CN115372964B - Double-frequency multi-scale earth surface deformation measurement test system - Google Patents
Double-frequency multi-scale earth surface deformation measurement test system Download PDFInfo
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/885—Radar or analogous systems specially adapted for specific applications for ground probing
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/16—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
- G01S13/9021—SAR image post-processing techniques
- G01S13/9023—SAR image post-processing techniques combined with interferometric techniques
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
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Abstract
The invention discloses a double-frequency multi-scale earth surface deformation measurement test system, and belongs to the technical field of radar interferometry. The invention comprises two sets of X-band polarized antennas, two sets of L-band polarized antennas, two sets of X-band front end receiving equipment, two sets of L-band front end receiving equipment, two sets of transmitting equipment, two sets of calibration equipment, one set of integrated control single machine, two sets of wave control units, two sets of servo mechanisms, two sets of inertial navigation equipment and one set of recording equipment; the two sets of X-band polarized antennas transmit and receive polarized signals of X bands, and the polarized signals are respectively arranged on the left side and the right side of the antenna frame to form X-band cross-track interference baselines; the two sets of L-band polarized antennas transmit and receive L-band polarized signals which are respectively arranged on the left side and the right side of the antenna frame to form an L-band cross-track interference baseline. The invention can realize the recording of the full polarization data of the X wave band and the L wave band in the same time and the same irradiation area through single navigation, and has the advantages of low development cost, easy realization, complex and various functions and high data precision.
Description
Technical Field
The invention belongs to the technical field of radar interferometry, and particularly relates to a dual-frequency multi-scale earth surface deformation measurement test system.
Background
Compared with the traditional optical detection means, the Synthetic Aperture Radar (SAR) has the advantages of all-weather, strong penetrability and no influence of weather such as cloud, rain, haze and the like, thereby being widely applied to the fields of agriculture, hydrology, geology, surveying and mapping, disaster reduction and prevention and military affairs. The interference SAR acquires elevation data by using an antenna baseline and through the phase difference of two SAR images in the same area, and meanwhile, the polarized SAR can provide richer target scattering information, so that the polarized interference SAR technology is greatly popularized in the fields of topographic mapping and surface deformation measurement.
According to the antenna installation position, the working mode and the like, the interference SAR is divided into three modes of single-antenna heavy-rail measurement, formation single-rail measurement and single-rail double-antenna measurement, the former two modes are mainly applied to a satellite-borne platform, and the third mode is mainly applied to an airborne platform.
A typical foreign single-antenna heavy-orbit measurement satellite platform comprises an ERS-2 in Europe, a JERS-1 in Japan, a Sentinel-1A in the European and air Bureau and the like, but the system has the characteristic of long revisit period and cannot give elevation and deformation information of the earth surface in real time.
Typical formation single-track measurement satellite platforms include a German Tan DEM-X/Terra SAR-X double-star system, a Chinese sky drawing No. two and the like, the system can adjust the length of a base line in real time, flexibly coordinate relative running states among constellations and the like, but also have the problems of high-precision measurement of the base line, high-precision synchronization among the constellations, high-precision control of formation and the like.
A typical single-track double-antenna measurement platform comprises a radar terrain surveying and mapping task (SRTM) of a space shuttle in the United states, terrain data of low-latitude areas in the world are successfully acquired by using an SIR-C/X-SAR imaging radar carried on the space shuttle, the absolute elevation precision of Digital Elevation Model (DEM) data reaches 16 m and the relative elevation precision reaches 6 m through post-processing, but an X-band antenna of the system can only work in a single polarization mode and is not beneficial to comparison of polarization data of two bands; meanwhile, the method can only work in a main sending and double receiving mode, and mutual verification of measurement results in various baseline modes cannot be realized. In addition, because the space shuttle is taken as a carrying platform and the development time is earlier, the measuring platform also has the problems of long development period, high development cost, low measurement precision and the like.
In a word, the polarimetric interference SAR system of satellite-borne platform is wide in surveying and mapping range, the platform is less influenced by external environment, data processing is simpler, but compared with an airborne platform, the polarimetric interference SAR system has the defects of long revisit period, low data resolution, fixed track and the like. The airborne platform can just make up the defects, has good maneuverability and enables the mapping place to be flexible and selectable; meanwhile, the method also has the advantages of low development cost and easy operation and realization. The advantages enable the airborne polarization interference SAR system to have wide application prospect in rapid earth surface deformation monitoring or earth surface deformation monitoring with high precision requirement. However, the single-track double-antenna measuring platform mounted on the aerospace plane has the problems that the X-band antenna can only work in a single polarization mode and can only work in a main transmitting and receiving mode, the development period is long, the cost is high and the like. Therefore, there is an urgent need to develop a single-track dual-antenna interferometric measuring platform that can simultaneously implement dual-band, full polarization, multiple base lines, low cost and short development cycle.
Disclosure of Invention
The invention aims to provide a dual-frequency multi-scale ground surface deformation measurement test system, which utilizes a dual-waveband antenna carried on a common airplane to transmit a full-polarization signal in a multi-baseline working mode, can realize full-polarization data recording of the same X and L wavebands in the same time and in the same irradiation area under single navigation, effectively ensures the consistency of data, provides effective data support for multi-scale ground surface deformation measurement, and has the advantages of low development cost, easy realization, complex and various functions and high data precision.
