A method for calibrating the radiation characteristics of a spaceborne active microwave sensor in a coordinated space-ground operation

Abstract

This invention discloses a space-ground coordinated radiometric characteristic calibration method for spaceborne active microwave sensors in the field of radar Earth observation technology. It constructs a space-ground coordinated calibration system consisting of a radiation reference source satellite and a ground calibration processing station. The method includes: determining the orbital parameters of the radiation reference source satellite; the satellite transmitting signals to the ground station in Earth observation mode, using a known RCS target on the ground to calibrate its own antenna gain and link gain; receiving signals from the satellite to be calibrated in Earth observation mode, accurately calculating and transmitting echo signals based on the calibrated parameters; and the satellite to be calibrated calibrating its own transmit / receive link gain based on the received echo signals. This invention can be widely applied to the on-orbit radiometric calibration of active microwave sensors such as synthetic aperture radar, altimeters, and microwave scatterometers, significantly improving calibration frequency and accuracy, supporting multi-band, high-stability quantitative remote sensing tasks, and providing reliable technical support for precise observation in fields such as ocean monitoring, weather forecasting, and topographic mapping.

Description

Technical Field

[0001] This invention relates to the field of radar Earth observation technology, specifically to a method for calibrating the radiation characteristics of a spaceborne active microwave sensor in a coordinated space-ground operation. Background Technology

[0002] Spaceborne active microwave sensors (such as synthetic aperture radar, radar altimeters, and microwave scatterometers) possess all-weather, all-time observation capabilities and are widely used in fields such as marine monitoring, topographic mapping, and weather forecasting. To ensure the quantitative accuracy of observation data, their radiometric characteristics must be calibrated regularly in orbit. Currently, calibration mainly relies on targets with known radar cross-sections (RCS) (such as corner reflectors and active calibrators) deployed in ground calibration fields. This method is constrained by geographical conditions, satellite revisit cycles, and atmospheric propagation, resulting in problems such as low calibration frequency and limited accuracy.

[0003] The existing technology has the following main bottlenecks: First, it is geographically limited, requiring the satellite beam to intersect with a fixed ground calibration field within my country, making it difficult to cover the entire globe or overseas regions; second, calibration opportunities are limited, as the number of times the beam intersects with the ground station is low due to the influence of satellite orbit and Earth's rotation; and third, signal transmission loss is high, with errors introduced over long distances and through the atmosphere, affecting the stability and accuracy of calibration.

[0004] Based on this, the present invention designs a method for calibrating the radiation characteristics of a spaceborne active microwave sensor in a space-ground coordinated manner to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a space-ground coordinated calibration method for the radiation characteristics of a spaceborne active microwave sensor. This method uses a radiation reference source satellite equipped with a receiver, transmitter, and RFSoc modules, along with a ground calibration processing station, to form a space-ground coordinated calibration system. This system calibrates the radiation characteristics of the spaceborne active microwave sensor, overcoming the geographical limitations of ground-based calibration, increasing the calibration frequency and accuracy, and enabling more precise values ​​for signal transmission and reception from the active microwave sensor to other targets. This achieves high-precision, high-frequency execution of the calibration task, thus solving the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for calibrating the radiation characteristics of a spaceborne active microwave sensor using a space-ground coordinated approach is proposed. This method constructs a space-ground coordinated calibration system consisting of a radiation reference source satellite and a ground calibration processing station. The radiation reference source satellite switches between "ground-based mode" and "space-based mode" and transfers parameters to complete the following calibration process:

[0008] S1. Determine the orbital parameters of the satellite carrying the radiation reference source;

[0009] S2. When the beam of the radiation reference source satellite antenna sweeps across the ground calibration processing station, it switches to ground-to-ground mode and actively transmits pulse signals.

[0010] S3. Simultaneously measure and calibrate the main lobe gain and transceiver link gain of the satellite payload antenna of the radiation reference source using a ground calibration processing station;

[0011] S4. When the radiation reference source satellite passes through the beam of the onboard active microwave sensor, it switches to the sky-viewing mode to receive the pulse signals emitted by it.

[0012] S5. The radiation reference source satellite quantitatively calculates the required echo signal power based on the gain value obtained from the calibration in the Earth observation model.

