A method and device for on-orbit calibration of GNSS-R reflective antenna patterns

Abstract

The present invention relates to a method and device for on-orbit calibration of GNSS-R reflector antenna patterns. The method comprises: transmitting a calibration signal through a ground-based L-band signal transmission source system; utilizing an on-orbit GNSS-R signal receiving system to receive the calibration signal transmitted by the ground-based L-band signal transmission source system and generate a delay-Doppler-correlated power waveform of the calibration signal; processing the delay-Doppler-correlated power waveforms of the multi-orbit calibration signals to obtain GNSS-R reflector antenna patterns at different elevation and azimuth angles; and performing two-dimensional linear interpolation processing on the GNSS-R reflector antenna patterns at different elevation and azimuth angles to achieve on-orbit calibration of the GNSS-R reflector antenna pattern. The device comprises: an L-band signal transmission source system, an on-orbit GNSS-R signal receiving system, and a ground-based data processing system. The present invention achieves on-orbit calibration of the GNSS-R reflector antenna pattern.

Description

Technical Field

[0001] The present invention relates to the field of GNSS reflected signal remote sensing technology, and discloses a method and device for on-orbit calibration of a GNSS-R reflective antenna pattern. Background Art

[0002] Around the 1990s, research discovered that in addition to basic functions such as positioning, navigation, and timing, GNSS (Global Navigation Satellite System) signals reflected from the Earth's surface can be received and used for remote sensing of the physical parameters of the surface's reflecting surfaces. This led to the development of a new remote sensing technology: GNSS Reflection or GNSS Reflectometry (GNSS-R). GNSS-R is essentially a dual (or multi-)base radar with separate transmitters and receivers. By receiving and collaboratively processing direct and reflected signals from GNSS satellites, it inverts surface parameters based on changes in the amplitude, polarization, and phase of GNSS signals caused by surface reflections. Currently, this technology has been used for GNSS-R altimetry and remote sensing of various physical parameters such as sea surface wind fields, soil moisture, sea ice cover, total surface biomass, and surface freeze-thaw.

[0003] Reflector antennas are key components for receiving ground-reflected signals during GNSS-R remote sensing. Their directivity is one of their most important physical parameters, directly impacting signal reception quality. Typically, GNSS-R reflector antenna patterns are calibrated in a laboratory in a microwave anechoic chamber before installation. However, after installation and launch into orbit, the reflector antenna pattern often experiences some distortion due to factors such as the surrounding equipment, the reflector antenna's own deformation, and device aging. When this distortion is significant, using the antenna pattern measured in the microwave anechoic chamber to process and invert the GNSS-R reflected signal observations output by the receiver will introduce processing errors, impacting the accuracy of the final inversion product. Therefore, operational, periodic, on-orbit calibration of GNSS-R reflector antenna patterns is essential for improving the accuracy of satellite inversion products. Currently, there are no publicly available methods and devices for on-orbit calibration of GNSS-R reflector antenna patterns. Summary of the Invention

[0004] The purpose of the present invention is to address the problem that after a GNSS-R reflector antenna is mounted on a satellite and launched into space orbit, the reflector antenna's radiation pattern is distorted due to the combined influence of factors such as the surrounding equipment at the installation location, the reflector antenna's own deformation, and device aging. A method and device for in-orbit calibration of the GNSS-R reflector antenna's radiation pattern is proposed.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions.

[0006] The present invention proposes a method for on-orbit calibration of a GNSS-R reflector antenna pattern, the method comprising:

[0007] The calibration signal is transmitted through the ground-based L-band signal transmitting source system;

[0008] The on-orbit GNSS-R signal receiving system receives the calibration signal transmitted by the ground-based L-band signal transmitting source system and generates the delay-Doppler correlation power waveform of the calibration signal.