Specifically, the invention provides a dual-frequency multi-scale earth surface deformation measurement test system, which comprises:
the system comprises two sets of X-band polarized antennas, two sets of L-band polarized antennas, two sets of X-band front-end receiving equipment, two sets of L-band front-end receiving equipment, two sets of transmitting equipment, two sets of calibration equipment, one set of integrated control single machine, two sets of wave control units, two sets of servo mechanisms, two sets of inertial navigation equipment and one set of recording equipment;
the two sets of X-band polarized antennas are used for transmitting and receiving polarized signals of X bands, comprise Xa antennas and Xb antennas and are respectively arranged on the left side and the right side of the antenna frame to form X-band cross-track interference baselines;
the two sets of L-band polarized antennas transmit and receive L-band polarized signals, comprise La antennas and Lb antennas, and are respectively arranged on the left side and the right side of the antenna frame to form L-band cross-track interference baselines;
the X-band front-end receiving device receives an echo signal transmitted from the X-band polarized antenna, performs down-conversion, filtering amplification and digital sampling processing on the echo signal, and transmits a processing result to the recording device for storage;
the L-band front-end receiving device receives an echo signal transmitted from the L-band polarized antenna, performs down-conversion, filtering amplification and digital sampling on the echo signal, and transmits a processing result to the recording device for storage;
the transmitting equipment is used for transmitting the reference signal to an X-band polarized antenna or an L-band polarized antenna corresponding to a required corresponding X-band or L-band after frequency doubling of the reference signal, and radiating the reference signal to a specific direction through the X-band polarized antenna or the L-band polarized antenna corresponding to the band;
the calibration equipment is used for testing and correcting the reference, receiving and transmitting links of the X wave band or the L wave band;
the comprehensive control single machine is used for parameter calculation, mode control and timing sequence generation of the whole system;
the wave control unit is used for controlling the scanning of the azimuth beam of the corresponding wave band antenna;
the servo mechanism is used for controlling the distance of the corresponding wave band antenna to scan the wave beam;
the inertial navigation equipment is used for recording position, speed and angle information of an airborne platform and further transmitting the information to the integrated control single machine, so that the directional correction of corresponding wave band antenna beams is realized, and the motion compensation is performed when the inversion processing is performed on data recorded in a dual-frequency multi-scale earth surface deformation measurement test.
Further, the lengths of the X-wave band cross-track interference baseline and the L-wave band cross-track interference baseline are the same.
Furthermore, the comprehensive control single machine calibrates the state of the whole system transmission link through three calibration modes by controlling the calibration equipment, wherein the three calibration modes comprise a reference calibration mode, a receiving calibration mode and a transmitting calibration mode;
in the reference calibration mode, the transmitting equipment outputs an excitation signal to the calibration equipment from the calibration port, the front-end receiving equipment receives the calibration signal of the calibration equipment by adopting the calibration port, and all components in the antenna work in a load state at the moment, so that the amplitude-phase characteristic measurement of the calibration equipment and the front-end receiving equipment is completed;
in the receiving calibration mode, the transmitting equipment outputs an excitation signal to the calibration equipment from a calibration port and outputs the excitation signal to the corresponding wave band antenna through a calibration link, the front-end receiving equipment receives the calibration signal from the corresponding wave band antenna by adopting a receiving port, and all components in the antenna work in a receiving state, so that the amplitude-phase characteristic measurement of the receiving link of the antenna in different working states is completed;
in the transmission calibration mode, the transmitting equipment outputs an excitation signal to the corresponding waveband antenna from the transmitting port, then transmits the signal to the calibration equipment through the calibration link, the front-end receiving equipment receives the calibration signal of the calibration equipment by adopting the calibration port, and all components in the antenna work in a transmitting state at the moment, so that the amplitude-phase characteristic measurement of the transmitting link of the antenna in different working states is completed.
Further, the calibration device comprises an X-band calibration device and an L-band calibration device, wherein the X-band calibration device is responsible for calibrating the Xa antenna and the Xb antenna, and the L-band calibration device is responsible for calibrating the La antenna and the Lb antenna; and the X-band calibration equipment and the L-band calibration equipment work simultaneously, and the X-band calibration equipment or the L-band calibration equipment performs time-sharing calibration on two antennas in the same band.
Further, the comprehensive control single machine sends different working timing sequences to the two sets of wave control units, so that an H polarization and V polarization alternate working mode of the dual-frequency multi-scale earth surface deformation measurement test system is realized;
the comprehensive control single machine controls the X-band polarized antenna and the L-band polarized antenna to realize two virtual baseline working modes including a single baseline mode and a double baseline mode by sending different mode words; in the single-baseline mode, only the antenna on the left side or the right side of the antenna frame works during transmitting, and the antennas on the left side and the right side of the antenna frame work during receiving; in the double-baseline mode, the antennas on the left and right sides of the antenna frame alternately work during transmission, and the antennas on the left and right sides of the antenna frame both work during reception.
Furthermore, in the single baseline mode, two pulses in a timing sequence are a period, in the first pulse, an Xa antenna and a La antenna transmit signals in an H polarization mode simultaneously, the Xa antenna and an Xb antenna receive signals in an H polarization mode simultaneously, and the La antenna and the Lb antenna receive signals in an H polarization mode simultaneously; in the second pulse, an Xa antenna and a La antenna simultaneously transmit signals in a V polarization mode, an Xa antenna and an Xb antenna simultaneously receive signals in a V polarization mode, and an La antenna and an Lb antenna simultaneously receive signals in a V polarization mode.
Further, in the dual baseline mode, four pulses in a timing sequence are a period, in the first pulse, an Xa antenna and a La antenna transmit signals in an H polarization mode simultaneously, the Xa antenna and an Xb antenna receive signals in an H polarization mode simultaneously, and the La antenna and the Lb antenna receive signals in an H polarization mode simultaneously; in the second pulse, xb antenna and Lb antenna transmit signals in H polarization mode at the same time, xa antenna and Xb antenna receive signals in H polarization mode at the same time, la antenna and Lb antenna receive signals in H polarization mode at the same time; in the third pulse, an Xa antenna and a La antenna simultaneously transmit signals in a V polarization mode, the Xa antenna and the Xb antenna simultaneously receive signals in the V polarization mode, and the La antenna and the Lb antenna simultaneously receive signals in the V polarization mode; in the fourth pulse, xb antenna and Lb antenna transmit signals in V polarization mode at the same time, xa antenna and Xb antenna receive signals in V polarization mode at the same time, and La antenna and Lb antenna receive signals in V polarization mode at the same time.