[0013] S6. The active microwave sensor calibrates its own transmit / receive link gain based on the high-precision echo signal from the radiation reference source satellite.

[0014] Furthermore, the spaceborne active microwave sensors include active microwave sensors such as synthetic aperture radar (SAR), altimeters, and microwave scatterometers. Both the spaceborne active microwave sensors and the radiation reference source satellite have the same transmitting and receiving antennas, meaning the transmitting and receiving antenna gains are the same, but the transmitting and receiving links are different, meaning the transmitting and receiving link gains are different.

[0015] Furthermore, the orbital altitude of the radiation reference source satellite is lower than that of the target active microwave sensor satellite;

[0016] In specific settings, a domestic ground calibration station with a clearly known latitude and longitude range should be used as a reference target to ensure that the beam of the radiation reference source satellite can scan the ground calibration station at a high frequency during operation. At the same time, the radiation reference source satellite should pass through the beam range of the active microwave sensor satellite as many times and for as long as possible during operation, so that the active microwave sensor can use it to complete the radiation characteristic calibration.

[0017] Furthermore, the radiation reference source satellite includes a receiving link, a transmitting link, a transceiver antenna, and an RFSoc processing board. The radio frequency signal received by the receiving antenna of the radiation reference source satellite is processed by the receiving link and converted into a direct-sampled radio frequency digital signal at the RFSoc receiver. The radio frequency digital signal transmitted by the RFSoc is processed by the transmitting link and then transmitted from the transmitting antenna.

[0018] When the radiation reference source satellite beam sweeps across the ground calibration station, it actively transmits a pulse signal to the ground calibration station after being processed by antenna smart beamforming (DBF). This suppresses external signal interference and directs the main beam toward the ground target. The transmitted signal can cover multiple frequency ranges, and the transmission power can be adjusted for each.

[0019] Furthermore, the ground calibration station uses the radar cross-section (RCS) value to identify the reflected pulse of a known standard reflector, or processes the pulse using a standard transceiver before transmitting the echo. After receiving the echo signal, the radiation reference satellite can uniformly calibrate its transceiver link gain and the main lobe gain of its transceiver antenna. The corresponding expression for the relationship model is:

[0020]

[0021] In the formula, G receive For the satellite receiver link gain of the radiation reference source, G transmit For transmit link gain, G cal P represents the gain of the transmit / receive antenna. rRF P represents the digital signal power transmitted from the RFSoc terminal inside the radiation reference source satellite. tRF R is the digital signal power received at its end. cal σ is the distance between the radiating reference source antenna and the ground standard reflector or transceiver, λ is the wavelength of the transmitted signal, and σ is the distance between the antenna and the ground standard reflector or transceiver. ref This represents the RCS value of a standard ground reflector or the fitted RCS value of a standard transceiver.

[0022] Furthermore, when the radiation reference source satellite passes through the beam of the active microwave sensor satellite, it uses antenna smart beamforming (DBF) to align its main lobe with the main lobe range of the onboard active microwave sensor and receive the pulse signals emitted by it. The signals emitted by the active microwave sensor can cover multiple frequency ranges, and the transmission power can be adjusted accordingly.

[0023] Furthermore, after receiving the pulse signal from the onboard active microwave sensor, the radiation reference source satellite calculates the required echo signal power based on parameters such as the satellite's current RCS setting, the main lobe antenna calibrated during the Earth-to-ground process, and the transmit / receive link gain. It then transmits the echo signal, which has also undergone DBF processing, to ensure that the onboard active microwave sensor receives an accurate echo response. The corresponding expression for the relational model is:

[0024]

[0025] Among them, P 2RF P represents the power of the digital signal emitted by the RFSoc transmitter of the radiation reference source satellite. 1RF For the RF direct sampling digital signal power at its receiving end, σ cal The RCS setting value for the radiation reference source satellite can be set between 0-40 dBsm as needed; λ represents the combined gain of the radiation reference source satellite transceiver link and transceiver antenna obtained from the calibration in the Earth-based model, where λ is the wavelength of the transmitted signal.

