CN115343712A - High-low frequency polarization interference test system for inversion of vegetation elevation - Google Patents
High-low frequency polarization interference test system for inversion of vegetation elevation Download PDFInfo
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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
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C5/00—Measuring height; Measuring distances transverse to line of sight; Levelling between separated points; Surveyors' levels
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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
Abstract
The invention relates to a high-low frequency polarization interference test system for inverting vegetation elevation, which comprises two sets of full polarization antennas with L, X and Ku wave bands, wherein one set of excitation source, one set of inner calibrator, two sets of receiver, one set of reference source, one set of control single machine and two sets of wave control machine, servo and position attitude measurement systems are respectively corresponding to the antennas with each wave band; the L1, X1 and Ku1 antennas are respectively fixed on the left side of the array surface, the L2, X2 and Ku2 antennas are respectively fixed on the right side of the corresponding positions of the array surface, and a certain interval exists between the array surfaces to form an intersection-orbit interference baseline. The invention can obtain the complete polarization interference data of three wave bands in the same area by single navigation, respectively measure different positions of vegetation through the characteristics of high and low frequency bands, and invert the elevation information of the vegetation.
Description
Technical Field
The invention relates to the technical field of radar signal processing, in particular to a high-low frequency polarization interference test system for inverting vegetation elevation.
Background
Synthetic Aperture Radar (SAR) is a space microwave remote sensing technology with all-weather and strong penetrability all day long, and can carry out two-dimensional high-resolution imaging on a ground target. After years of development, the SAR system has evolved from single polarization, single band to multi polarization, multi band. Polarimetric SAR is a hot research topic appearing in recent years, and high-resolution qualitative imaging of an SAR system is converted into high-resolution quantitative measurement by effectively combining polarimetric information and interference information. The polarization interference SAR has the characteristics of the polarization SAR and the advantages of the interference SAR, can sense the shape and the direction of the vegetation scatterers, can measure the spatial distribution of the vegetation scatterers, and accurately obtains the scattering characteristics and the vertical structure information of the vegetation. In addition, the high-band electromagnetic waves can provide detailed appearance characteristics of vegetation, but the penetration capability is poor, the low-band electromagnetic waves can penetrate through leaf clusters and the ground surface, hidden ground and feature structures are displayed, but the detailed appearance information of the vegetation cannot be acquired, and the accuracy and the breadth of measurement of the SAR system on the vegetation ground surface and the like can be improved by mutually fusing the data of high and low frequency bands. Therefore, the multi-band polarization interference SAR system is widely concerned and applied in the fields of vegetation measurement, homeland surveying and mapping and the like.
The most representative polarimetric SAR systems at home and abroad currently include the SRTM program in the United states and the TerrraSAR-X/TanDEM-X two-star system in Germany. The SRTM plan is that a SIR-C/X-SAR system is upgraded, two sets of receiving antennas with C wave bands and X wave bands are additionally arranged on a telescopic long arm on a space shuttle, polarization and interference data are acquired simultaneously in a single-time navigation, and topographic mapping information of eighty percent of the global area is acquired. According to the method, two similar X-waveband SAR satellites are transmitted in sequence in Germany, the operation is carried out in a formation operation and baseline adjustable mode, the interference mapping of global land elevation is completed, the absolute elevation precision is superior to 10m through data combined processing and evaluation, a sample superior to 1.13m accounts for 90%, the relative elevation precision is about 0.8m, and the absolute elevation precision is far superior to the design index. In addition, the Envisat ASAR system in canada and the ALOS PalSAR system in japan also enable multi-polar interferometric mapping. In the aspect of an airborne platform, a set of F-SAR system is newly developed in 2021 in Germany, can work in full polarization in 5 frequency bands (X, C, S, L and P wave bands), and can simultaneously acquire data of different wave bands and polarization. The domestic polarimetric SAR technology starts late, but reaches the international leading level in some fields through the development of recent years. A sky plot No. two emitted in 2019 is a first interference SAR mapping satellite in China and a first short-distance formation satellite system in China, the system works in an X wave band, radar interference data are obtained in real time in a one-shot and two-shot mode, joint processing is carried out on the data obtained for multiple times, the absolute elevation precision is between 2 and 10m, and the relative elevation precision is between 1.6 and 1.9 m. The sky plot II firstly provides a method for simultaneously imaging the same region through double frequencies, solves the absolute ambiguity problem of the interference phase and thoroughly gets rid of the dependence on ground control data. The L-band differential interference satellite launched in 2022 is the first polarized interference satellite in China, and flies in a two-satellite formation manner, so that heavy-orbit differential interference deformation measurement and interference terrain mapping are respectively realized in two flying modes of following flight and flying winding, effective data support is provided for high-precision ground surface deformation monitoring under complex conditions, and long-term dependence of related industries on foreign SAR satellites is greatly changed.
