CN112485757B - On-orbit calibration method and system for antenna electric shaft of satellite-borne terahertz detector - Google Patents
On-orbit calibration method and system for antenna electric shaft of satellite-borne terahertz detector Download PDFInfo
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- CN112485757B CN112485757B CN202011153960.3A CN202011153960A CN112485757B CN 112485757 B CN112485757 B CN 112485757B CN 202011153960 A CN202011153960 A CN 202011153960A CN 112485757 B CN112485757 B CN 112485757B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S3/00—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received
- G01S3/02—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using radio waves
- G01S3/14—Systems for determining direction or deviation from predetermined direction
- G01S3/46—Systems for determining direction or deviation from predetermined direction using antennas spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
- G01R29/08—Measuring electromagnetic field characteristics
- G01R29/10—Radiation diagrams of antennas
Abstract
The invention discloses an on-orbit calibration method and system for an antenna electric axis of a satellite-borne terahertz detector. The on-orbit calibration method comprises the following steps: selecting a radio star and setting a reference standard antenna electric axis; determining an antenna on-track directional diagram and a relative relation between each frequency band by receiving signals of the radio stars based on the selected radio stars, and calibrating an antenna electric axis of each frequency band; and obtaining the relative relation between the antenna electric axes of each frequency band according to the relative relation between the antenna electric axes of each frequency band and the reference antenna electric axes, and then outputting the relative calibration relation between the antenna electric axes of each frequency band. The invention can avoid the error caused by atmospheric attenuation and interference, and can synchronously calibrate the antenna electric axis with wide frequency spectrum and multiple frequency bands.
Description
Technical Field
The invention relates to an on-orbit calibration method for an antenna electric axis of a satellite-borne terahertz detector, and also relates to a corresponding on-orbit calibration system, belonging to the technical field of satellite remote sensing.
Background
For microwave loads, the pointing accuracy of the antenna is an important factor influencing the application of microwave detection data, and not only directly influences the accuracy of the geographical positioning of an observed target, but also has an important influence on the radiometric calibration accuracy of the detection data. In particular, with the increasing application requirements and technological processes, the large-aperture antenna gradually changes from ground-based detection to satellite-based detection. How to ensure the antenna pointing accuracy of the large-aperture antenna in a complex space environment is still a key problem to be solved.
For a satellite-borne terahertz detector, the pointing accuracy of an antenna is finally reflected in the calibration accuracy of an electric axis of the antenna. Because the antenna electric axis parameters directly determine the antenna pointing direction, the deviation not only directly influences the pointing control of the detection target, but also influences the positioning accuracy of the detection data. Therefore, the on-orbit calibration of the antenna electric axis of the terahertz detector after the terahertz detector is in orbit is the basis for the work of the satellite-borne terahertz detector. The antenna electric axis is mainly comprehensively influenced by various factors such as the shape, the mounting bracket, the feed source, the assembly relation of the reflecting surface and the like of the antenna, and the parameters of the antenna electric axis can be visually described by a directional diagram of the antenna electric axis. After the whole satellite is installed, the satellite-borne antenna usually performs ground calibration of antenna parameters on the ground.
For the satellite-borne terahertz detector carried by the static orbit satellite, due to the fact that the antenna structure of the satellite-borne terahertz detector is complex, the number of components is large, and the size of a supporting structure is large, particularly after the satellite-borne terahertz detector enters the orbit, the satellite-borne terahertz detector is not only subjected to severe transmitting vibration, but also influenced by the space thermal environment of the static orbit and gravity release and other factors, the shape, the structure and the like of the antenna are deformed, and the actual electric axis of the satellite-borne terahertz detector in the orbit deviates from the ground calibration electric axis. After the satellite-borne terahertz detector works in the orbit, the change of the actual electric axis in the orbit mainly comprises the following steps:
(1) Combined change of mechanical and electric axes
A main beam central axis of the antenna of the satellite-borne terahertz detector is called an electric axis, after in-orbit operation, scanning and observation of the instrument on the earth are realized by controlling mechanical axis motion of a satellite, the electric axis scans the earth essentially, and the relation between the electric axis and an observation target needs to be accurately known. In the design and adjustment before satellite launching, the electric axis should be consistent with the mechanical axis of the satellite platform as much as possible, and needs to be accurately calibrated. However, the environmental changes after the satellite enters the orbit bring changes to both the mechanical axis and the electrical axis, and the comprehensive changes cause the geographical position of the remote sensing target observed in the detection direction to be shifted.