[0026] Furthermore, after receiving the echo from the radiation reference source satellite, the active microwave sensor calculates its own transmit / receive link current gain using standard radar equations to ensure the accuracy of its transmitted and received signals, thus completing the radiation characteristic calibration task. The expression corresponding to the relational model is:

[0027]

[0028] Among them, G tAMS G represents the gain value of the active microwave sensor transmit link. rAMS Given its receive link gain value, calculating both simultaneously yields the total fitted gain of the active microwave sensor's transceiver link; P rAMS P represents the signal power received by the internal processing module of the active microwave sensor. tAMS σ is the transmitting signal power; R is the distance between the active microwave sensor antenna and the radiation reference satellite antenna; G is the main lobe gain of the active microwave sensor transceiver antenna; λ is the wavelength of the transmitted signal; σ cal Set the RCS value for the radiation reference source satellite.

[0029] Furthermore, by adjusting the signal frequency to change the wavelength, a truth table of the transceiver link gain of the active microwave sensor in a multi-frequency range can be obtained, thereby enabling high-precision execution of subsequent tasks such as quantitative microwave remote sensing.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. The space-ground collaborative calibration method proposed in this invention can overcome the geographical limitations of ground-based calibration methods, enabling spaceborne active microwave sensors to complete radiation characteristic calibration even in non-domestic airspace;

[0032] 2. The method of this invention increases the frequency of radiation characteristic calibration for active microwave sensors;

[0033] 3. In the method of the present invention, the distance between the spaceborne active microwave sensor and the radiation reference source satellite is closer than that of the ground calibration processing station, and the clutter in the space environment is easier to distinguish than that in the ground environment, thus improving the accuracy of calibration;

[0034] 4. The method of the present invention achieves long-term stability of the calibration load through a calibration system that integrates space and ground, ensuring long-term high-precision and high-frequency execution of calibration tasks. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a flowchart of the spaceborne active microwave sensor radiation characteristic calibration method based on a radiation reference source according to the present invention.

[0037] Figure 2 The simulation results of the convergence of ground-based models over a period of one month;

[0038] Figure 3 This is a simulation of the convergence of the sky modes over a period of one month;

[0039] Figure 4 A schematic diagram of the structure of each part of the space-ground collaborative calibration system;

[0040] Figure 5 Simulation diagram showing the variation of the total gain of the Earth-based reference satellite as a function of its processing terminal's transmit power;

[0041] Figure 6 A simulation diagram showing the variation of the error between the calculated and actual values ​​of the gain of the Earth-based reference satellite as a function of the transmission power of its processing terminal.

[0042] Figure 7 This is a simulation diagram showing the trend of different RCS values ​​of the inverse reference source in the sky-viewing mode as a function of the transmit power of the active microwave sensor processing terminal.

[0043] Figure 8 Simulation diagram of the time dimension calibration effect of the space-ground collaborative calibration method. Detailed Implementation

[0044] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Please refer to the accompanying drawings. This invention provides a technical solution:

[0046] A method for calibrating the radiation characteristics of a spaceborne active microwave sensor using a space-ground collaborative calibration system is proposed. This method constructs a collaborative calibration system consisting of a radiation reference source satellite and a ground station, enabling real-time, high-frequency, and high-precision gain calibration on-board. This significantly improves the data reliability and quantitative remote sensing capabilities of the active microwave sensor, and is suitable for multi-band, multi-payload on-orbit calibration and long-term performance monitoring tasks. Figure 1 As shown, it includes the following steps:

[0047] Step 1: Determine the orbital parameters of the satellite carrying the radiation reference.

[0048] To increase the calibration frequency, the orbit of the radiation reference source satellite can be selected to be the same type as that of the active microwave sensor satellite, with a suitable orbital altitude difference and similar orbital inclination, so that the two form a relative motion; and the azimuth and range beamwidths should be adjusted to ensure that the radiation reference source satellite is visible in the beam of the active microwave sensor; it is also necessary to determine the specific latitude and longitude range of the ground calibration processing stations that can be used in China so that the radiation reference source satellite can intersect with the calibration stations at a high frequency as much as possible.