In view of the defects of large development difficulty, difficult debugging and high cost of the satellite-borne platform SAR system, a polarization interference SAR system based on an airborne platform needs to be designed and realized, cross-track interference data of different polarizations can be recorded simultaneously by a single navigation, different scattering characteristic information of vegetation is acquired, and inversion of vegetation elevation is realized.
Disclosure of Invention
In order to solve the technical problem in the prior art, the invention provides a high-low frequency polarization interference test system for inverting vegetation elevation, and full polarization cross-track interference data of three wave bands of L, X and Ku in the same area can be acquired by single navigation.
The technical scheme adopted by the invention is as follows: two sets of L, X and Ku wave band full polarization antennas, one set of corresponding excitation source, one set of internal calibrator, two sets of receiver, one set of reference source, one set of single control unit, and two sets of wave control machine, servo and position attitude measurement system. The reference source provides 100MHz reference signals for the excitation source and the receiver, the excitation source converts the reference signals to corresponding wave bands, and then the reference signals radiate to a specific space through the full-polarization antenna; the electromagnetic wave reflected by the ground object is received by the corresponding antenna, and the analog echo signal is converted into a digital signal through the down-conversion, filtering and sampling of the receiver. The single control machine is responsible for controlling the mode and time sequence of the whole system, and the wave control machine and the servo are responsible for adjusting the beam direction of the antenna.
The L1 antenna, the X1 antenna and the Ku1 antenna are respectively fixed on the left side of the array surface, the L2 antenna, the X2 antenna and the Ku2 antenna are respectively fixed on the right side of the corresponding positions of the array surface, and a certain interval exists between the array surfaces to form an intersection-orbit interference baseline.
Further, the test system of the present invention comprises the following improvements:
1. and selecting a frequency band.
The interference SAR is used for inversing elevation information of a target area through the phase difference of two pieces of antenna data. At present, three general methods for measuring the vegetation height through the interference SAR technology are available: the first method is to utilize a high-frequency interference SAR (synthetic aperture radar), the wavelength of electromagnetic waves in a high-frequency band is short, the penetrability is weak, the scattering is mainly dominated by canopy leaves, the scattering phase center is close to a vegetation canopy, and the height information of vegetation can be obtained by utilizing the original elevation information (DEM) of the earth surface; the second method is that high-low frequency interference SAR is utilized, the low-frequency band electromagnetic wave is longer in wavelength and strong in penetrability, a scattering phase center is close to the ground surface, and the vegetation height is calculated by utilizing the difference value of the high-low frequency phase center; and the third is to use polarization SAR to obtain two states with the maximum phase difference under all polarization scattering states, wherein one state corresponds to the interference phase of the vegetation upper-layer scattering area and is called a high-scattering phase center, the other state corresponds to the interference phase of the vegetation lower-layer scattering area and is called a low-scattering phase center, and the difference value of the two states is approximately equal to the vegetation height. According to the invention, high-low frequency full-polarization interference data required by the latter two methods are recorded by radiating full-polarization signals of three high-low frequency bands of L, X and Ku.