(2) Variation between electrical axes of different operating frequency bands (also called channels)
The feed source of the stationary track microwave detector is designed to not only fully utilize the energy gathered from the emitter to improve the receiving efficiency, but also reduce the mutual influence. From a design point of view, the electrical axis of each frequency band should coincide with the central optical axis of the antenna. However, this is very difficult. Thus, the relationship between them is accurately tested and calibrated at the surface, and processed as the data is acquired to ensure registration. The relative relationship of the electrical axes changes after the satellite is in orbit. Their changes can lead to changes in registration between the channels of the telemetric data.
For the antenna electric axis deviation before transmission, preliminary calibration can be carried out in a laboratory. However, for the antenna electric axis deviation after the satellite-borne terahertz detector emits into the orbit, a feasible method needs to be found for on-orbit calibration.
As shown in fig. 6, in the existing antenna electric axis on-orbit calibration method, a ground measurement and control station is used as a reference, and a satellite antenna is scanned and tracked by the ground station based on the measurement and control signal power, so that the satellite-ground alignment pointed by the antenna is realized, and an application target of the pointing alignment between the ground observation station and the satellite-borne ground antenna is mainly realized. The calibration process is mainly carried out in a ground-fixed coordinate system, and the signals between the satellite end and the observation station are influenced by atmospheric interference in propagation to realize the calibration result, which brings the following disadvantages: 1) the calibration result of the antenna direction is not the calibration of the antenna per se, but the calibration of the antenna per se with various effects such as atmospheric interference, ground system errors and the like due to the deviation of the antenna per se; 2) the calibration result can only be limited to the calibration of the antenna direction between the ground fixed receiving station and the satellite, but cannot be applied to the calibration between the antenna and other ground observation stations; and the method can not be applied to the calibration of the antenna electric axis under other orientations.
Disclosure of Invention
The invention aims to solve the primary technical problem of providing an on-orbit calibration method for an antenna electric axis of a satellite-borne terahertz detector.
The invention aims to solve another technical problem of providing an on-orbit calibration system for an antenna electric axis of a satellite-borne terahertz detecting instrument.
In order to achieve the purpose, the invention adopts the following technical scheme:
according to a first aspect of the embodiment of the invention, an on-orbit calibration method for an antenna electric axis of a satellite-borne terahertz detection instrument is provided, and comprises the following steps:
s1: selecting a radio star and setting a reference standard antenna electric axis;
s2: based on the selected radio star, determining an antenna on-track directional diagram and a relative relation between each frequency band by receiving signals of the radio star, and calibrating an antenna electric axis of each frequency band;
s3: obtaining the relative relation between the antenna electric axes of each frequency band according to the relative relation between the antenna electric axes of each frequency band and the reference antenna electric axes, and then outputting the relative calibration relation between the antenna electric axes of each frequency band;
the antenna in-orbit directional diagram is constructed by selecting an antenna ideal electric axis coordinate system as a reference coordinate system, carrying out consistency processing on the mth resident observation pointing reference by taking the 1 st observation as a reference, and then associating the mth resident observation pointing reference with a radiation digital signal value, wherein m is a positive integer.
Preferably, the step S2 includes the following steps:
obtaining an expected observation direction and an actual observation direction of a radio star in a directional diagram of the terahertz detector antenna;
establishing a deviation of the actual observed orientation from the expected observed orientation;
equating a phase corresponding to an actually observed peak value as an actual observation vector under an antenna ideal coordinate system, and obtaining a deviation value of an actual observation direction and an expected observation direction of the radio satellite according to an ideal observation vector of a direction vector of the antenna pointing to the position of the radio satellite under the antenna ideal coordinate system under the actual observation time corresponding to the actually observed peak value;
repeating the steps, obtaining the deviation value of each radio star one by one, and establishing a deviation equation of the actual observation direction and the expected observation direction;
and solving the deviation equation through an optimization solving algorithm, and outputting a calibration result of the antenna electric axis.
Preferably, the step S2 further includes the following steps:
s21: setting a calibration frequency band of an antenna to be calibrated;
s22: selecting a plurality of radio stars in the frequency band to be calibrated, and arranging an observation plan;
S23: according to the observation plan, in two directions of transverse scanning and longitudinal stepping, carrying out grid coverage type scanning observation on one radio star by using a reference center, and recording observation data;
s24: according to the radiation digital signal value of the radio satellite, and auxiliary data such as satellite position and attitude are integrated, space reference consistency processing is carried out on the observation direction, and an antenna in-orbit actual measurement directional diagram is constructed;
s25: calculating an expected observation direction of the radio satellite under an ideal electric axis reference condition according to auxiliary data such as the self-observation geometric parameters, the satellite position and the attitude of the terahertz detector;
s26: comparing the deviation between the actual observation position and the expected observation position of the radio star;
s27: repeating the steps S23-S26, and selecting a plurality of satellite observation data;
s28: and calibrating the center and the direction of the antenna reference electric axis through an optimization solving algorithm.
