A method for tracking and monitoring satellites by a ground-based microwave radiometer

Abstract

The application discloses a method for tracking and monitoring satellites by using a ground-based microwave radiometer, wherein the equivalent radiation power, orbit and orbit parameters of the satellites can be calculated by using the ground-based microwave radiometer to remotely sense the electromagnetic wave radiation intensity and direction of the satellites, and the tracking and monitoring of the satellite orbit and the electromagnetic wave power information can be realized without other professional and complex testing instruments and equipment, so that the method has the advantages of low requirement on the observation environment, easy realization, automatic tracking and observation, etc.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of passive microwave remote sensing detection, and particularly relates to a method for tracking and monitoring satellites by a ground-based microwave radiometer. BACKGROUND

[0002] Nowadays, satellites for various purposes are launched more and more frequently, and the main scientific purposes of satellite tracking technology include: (1) determining the fine structure of the earth's gravity field and the change of the long-wave gravity field with time; (2) precisely determining the magnetic field on a global scale; (3) detecting the global atmosphere and ionosphere. The implementation of this technology has made great contributions to the study of the earth's lithosphere, hydrosphere and atmosphere and their interactions in modern earth science, and has become the frontier and hotspot of current physical geodesy research.

[0003] The existing satellite communication mainly uses C and Ku bands, which do not coincide with the working frequency bands of the ground-based microwave radiometer. However, with the surge in demand, the existing satellite communication frequency band resources are already very crowded in use, and the satellite communication frequency band gradually develops from the low-frequency C and Ku bands to the high-frequency channel such as Ka. In this way, the satellite communication not only can obtain a wider working frequency band and increase the communication capacity, but also can realize a narrower beam and reduce the antenna size. The equivalent radiation power of the electromagnetic wave emitted by the satellite is several tens of dBW, and after the space transmission attenuation and the atmospheric transmission attenuation, the radiation brightness temperature reaching the ground can still reach several tens or even several hundred K.

[0004] However, the tracking and monitoring of satellites requires high requirements, and professional equipment is generally used to observe the satellite position and running track, and auxiliary equipment is used to monitor the satellite emission electromagnetic wave radiation intensity, etc. However, these devices have high requirements for the observation environment, and in rainy, snowy and foggy weather, the tracking and monitoring of satellites cannot be completed or accurately completed.

[0005] The ground-based multi-channel microwave radiometer is a passive atmospheric remote sensing detection device, which can observe the atmospheric microwave thermal radiation brightness temperature in real time and obtain high temporal and spatial resolution atmospheric temperature and humidity profiles and other parameters by inversion. It has the characteristics of high sensitivity, and can also be used to observe satellite emission electromagnetic wave signals.

[0006] In view of this, in order to solve the problems of multiple monitoring devices and high requirements for the monitoring environment, and to fully develop the microwave remote sensing observation potential of the ground-based microwave radiometer, it is necessary to study a method for tracking and monitoring satellites by a ground-based microwave radiometer. In addition, this method can also conduct in-depth analysis on the influence of satellites on the ground-based microwave radiometer observation network built by the China Meteorological Administration. SUMMARY

[0007] In view of the above problems, the application provides a method for tracking and monitoring satellites by a ground-based microwave radiometer, which does not need the assistance of other instruments and equipment, has low requirements on the observation environment and is easy to implement, and can realize automatic tracking observation.

[0008] The application is implemented by the following technical scheme, and provides a method for tracking and monitoring satellites by a ground-based microwave radiometer, comprising the following steps:

[0009] S1: a microwave radiometer turntable is controlled to enable an antenna to search a sky target, and a maximum radiation brightness temperature direction obtained is a satellite direction, the turntable is an azimuth turntable and an elevation turntable, and the brightness temperature is a brightness temperature of electromagnetic waves emitted by the satellite after space transmission attenuation and atmospheric attenuation and reaching the microwave radiometer antenna;

[0010] S2: S1 is repeated to search and observe a target position in real time, an observation azimuth and an elevation angle are recorded, tracking and monitoring of a satellite moving track are realized, a satellite orbit period and an orbit height are obtained through long-term observation;

[0011] S3: a satellite equivalent radiation power is calculated according to the brightness temperature observed by the microwave radiometer;

[0012] S4: a spatial position of the satellite, an included angle and a distance between an observation station and the satellite are calculated according to the satellite azimuth, the elevation and the height monitored, and a satellite subsatellite point track and orbit parameters are calculated through continuous observation.