2. And (5) designing the aperture of the antenna.
The azimuth dimension is determined by the radar azimuth resolution. Through azimuth beamwidthθ a =λ/D a Doppler bandwidthB a =2vθ a /λAzimuthal resolutionρ a =v/B a Obtaining the azimuth dimensionD a =2ρ a Wherein, in the step (A), vin order to be able to speed up the operation of the platform,λis the wavelength.
The dimension in the radial direction is determined mainly by the irradiation width. Through distance to beam widthθ r =λ/D r Lower angle of viewσ= arccos(h/R)Near end distance of beamR 0 =h/cos(σ-θ r /2)Distance of beam from far endR 1 =h/cos(σ+θ r /2)Width of irradiationΔR=R 1 -R 0 WhereinhThe platform is the operation height of the platform,Ris the distance of the platform to the target area. The smaller the distance dimension is, the larger the beam width is, the larger the amplitude is, and the pulse repetition frequency is reduced on the premise of not generating distance ambiguity; in addition, the antenna gain is reduced, resulting in reduced radar power. Therefore, the distance dimension is preferably selected according to the minimum width index.
Further, when the antennas of multiple bands are designed uniformly, the relationship between the scattering intensity and the frequency point needs to be considered: ground surfaceThe scattering intensity of the target is in direct proportion to the size of the frequency point. The lower the frequency point is, the smaller the target reflection intensity is, and in order to make the echo intensities of a plurality of frequency bands equivalent, the antenna gain of the low frequency band needs to be increased. According to the principle of radar, it is known that,G=4πA/λ 2 wherein A is the effective area of the radar. The antenna gain is increased only by increasing the effective area of the antenna, namely the aperture of the antenna is increased.
3. Designing an interference baseline.
The baseline is a parameter specific to the interferometric radar system. On one hand, the longer the base line is, the denser the interference fringes caused by the same height change are, the more sensitive the system is to the reflecting capability of the height change, and the smaller the height measurement error caused by the uncertainty of the phase difference and the length of the base line is; on the other hand, the longer the baseline, the lower the coherence between the two acquired signals, and the lower the interference phase estimation accuracy. There is therefore a baseline, i.e., an optimal baseline, at which the interferometric system operates optimally with minimal altimetric error.
The distance of the interference SAR system is limited to the signal bandwidth, when the spectral offset of two received signals exceeds the bandwidth, the two received signals are incoherent, and an effective interference phase cannot be obtained, wherein the baseline at the moment is called as a limit baseline:
Also closely related to baseline magnitude in polarimetric interferometric SAR is volume scattering decoherenceγ Vol ：
. And is provided with
，p=2σ 0 /cosθ，p 1 =p+jk z ，k z =2kπB ⊥ /（λhtanθ）. Wherein the content of the first and second substances,μthe earth volume amplitude ratio tends to infinity to indicate that the earth scattering is dominant and tends to zero to indicate that the volume scattering is dominant;γ v is the volume scattering coefficient;h v is the vegetation height;k z to a high degree of sensitivity, the inverse number thereof1/k z Is a high blur number;σ 0 is the extinction coefficient; b is ⊥ Is a vertical baseline;kfor parameters relating to the mode of operation, in a single transmission modek=1In ping-pong transmission modek=2. Meanwhile, the system performance of the polarization interference SAR is measured by the distinguishing accuracy of the phase centers of different scattering mechanisms, and is related to the measurement accuracy of the phase center position and the phase center under each polarization mode. The former being usableγ Vol Expressed in terms of the standard deviation of the phase estimateσ φ Represents:
，
. Wherein the content of the first and second substances,φis composed ofγ Vol The phase angle of (a) is determined, P φ for the phase estimation of the probability density function, nin order to be an equivalent view number,Fis a gaussian hypergeometric function and Γ is a gamma function. Defining the variation of the amplitude ratio of the earthΔμThen, thenΔμThe variation of the phase center in the range is equal to the midpointμ 0 2 times the standard deviation of the phase: 2 sigma φ =φ 1 （μ 0 -Δμ/2）-φ 2 （μ 0 +Δμ/2). Solving the optimal baseline by solving the equationΔμWith respect to B ⊥ Then let its partial derivative be 0 to get the optimal baseline value.