Preferably, the step S24 includes the following steps:
1) determining a zero-degree reference pointing vector of an ideal electric axis in a satellite coordinate system before transmission;
2) for the kth fixed star and the mth residence observation, acquiring satellite position and attitude information according to the detection moment of the mth residence, wherein k is a positive integer;
3) According to the zero-degree reference pointing vector of the ideal electric axis, determining the zero-degree reference pointing vector as a relative pointing change azimuth relative to the 1 st residence observation time at the mth residence time by comprehensively utilizing the instantaneous position and the attitude of the satellite;
4) calculating the pointing angles of the two directions normalized by the 1 st observation reference according to the actually measured pointing angle and the relative pointing change direction;
5) respectively taking the pointing angle as an X-axis coordinate and a Y-axis coordinate, and taking the radiation digital signal value as a Z-axis, and establishing an on-orbit actual measurement directional diagram of the antenna;
6) and determining the position of a radiation center through characteristic analysis of a radiation energy distribution curved surface according to the antenna direction distribution diagram to obtain the actual observation direction of the radio star.
Preferably, in the step S28, the solution of the comprehensive evaluation equation system AU is utilizedk-Vk＝εkCalibrating the position of the antenna electric axis in a mode of an optimization problem with the minimum error;
wherein epsilonkFor the k radio star, at the strongest peak of the measured signal, the expected observation direction vector UkAfter correction, the orientation vector V is compared with the actual observation orientation vectorkThe residual error between (k is 1, 2, …, N), and N is the number of valid observed stars.
Preferably, the step S3 includes the following steps:
s31: setting antennas of a plurality of frequency bands to be calibrated, and numbering one by one;
s32: calibrating the antenna electric axis of the w-th frequency band to obtain an error conversion matrix A between the actual on-track antenna electric axis and the ideal electric axiswWherein W is 1, 2, …, W; for arbitrary w1，w2Electric axes of the antennas in two frequency bands, then w2Relative w1The error transformation matrix of (a) is:
According to a second aspect of the embodiments of the present invention, there is provided an on-orbit calibration system for an antenna electric axis of a satellite-borne terahertz detector, including a processor and a memory, where the processor reads a computer program in the memory, and is configured to perform the following operations:
selecting a radio star and setting a reference standard antenna electric axis;
based on the selected radio star, determining an antenna on-track directional diagram and a relative relation between each frequency band by receiving signals of the radio star, and calibrating an antenna electric axis of each frequency band;
obtaining the relative relation between the antenna electric axes of each frequency band according to the relative relation between the antenna electric axes of each frequency band and the reference antenna electric axes, and then outputting the relative calibration relation between the antenna electric axes of each frequency band;
The antenna in-orbit directional diagram is constructed by selecting an antenna ideal electric axis coordinate system as a reference coordinate system, carrying out consistency processing on the mth resident observation pointing reference by taking the 1 st observation as a reference, and then associating the mth resident observation pointing reference with a radiation digital signal value, wherein m is a positive integer.
According to the on-orbit calibration method for the antenna electric shaft of the satellite-borne terahertz detector, the whole calibration and observation process is completed in space, the radio-frequency source is directly observed from the antenna of the satellite-borne terahertz detector, all observation links do not pass through an atmospheric system, the on-orbit calibration is feasible, and atmospheric interference is avoided. Therefore, the on-orbit calibration method truly realizes high-precision on-orbit calibration of the self deviation of the antenna electric axis of the satellite-borne terahertz detector, and effectively avoids errors caused by atmospheric attenuation and interference.
On the other hand, the on-orbit calibration method for the antenna electric axis of the satellite-borne terahertz detector provided by the invention has the advantage of comprehensively calibrating the antenna electric axis with wide frequency spectrum and multiple frequency bands. Because the on-orbit calibration method adopts the radio star as a reference, the on-orbit calibration method can calibrate the antenna electric axis of the corresponding frequency band as long as the radio star can cover the frequency spectrum range; while a radio star has an extremely wide spectrum coverage as a natural celestial body in space. Therefore, the on-orbit calibration method can calibrate the antenna electric axes of wide frequency spectrum and multiple frequency bands one by one or synchronously, and realize the calibration of the relative relation between the antenna electric axes under each frequency band.