[0013] In particular, S1 is implemented according to the following method:

[0014] S11: compared with atmospheric radiation, the satellite target has strong radiation characteristics, and therefore, the microwave radiometer antenna can be quickly searched to the satellite target in the sky by controlling the azimuth turntable and the elevation turntable to point the microwave radiometer antenna;

[0015] S12: after the strong radiation signal is observed, scanning (for example, -10°-10°) is performed around the direction to obtain a maximum radiation direction, and in order to eliminate pointing errors, the maximum value is obtained through fitting and the pointing errors are eliminated.

[0016] In particular, the brightness temperature observed by the microwave radiometer in S1 and S2 comprises a brightness temperature of electromagnetic waves emitted by the satellite after space transmission attenuation and atmospheric attenuation and reaching the antenna and an atmospheric radiation brightness temperature, and when the satellite is in a microwave radiometer antenna beam, the brightness temperature observed by the antenna is calculated according to the following formula:

[0017]

[0018] When the satellite is not in the microwave radiometer antenna beam, the brightness temperature of the observed sky is calculated as follows:

[0019]

[0020] The satellite emitted electromagnetic wave brightness temperature through atmospheric attenuation to the antenna received brightness temperature is obtained by subtracting formula (1) and formula (2), and after arrangement, the following formula is obtained:

[0021]

[0022] In formula (1)-(3), the is the antenna azimuth angle; θ is the elevation angle; T m is the average radiation brightness temperature of the atmosphere; T bg = 2.75K, is the cosmic background radiation; T s is the satellite emitted electromagnetic wave brightness temperature through space transmission attenuation to the antenna without atmospheric attenuation; T' sky is the atmospheric radiation brightness temperature received by the radiometer when only observing the atmosphere; ΔT' s is the brightness temperature received by the radiometer after the satellite attenuates through the atmosphere in the antenna beam; τ(θ) is the atmospheric attenuation of the direction pointed by the antenna, which is related to the atmospheric conditions, and in the case of clear sky or uniform atmospheric distribution, it is considered to be only related to the elevation angle, therefore the atmospheric attenuation τ(θ) of the direction pointed by the antenna is calculated as follows:

[0023]

[0024] In formula (4), the average radiation temperature T m of the atmosphere can be approximately replaced by the ground temperature, so the atmospheric attenuation calibration can be performed by observing the atmospheric radiation brightness temperature at the same elevation angle.

[0025] In particular, in S2, S1 is repeated, and the maximum radiation direction, i.e. the satellite motion trajectory, is continuously tracked and searched, the periodic change of the satellite trajectory is obtained through long-term tracking and monitoring, and the satellite operation period T is obtained, after obtaining the orbit period, according to Kepler's law, the satellite operation orbit height H is calculated as follows:

[0026]

[0027] In formula (5), R is the radius of the earth (about 6371km), μ is a constant, μ=3.986005×10 -14 m 3 / s 2 .

[0028] In particular, in S3, the satellite equivalent radiation power P EIRP is calculated as follows:

[0029] P EIRP = P r + L s + L r (6),

[0030] In formula (6), P r is the radiation power of the satellite transmitting electromagnetic wave to the antenna port surface, L r is the polarization attenuation, unit dBW, which is estimated by the maximum 3dB, L s is the free space transmission attenuation, unit dB, the radiation power P r of the satellite transmitting electromagnetic wave to the antenna port surface is calculated as follows:

[0031] P r = T s Bk (7),

[0032] In formula (7), k is the Boltzmann constant, k = 1.38 x 10 -23 J / K, B is the microwave radiometer operating bandwidth;

[0033] The free space transmission attenuation L s is calculated as follows:

[0034] L s = 32.45 + 20log 10 (f) + 20log 10 (r) (8),

[0035] In formula (8), f is the operating frequency, unit MHz, r is the signal transmission distance, unit km.