Furthermore, the dual-frequency multi-scale ground surface deformation measurement test system screens out effective voyages of which the average distance difference and the course parallelism are within a preset threshold value through the limiting conditions of the distance difference and the course parallelism, and when the number of the effective voyages is accumulated to a specified number, the test requirement is met, and the recording of measurement test data is completed; the limiting conditions of the distance difference and the course parallelism comprise:
when the average distance difference of a certain navigated track is larger than a preset value or the parallel degree of the flight path is larger than a preset angle, judging that the navigation is invalid, otherwise, judging that the navigation is valid.
Furthermore, the dual-frequency multi-scale ground surface deformation measurement test system also comprises two deformation angle reversers, and the positions of the two deformation angle reversers on the ground are adjusted along the vertical direction of the sailing route before each sailing so as to simulate ground surface deformation; one deformation angle moves a first movement amount every time to simulate the micro deformation of the earth surface; the other deformation angle is moved by a second movement amount each time to simulate large-scale deformation of the earth surface.
Further, according to the limitation of the emission pulse and the subsatellite point echo of the dual-frequency multi-scale ground surface deformation measurement test system on the shielding of the received echo, selecting the pulse repetition frequency and the lower visual angle which meet the requirements; setting the signal bandwidth of the system according to the distance of the dual-frequency multi-scale earth surface deformation measurement test system to the resolution; setting the signal sampling rate of the system according to the oversampling rate of the dual-frequency multi-scale earth surface deformation measurement test system;
the limiting condition of the transmitting pulse to the shielding of the received echo is shown in a formula 1-3, the limiting condition of the point echo under the satellite to the shielding of the received echo is shown in a formula 4, the method for calculating the signal bandwidth through the distance direction resolution is shown in a formula 5, and the method for calculating the signal sampling rate of the system through the oversampling rate of the system is shown in a formula 6;
in formula 1, rmax is the slant distance of the far point of the observation region, rmin is the slant distance of the near point of the observation region, c is the speed of light, m is the serial number of the transmitted pulse, PRF is the pulse repetition frequency, tp is the pulse width of the transmitted signal, and T is the protection time of the receiver, which is generally a fraction of the pulse width of the transmitted signal;
in the formula 2 and the formula 3, H is the height of the airborne platform, theta is the beam width, and beta is the downward viewing angle;
in equation 4, H is the height of the airborne platformDegree, c is the speed of light, T p For the pulse width of the transmitted signal, k is the sequence number of the echo of the subsatellite point, PRF is the pulse repetition frequency, R max Is the slope distance of the far point of the observation area, R min The slope distance of a near point of an observation area is shown, and T is the protection time of the receiver;
in equation 5,. Rho r The distance resolution of the system is shown, c is the speed of light, and B is the signal bandwidth;
in equation 6, f s Is the signal sampling rate of the system, alpha r B is the over-sampling rate of the system and B is the signal bandwidth.
The dual-frequency multi-scale ground surface deformation measurement test system has the following beneficial effects:
according to the double-frequency multi-scale ground surface deformation measurement test system, the airborne platform is carried, so that the revisit period of a target area is greatly shortened; and the system has fixed base line length, and does not have the problem of processing precision caused by base line measurement errors.
According to the dual-frequency multi-scale earth surface deformation measurement test system, the two wave bands share the integrated control single machine, the servo mechanism, the wave control unit, the inertial navigation equipment and the like, the work of the dual-frequency polarization interference SAR system is realized on the basis of not additionally increasing hardware equipment, the equipment quantity of the system is greatly reduced, the development period is shortened, and the development cost is reduced.
The double-frequency multi-scale earth surface deformation measurement test system realizes H polarization and V polarization working modes of the system by comprehensively controlling a single machine to send different timing sequences, and is convenient for recording and comparing polarization data.
According to the dual-frequency multi-scale earth surface deformation measurement test system, different mode words are sent by the integrated control single machine, so that two virtual baseline working modes of the antenna can be realized, the admission of multi-baseline interference data is facilitated, and the measurement precision is improved.
The dual-frequency multi-scale earth surface deformation measurement test system uniformly controls the servo mechanism and the wave control unit, can realize irradiation of left and right side antennas to the same area and logging of dual-frequency polarization interference SAR data for verifying earth surface deformation measurement, is convenient for comparison and mutual check of the dual-frequency polarization interference SAR data when inversion processing is carried out on the logged data subsequently, and greatly improves the accuracy of earth surface deformation measurement.
The dual-frequency multi-scale surface deformation measurement test system has the advantages of low development cost, easiness in operation and realization, complex and various realization functions, high data precision and the like.
Drawings
FIG. 1 is a design flow diagram of an embodiment of the present invention.
FIG. 2 is a schematic composition diagram of an embodiment of the present invention.
Fig. 3 is a schematic view of an antenna installation according to an embodiment of the present invention.
Fig. 4 is a schematic diagram of three scaling mode signal flows according to an embodiment of the present invention.
Fig. 5 is a scaled timing diagram of an embodiment of the invention.
Fig. 6 is a timing diagram of the operation of the system of an embodiment of the present invention.
Fig. 7 is a timing diagram for single baseline operation of an embodiment of the present invention.
Fig. 8 is a timing diagram for dual baseline operation of an embodiment of the present invention.