Drawings
Fig. 1 is a flowchart of an on-orbit calibration method for an antenna electric axis of a satellite-borne terahertz detector provided by the invention;
FIG. 2 is a schematic diagram of a grid-type scanning observation of a radio star by a satellite-borne terahertz detector;
FIG. 3 is a schematic diagram of reconstructing the direction of the electrical axis of an on-track antenna using grid observation information for a radio star;
FIG. 4 is a flow chart of in-orbit calibration of an antenna electric axis of a satellite-borne terahertz detector under a specific calibration frequency band;
fig. 5 is a schematic structural diagram of an on-orbit calibration system for an antenna electric axis of a satellite-borne terahertz detector provided by the invention;
fig. 6 is a flowchart of a calibration method for an antenna electric axis of a satellite-borne terahertz detector in the prior art.
Detailed Description
The technical contents of the invention are described in detail below with reference to the accompanying drawings and specific embodiments.
The invention relates to a method for calibrating an antenna electric axis of a wide-frequency-spectrum and multi-frequency-band satellite-borne terahertz detector in an on-orbit high-precision manner by taking a radio star as a spatial reference. The on-orbit calibration method takes the radio star as a spatial reference, the radio star is directly observed from the antenna of the satellite-borne terahertz detector in the space, all observation links do not pass through the earth atmosphere system, the relative relation between an antenna on-orbit directional diagram and each frequency band is determined by receiving the signal of the radio star, and the on-orbit calibration of the electric axis of the antenna of the satellite-borne terahertz detector is realized.
The on-orbit calibration method for the antenna electric axis of the satellite-borne terahertz detecting instrument provided by the embodiment of the invention is described in detail below with reference to fig. 1 to 4. As shown in fig. 1, the on-orbit calibration method includes the following steps:
s1: selecting a radio star and setting a reference antenna electric axis
This is a conventional approach and will not be described in further detail herein.
S2: calibrating the antenna electric axis of each frequency band based on the selected radio star
A plurality of calibration frequency bands (detection frequency bands) to be calibrated and a calibration time period (detection time period) are preset. In practical application, the calibration frequency band is a specific frequency band selected from a band list of the load detection band according to application requirements, and then the antenna electric axis is calibrated. And selecting a certain number of radio stars in each corresponding frequency band and corresponding time period, and establishing a corresponding relation of frequency band-time period-radio stars. Whether the frequency bands are overlapped or not can be calibrated.
Further, if a plurality of frequency bands are calibrated, on the basis of a single-frequency band electric axis calibration method, radio stars in different frequency bands are utilized to calibrate the electric axes of the antennas in the various frequency bands of the terahertz detector one by one. The following describes the calibration procedure for the antenna electrical axis of a single frequency band in detail.
As shown in fig. 2, in actual observation, assuming that an ideal radio star position is S at the center time T of a calibration period, the main beam of the antenna array is directed at the radio star S for scanning observation with S as the center. In the E, H directions of the antenna, the step-by-step resident directional design of the antenna direction is respectively carried out at fixed intervals, and the grid coverage type step-by-step resident observation is carried out around the center of an ideal radio star, so that the electric axis directional diagram of the on-orbit antenna shown in the figure 3 is obtained.
As shown in fig. 4, the method for calibrating the electric axis of the antenna of the satellite-borne terahertz detector at a specific calibration frequency band for multiple radio stars includes the following steps:
s21: setting a calibration frequency band of an antenna to be calibrated;
s22: selecting a plurality of radio stars in a frequency band to be calibrated, and arranging an observation plan;
and compiling an observation plan for the plurality of radio stars in the calibration frequency band, so as to realize the one-by-one observation of the N radio stars.
S23: according to an observation plan, in two directions of transverse scanning and longitudinal stepping, carrying out grid coverage type scanning observation on one radio star by using a reference center, and recording observation data;
and in the calibration frequency band, selecting N (N is more than or equal to 3) radio stars for observation. For each radio star, the kth radio star is not taken as an example (k is 1, 2, …, N), and it is assumed that the central time T of the detection period is kCThe ideal radio star position is SkWith SkAiming the main beam of the antenna array at the radio star S for the ideal radio star centerk(as shown in FIG. 2), the two directions of the antenna E, H may correspond to a unique observation direction, and are not marked as (E)kC，HkC)。
To observe the pointing direction (E)kC，HkC) And step-by-step resident pointing design of the antenna orientation is carried out at fixed intervals delta alpha in two directions E, H of the antenna as a reference center, and grid coverage type step-by-step resident observation is carried out around the center of an ideal radio star. Assuming that the parking positions are divided into 2S +1 in the direction E, H, a mesh parking grid of (2S +1) rows and (2S +1) columns is formed, and M is (2S +1)2Sub-step dwell observation. For example, at the first row and the first column, the designed resident observation pointing angle is (DE)1，1，DH1，1) Can be expressed as
DE1，1＝EkC-SΔα，DH1，1＝HkC-SΔα；
At row i and column j, the designed resident observation pointing angle is (DE)i，j，DHi，j) Wherein
DEi，j＝EkC+(i-1-S)Δα，
DHi，j＝HkC+(i-1-S)Δα，
(i＝1，2，…，S；j＝1，2，…，S)。
For convenience of description, the numbering sequence (i, j) of the 2-dimensional space residency is described by a 1-dimensional serial number m, wherein the relation between m and the step residency observation row number is (i-1) × (2S +1) + j.
