than the decision threshold, it is considered that the lunar radiation does not interfere with the cold sky field of view; Process the observation data of the spaceborne microwave radiometer affected by lunar radiation to suppress the interference of the moon on the cold space field of view, including: When it is determined that the current data has an identifier, perform sliding window weighted interpolation processing on the current data, and use the data of the first N c and the last N scan lines for weighted smoothing. After obtaining the weighted value, interpolate the data at this moment into the added The weights are used to eliminate the deviated observed data, thereby completing the suppression of the interference of the moon on the cold sky field of view; N c is a positive integer.

2. A method for detecting and suppressing the interference of the moon on the cold sky field of view of a spaceborne microwave radiometer according to claim 1, characterized in that, The interval of the WGS-84 coordinate data of the moon is selected as 1 second.

3. A method for detecting and suppressing the interference of the moon on the cold sky field of view of a spaceborne microwave radiometer according to claim 2, characterized in that, If the time difference between the lunar coordinates at the same moment obtained by matching according to the starting moment and ending moment is less than 10 seconds, it is considered that the matching is successful.

4. A method for detecting and suppressing the interference of the moon on the cold sky field of view of a spaceborne microwave radiometer according to claim 3, characterized in that The interpolation of the position vector and velocity vector of the spaceborne microwave radiometer includes: Interpolate the position vector and velocity vector of the spaceborne microwave radiometer to store a set of data every 1 second, and correct it to be the same as the interval of the lunar coordinate data.

5. A method for detecting and suppressing the interference of the moon on the cold sky field of view of a spaceborne microwave radiometer according to claim 4, characterized in that, The conversion of the beam boresight vector of the cold space mirror from the satellite body coordinate system to the satellite orbit coordinate system includes: It is known from satellite data that the observation angle of the cold sky mirror in the satellite body coordinate system is α, and the scanning azimuth angle is Then, the cold sky mirror beam boresight vector Z in the satellite body coordinate system ben is expressed as: Z ben The conversion from the satellite body coordinate system to the satellite orbit coordinate system is as follows: Z orb = M orb ·Z ben , Among them, M orb is the transformation matrix, and Z orb is the beam boresight vector of the cold sky mirror in the satellite orbit coordinate system; Transformation matrix M orb It is expressed as: Where y, r, and p are the yaw angle, roll angle, and pitch angle respectively, which are satellite attitude parameters.

6. A method for detecting and suppressing the interference of the moon on the cold sky field of view of a spaceborne microwave radiometer according to claim 5, characterized in that, The coordinate conversion formula for converting the beam boresight vector of the cold space mirror from the satellite orbit coordinate system to the WGS-84 coordinate system is: Among them, Z ecf represents the cold air mirror beam line-of-sight vector in the WGS-84 coordinate system, and M ecf is the transformation matrix: Among them, respectively correspond to the unit vectors of the X, Y, and Z axes in the WGS-84 coordinate system.

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