[0009] Absolute power calibration and data processing are performed on the delay-Doppler correlation power waveform of the multi-track calibration signal to obtain the GNSS-R reflector antenna pattern at different elevation and azimuth angles;

[0010] Two-dimensional linear interpolation processing is performed on the GNSS-R reflector antenna patterns at different elevation and azimuth angles to achieve on-orbit calibration of the GNSS-R reflector antenna patterns.

[0011] As one of the improvements to the above technical solution, the calibration signal emitted by the L-band signal transmitter system is an electromagnetic wave signal modulated with a pseudo-random code that can be recognized by the on-orbit GNSS-R receiver, and the frequency and polarization of the electromagnetic wave signal are consistent with the frequency and polarization of the GNSS-R reflector antenna pattern to be calibrated; the signal radiation power density is within the range of the GNSS reflection signal radiation power density on the ground.

[0012] As one of the improvements to the above technical solution, the on-orbit calibration results of the GNSS-R reflective antenna patterns of multiple tracks with different elevation angles and azimuth angles are subjected to two-dimensional linear interpolation to obtain the GNSS-R reflective antenna pattern, which is calculated as follows:

[0013]

[0014] Where, is the radiation pattern of the reflecting antenna, P r is the peak absolute power value of the reflected signal extracted from the delay-Doppler correlation power waveform after absolute power calibration, is the equivalent isotropic radiated power of the ground active calibrator, λ is the carrier wavelength of the signal transmitted by the L-band signal source, R is the geometric distance between the GNSS-R reflector antenna and the L-band signal source, l is the attenuation term such as atmospheric absorption and rain attenuation, θ and are the elevation angle and azimuth angle of the L-band signal transmitter in the spherical coordinate system with the GNSS-R reflector antenna as the origin.

[0015] The present invention also proposes a device for on-orbit calibration of a GNSS-R reflective antenna pattern, which completes on-orbit calibration of the GNSS-R reflective antenna pattern based on one of the above-mentioned methods. The device includes: an L-band signal transmission source system, an on-orbit GNSS-R signal receiving system, and a ground data processing system.

[0016] The L-band signal transmitting source system is used to transmit a calibration signal;

[0017] The on-orbit GNSS-R signal receiving system is used to receive the calibration signal, process the calibration signal to generate a delay-Doppler correlation power waveform, and transmit the delay-Doppler correlation power waveform to the ground data processing system via the satellite platform; and

[0018] The ground data processing system is used to perform subsequent processing on the delay-Doppler correlation power waveform to obtain the on-orbit calibration GNSS-R reflection antenna pattern.

[0019] As one of the improvements of the above technical solution, the L-band signal transmission source system includes: an L-band signal transmission module, a ground GNSS positioning antenna and a GNSS positioning receiver;

[0020] The L-band signal transmission module includes: an L-band signal source and an L-band transmitting antenna including a servo system, which is used to generate and transmit a calibration signal with adjustable direction;

[0021] The GNSS positioning receiver and the ground GNSS positioning antenna are used to determine the geographical coordinates of the L-band signal transmission source system.

[0022] As one of the improvements of the above technical solution, the on-orbit GNSS-R signal receiving system includes: a GNSS-R receiver host, an on-orbit GNSS positioning antenna and a GNSS-R reflector antenna;

[0023] The on-orbit GNSS positioning antenna and GNSS-R receiver host combination is used to perform real-time positioning of the on-orbit GNSS-R signal receiving system;

[0024] The GNSS-R reflector antenna and the GNSS-R receiver host are combined to receive a calibration signal and correlate the calibration signal with a modulated calibration-specific PRN pattern to generate a delay-Doppler correlation power waveform;

[0025] The GNSS-R receiver host is used to calculate the elevation angle and azimuth angle of the L-band transmitter system in a spherical coordinate system with the GNSS-R reflector antenna as the origin using the on-orbit real-time positioning results and the stored geographical location of the L-band signal transmitter; at the same time,

[0026] The GNSS-R receiver host has a signal absolute power calibration function; at the same time,

[0027] The GNSS-R receiver host is used to transmit the generated delay-Doppler correlation power waveform to the ground data processing system via the satellite platform.