4. And designing a polarization mode and a transmitting and receiving time sequence.
The invention designs a working mode of variable polarization transmission and simultaneous dual polarization reception. The quasi-real-time acquisition of the four kinds of polarization information of the system is realized through the polarization conversion switch during transmission and through different control and area division of the array surface during receiving. The method compromises the complexity of the system and the real-time performance of the system, is easy to realize, and most of the foreign polarized SAR adopt the method. The antenna of each band is divided into two channels, namely a channel 1 and a channel 2. The signal is transmitted by a full array surface when being transmitted, the channel 1 is received by H polarization when being received, and the channel 2 is received by V polarization. Therefore, the recording of the full polarization echo signal can be completed in two continuous pulse repetition periods.
The invention designs a time sequence for simultaneously receiving and transmitting three wave bands. If the transmitting and receiving time sequence is not restricted, the receiving and transmitting time windows of the three wave bands are overlapped, harmonic waves generated during the transmitting of the low wave band can be modulated to the high wave band, the problem of serious interference is generated during the receiving of the high wave band, and the receiver can be saturated or components can be damaged when the problem is serious. Firstly, in order to simplify the design, the system uses a uniform pulse repetition frequency, six sets of antennas simultaneously transmit and receive signals, and the problem of disordered receiving and transmitting is avoided in the system design; then, the timing sequence of the system is uniformly controlled by a timing module in the digital single machine. In a pulse repetition period, the active transmitting antennas trigger the transmitting signals at the same time, and the receiving triggering leading edges of all the antennas are set according to the actual requirements of each wave band, but the receiving trailing edges are ensured not to exceed the leading edge of the next transmitting pulse.
The invention designs two receiving and transmitting time sequences and expands the number of base lines. The first mode is a single-transmitting and double-receiving mode, the L1, X1 and Ku1 antennas of the left array surface actively transmit signals, and the reflected echo waves are received by the corresponding antennas of the right array surface simultaneously; the second mode is a ping-pong mode, wherein the L1, X1 and Ku1 antennas of the left array surface and the L2, X2 and Ku2 antennas of the right array surface alternately transmit signals, and the two antennas simultaneously receive reflected echoes. The ping-pong mode is equivalent to doubling the effective baseline length relative to the single-transmission double-reception mode. The two modes can be switched by controlling a single machine, and data recorded in the two modes can be mutually corrected, so that the target elevation inversion precision is improved.
5. And (4) designing an external scaling.
In the invention, the distance measurement error of the system is corrected by paving an angle inverse on a test site. Firstly, recording the real coordinates of the lower corner inverse, and calculating the distance between the corner inverse and the aperture center platform
6. And designing a real-time imaging function.
When the system is designed, the acquired original echo is divided into two paths, one path transmits a signal to a recorder through an optical fiber, the other path transmits the signal to a signal processing module through an interface for real-time processing, and a coarse imaging result is transmitted to a display control interface for display after the processing. The echo of any antenna, any polarization and any channel can be selected on the display and control interface for real-time processing and display. The function is that the beam irradiation area can be presented in real time, and if the pointing deviation occurs, the beam angle is adjusted in time; secondly, whether the parameter settings such as MGC are reasonable or not can be judged through images, and the parameter settings are adjusted in time when signals are saturated or small, so that the quality of the acquired signals is ensured; thirdly, the running state of the system can be monitored through the speed or the existence of image updating, and the system can be reset or restarted in time when unknown errors occur; and fourthly, corresponding parameters of the image, such as bandwidth, pulse width, pulse repetition frequency, imaging time and the like, can be displayed in real time, so that the phenomenon that the radar parameters are changed by display control without response of the system is prevented.