FIG. 9 is a schematic diagram of relative positions between flights according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following examples and the accompanying drawings.
Example 1:
one embodiment of the present invention is a dual-frequency multi-scale surface deformation measurement testing system (hereinafter referred to as system), and the design flow thereof is shown in fig. 1. Firstly, determining the composition of radar equipment, then determining radar parameters of a system, a calibration scheme, a working timing sequence and an onboard aviation line real-time monitoring scheme, and then determining test corollary equipment (such as deformation angle reversal) related to deformation measurement. After the design of the dual-frequency multi-scale surface deformation measurement test system is finished, the system is used for developing experiments and recording relevant data of the experiments and measuring and calculating the surface deformation quantity.
Determining radar device composition and antenna mounting location
As shown in fig. 2, the dual-frequency multi-scale ground surface deformation measurement test system of this embodiment includes two sets of X-band polarized antennas (Xa antenna and Xb antenna), two sets of L-band polarized antennas (La antenna and Lb antenna), two sets of X-band front end receiving devices (Xa front end receiving device and Xb front end receiving device), two sets of L-band front end receiving devices (La front end receiving device and Lb front end receiving device), two sets of transmitting devices (X-band transmitting device and L-band transmitting device), two sets of calibration devices (X-band calibration device and L-band calibration device), one set of integrated control unit, two sets of wave control units, two sets of servomechanisms, two sets of inertial navigation devices, and one set of recording device.
The two sets of X-band polarized antennas are used for transmitting and receiving X-band polarized signals and comprise Xa antennas and Xb antennas which are respectively arranged on the left side and the right side of an antenna frame, and a certain distance exists in a space position to form an X-band cross-track interference baseline. The two sets of L-band polarized antennas are used for transmitting and receiving L-band polarized signals, comprise La antennas and Lb antennas, and are also respectively arranged on the left side and the right side of the antenna frame, and a certain distance exists in a spatial position to form an L-band cross-track interference baseline.
Preferably, in another embodiment, the lengths of the X-band cross-track interference baseline and the L-band cross-track interference baseline are the same, for example, 3.25 m. The length of the X-wave band cross-track interference baseline is the same as that of the L-wave band cross-track interference baseline, so that the comparison and mutual check of the X-wave band measurement result and the L-wave band measurement result are facilitated, and the measurement precision is higher.
And the transmitting equipment is used for transmitting the signals to an X-band polarized antenna or an L-band polarized antenna corresponding to the waveband through a radio frequency cable after frequency doubling of the reference signals to the required corresponding X-band or L-band, and radiating the signals to a specific direction through the X-band polarized antenna or the L-band polarized antenna corresponding to the waveband. Meanwhile, the antennas (Xa antenna, xb antenna, la antenna and Lb antenna) receive echoes reflected by the ground, and echo signals are transmitted to corresponding front-end receiving equipment through radio frequency cables. The X-band front-end receiving device is used for receiving an echo signal transmitted from the X-band polarized antenna, carrying out down-conversion, filtering amplification and digital sampling processing on the echo signal, and transmitting a processing result to the recording device for storage; and the L-band front-end receiving device is used for receiving the echo signal transmitted from the L-band polarized antenna, performing down-conversion, filtering amplification and digital sampling on the echo signal, and transmitting a processing result to the recording device for storage.
The calibration equipment is used for testing and correcting the X-band or L-band reference, receiving and transmitting links; the integrated control single machine is used for parameter calculation, mode control and timing sequence generation of the whole system; the wave control unit is used for controlling the scanning of the azimuth beam of the corresponding wave band antenna; the servo mechanism is used for controlling the scanning of the distance of the corresponding wave band antenna to the wave beam; and the inertial navigation equipment is used for recording the position, speed and angle information of the airborne platform and further transmitting the information to the integrated control single machine, so that the directional correction of corresponding wave band antenna beams is realized, and the motion compensation is performed when the inversion processing is performed on the data recorded in the dual-frequency multi-scale ground surface deformation measurement test.
Determining radar parameters of a system
Selecting a Pulse Repetition Frequency (PRF) and a lower visual angle which meet the requirements according to the limitation of the transmitting pulse and the subsatellite point echo of the system on the shielding of the received echo; setting the signal bandwidth of the system to the resolution ratio according to the distance of the system; and setting working parameters such as the signal sampling rate of the system according to the oversampling rate of the system.
Preferably, in another embodiment, the limitation condition of the transmitting pulse to the receiving echo shielding is shown in formula 1-3, and the limitation condition of the point-under-satellite echo to the receiving echo shielding is shown in formula 4, wherein the pulse repetition frequency PRF and the lower viewing angle beta meeting the limitation condition are selected. Range-wise resolution ρ through the system r The signal bandwidth B is calculated, see equation 5. Over-sampling ratio alpha through the system r Calculating the signal sampling rate f of the system s See equation 6.
In formula 1, rmax is the slant distance of the far point of the observation region, rmin is the slant distance of the near point of the observation region, c is the speed of light, m is the serial number of the transmitted pulse, PRF is the pulse repetition frequency, tp is the pulse width of the transmitted signal, and T is the receiver protection time, which is generally a fraction of the pulse width of the transmitted signal.
In formula 2 and formula 3, H is the height of the airborne platform, θ is the beam width, and β is the down-angle.
In equation 4, H is the height of the airborne platform, c is the speed of light, T p For the pulse width of the transmitted signal, k is the sequence number of the echo of the subsatellite point, PRF is the pulse repetition frequency, R max Is the slope distance of the far point of the observation area, R min The slope distance of the near point of the observation area is T, and the protection time of the receiver is T.
In equation 5,. Rho r For the range-wise resolution of the system, c is the speed of light and B is the signal bandwidth.