Thus, the dwell observation pointing angle designed at row i and column j is (DE)i，j，DHi，j) Equivalently, the dwell observation pointing angle designed at the mth dwell position is (DE) m，DHm) (ii) a Further for more accurate representation, the observation azimuth angle designed for the kth star at the mth dwell position is shown as (DE)k，m，DHk，m). In addition, i, j, k, M, N, and the like are all positive integers.
Similarly, sequentially observing the N radio stars, and sequentially recording original radiation digital signal values (called original DN values for short) when the loads observe the radio stars; and simultaneously recording the number of the radio satellite, the observation time, the observation direction, and the satellite orbit position and attitude at the corresponding time.
Within one observation period, the same radio star S is measuredkA total of M observations were made, where M ═ 2S +1)2. Multiple observations within a period of time are m observations residing step by step. In a complete experiment, the frequency band is fixed.
S24: according to a radiation digital signal value (namely DN value) of the radio satellite, and auxiliary data such as satellite position and attitude are synthesized, space reference consistency processing is carried out on an observation direction, and an antenna in-orbit actual measurement directional diagram is constructed;
since the radio satellites are respectively positioned at different directions of the antenna at different observation moments, and the attitude and orbit states of the satellites also change at the moments, namely, the space observation reference conditions of the space observation reference conditions are changed and are inconsistent. Therefore, it is necessary to convert all the imaging orientations of the resident satellites under the same antenna spatial reference condition into spatial orientation descriptions of spatial reference consistency.
For convenience of data processing, an ideal electric axis coordinate system of the antenna is not selected as a reference coordinate system, the 1 st observation is used as a reference, the mth resident observation pointing reference is processed in a consistent mode and then is associated with a radiation digital signal value, and a real antenna in-orbit actual measurement directional diagram can be constructed. The method comprises the following specific steps:
1) the relative position relation between the ideal electric shaft, the ideal mechanical shaft and the satellite can be determined through a ground experiment before transmission; therefore, when the scanning rotation angle is zero degree, the zero degree reference pointing vector of the ideal electric axis in the satellite coordinate system is determined.
2) And for the kth fixed star and the mth resident observation, acquiring satellite position and attitude information according to the detection time of the mth resident observation.
3) According to the zero-degree reference pointing vector of the electric axis, the instantaneous position and the attitude of the satellite are comprehensively utilized, the zero-degree reference pointing vector can be uniquely determined, and the relative pointing variation azimuth (rE) of the mth residence time relative to the 1 st residence observation timek，m，rHk，m)。
4) According to the measured pointing angle (DE)k，m，DHk，m) And relative pointing variation orientation (rE)k，m，rHk，m) Pointing angles of two directions normalized by the 1 st observation reference (UE) can be calculatedk，m，UHk，m)＝(DEk，m，DHk，m)+(rEk，m，rHk，m)。
5) Are respectively provided with (UE)k，m，UHk，m) And as the X-axis and Y-axis coordinates, the radiation digital signal value is taken as the Z axis, and the antenna direction distribution diagram in the three-dimensional direction actually measured on the track can be established.