[0049] Both the active microwave sensor and the reference source satellite can adopt a near-sun-synchronous orbit. The active microwave sensor satellite's orbital elements are set as follows: semi-major axis a = 7158.137 km (altitude ≈ 780 km), eccentricity e = 0.001, orbital inclination i = 98.62°, right ascension of ascending node Ω = 80.000°, perigee angle ω = 90.000°, true anomaly angle f = 0.000°. The radiation reference source satellite is in a forward-flying low-Earth orbit, with the following six elements: a = 6988.137 km (altitude ≈ 610 km), e = 0.001, i = 98.00°, Ω = 80.000°, ω = 90.000°, f = 20.000°. The ground calibration processing station can use the Ningxia Zhongwei calibration field (approximately 105°11′E, 37°51′N).

[0050] The simulation results of the ground-to-sky co-calibration method of this invention over a period of one month are as follows: Figure 2 , Figure 3 As shown. The simulation scenario spans from December 4, 2025 to January 4, 2026, a duration of one month. It can be seen that in the Earth-based simulation, the radiation reference source satellite and the Zhongwei calibration field intersect 9 times within the one-month simulation period, with an intersecting cycle of approximately once every 4 days and an average intersecting duration of 107.994 seconds. In the Sky-based simulation, the active microwave sensor satellite and the radiation reference source satellite intersect 14 times within the one-month simulation period, with an intersecting cycle of approximately twice every 4 days and an average intersecting duration of 51.234 seconds.

[0051] It is evident that the ground-to-space collaborative calibration method has a high frequency of intersection between the ground-to-space mode and the space-to-space mode, and the duration of a single intersection is long enough to achieve high-frequency and high-stability calibration of the target satellite-borne active microwave sensor.

[0052] Step 2: When the satellite antenna beam of the radiation reference source sweeps across the ground calibration processing station, it switches to ground-to-ground mode and actively transmits a pulse signal of a certain power.

[0053] Specifically, such as Figure 4As shown, the radiation reference source satellite mainly consists of a receiving link, a transmitting link, transceiver antennas, and an RFSoc processing board. The transceiver antennas are phased array antennas to achieve intelligent beamforming (DBF), which can suppress external signal interference and direct the main beam towards the ground target. The beam range and beam direction of the radiation reference source satellite are determined in advance. When the radiation reference source satellite beam passes the ground calibration station, it actively transmits pulse signals processed by intelligent beamforming (DBF) to the ground calibration station. The transmitted signal can be adjusted to multiple power and frequency values.

[0054] Step 3: Simultaneously measure and calibrate the main lobe gain and transmit / receive link gain of the satellite payload antenna of the radiation reference source using a ground calibration processing station.

[0055] Ground calibration stations use standard reflectors with known RCS values ​​to reflect pulses, or process the pulses with a standard transceiver before transmitting the echoes. Upon receiving the echo signals, the radiation reference satellite can simultaneously calibrate its transmit / receive link gain and the main lobe gain of its transmit / receive antenna based on standard radar equations. This allows for the recording of the transmit / receive link and main lobe gain values ​​of the radiation reference source at different frequency points, ready for use in the next sky-monitoring mode.

[0056] Specifically, the expression corresponding to the relational model is:

[0057]

[0058] In the formula, G receive G is the satellite receive link gain of the radiation reference source. transmit For transmit link gain, G cal P represents the gain of the transmit / receive antenna. rRF P represents the digital signal power emitted by the RFSoc terminal inside the radiation reference source satellite. tRF R is the digital signal power received at its end. cal σ is the distance between the radiating reference source antenna and the ground standard reflector or transceiver, λ is the wavelength of the transmitted signal, and σ is the distance between the antenna and the ground standard reflector or transceiver. ref The RCS value of the ground standard reflector or the fitted RCS value of the standard transceiver.

[0059] like Figure 5 As shown, the calculated value G of the radiation reference source satellite transceiver link and antenna total gain in the ground-based calibration mode is plotted. total and actual value G real With the reference source satellite RFSoc processor transmitter power P tRF The trend simulation graph shows the changes, where:

[0060]

[0061] And G totalIt also includes additive noise, atmospheric attenuation, and other error terms outside the reference source system. In the simulation settings, the reference source satellite's RFSoc processor transmits a C-band signal with a center frequency of 5.4 GHz. The distance between the radiating reference source satellite and the ground standard reflector is 650 km. The reference source satellite's transceiver antenna gain is 22 dBi, the transmit link gain is set to 45 dB, the receive link gain is set to 38 dB, the digital signal power range at the transmitting end is -10 to 5 dBm, the RCS value of the ground standard reflector is 40 dBsm, and the atmospheric loss of C-band electromagnetic waves is approximately 0.04 dB.