In equation 6, f s Is the signal sampling rate of the system, alpha r B is the over-sampling rate of the system and B is the signal bandwidth.
For example, the height of the airborne platform is H =5000 m, the flying speed is 110 m/s, and the pulse width of the transmitted signal is T p =10×10 -6 s, receiver guard time T =1 × 10 -6 s, the target area is set at a vertical height of 5000 m from the flight path, the downward viewing angle of the system is 45 degrees at this time, the serial number m of the transmitted pulse and the serial number k of the echo of the off-satellite point are both set to be 0, and it can be known from the above limiting conditions that the transmitted pulse and the off-satellite point cannot be shielded when the PRF =2000 Hz. In addition, the system requires a range resolution ρ r =0.5 m, and the signal bandwidth B =400 MHz is taken in consideration of the loss and error of the system. Setting the oversampling ratio alpha of the desired system r Not less than 1.25, and the sampling rate f can be selected to facilitate the design of front-end receiving equipment s =600 MHz。
Determining a scaling scheme for a system
Based on the correction of the transmission link of the dual-frequency multi-scale earth surface deformation measurement test system, the dual-frequency multi-scale earth surface deformation measurement test system has a high-precision internal calibration function, and the states of the transmission link of the whole system are calibrated through three calibration modes, including a reference calibration mode, a receiving calibration mode and a transmitting calibration mode. The specific flow of signals in each scaling mode is shown in fig. 4.
In the reference calibration mode, the transmitting device outputs the excitation signal to the calibration device from the calibration port, and the front-end receiving device also receives the calibration signal of the calibration device by using the calibration port, and all components in the antenna work in a load state at the moment, so that the amplitude-phase characteristic measurement of the calibration device and the front-end receiving device is completed.
In the receiving calibration mode, the transmitting equipment outputs an excitation signal to the calibration equipment from a calibration port and outputs the excitation signal to the antenna through a calibration link, the front-end receiving equipment receives the calibration signal from the antenna by adopting a receiving port, and all components in the antenna work in a receiving state, so that the amplitude-phase characteristic measurement of the receiving link of the antenna in different working states is completed.
In the transmitting scaling mode, the transmitting equipment outputs an excitation signal to the antenna from the transmitting port, then the signal is transmitted to the scaling equipment through the scaling link, the front-end receiving equipment receives the scaling signal of the scaling equipment by adopting the scaling port, and all components in the antenna work in a transmitting state at the moment, so that the amplitude-phase characteristic measurement of the transmitting link of the antenna in different working states is completed.
In the three calibration modes, the magnitude of the signal amplitude is realized by controlling the attenuation module in the calibration equipment through the comprehensive control single machine. The dual-frequency multi-scale earth surface deformation measurement test system can eliminate the influence of the whole transmission link on signals by the signal cancellation of the reference link, the receiving link and the transmitting link.
Preferably, in another embodiment, based on the consideration of saving system equipment amount and development cost, a scheme that the antennas in the same wave band share the scaling equipment is adopted; and simultaneously, in order to prevent cross aliasing of calibration signals, a time sequence that calibration equipment of two wave bands works simultaneously and a single calibration equipment performs time-sharing calibration on two antennas of the same wave band is adopted.
Specifically, the calibration task of four sets of antennas is completed by using two calibration devices, wherein the calibration devices include an X-band calibration device and an L-band calibration device, the X-band calibration device is responsible for calibration of the Xa antenna and the Xb antenna, and the L-band calibration device is responsible for calibration of the La antenna and the Lb antenna. Meanwhile, in order to ensure the independence of the calibration signals of all the antennas, the timing sequence that two calibration devices work simultaneously and a single calibration device performs time-sharing calibration on two antennas in the same wave band is adopted. The specific scaling timing is shown in fig. 5, that is, xa and La simultaneously operate in the reference scaling mode within the pulse 1 time, xb and Lb are in a load state; in the pulse 2 time, xa and Lb work in the reference scaling mode simultaneously, xa and La are in the load state, and so on, and every 6 pulses are a scaling period. In the working process of the system, the calibration is carried out once at intervals, and the specific time can be set by the integrated control single machine.
Determining timing of system operation
As shown in fig. 6, in order to ensure that the echo signals of two bands do not interfere with each other, the single integrated control unit controls the timing sequence in a unified manner, and strictly ensures that the signals of two bands are transmitted simultaneously, and the reception is performed according to the time corresponding to the respective gates, thereby avoiding the phenomenon that the transmitting window of a certain band overlaps with the receiving window of another band.
In order to acquire various polarization data, the integrated control single machine uniformly controls and sends different timing sequences, so that an H polarization and V polarization alternate working mode of the system is realized, and the recording and the comparison of the polarization data are facilitated.
In order to improve the precision of data processing, the integrated control single machine controls the antenna to realize two virtual baseline working modes including a single baseline mode and a double baseline mode by sending different mode words, thereby being convenient for the recording of multi-baseline interference data and improving the measurement precision.
As shown in fig. 7, in the single-baseline mode, only the antennas located on the left or right side of the antenna frame operate during transmission, and the antennas located on the left and right sides of the antenna frame operate during reception. The method comprises the following specific steps: two pulses in the timing sequence are a period, in the first pulse, an Xa antenna and a La antenna simultaneously transmit signals in an H polarization mode, the Xa antenna and the Xb antenna simultaneously receive the signals in the H polarization mode, and the La antenna and the Lb antenna simultaneously receive the signals in the H polarization mode; in the second pulse, an Xa antenna and a La antenna transmit signals in a V polarization mode at the same time, the Xa antenna and the Xb antenna receive signals in the V polarization mode at the same time, and the La antenna and the Lb antenna receive signals in the V polarization mode at the same time.