6) According to the antenna direction distribution diagram, the position of the radiation center, namely the actual observation direction (TE) of the radio star can be determined through characteristic analysis of the radiation energy distribution curved surfacek，THk)。
S25: calculating an expected observation direction of the radio satellite under an ideal electric axis reference condition according to auxiliary data such as the self-observation geometric parameters, the satellite position and the attitude of the terahertz detector;
the calculation method of the expected observation position has the same basic algorithm steps as the step S24, and the difference between the two steps is that: and predicting the position of the radio star according to the moment corresponding to the radiation center, and calculating the ideal observation direction of the radio star. 1) The rotation angle, the position of the rotating shaft and the zero-degree reference pointing vector of the mechanical shaft are measured in real time according to the terahertz detector, and the center pointing vector of the ideal electric shaft can be calculated in real time; 2) according to the detection time, the satellite position and attitude information at the time can be obtained; 3) according to the pointing vector of the instantaneous center of the electric axis, the instantaneous position and the attitude of the satellite, the three-dimensional solid geometric relation between the radio star-satellite-ideal electric axis center pointing vector is established, and the instantaneous expected observation orientation (PE) of the radio star relative to the ideal electric axis can be uniquely determinedk，PHk)。
S26: comparing the deviation between the actual observation position and the expected observation position of the radio star;
Calculating a deviation value (deltaE) between the actual observation orientation and the expected observation orientation for the actual spatial orientation (i.e., the value obtained in step S24) calculated by observing the same radio satellite for a plurality of times and the expected observation orientation calculated in step S25k，δHk)＝(TEk-PEk，THk-PHk)。
S27: repeating the steps S23-S26, and selecting a plurality of satellite observation data;
repeating the steps S23-S26 to obtain observation data of different radio stars and further obtain deviation values (delta E) between the actual observation direction and the expected observation direction of each radio star in the same calibration frequency bandk，δHk) Where k is 1, 2, …, N.
S28: calibrating the center and the direction of the antenna reference electric axis through an optimization solving algorithm;
due to (delta E)k，δHk) The method is two-dimensional error information, although the deviation relation of the electric axis can be simply described under the condition of low precision requirement; it cannot essentially accurately describe the error information of the antenna in three-dimensional space. Therefore, in order to space the antenna in three dimensionsAnd calibrating errors in the process, and describing the three-dimensional errors by using a three-dimensional space error transfer relationship matrix.
Since the observation azimuth vector is directly determined at the observation azimuth angle in the direction E, H for the kth radio satellite, the kth radio satellite is based on the actual observation azimuth (TE) k，THk) Can obtain the actual three-dimensional observation orientation vector Vk(ii) a According to the expected observation orientation (PE)k，PHk) Can calculate the observation orientation vector Uk；Assuming that the two orientation vectors can establish an equivalent transformation relation through the error transformation matrix a:
AUk＝Vkwherein the error conversion matrix
In the embodiment of the invention, for N radio stars, N equivalence relations may be respectively constructed. By utilizing the principle of minimizing the comprehensive deviation, the N equivalent equation sets are combined, so that the problem of electric axis error calibration can be converted into a comprehensive evaluation equation set AUk-Vk＝εkAnd (4) optimizing the problem with the minimum error. Wherein epsilonkFor the k radio star, at the strongest peak of the measured signal, the expected observation direction vector UkAfter correction, the orientation vector V is compared with the actual observation orientation vectorkThe residual error between (k is 1, 2, …, N), and N is the number of valid observed stars. Solving the optimization problem through a numerical solving algorithm to obtain a deviation conversion matrix A of the distance between the center of the electric axis of the frequency band antenna and the ideal electric axis; and (4) the position of the antenna electric axis can be calibrated by bringing the A into the position.
S29: outputting an on-orbit deviation calibration value of the frequency band antenna electric axis;
s3: and outputting the relative calibration relation between the antenna electric axes under a plurality of frequency bands.
And obtaining the relative relation between the antenna electric axes under each frequency band according to the relative relation between the antenna electric axes and the reference electric axes under each frequency band, thereby realizing the calibration of the mutual relation of the antenna electric axes of the terahertz multi-band detector under different frequency bands.
The method for calculating the relative relation between the antenna electric axes under each frequency band comprises the following steps:
s31: setting antennas of a plurality of frequency bands to be calibrated, and numbering one by one;
it is assumed that the electric axes of the antennas in the W frequency bands need to be calibrated.
S32: according to the numbering sequence of the step S31, assuming that the antenna electric axis of the w-th frequency band is calibrated, obtaining an error conversion matrix A between the actual on-track antenna electric axis and the ideal electric axiswWhere W is 1, 2, …, W.
The error transfer matrix relationship between any two antenna electrical axes can be described by the following relationship. For arbitrary w1，w2Electric axes of the antennas in two frequency bands, then w2Relative w1An error conversion matrix of
In order to realize the on-orbit calibration method of the antenna electric shaft of the satellite-borne terahertz detector, the invention also provides an on-orbit calibration system of the antenna electric shaft of the satellite-borne terahertz detector. As shown in fig. 5, the on-orbit calibration system includes a memory 51 and a processor 52, and may further include a communication component, a sensor component, a power supply component, and an input/output interface according to actual needs. The memory 51, the communication module, the sensor module, the power module, and the input/output interface are all connected to the processor 52. The memory 51 may be a Static Random Access Memory (SRAM), an Electrically Erasable Programmable Read Only Memory (EEPROM), an Erasable Programmable Read Only Memory (EPROM), a Programmable Read Only Memory (PROM), a Read Only Memory (ROM), a magnetic memory, a flash memory, etc., and the processor 52 may be a Central Processing Unit (CPU), a Graphic Processing Unit (GPU), a Field Programmable Gate Array (FPGA), an Application Specific Integrated Circuit (ASIC), a Digital Signal Processing (DSP) chip, etc. Other communication components, sensor components, power components, etc. may be implemented using common components found in existing smart devices and are not specifically described herein.