[0028] As one of the improvements to the above technical solution, the L-band transmitting antenna adopts a high-gain narrow-beam transmitting antenna, and the antenna beam center is pointed parallel to the beam center of the GNSS-R reflective antenna to be calibrated, but in the opposite direction.

[0029] The on-orbit calibration method for the GNSS-R reflector antenna pattern provided in this application can realize the calibration of the GNSS-R reflector antenna pattern at any stage of its entire on-orbit life cycle.

[0030] The advantages of the present invention are:

[0031] 1. This application proposes an on-orbit calibration method for GNSS-R reflector antenna patterns based on the collaborative working mode of a ground-based L-band signal transmitter system and an on-orbit GNSS-R signal receiving system. The calibration test results of multi-orbit reflector antenna patterns at different elevation and azimuth angles calculated by the peak absolute power of the calibration signal delay-Doppler correlation power waveform are used to obtain the on-orbit calibration method of GNSS-R reflector antenna patterns using a two-dimensional linear interpolation method.

[0032] 2. By adjusting the PRN code, frequency, and polarization mode of the L-band signal transmitter, the present invention can achieve on-orbit calibration of the reflection antenna pattern based on the delay-Doppler correlation power waveform of different PRN codes, frequencies, and polarization modes. By changing the two-dimensional interpolation method, equivalent reflection antenna pattern calibration results can be obtained.

[0033] 3. The present invention can achieve high-precision on-orbit calibration of the GNSS-R reflector antenna pattern by adding calibration results of GNSS-R reflector antenna patterns at different elevation angles and azimuth angles for two-dimensional linear interpolation processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a diagram of the on-orbit calibration system for GNSS-R reflector antenna patterns;

[0035] Figure 2 is the true value of the GNSS-R reflector antenna pattern;

[0036] Figure 3 The multi-track calibration results for GNSS-R reflector antenna patterns;

[0037] Figure 4 The GNSS-R reflector antenna pattern is obtained by two-dimensional linear interpolation based on the multi-track calibration results. DETAILED DESCRIPTION

[0038] The technical solution provided by the present invention is further illustrated below with reference to embodiments.

[0039] Example 1

[0040] The present invention proposes a method for calibrating the GNSS-R reflector antenna pattern on-orbit. The technical solution adopted by the method of the present invention is as follows:

[0041] The calibration signal is transmitted by the L-band signal transmitting source system located on the ground. The GNSS-R signal receiving system operating in orbit receives the calibration signal transmitted by the L-band signal transmitting source system on the ground and generates a delay-Doppler correlation power waveform. The delay-Doppler correlation power waveform of the calibration signal is transmitted to the ground through data processing. After absolute power calibration and data processing, the GNSS-R reflector antenna radiation pattern at different elevation and azimuth angles is obtained. The GNSS-R reflector antenna radiation pattern at different elevation and azimuth angles of multiple tracks is subjected to two-dimensional linear interpolation to realize the on-orbit calibration of the GNSS-R reflector antenna radiation pattern.

[0042] In this technical solution, the L-band signal transmitter system located on the ground is responsible for transmitting an electromagnetic wave signal modulated with a pseudo-random noise code (PRN) that can be recognized by the on-orbit GNSS-R receiver. The frequency of the electromagnetic wave signal is consistent with the frequency point of the proposed calibration reflector antenna pattern.

[0043] The on-orbit GNSS-R signal receiving system receives the calibration signal and processes it to generate the delay-Doppler correlation power waveform. Once the calibration signal delay-Doppler correlation power waveform is transmitted to the ground, absolute power calibration and data processing are performed to obtain the on-orbit calibration results for the GNSS-R reflector antenna's different elevation and azimuth patterns.