As shown in fig. 8, in the dual-baseline mode, the antennas located on the left and right sides of the antenna frame alternately operate during transmission, and both the antennas located on the left and right sides of the antenna frame operate during reception. The method comprises the following specific steps: in the timing sequence, four pulses are a period, in the first pulse, an Xa antenna and a La antenna transmit signals in an H polarization mode at the same time, the Xa antenna and the Xb antenna receive the signals in the H polarization mode at the same time, and the La antenna and the Lb antenna receive the signals in the H polarization mode at the same time; in the second pulse, xb antenna and Lb antenna transmit signals in H polarization mode at the same time, xa antenna and Xb antenna receive signals in H polarization mode at the same time, la antenna and Lb antenna receive signals in H polarization mode at the same time; in the third pulse, an Xa antenna and a La antenna transmit signals in a V polarization mode at the same time, the Xa antenna and the Xb antenna receive signals in the V polarization mode at the same time, and the La antenna and the Lb antenna receive signals in the V polarization mode at the same time; in the fourth pulse, xb antenna and Lb antenna transmit signals in V polarization mode at the same time, xa antenna and Xb antenna receive signals in V polarization mode at the same time, and La antenna and Lb antenna receive signals in V polarization mode at the same time.
Scheme for determining real-time monitoring of on-board airline
In the test process, due to the wind speed of the airborne platform, the operation of flight personnel and the like, a certain deviation (namely, the deviation of navigation) exists between the actual navigation track and the preset navigation line, and the deviation cannot be avoided. The system operator cannot directly judge whether each voyage deviation meets the test requirement or not on the machine and cannot judge whether the number of effective voyages meets the test requirement or not, so that the function of monitoring and processing the voyage line on the machine in real time needs to be realized.
In order to judge the navigation effectiveness in the test process, the dual-frequency multi-scale ground surface deformation measurement test system has the real-time monitoring function of the onboard air route, and the effective navigation with the average distance difference and the air route parallelism within the preset threshold is screened out through the limiting conditions of the distance difference and the air route parallelism, so that the effectiveness of test data recording is ensured.
Preferably, in another embodiment, according to the position information of the airborne platform, a current sailing track is drawn, and the distance difference and the flight path parallelism between the track and a preset flight path are calculated. When the average distance difference of a certain navigated track is larger than a preset value (for example, 20 m) or the parallel degree of a flight path is larger than a preset angle (for example, 1 degree), judging that the navigation is invalid navigation, otherwise, judging that the navigation is valid navigation; and when the number of the effective navigated data is accumulated to the specified number, the test requirements are met, and the recording of the measured test data is completed.
As shown in fig. 9, the preset course line of the measurement test is a solid line L, the track of the flight 1 is L1, the track of the flight 2 is L2, and when the platform approaches the target region of the deformation angle, the platform starts to enter the judgment condition.
The method for determining whether the average distance difference of a certain navigated trajectory is greater than the preset threshold value is to calculate the average distance R between two corresponding points between the navigated trajectory 1 (L1 in fig. 9) and the preset route (L in fig. 9) within a period of time from the approach to the target area to the departure from the target area, see formula 7. When R is greater than a preset value (e.g., 20 m), the voyage 1 is considered as a dead voyage.
The method for determining whether the parallelism of the flight path of a certain flight path (e.g. flight path 2) meets the requirement includes calculating an average included angle between direction vectors of two adjacent points in the N points of the flight path 2 (L2 in fig. 9) and direction vectors of two adjacent points in the N points corresponding to the preset flight path (L in fig. 9) within a period of time from approaching the target area to leaving the target area, that is, the parallelism between the flight path 2 and the preset flight path, see formula 8.
In the formula 7, N is the number of corresponding points on a certain navigated track and a preset route, and the size of N is related to the irradiation time of a target area; r is n Is the distance between corresponding points in meters.
In the formula 8, the first and second groups of the compound,
is the direction vector of two adjacent points of the preset route,
the vector is the vector of the direction of two adjacent points navigating through 2, the unit of the average included angle theta is radian, and the range is (0, pi).
That is, when θ' >1 °, the voyage 2 is considered as an invalid voyage. Only when R is less than or equal to 20 m and theta' is less than or equal to 1 degree, the voyage is considered as effective voyage.
In the test process, in order to meet the requirement of the system on the deformation quantity of the ground surface, two deformation angle reversals are arranged and placed on the ground surface. Before testing, measuring detailed three-dimensional coordinates of the deformation angle reflections, and before each voyage, adjusting the positions of the two deformation angle reflections on the ground along the vertical direction of the voyage route for simulating the deformation of the ground surface; one of the deformation angles moves a first movement amount (for example, 4 cm) each time to simulate the micro deformation of the earth surface; another deformation angle is moved by a second movement amount (for example, 20 cm) each time to simulate large-scale deformation of the earth surface; the direction and distance of the two opposite deformation angle phases for the initial position adjustment during each voyage are recorded.
According to the double-frequency multi-scale ground surface deformation measurement test system, the airborne platform is carried, so that the revisit period of a target area is greatly shortened; and the system has fixed base line length, and does not have the problem of processing precision caused by base line measurement errors.
According to the dual-frequency multi-scale surface deformation measurement test system, the two wave bands share the integrated control single machine, the servo mechanism, the wave control unit, the inertial navigation equipment and the like, the work of the dual-frequency polarization interference SAR system is realized on the basis of not additionally increasing hardware equipment, the equipment quantity of the system is greatly reduced, the development period is shortened, and the development cost is reduced.
The dual-frequency multi-scale earth surface deformation measurement test system realizes H polarization and V polarization working modes of the system by comprehensively controlling a single machine to send different timing sequences, and is convenient for recording and comparing polarization data.