On the other hand, in the on-orbit calibration system, the processor 52 reads the computer program in the memory 51 for executing the following operations:
selecting a radio star and setting a reference standard antenna electric axis;
determining an on-orbit directional diagram of the antenna and a relative relation between each frequency band through receiving signals of the radio stars based on the selected radio stars, and calibrating an antenna electric axis of each frequency band;
obtaining the relative relation between the antenna electric axes of each frequency band according to the relative relation between the antenna electric axes of each frequency band and the reference antenna electric axes, and then outputting the relative calibration relation between the antenna electric axes of each frequency band;
the antenna in-orbit directional diagram is constructed by selecting an antenna ideal electric axis coordinate system as a reference coordinate system, taking the 1 st observation as a reference, carrying out consistency processing on the mth resident observation pointing reference, and then associating the mth resident observation pointing reference with a radiation digital signal value.
According to the on-orbit calibration method for the antenna electric shaft of the satellite-borne terahertz detector, the whole calibration and observation process is completed in space, the radio-frequency source is directly observed from the antenna of the satellite-borne terahertz detector, all observation links do not pass through an atmospheric system, the on-orbit calibration is feasible, and atmospheric interference is avoided. Therefore, the on-orbit calibration method truly realizes high-precision on-orbit calibration of the self deviation of the antenna electric axis of the satellite-borne terahertz detector, and effectively avoids errors caused by atmospheric attenuation and interference.
On the other hand, the on-orbit calibration method for the antenna electric axis of the satellite-borne terahertz detector provided by the invention has the advantage of comprehensively calibrating the wide-frequency-spectrum and multi-frequency-band antenna electric axis. Because the on-orbit calibration method adopts the radio stars as reference, the on-orbit calibration method can calibrate the antenna electric axes of corresponding frequency bands as long as the radio stars can cover the frequency spectrum range; and a radio star has an extremely wide spectrum coverage as a natural celestial body in space. Therefore, the on-orbit calibration method can calibrate the antenna electric axes of wide frequency spectrum and multiple frequency bands one by one or synchronously, and realize the calibration of the relative relationship between the antenna electric axes under each frequency band.
The present invention has been described in detail above. It will be apparent to those skilled in the art that any obvious modifications thereof can be made without departing from the spirit of the invention, which infringes the patent right of the invention and bears the corresponding legal responsibility.
Claims (7)
1. An on-orbit calibration method for an antenna electric axis of a satellite-borne terahertz detector is characterized by comprising the following steps:
s1: selecting a radio star and setting a reference standard antenna electric axis;
s2: based on the selected radio star, determining an on-orbit actual measurement directional diagram of the antenna and a relative relation between each frequency band through receiving signals of the radio star, and calibrating an antenna electric axis of each frequency band;
S3: obtaining the relative relation between the antenna electric axes of each frequency band according to the relative relation between the antenna electric axes of each frequency band and the reference antenna electric axes, and then outputting the relative calibration relation between the antenna electric axes of each frequency band;
the antenna in-orbit actual measurement directional diagram is constructed by selecting an antenna ideal electric axis coordinate system as a reference coordinate system, taking the 1 st observation as a reference, carrying out consistency processing on the mth resident observation pointing reference, and then associating the mth resident observation pointing reference with a radiation digital signal value, wherein m is a positive integer.
2. The on-orbit calibration method for the electric axis of the antenna of the spaceborne terahertz detector as claimed in claim 1, wherein the step S2 comprises the following steps:
selecting a plurality of radio stars in a frequency band to be calibrated to obtain an expected observation direction and an actual observation direction of one radio star in a directional diagram of the antenna of the terahertz detector;
establishing a deviation of the actual observed orientation from the expected observed orientation;
equating a phase corresponding to an actually observed peak value as an actual observation vector under an antenna ideal coordinate system, and obtaining a deviation value of an actual observation direction and an expected observation direction of the radio satellite according to an ideal observation vector of a direction vector of the antenna pointing to the position of the radio satellite under the antenna ideal coordinate system under the actual observation time corresponding to the actually observed peak value;
Repeating the steps, obtaining the deviation value of each radio star one by one, and establishing a deviation equation of the actual observation direction and the expected observation direction;
and solving the deviation equation through an optimization solving algorithm, and outputting a calibration result of the antenna electric axis.