[0036] In particular, in the S4, the relationship between the elevation angle of the observation station and the spatial position of the satellite is shown in the following formula:

[0037]

[0038] In formula (9), θ is the elevation angle of the microwave radiometer observing the satellite, γ is the angle between the satellite subsatellite point and the observation station to the center of the earth;

[0039] The distance d between the satellite and the microwave radiometer observation station is calculated as follows:

[0040]

[0041] In the tetrahedron composed of the center of the earth, the observation point, the subsatellite point and the north pole (the south pole can be analogized), according to the relationship of the tetrahedron vertex angle, it is expressed as follows:

[0042]

[0043] In formula (11), ω is the latitude of the observation station, is the latitude of the subsatellite point, and δ is the azimuth of the observation station observing the satellite;

[0044] The spherical sine formula is as follows:

[0045]

[0046] In formula (12), ω m is the longitude of the observation station, ω s is the longitude of the subsatellite point, and formula (12) is transformed to calculate the subsatellite point longitude ω s of the satellite according to the following formula:

[0047]

[0048] The above is the process of estimating the satellite equivalent radiation power and the orbit spatial position of the satellite by using the ground-based microwave radiometer observation, and the satellite subsatellite point trajectory can be further obtained through continuous observation and calculation, and the maximum latitude that can be reached by the satellite is the satellite orbit inclination.

[0049] The application provides a method for tracking and monitoring a satellite by using a ground-based microwave radiometer, and has the following beneficial effects:

[0050] 1) The method does not need other precise instruments and equipment, and can realize observation on the satellite electromagnetic wave signal radiation intensity, spatial position and other parameters by using only the ground-based microwave radiometer, thereby reducing the complexity of observation and lowering the requirement on the environment;

[0051] 2) The method realizes tracking and observation on the satellite by using the microwave radiometer itself, adopts a pure passive observation technology, does not need to emit electromagnetic waves, the calculation process is simple, and the result is accurate and reliable;

[0052] 3) The method can be used for monitoring the change of the satellite radiation power and the orbit, and expands the application field of the microwave radiometer. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 FIG. 1 is a schematic diagram for observing a satellite by using a ground-based microwave radiometer;

[0054] Figure 2 FIG. 2 is the spatial relationship among the satellite, the earth and the observation station; in the figure, O represents the earth center, S represents the satellite, S0 represents the subsatellite point, M represents the observation point, R is the earth radius, H is the satellite height from the earth, θ is the microwave radiometer observation satellite elevation angle, γ is the angle between the subsatellite point and the observation station to the earth center, is the latitude of the observation station, is the latitude of the subsatellite point, and ω m is the longitude of the observation station, ωs δ represents the longitude of the nadir point, and δ represents the azimuth of the satellite observed by the observation station.

[0055] Figure 3 The results are from scanning observations of the satellite using a microwave radiometer.

Detailed Implementation Methods

[0056] In this invention, the sky scanning refers to the process of scanning the sky by automatically changing the elevation angle and azimuth of the microwave radiometer antenna through software. To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments.

[0057] Please see Figures 1-3 This invention provides a method for tracking and monitoring satellites using a ground-based microwave radiometer, comprising the following steps:

[0058] S1 controls the microwave radiometer turntable to perform a full-sky search, and the direction of maximum radiation obtained is the satellite direction. The turntable is an azimuth turntable and a pitch turntable. The brightness temperature observed by the microwave radiometer includes the brightness temperature of the electromagnetic waves emitted by the satellite reaching the antenna after space transmission attenuation and atmospheric attenuation, as well as the atmospheric radiation brightness temperature. When the satellite is within the microwave radiometer antenna beam, the brightness temperature observed by the antenna is expressed by the following formula:

[0059]

[0060] When the satellite is not within the microwave radiometer antenna beam, the brightness temperature of the observed sky is calculated using the following formula:

[0061]

[0062] The brightness temperature of the electromagnetic wave emitted by the satellite, after atmospheric attenuation, reaches the antenna and is received by the antenna. This is obtained by subtracting formula (1) and formula (2), and then rearranging to get the following formula:

[0063]