[0062] The results show that as P tRF As the value increases, G total With G real The values ​​all show a decreasing trend compared to the original setting value G. set The deviation increased, but the overall deviation remained within 0.25 dB.

[0063] like Figure 6 As shown, G is plotted under the same simulation settings as above. total With G real Error varies with P tRF Simulation graph showing the changing trend. It can be seen that as P... tRF As the value increases, G total With G real The error value first decreased from 0.2dB and then tended to a stable value of about 0.08dB.

[0064] Step 4: When the radiation reference source satellite passes through the beam of the onboard active microwave sensor, it switches to the sky-viewing mode to receive the pulse signal emitted by it.

[0065] When the radiation reference source satellite passes through the beam of the onboard active microwave sensor, the two can transmit and receive signals. When the distance between them meets the signal-to-noise ratio (SNR) condition, the radiation reference source satellite uses antenna smart beamforming (DBF) technology to align its antenna beam main lobe with the main lobe range of the onboard active microwave sensor and receive the pulse signals transmitted by it.

[0066] Step 5: The radiation reference source satellite quantitatively calculates the required echo signal power based on the gain value obtained from the calibration in the Earth observation mode.

[0067] After receiving the pulse signal from the active microwave sensor, the radiation reference source satellite calculates the power of the echo signal to be transmitted based on parameters such as the current RCS setting of the radiation reference source satellite, the main lobe antenna calibrated during the ground process, and the transmit / receive link gain. It then transmits the echo signal, which has also been processed by DBF, to ensure that the onboard active microwave sensor receives an accurate echo response.

[0068] Specifically, the expression corresponding to the relational model is:

[0069]

[0070] Among them, P 2RF P represents the digital signal power emitted by the RFSoc transmitter of the aforementioned radiation reference source satellite. 1RF For the RF direct sampling digital signal power at its receiving end, σ cal The RCS setting value for the radiation reference source satellite can be set between 0-40 dBsm as needed; λ represents the combined gain of the radiation reference source satellite transceiver link and transceiver antenna obtained from the calibration in the Earth-based model, where λ is the wavelength of the transmitted signal.

[0071] Step 6: The onboard active microwave sensor calibrates its own transmit / receive link gain based on the high-precision echo signal from the radiation reference source satellite.

[0072] After receiving the echo from the radiation reference satellite, the spaceborne active microwave sensor calculates its own current gain value for the transceiver link according to the standard radar equation, so as to calibrate the accuracy of its transmitted and received signals and complete the radiation characteristic calibration task.

[0073] Specifically, the expression corresponding to the relational model is:

[0074]

[0075] Among them, G tAMS G represents the gain value of the active microwave sensor transmit link. rAMS Given its receive link gain value, calculating both simultaneously yields the total fitted gain of the active microwave sensor's transceiver link; P rAMS P represents the signal power received by the internal processing module of the active microwave sensor. tAMS σ is the transmitting signal power; R is the distance between the active microwave sensor antenna and the radiation reference satellite antenna; G is the main lobe gain of the active microwave sensor transceiver antenna; λ is the wavelength of the transmitted signal; σ cal Set the RCS value for the radiation reference source satellite.

[0076] By adjusting the signal frequency to change the wavelength, the truth table of the transceiver link gain of the active microwave sensor in a multi-band range can be obtained, thereby enabling high-precision execution of subsequent tasks such as multi-band quantitative microwave remote sensing.

[0077] After the radiation characteristics of the spaceborne active microwave sensor are calibrated once in the sky mode, the reference source satellite can be set to different RCS values. The active microwave sensor then performs multiple RCS value calculations on the reference source satellite to back-infer the values. The calibration effect is measured by the average value, standard deviation and other statistical quantities of the calculated RCS values, as well as the error between the calculated RCS values ​​and the set values.

[0078] like Figure 7As shown, a simulation graph depicts the trend of different RCS values ​​of the reference source in the sky-viewing mode as a function of the transmit power of the active microwave sensor processing terminal. A C-band signal with a center frequency of 5.4 GHz was used, with the reference source RCS settings at 15 dBsm, 20 dBsm, and 25 dBsm. The transmit digital signal power range of the active microwave sensor processing terminal was -20 dBm to 10 dBm, and the distance between the sensor and the reference source satellite was set to 50 km.