According to the dual-frequency multi-scale ground surface deformation measurement test system, different mode words are sent by the integrated control single machine, so that two virtual base line working modes of the antenna can be realized, the recording of multi-base line interference data is facilitated, and the measurement precision is improved.
The dual-frequency multi-scale earth surface deformation measurement test system uniformly controls the servo mechanism and the wave control unit, can realize irradiation of left and right side antennas to the same area and logging of dual-frequency polarization interference SAR data for verifying earth surface deformation measurement, is convenient for comparison and mutual check of the dual-frequency polarization interference SAR data when inversion processing is carried out on the logged data subsequently, and greatly improves the accuracy of earth surface deformation measurement.
In summary, the test system for dual-frequency multi-scale ground surface deformation measurement provided by the invention has the advantages that the radar parameters, the calibration scheme and the working timing sequence of the system, the onboard air line real-time monitoring scheme and the like are determined by determining the equipment composition and the antenna installation position, and the dual-frequency polarization interference SAR data for verifying ground surface deformation measurement can be recorded and acquired by means of the onboard test platform.
Although the present invention has been described in terms of the preferred embodiment, it is not intended that the invention be limited to the embodiment. Any equivalent changes or modifications made without departing from the spirit and scope of the present invention also belong to the protection scope of the present invention. The scope of the invention should therefore be determined with reference to the appended claims.
Claims (10)
1. A dual-frequency multi-scale earth surface deformation measurement test system is characterized by comprising:
the system comprises two sets of X-band polarized antennas, two sets of L-band polarized antennas, two sets of X-band front-end receiving equipment, two sets of L-band front-end receiving equipment, two sets of transmitting equipment, two sets of calibration equipment, one set of integrated control single machine, two sets of wave control units, two sets of servo mechanisms, two sets of inertial navigation equipment and one set of recording equipment;
the two sets of X-band polarized antennas are used for transmitting and receiving X-band polarized signals and comprise Xa antennas and Xb antennas which are respectively arranged on the left side and the right side of the antenna frame to form an X-band cross-track interference baseline;
the two sets of L-band polarized antennas are used for transmitting and receiving L-band polarized signals and comprise La antennas and Lb antennas which are respectively arranged on the left side and the right side of the antenna frame to form L-band cross-track interference baselines;
the X-band front-end receiving device receives an echo signal transmitted from the X-band polarized antenna, performs down-conversion, filtering amplification and digital sampling processing on the echo signal, and transmits a processing result to the recording device for storage;
the L-band front-end receiving device receives an echo signal transmitted from the L-band polarized antenna, performs down-conversion, filtering amplification and digital sampling on L-echo data on the echo signal, and transmits a processing result to the recording device for storage;
the transmitting equipment is used for transmitting the reference signal to an X-band polarized antenna or an L-band polarized antenna corresponding to a required corresponding X-band or L-band after frequency doubling of the reference signal, and radiating the reference signal to a specific direction through the X-band polarized antenna or the L-band polarized antenna corresponding to the band;
the calibration equipment is used for testing and correcting the reference, receiving and transmitting links of the X wave band or the L wave band;
the integrated control single machine is used for parameter calculation, mode control and timing sequence generation of the whole system;
the wave control unit is used for controlling the scanning of the azimuth beam of the corresponding wave band antenna;
the servo mechanism is used for controlling the distance of the corresponding wave band antenna to scan the wave beam;
the inertial navigation equipment is used for recording position, speed and angle information of an airborne platform and further transmitting the information to the integrated control single machine, so that the directional correction of corresponding wave band antenna beams is realized, and the motion compensation is performed when the inversion processing is performed on data recorded in a dual-frequency multi-scale earth surface deformation measurement test.
2. The dual-frequency multi-scale surface deformation measurement testing system of claim 1, wherein the lengths of the X-band cross-track interference baseline and the L-band cross-track interference baseline are the same.
3. The dual-frequency multi-scale earth surface deformation measurement test system according to claim 1, wherein the integrated control unit calibrates the state of the whole system transmission link through three calibration modes including a reference calibration mode, a receiving calibration mode and a transmitting calibration mode by controlling the calibration equipment;
in the reference calibration mode, the transmitting equipment outputs an excitation signal to the calibration equipment from a calibration port, the front-end receiving equipment receives the calibration signal of the calibration equipment by adopting the calibration port, and all components in the antenna work in a load state at the moment, so that the amplitude-phase characteristic measurement of the calibration equipment and the front-end receiving equipment is completed;
in the receiving calibration mode, the transmitting equipment outputs an excitation signal to the calibration equipment from a calibration port and outputs the excitation signal to the corresponding wave band antenna through a calibration link, the front-end receiving equipment receives the calibration signal from the corresponding wave band antenna by adopting a receiving port, and all components in the antenna work in a receiving state, so that the amplitude-phase characteristic measurement of the receiving link of the antenna in different working states is completed;
in the transmission calibration mode, the transmitting equipment outputs an excitation signal to the corresponding waveband antenna from the transmitting port, then transmits the signal to the calibration equipment through the calibration link, the front-end receiving equipment receives the calibration signal of the calibration equipment by adopting the calibration port, and all components in the antenna work in a transmitting state at the moment, so that the amplitude-phase characteristic measurement of the transmitting link of the antenna in different working states is completed.
4. The dual-frequency multi-scale surface deformation measurement test system according to claim 3, wherein the calibration equipment comprises X-band calibration equipment and L-band calibration equipment, wherein the X-band calibration equipment is responsible for calibration of the Xa antenna and the Xb antenna, and the L-band calibration equipment is responsible for calibration of the La antenna and the Lb antenna; and the X-band calibration equipment and the L-band calibration equipment work simultaneously, and the X-band calibration equipment or the L-band calibration equipment performs time-sharing calibration on two antennas in the same band.