[0064] In formulas (1) to (3), the θ is the antenna azimuth angle; θ is the elevation angle; T m T is the average radiative brightness temperature of the atmosphere. bg =2.75K, which is the cosmic microwave background radiation; T s The brightness temperature of the electromagnetic waves transmitted by the satellite and attenuated during space transmission to the antenna under conditions of no atmospheric attenuation; T′ sky ΔT′ is the atmospheric radiation brightness temperature received by the radiometer when it only observes the atmosphere. sT(θ) is the atmospheric attenuation in the direction of the antenna, which is related to atmospheric conditions, and in the case of clear weather or uniform atmospheric distribution, it is considered to be related only to the elevation angle, so the atmospheric attenuation T(θ) in the direction of the antenna is calculated as follows:

[0065]

[0066] In formula (4), the average atmospheric radiation temperature T m The ground atmospheric temperature can be used as an approximation, so the atmospheric attenuation calibration can be performed by observing the atmospheric radiation brightness temperature at the same elevation angle.

[0067] S2 repeats S1, continuously tracking the maximum radiation direction, i.e., the satellite motion trajectory, and through long-term tracking and monitoring of the periodic changes of the satellite trajectory, the satellite operation period is obtained, and the orbit altitude of the satellite is calculated. According to Kepler's law, the satellite operation period and the orbit altitude have a specific relationship, so the orbit altitude of the satellite orbit is calculated as follows:

[0068]

[0069] In formula (5), T is the satellite period, R is the radius of the earth (about 6371 km), and μ is a constant, μ = 3.986005 x 10 -14 m 3 / s 2 .

[0070] S3 calculates the satellite equivalent radiation power according to the brightness temperature observed by the microwave radiometer, and the satellite equivalent radiation power P EIRP is calculated as follows:

[0071] P EIRP = P r + L s + L r (6),

[0072] In formula (6), P r is the radiation power of the satellite electromagnetic wave reaching the antenna port surface, L r is the polarization attenuation, unit dBW, and the polarization attenuation can be estimated to be a maximum of 3 dB, L s is the free space transmission attenuation, unit dB, and the radiation power of the satellite electromagnetic wave reaching the antenna port surface P r is calculated as follows:

[0073] P r = T s Bk (7),

[0074] In formula (7), k is the Boltzmann constant (1.38 x 10 -23 J / K), B is the microwave radiometer operating bandwidth;

[0075] The free space transmission attenuation L s is calculated as follows:

[0076] L s = 32.45 + 20log 10 (f) + 20log 10 (r) (8),

[0077] In formula (8), f is the operating frequency, in MHz, and r is the signal transmission distance, in km.

[0078] S4 calculates the spatial position of the satellite and the angle and distance between the observation station and the satellite according to the satellite azimuth, elevation and height obtained through monitoring, and calculates the satellite subsatellite point trajectory and orbit parameters through continuous observation.

[0079] In S4, according to Figure 2 It can be seen that the relationship between the observation station elevation angle and the spatial position of the satellite is shown in the following formula:

[0080]

[0081] In formula (9), θ is the elevation angle of the satellite observed by the microwave radiometer, γ is the angle between the subsatellite point and the observation station to the center of the earth, and the angle between the subsatellite point and the observation station to the center of the earth can be calculated when the satellite height is known.

[0082] The distance d between the satellite and the microwave radiometer observation station is calculated as follows:

[0083]

[0084] In the tetrahedron composed of the center of the earth, the observation point, the subsatellite point and the north pole (the south pole can be analogized), the relationship of the tetrahedron vertex angle is shown as follows:

[0085]

[0086] In formula (11), φ is the latitude of the observation station, is the latitude of the subsatellite point, and δ is the azimuth of the satellite observed by the observation station;

[0087] The spherical sine formula is as follows:

[0088]

[0089] In formula (12), ω m is the longitude of the observation station, ωs For the subsatellite point longitude, the satellite subsatellite point longitude ω can be calculated according to the following formula after the transformation of formula (12) s :

[0090]

[0091] The satellite subsatellite point trajectory can be further obtained through continuous observation calculation, and the maximum latitude that the satellite can reach is the orbit inclination of the satellite.