[0079] It can be seen that with the RCS value remaining constant, as P... tAMS As the value increases, the error between the calculated RCS value and the set standard value decreases; P tAMS When the value is minimum, the back-reasoning error of the reference source with an RCS of 15 dBsm is relatively large, about 0.5 dB; the back-reasoning error of the reference source with an RCS of 25 dBsm is about 0.2 dBsm; P tAMS When the value is above -3dBm, the back-derived RCS value from the reference source is essentially equal to the set value. In P tAMS When the values ​​are the same, the larger the RCS setting value, the smaller the error between the calculated value and the setting value; P tAMS When the value is at its minimum, the RCS setting of 15dBsm differs from the reference source back-derived value of 25dBsm by approximately 0.3dB.

[0080] like Figure 8 The figure shows a simulation of the RCS calculation value of the reference source changing over time under the space-ground collaborative mode. The simulation duration is set to 60 days, and the time dimension needs to reflect the calibration cycles of the space and ground.

[0081] When the celestial period is set to 2 days and the terrestrial period is set to 4 days, it can be seen in the figure that the sampling period is once every 2 days, and the RCS calculation value will return to the vicinity of the standard value every 4 days, which means that the celestial calibration makes the celestial calibration result accurate.

[0082] In this simulation, the standard value of RCS was set to 20 dBsm. As can be seen from the figure, the average value of the calculated RCS over the 60-day simulation period was 20.008 dBsm, and the standard deviation was 0.076 dBsm. This indicates that the space-ground collaborative calibration method played a good calibration role in the radiation characteristics of the active microwave sensor over a long period of time, and can ensure the high-frequency and high-precision calibration of the spaceborne active microwave sensor.

[0083] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0084] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to any specific implementation. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for calibrating the radiation characteristics of a spaceborne active microwave sensor using a combined space-ground approach, characterized in that... By constructing a space-ground collaborative calibration system consisting of a radiation reference source satellite and a ground calibration processing station, the radiation reference source satellite can switch between "Earth-based mode" and "space-based mode" and transfer parameters to complete the following calibration process: S1. Determine the orbital parameters of the satellite carrying the radiation reference source; S2. When the beam of the radiation reference source satellite antenna sweeps across the ground calibration processing station, it switches to ground-to-ground mode and actively transmits pulse signals. S3. Simultaneously measure and calibrate the main lobe gain and transceiver link gain of the satellite payload antenna of the radiation reference source using a ground calibration processing station; S4. When the radiation reference source satellite passes through the beam of the onboard active microwave sensor, it switches to the sky-viewing mode to receive the pulse signals emitted by it. S5. The radiation reference source satellite quantitatively calculates the required echo signal power based on the gain value obtained from the calibration in the Earth observation model. S6. The active microwave sensor calibrates its own transmit / receive link gain based on the high-precision echo signal from the radiation reference source satellite.

2. The method for calibrating the radiation characteristics of a spaceborne active microwave sensor using a combined space-ground approach, as described in claim 1, is characterized in that... The spaceborne active microwave sensor includes a synthetic aperture radar (SAR), an altimeter, and a microwave scatterometer. The spaceborne active microwave sensor and the radiation reference source satellite have the same transmitting and receiving antennas, i.e., the transmitting and receiving antenna gains are the same, but the transmitting and receiving links are different, i.e., the transmitting and receiving link gains are different.

3. The method for calibrating the radiation characteristics of a spaceborne active microwave sensor using a combined space-ground approach, as described in claim 1, is characterized in that... The orbital altitude of the radiation reference source satellite is lower than that of the target active microwave sensor satellite. When setting it, a domestic ground calibration station with a clearly known latitude and longitude range is used as a reference target to ensure that the beam of the radiation reference source satellite can scan the ground calibration station at a high frequency during operation. At the same time, the radiation reference source satellite should pass through the beam range of the active microwave sensor satellite as many times and for as long as possible during operation, so that the active microwave sensor can use it to complete the radiation characteristic calibration.