3. The on-orbit calibration method for the electric axis of the antenna of the satellite-borne terahertz detector according to claim 1 or 2, wherein the step S2 further comprises the following steps:
s21: setting a calibration frequency band of an antenna to be calibrated;
s22: selecting a plurality of radio stars in the frequency band to be calibrated, and arranging an observation plan;
s23: according to the observation plan, in two directions of transverse scanning and longitudinal stepping, carrying out grid coverage type scanning observation on one radio star by using a reference center, and recording observation data;
s24: according to the radiation digital signal value of the radio satellite, the satellite position and the satellite attitude are integrated, the observation direction is subjected to space reference consistency processing, and an antenna in-orbit actual measurement directional diagram is constructed;
s25: calculating an expected observation direction of the radio star under an ideal electric axis reference condition according to the self-observation geometric parameters, the satellite position and the attitude of the terahertz detector;
s26: comparing the deviation between the actual observation position and the expected observation position of the radio star;
S27: repeating the steps S23-S26, and selecting a plurality of radio stars observation data;
s28: and calibrating the center and the direction of the antenna reference electric axis through an optimization solving algorithm.
4. The on-orbit calibration method for the electric axis of the antenna of the spaceborne terahertz detector as claimed in claim 3, wherein the step S24 comprises the following steps:
1) determining a zero-degree reference pointing vector of an ideal electric axis in a satellite coordinate system before transmission;
2) for the kth fixed star and the mth residence observation, acquiring satellite position and attitude information according to the detection moment of the mth residence, wherein k is a positive integer;
3) according to the zero-degree reference pointing vector of the ideal electric axis, determining the zero-degree reference pointing vector as a relative pointing change azimuth relative to the 1 st residence observation time at the mth residence time by comprehensively utilizing the instantaneous position and the attitude of the satellite;
4) calculating the pointing angles of the two directions normalized by the 1 st observation reference according to the actually measured pointing angle and the relative pointing change direction;
5) respectively taking the pointing angle as an X-axis coordinate and a Y-axis coordinate, and taking the radiation digital signal value as a Z-axis, and establishing an on-orbit actual measurement directional diagram of the antenna;
6) and determining the position of a radiation center through characteristic analysis of a radiation energy distribution curved surface according to the antenna in-orbit actual measurement directional diagram to obtain the actual observation direction of the radio star.
5. The on-orbit calibration method for the electric axis of the antenna of the satellite-borne terahertz detector as claimed in claim 3, wherein in the step S28, the solution of the comprehensive evaluation equation set AU is utilizedk-Vk＝εkCalibrating the center and the direction of the antenna reference electric axis in an optimization problem mode with the minimum error;
wherein epsilonkTo the k-th radio star, at the measured signalAt the strongest peak, for the expected observation orientation vector UkAfter correction, the orientation vector V is compared with the actual observation orientation vectorkThe residual error between (k is 1,2, …, N), and N is the number of valid observed stars.
6. The on-orbit calibration method for the electric axis of the antenna of the spaceborne terahertz detector as claimed in claim 1, wherein the step S3 comprises the following steps:
s31: setting antennas of a plurality of frequency bands to be calibrated, and numbering one by one;
s32: calibrating the antenna electric axis of the w-th frequency band to obtain an error conversion matrix A between the actual on-track antenna electric axis and the ideal electric axiswWherein W is 1,2, …, W; for arbitrary w1,w2Antenna electric axes of two frequency bands, then w2Relative w1The error transformation matrix of (a) is:
7. An on-orbit calibration system for an antenna electric axis of a satellite-borne terahertz detector is characterized by comprising a processor and a memory, wherein the processor reads a computer program in the memory and is used for executing the following operations:
Selecting a radio star and setting a reference standard antenna electric axis;
based on the selected radio star, determining an on-orbit actual measurement directional diagram of the antenna and a relative relation between each frequency band through receiving signals of the radio star, and calibrating an antenna electric axis of each frequency band;
obtaining the relative relation between the antenna electric axes of each frequency band according to the relative relation between the antenna electric axes of each frequency band and the reference antenna electric axes, and then outputting the relative calibration relation between the antenna electric axes of each frequency band;
the antenna in-orbit actual measurement directional diagram is constructed by selecting an antenna ideal electric axis coordinate system as a reference coordinate system, taking the 1 st observation as a reference, carrying out consistency processing on the mth resident observation pointing reference, and then associating the mth resident observation pointing reference with a radiation digital signal value, wherein m is a positive integer.
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