[0092] The following uses the MWP967KV type ground-based multi-channel microwave radiometer located in Chang'an District, Xi'an City (east longitude: 108.873°, north latitude: 34.159°) to carry out satellite tracking observation experiments. In this embodiment, the satellite target is scanned and tracked, and the data obtained by observation is calculated according to the above method. Through calculation, the satellite electromagnetic wave radiation brightness temperature is obtained, the satellite spatial position is recorded, and the satellite period, orbit height and other parameters are obtained through continuous tracking observation.

[0093] On October 22 and 23, 2022, the sky was scanned and observed using a microwave radiometer, and the observation frequency was 25 GHz. During the observation period, the satellite targets obtained by observation were continuously tracked and scanned, and it was found through two days of tracking observation that the target satellite had a period of 24 hours. According to this, it can be judged that the satellite is in geostationary orbit, and the orbit height is about 36000 km. Since the satellite is not stationary, it is an inclined geostationary satellite. The characteristic of this type of satellite is that the subsatellite point trajectory on the ground is an "8" shape, intersecting at a certain longitude on the equator, which is different from the stationary geostationary satellite which is stationary over the equator.

[0094] The following is to implement the method provided by the present application at one observation time point, and the calculation at other time points is the same. Figure 3 For the scanning result of the satellite at 12:20 on October 22, 2022, the observation azimuth is -80.1° (azimuth north is 0, east is positive), and the pitch angle is 86.73°, Figure 3 The original observation brightness temperature, the brightness temperature after deducting the atmospheric background radiation and the brightness temperature after atmospheric attenuation calibration are shown in FIG. 2, and the maximum value is in the direction of the center of the radiometer antenna, and the maximum brightness temperature is 418.5 K.

[0095] Using the above formula (6), the power received by the radiometer antenna is calculated to be -117.6 dBm with a bandwidth of 300 MHz of the microwave radiometer. Using the above formulas (7) and (8), the equivalent radiation power of the satellite is calculated to be about 66.9 dBW (96.9 dBm).

[0096] In this embodiment, the microwave radiometer observation elevation angle is 86.73°, which is brought into formula (9) to obtain the satellite subsatellite point and observation station angle to the center of the earth of 2.78° by iterative calculation; and then, formula (10) is combined to obtain the satellite and observation station distance of 36015km.

[0097] Then, the observation station latitude of 34.159°, the radiometer observation azimuth of 80.1°, the satellite subsatellite point and observation station angle to the center of the earth of 2.78° are brought into formula (11) to obtain the satellite subsatellite point latitude of 34.6°; next, the observation station longitude of 108.873°, the subsatellite point latitude of 34.6°, the radiometer observation azimuth of 80.1°, the satellite subsatellite point and observation station angle to the center of the earth of 2.78° are brought into formula (12) to obtain the satellite subsatellite point and longitude of 105.545°.

[0098] The satellite subsatellite point trajectory can be calculated by using the microwave radiometer for long time continuous observation and combining the above implementation process. The maximum latitude of the satellite can be obtained by continuous tracking observation, and the satellite orbit inclination, i.e. the maximum latitude that the satellite can reach, can be obtained for the satellite. In this test, the maximum latitude that the satellite reaches is 54.5 degrees, i.e. the orbit inclination of the satellite is 54.5°, by continuous observation and fitting to eliminate observation errors.

[0099] Through the above implementation process, it is proved that the microwave radiometer can realize the monitoring of the equivalent isotropically radiated power and the spatial position of the satellite, and the method is simple and effective, which expands the application field of the ground-based microwave radiometer.