4. The method for calibrating the radiation characteristics of a spaceborne active microwave sensor using a combined space-ground approach, as described in claim 1, is characterized in that... The radiation reference source satellite includes a receiving link, a transmitting link, a transceiver antenna, and an RFSoc processing board; The radio frequency signal received by the radiation reference source satellite receiving antenna is processed by the receiving link and converted into a direct radio frequency sampling digital signal at the RFSoc receiving end. The radio frequency digital signal transmitted by the RFSoc end is processed by the transmitting link and then transmitted from the transmitting antenna. When the radiation reference source satellite beam sweeps across the ground calibration station, it actively transmits pulse signals to the ground calibration station after being processed by antenna smart beamforming (DBF). This can suppress external signal interference, direct the main beam toward the ground target, and the transmitted signal can cover multiple frequency ranges, with the transmission power adjusted accordingly.

5. The method for calibrating the radiation characteristics of a spaceborne active microwave sensor using a combined space-ground approach, as described in claim 1, is characterized in that... The ground calibration processing station uses the radar cross-section (RCS) value to determine the reflected pulse of a known standard reflector, or processes the pulse using a standard transceiver before transmitting the echo. After receiving the echo signal, the radiation reference source satellite can uniformly calibrate its transceiver link gain and the main lobe gain of its transceiver antenna. The expression corresponding to the relationship model is: In the formula, G receive For the satellite receiver link gain of the radiation reference source, G transmit For transmit link gain, G cal P represents the gain of the transmit / receive antenna. rRF P represents the digital signal power transmitted from the RFSoc terminal inside the radiation reference source satellite. tRF R is the digital signal power received at its end. cal σ is the distance between the radiating reference source antenna and the ground standard reflector or transceiver, λ is the wavelength of the transmitted signal, and σ is the distance between the antenna and the ground standard reflector or transceiver. ref The RCS value of the ground standard reflector or the fitted RCS value of the standard transceiver.

6. The method for calibrating the radiation characteristics of a spaceborne active microwave sensor using a combined space-ground approach, as described in claim 1, is characterized in that... When the radiation reference source satellite passes through the beam of the active microwave sensor satellite, it uses antenna smart beamforming (DBF) to align its main lobe with the main lobe range of the onboard active microwave sensor and receive the pulse signals emitted by it. The signals emitted by the active microwave sensor can cover multiple frequency ranges, and the transmission power can be adjusted for each.

7. The method for calibrating the radiation characteristics of a spaceborne active microwave sensor using a combined space-ground approach, as described in claim 1, is characterized in that... After receiving the pulse signal from the onboard active microwave sensor, the radiation reference source satellite calculates the required echo signal power based on parameters such as the satellite's current RCS setting, the main lobe antenna calibrated during the Earth-to-ground process, and the transmit / receive link gain. It then transmits the echo signal, which has also undergone DBF processing, to ensure the onboard active microwave sensor receives an accurate echo response. The expression corresponding to the relationship model is: Among them, P 2RF P represents the digital signal power emitted by the RFSoc transmitter of the aforementioned radiation reference source satellite. 1RF For the RF direct sampling digital signal power at its receiving end, σ cal The RCS setting value for the radiation reference source satellite can be set between 0-40 dBsm as needed; λ represents the combined gain of the radiation reference source satellite transceiver link and transceiver antenna obtained from the calibration in the Earth-based model, where λ is the wavelength of the transmitted signal.

8. The method for calibrating the radiation characteristics of a spaceborne active microwave sensor using a combined space-ground approach, as described in claim 1, is characterized in that... After receiving the echo from the radiation reference source satellite, the active microwave sensor calculates its current transceiver link gain using standard radar equations to ensure the accuracy of its transmitted and received signals and complete the radiation characteristic calibration task. The expression corresponding to the relational model is as follows: Among them, G tAMS G represents the gain value of the active microwave sensor transmit link. rAMS Given its receive link gain value, calculating both simultaneously yields the total fitted gain of the active microwave sensor's transceiver link; P rAMS P represents the signal power received by the internal processing module of the active microwave sensor. tAMS σ is the transmitting signal power; R is the distance between the active microwave sensor antenna and the radiation reference satellite antenna; G is the main lobe gain of the active microwave sensor transceiver antenna; λ is the wavelength of the transmitted signal; σ cal Set the RCS value for the radiation reference source satellite.

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