[0044]

[0045] Where, is the radiation pattern of the reflecting antenna, P r is the peak absolute power value of the reflected signal extracted from the delay-Doppler correlation power waveform after absolute power calibration, is the equivalent isotropic radiated power of the ground active calibrator, λ is the carrier wavelength of the signal transmitted by the L-band signal source, R is the geometric distance between the GNSS-R reflector antenna and the L-band signal source, and l is the attenuation term such as atmospheric absorption and rain attenuation.

[0046] By performing two-dimensional linear interpolation on the GNSS-R reflection antenna patterns of multiple tracks with different elevation and azimuth angles, the calibration results of the reflection antenna patterns of any specified antenna elevation and azimuth angles can be obtained.

[0047] This solution includes the following technical features:

[0048] 1. The L-band signal transmission source system includes: an L-band signal source, an L-band transmitting antenna with a servo system, an uninterruptible power supply (UPS), a GNSS positioning antenna, and a GNSS positioning receiver;

[0049] 2. The PRN code, frequency, and polarization of the signal transmitted by the L-band signal source must be consistent with the PRN code, frequency, and polarization set in the reflector antenna pattern calibration mode of the on-orbit GNSS-R receiver;

[0050] 3. The L-band signal transmitter's signal transmission power is adjustable, ensuring that the signal radiation power density is within the range of the GNSS reflected signal radiation power density at the ground, thus preventing interference with other devices along the transmission path.

[0051] 4. GNSS positioning antenna and GNSS positioning receiver are used to determine the accurate geographic coordinates of the L-band signal transmission source system;

[0052] 5. The L-band signal transmitter system should be located in an area with low L-band interference signals and relatively stable noise levels. Once the location is selected, it should remain fixed during the calibration period.

[0053] 6. The transmitting antenna of the L-band signal transmitter should adopt a high-gain narrow-beam transmitting antenna;

[0054] 7. The transmitting antenna of the L-band signal transmitter is fixed on the servo system, and the beam center direction of the reflector antenna can be adjusted by the servo system;

[0055] 8. The on-orbit GNSS-R signal receiving system includes: GNSS-R receiver host, positioning antenna, and reflector antenna;

[0056] 9. The GNSS-R receiver host and positioning antenna combination has the receiver's on-orbit real-time positioning function;

[0057] 10. The GNSS-R receiver stores the geographic coordinates of the L-band signal transmitter, the calibration range of the reflector antenna elevation and azimuth angles, and the calibration-specific PRN pattern. These can all be controlled by ground command injection.

[0058] 11. The GNSS-R receiver and reflector antenna combination has the function of receiving the calibration signal and correlating it with the locally modulated calibration-specific PRN pattern to generate a delay-Doppler correlation power waveform.

[0059] 12. GNSS-R receivers have an absolute power calibration function, enabling them to perform on-orbit calibration of reflective antenna patterns.

[0060] 13. The GNSS-R receiver has a master switch to turn on and off the on-orbit calibration function for the reflective antenna pattern. The state of the master switch can be controlled by ground-based commands, determining whether the GNSS-R receiver can automatically trigger the on-orbit calibration mode for the reflective antenna pattern.

[0061] 14. The GNSS-R receiver has the function of calculating the elevation and azimuth of the L-band transmitter system in the reflector antenna coordinate system using the real-time on-orbit positioning results and the stored geographic location of the L-band signal transmitter;

[0062] 15. When the reflector pattern calibration function is enabled, the GNSS-R receiver can use the calculated elevation and azimuth angles of the transmitter in the reflector coordinate system to determine whether the receiver has entered the reflector pattern on-orbit calibration mode.

[0063] 16. The delay-Doppler correlation power waveform generated in the reflector antenna pattern calibration mode can be transmitted to the ground via the satellite platform. After data processing, the on-orbit calibration results of the reflector antenna pattern at different elevation and azimuth angles can be obtained.

[0064] 17. The calibration results of the multi-track reflector antenna's different elevation and azimuth angle patterns need to be obtained through two-dimensional linear interpolation to obtain the reflector antenna pattern.