5. The dual-frequency multi-scale ground surface deformation measurement test system according to claim 1, wherein the integrated control single machine sends different working timing sequences to the two sets of wave control units to realize an H-polarization and V-polarization alternate working mode of the dual-frequency multi-scale ground surface deformation measurement test system;
the comprehensive control single machine controls the X-band polarized antenna and the L-band polarized antenna to realize two virtual baseline working modes including a single baseline mode and a double baseline mode by sending different mode words; in the single-baseline mode, only the antenna positioned on the left side or the right side of the antenna frame works during transmitting, and the antennas positioned on the left side and the right side of the antenna frame work during receiving; in the dual-baseline mode, the antennas located on the left and right sides of the antenna frame alternately work during transmission, and the antennas located on the left and right sides of the antenna frame both work during reception.
6. The dual-frequency multi-scale earth surface deformation measurement test system according to claim 5, wherein in the single baseline mode, two pulses in the timing sequence are a period, in the first pulse, the Xa antenna and the La antenna simultaneously transmit signals in an H-polarization mode, the Xa antenna and the Xb antenna simultaneously receive signals in an H-polarization mode, and the La antenna and the Lb antenna simultaneously receive signals in an H-polarization mode; in the second pulse, an Xa antenna and a La antenna simultaneously transmit signals in a V polarization mode, an Xa antenna and an Xb antenna simultaneously receive signals in a V polarization mode, and an La antenna and an Lb antenna simultaneously receive signals in a V polarization mode.
7. The dual-frequency multi-scale earth deformation measurement test system according to claim 5, wherein in the dual baseline mode, four pulses in a timing sequence are a period, in a first pulse, an Xa antenna and a La antenna transmit signals in an H polarization mode at the same time, an Xa antenna and an Xb antenna receive signals in an H polarization mode at the same time, and an La antenna and an Lb antenna receive signals in an H polarization mode at the same time; in the second pulse, xb antenna and Lb antenna transmit signals in H polarization mode at the same time, xa antenna and Xb antenna receive signals in H polarization mode at the same time, la antenna and Lb antenna receive signals in H polarization mode at the same time; in the third pulse, an Xa antenna and a La antenna transmit signals in a V polarization mode at the same time, the Xa antenna and the Xb antenna receive signals in the V polarization mode at the same time, and the La antenna and the Lb antenna receive signals in the V polarization mode at the same time; in the fourth pulse, xb antenna and Lb antenna transmit signals in V polarization mode at the same time, xa antenna and Xb antenna receive signals in V polarization mode at the same time, and La antenna and Lb antenna receive signals in V polarization mode at the same time.
8. The dual-frequency multi-scale ground surface deformation measurement test system according to claim 1, wherein the dual-frequency multi-scale ground surface deformation measurement test system screens out effective voyages of which the average distance difference and the course line parallelism are within a preset threshold value through limiting conditions of the distance difference and the course line parallelism, and when the number of the effective voyages is accumulated to a specified number, the test requirements are met, and recording of measurement test data is completed; the limiting conditions of the distance difference and the course parallelism comprise:
when the average distance difference of a certain navigated track is larger than a preset value or the parallel degree of the flight path is larger than a preset angle, judging that the navigation is invalid, otherwise, judging that the navigation is valid.
9. The dual-frequency multi-scale earth surface deformation measurement testing system of claim 1, further comprising two deformation angle reversals, wherein the positions of the two deformation angle reversals on the ground are adjusted in the vertical direction of the voyage course before each voyage for simulating earth surface deformation; one deformation angle moves a first movement amount every time to simulate the micro deformation of the earth surface; the other deformation angle is moved by a second movement amount each time to simulate large-scale deformation of the earth surface.
10. The dual-frequency multi-scale earth surface deformation measurement test system according to claim 1, wherein a pulse repetition frequency and a lower view angle meeting requirements are selected according to the limitation of the emission pulse and the subsatellite point echo of the dual-frequency multi-scale earth surface deformation measurement test system on the shielding of a received echo; setting the signal bandwidth of the system according to the distance of the dual-frequency multi-scale earth surface deformation measurement test system to the resolution; setting the signal sampling rate of the system according to the oversampling rate of the dual-frequency multi-scale ground surface deformation measurement test system;
the limiting condition of the transmitting pulse to the shielding of the received echo is shown in a formula 1-3, the limiting condition of the point echo under the satellite to the shielding of the received echo is shown in a formula 4, the method for calculating the signal bandwidth through the distance direction resolution is shown in a formula 5, and the method for calculating the signal sampling rate of the system through the oversampling rate of the system is shown in a formula 6;
in formula 1, rmax is the slant distance of the far point of the observation region, rmin is the slant distance of the near point of the observation region, c is the speed of light, m is the serial number of the transmitted pulse, PRF is the pulse repetition frequency, tp is the pulse width of the transmitted signal, and T is the protection time of the receiver and is a fraction of the pulse width of the transmitted signal;
in the formula 2 and the formula 3, H is the height of the airborne platform, theta is the beam width, and beta is the downward viewing angle;
in formula 4, H is the height of the airborne platform, c is the speed of light, and T p For the pulse width of the transmitted signal, k is the sequence number of the echo at the sub-satellite point, PRF is the pulse repetition frequency, R max Is the slope distance of the far point of the observation area, R min The skew distance of a near point of an observation area is set, and T is the protection time of the receiver;
in equation 5,. Rho r The distance resolution of the system, c is the speed of light, and B is the signal bandwidth;
in equation 6, f s Is the signal sampling rate of the system, alpha r Is to be tied toThe over-sampling rate of the system, B is the signal bandwidth.
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