Claims

1. A method of ground-based microwave radiometer tracking and monitoring of satellites, characterized in that, It comprises the following steps: S1 controls the microwave radiometer turntable to make the antenna scan the sky, and the maximum radiation brightness temperature direction obtained is the satellite direction, the turntable is an azimuth turntable and an elevation turntable, and the brightness temperature is the brightness temperature of electromagnetic waves emitted by the satellite after space transmission attenuation and atmospheric attenuation and reaching the microwave radiometer antenna; S2 repeats S1 to search for the observation target position in real time, records the observation azimuth and elevation angle, realizes tracking and monitoring of the satellite moving track, and obtains the satellite orbit period and orbit height through long-term observation; in S2, the satellite operation period T is obtained according to the periodic change of the track through long-term continuous observation, and the satellite orbit height H is calculated according to the Kepler law according to the following formula: In equation (5), R is the radius of the earth, μ is a constant, μ = 3.986005 x 10 -14 m 3 / s 2 ; S3 calculates the satellite equivalent isotropically radiated power from the brightness temperature observed by the microwave radiometer; in the S3, the satellite equivalent isotropically radiated power P EIRP is calculated by the following equation: P EIRP = P r + L s + L r (6), In equation (6), P r is the radiated power of the electromagnetic wave transmitted by the satellite to the antenna aperture, L r is the polarization attenuation, in dBW, estimated with a maximum of 3 dB, L s is the free space transmission attenuation, in dB, of the radiated power P r is calculated as follows: P r = T s Bk(7), In equation (7), k is the Boltzmann constant, k = 1.38 x 10 -23 J / K, B is the bandwidth of the microwave radiometer. The free space transmission attenuation L s is calculated as follows: L s = 32.45 + 20 log 10 (f) + 20 log 10 (r) (8), In formula (8), f is the working frequency, the unit is MHz, and r is the signal transmission distance, the unit is km; S4 calculates the spatial position of the satellite and the included angle and distance between the observation station and the satellite according to the satellite azimuth, elevation and height obtained through monitoring, and obtains the satellite subsatellite point track and orbit parameters through continuous observation; in S4, the spatial position relationship between the observation station elevation angle and the satellite is shown in the following formula: In formula (9), θ is the microwave radiometer observation satellite elevation angle, and γ is the satellite subsatellite point and observation station included angle to the earth center; The distance d between the satellite and the microwave radiometer observation station is calculated according to the following formula: In the tetrahedron composed of the earth center, the observation point, the subsatellite point and the north / south pole, the tetrahedron vertex angle relationship is shown as follows: In equation (11), φ is the latitude of the observation station, φ is the latitude of the observation station, δ is the azimuth of the observation station observing the satellite; The spherical sine formula is as follows: In equation (12), ω m is the longitude of the observation station, ω s is the subpoint longitude, and equation (12) can be transformed to calculate the subpoint longitude ω s of the satellite according to the following equation: Thus, the satellite subsatellite point track and orbit parameters can be obtained through continuous observation calculation.

2. The method of claim 1, wherein the ground-based microwave radiometer is a ground-based radiometer. S1 is implemented according to the following method: S11 controls the microwave radiometer antenna to point to the target in the sky through the azimuth turntable and the elevation turntable; S12 when a strong radiation signal is observed, fine scanning is performed around the direction to obtain the maximum radiation direction, and in order to eliminate the pointing error, the maximum value is obtained through fitting to eliminate the pointing error.

3. The method of claim 1, wherein the ground-based microwave radiometer is a ground-based radiometer. The brightness temperature observed by the microwave radiometer in S1 and S2 comprises the brightness temperature of electromagnetic waves emitted by the satellite after space transmission attenuation and atmospheric attenuation and reaching the antenna and the atmospheric radiation brightness temperature, when the satellite is in the microwave radiometer antenna beam, the antenna observed brightness temperature is calculated according to the following formula: When the satellite is not in the microwave radiometer antenna beam, the brightness temperature when observing the sky is calculated according to the following formula: The brightness temperature of the satellite emitted electromagnetic waves received by the antenna after atmospheric attenuation is obtained by subtracting formula (1) from formula (2), and after arrangement, the following formula is obtained: In the formulas (1) to (3), the is the azimuth angle of the antenna, θ is the elevation angle, T m is the average radiance temperature of the atmosphere, which is replaced by the ground atmospheric temperature, T bg = 2.75 K is the cosmic background radiation, T s is the radiance temperature of the electromagnetic wave emitted by the satellite after the space transmission attenuation, T' sky is the radiance temperature of the atmosphere received by the radiometer when only observing the atmosphere, ΔT' s is the radiance temperature received by the radiometer after the satellite is attenuated by the atmosphere within the antenna beam, τ(θ) is the atmospheric attenuation in the direction pointed by the antenna, and in the case of clear weather or uniform atmospheric distribution, τ(θ) is calculated according to the following formula:

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