[0065] Example 2

[0066] like Figure 1 As shown, this is a diagram showing the composition of the device for on-orbit calibration of the GNSS-R reflection antenna diagram according to Example 2 of the present application. The specific implementation is as follows:

[0067] (1) Through on-site investigation, select an area with less L-band interference signals and relatively stable noise level as the location for the calibration test of the L-band signal transmitter system, install and debug the L-band signal transmitter system, such as Figure 1 As shown, Figure 2 is the true value of the on-orbit GNSS-R reflector antenna pattern to be calibrated.

[0068] (2) The geographical coordinates of the system are measured using the L-band signal transmitter system, and are then sent to the on-orbit GNSS-R receiver through the command injection method together with the frequency, elevation, and azimuth range of the GNSS-R reflector antenna pattern to be calibrated, the dedicated PRN code pattern to be used for calibration, and the calibration mode opening command.

[0069] (3) During the on-orbit operation of the GNSS-R receiver, the receiver is automatically triggered to enter the on-orbit calibration mode of the reflector antenna according to the geometric relationship between the calibration source position and the receiver, receives the calibration signal transmitted by the L-band signal source, and generates the delay-Doppler correlation power waveform of the calibration signal.

[0070] (4) After the GNSS-R receiver transmits the delay-Doppler correlation power waveform of the calibration signal to the ground, the on-orbit calibration results of the reflector antenna’s directional patterns at different elevation and azimuth angles are obtained through absolute power calibration and data processing, such as Figure 3 shown.

[0071] (5) The directional patterns of the multi-track GNSS-R reflector antennas at different elevation and azimuth angles are processed by two-dimensional linear interpolation of the on-orbit calibration results to generate the directional patterns of the reflector antennas, such as Figure 4 shown.

[0072] From the above specific description of the present invention, it can be seen that the present invention realizes the on-orbit calibration of the reflector antenna pattern by using the two-dimensional linear interpolation method to obtain the calibration test results of the multi-track reflector antenna pattern at different elevation and azimuth angles calculated by the peak absolute power of the calibration signal delay-Doppler correlation power waveform.

[0073] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and are intended to be encompassed by the claims of the present invention.

Claims

1. A method for calibrating a GNSS-R reflector antenna pattern on-orbit, the method comprising: The calibration signal is transmitted through the ground-based L-band signal transmitting source system; The calibration signal emitted by the L-band signal transmitter system is an electromagnetic wave signal modulated with a pseudo-random code recognizable by the on-orbit GNSS-R receiver, and the frequency and polarization of the electromagnetic wave signal are consistent with the frequency and polarization of the GNSS-R reflector antenna pattern to be calibrated; the signal radiation power density is within the range of the GNSS reflected signal radiation power density at the ground; The geographical coordinates of the system are measured using the L-band signal transmitter system, and are then sent to the on-orbit GNSS-R receiving system through command injection, along with the frequency, elevation, and azimuth range of the GNSS-R reflector antenna pattern to be calibrated, the PRN pattern to be used for calibration, and the calibration mode enable command. The on-orbit GNSS-R signal receiving system receives the calibration signal transmitted by the ground-based L-band signal transmitting source system and generates the delay-Doppler correlation power waveform of the calibration signal. Absolute power calibration and data processing are performed on the delay-Doppler correlation power waveform of the multi-track calibration signal to obtain the GNSS-R reflector antenna pattern at different elevation and azimuth angles; Perform two-dimensional linear interpolation on GNSS-R reflector antenna patterns at different elevation and azimuth angles to achieve on-orbit calibration of GNSS-R reflector antenna patterns. The on-orbit calibration results of the GNSS-R reflective antenna patterns of multiple tracks with different elevation angles and azimuth angles are subjected to two-dimensional linear interpolation to obtain the GNSS-R reflective antenna pattern, and the calculation formula is: Where, is the radiation pattern of the reflecting antenna, P r is the peak absolute power value of the reflected signal extracted from the delay-Doppler correlation power waveform after absolute power calibration, is the equivalent isotropic radiated power of the ground active calibrator, λ is the carrier wavelength of the signal transmitted by the L-band signal source, R is the geometric distance between the GNSS-R reflector antenna and the L-band signal source, l is the attenuation term such as atmospheric absorption and rain attenuation, θ and are the elevation angle and azimuth angle of the L-band signal transmitter in the spherical coordinate system with the GNSS-R reflector antenna as the origin.

2. A device for on-orbit calibration of a GNSS-R reflective antenna pattern, wherein the device performs on-orbit calibration of a GNSS-R reflective antenna pattern based on the method for on-orbit calibration of a GNSS-R reflective antenna pattern according to claim 1, characterized in that: The device includes: an L-band signal transmission source system, an on-orbit GNSS-R signal receiving system and a ground data processing system; The L-band signal transmitter system is used to transmit a calibration signal; the calibration signal transmitted by the L-band signal transmitter system is an electromagnetic wave signal modulated with a pseudo-random code recognizable by the on-orbit GNSS-R receiver, and the frequency and polarization mode of the electromagnetic wave signal are consistent with the frequency and polarization mode of the GNSS-R reflector antenna pattern to be calibrated; the signal radiation power density is within the radiation power density range of the GNSS reflected signal on the ground; the geographical coordinates of the system are measured using the L-band signal transmitter system, and are combined with the frequency, elevation, and azimuth range of the GNSS-R reflector antenna pattern to be calibrated, the proposed calibration-specific PRN code pattern, and the calibration mode opening instruction, and are sent to the on-orbit GNSS-R receiving system through the instruction injection method; The on-orbit GNSS-R signal receiving system is used to receive the calibration signal, process the calibration signal to generate a delay-Doppler correlation power waveform, and transmit the delay-Doppler correlation power waveform to the ground data processing system via the satellite platform; and The ground data processing system is used to perform subsequent processing on the delay-Doppler correlation power waveform to obtain the on-orbit calibration GNSS-R reflection antenna pattern.

3. The device for on-orbit calibration of GNSS-R reflection antenna patterns according to claim 2, characterized in that: The L-band signal transmission source system includes: an L-band signal transmission module, a ground GNSS positioning antenna and a GNSS positioning receiver; The L-band signal transmission module includes: an L-band signal source and an L-band transmitting antenna including a servo system, which is used to generate and transmit a calibration signal with adjustable direction; The GNSS positioning receiver and the ground GNSS positioning antenna are used to determine the geographical coordinates of the L-band signal transmission source system.

4. The device for on-orbit calibration of GNSS-R reflection antenna patterns according to claim 3, characterized in that: The on-orbit GNSS-R signal receiving system includes: a GNSS-R receiver host, an on-orbit GNSS positioning antenna and a GNSS-R reflector antenna; The on-orbit GNSS positioning antenna and GNSS-R receiver host combination is used to perform real-time positioning of the on-orbit GNSS-R signal receiving system; The GNSS-R reflector antenna and the GNSS-R receiver host are combined to receive a calibration signal and correlate the calibration signal with a modulated calibration-specific PRN pattern to generate a delay-Doppler correlation power waveform; The GNSS-R receiver host is used to calculate the elevation angle and azimuth angle of the L-band transmitter system in a spherical coordinate system with the GNSS-R reflector antenna as the origin using the on-orbit real-time positioning results and the stored geographical location of the L-band signal transmitter; at the same time, The GNSS-R receiver host has a signal absolute power calibration function; at the same time, The GNSS-R receiver host is used to transmit the generated delay-Doppler correlation power waveform to the ground data processing system via the satellite platform.

5. The device for on-orbit calibration of GNSS-R reflection antenna patterns according to claim 3, characterized in that: The L-band transmitting antenna adopts a high-gain narrow-beam transmitting antenna, and the center direction of the antenna beam is parallel to the center direction of the beam of the GNSS-R reflective antenna to be calibrated, but in the opposite direction.

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