The invention provides a high-low frequency polarization interference test system for inverting vegetation elevation, which can acquire full polarization interference data of three wave bands in the same area by single navigation, respectively measure different positions of vegetation through the characteristics of high and low frequency bands, and invert the elevation information of the vegetation; the elevation of the vegetation can be inverted through multi-polarization information of the same wave band, and the two modes are fused with each other, so that the accuracy of vegetation elevation measurement is improved; the method can provide effective data support for verification of a vegetation elevation inversion method by using high-frequency and low-frequency polarization interference technology.
Drawings
The following further illustrates embodiments of the present invention with reference to the drawings.
FIG. 1 is a block diagram of a high and low frequency polarization interference test system for inversion of vegetation elevation in accordance with the present invention;
FIG. 2 is a schematic diagram of the installation of the band antennas;
FIG. 3 is a diagram of antenna spatial geometry;
FIG. 4 is a timing diagram of the operation of the system;
FIG. 5 is a pictorial view of a corner array.
Detailed Description
With reference to fig. 1 to 5, the high-low frequency polarization interference test system for inversion of vegetation elevation comprises two sets of full polarization antennas with L, X and Ku wave bands, one set of corresponding excitation source, one set of internal calibrator, two sets of receiver, one set of reference source, one set of control unit, and two sets of wave control machine, servo and position and attitude measurement system.
When the system works, the flow chart is shown in figure 1. The reference source provides 100MHz reference signals for the excitation source and the receiver, the excitation source converts the frequency of the reference signals to corresponding wave bands, and then the reference signals radiate to a specific space through the full-polarization antenna; the electromagnetic wave reflected by the ground object is received by the corresponding antenna, and the analog echo signal is converted into a digital signal through the down-conversion, filtering and sampling of the receiver. The internal calibrator is matched with the antenna array surface to complete calibration of the reference, receiving and transmitting calibration links. The single control machine is responsible for controlling the mode and time sequence of the whole system, and the wave control machine and the servo are responsible for adjusting the beam direction of the antenna.
The test system of the present invention also includes the following improvements:
1. and selecting a frequency band.
The interference SAR is used for inversing elevation information of a target area through the phase difference of two pieces of antenna data. At present, three general methods for measuring the vegetation height through the interference SAR technology are available: the first method is to utilize a high-frequency interference SAR (synthetic aperture radar), the wavelength of electromagnetic waves in a high-frequency band is short, the penetrability is weak, the scattering is mainly dominated by canopy leaves, the scattering phase center is close to a vegetation canopy, and the height information of vegetation can be obtained by utilizing the original elevation information (DEM) of the earth surface; the second method is to utilize high-low frequency interference SAR, which is opposite to high frequency, the wavelength of low-frequency electromagnetic waves is longer, the penetrability is strong, a scattering phase center is close to the earth surface, and the vegetation height is calculated by utilizing the difference value of the high-low frequency phase center; and the third is to use polarization SAR to obtain two states with the maximum phase difference under all polarization scattering states, wherein one state corresponds to the interference phase of the vegetation upper-layer scattering area and is called a high-scattering phase center, the other state corresponds to the interference phase of the vegetation lower-layer scattering area and is called a low-scattering phase center, and the difference value of the two states is approximately equal to the vegetation height. The invention records the high-low frequency complete polarization interference data meeting the requirements of the latter two methods by radiating the complete polarization signals of three high-low frequency bands of L, X and Ku.
2. And (5) designing the aperture of the antenna.
The azimuth dimension is determined by the radar azimuth resolution. Through azimuth beamwidthθ a =λ/D a Doppler bandwidthB a =2vθ a /λAzimuthal resolutionρ a =v/B a Obtaining the azimuth dimensionD a =2ρ a Wherein, in the process,vis the speed at which the platform is operating,λis the wavelength.
The dimension in the direction of the distance is determined mainly by the irradiation width. Through range beam widthθ r =λ/D r Lower angle of viewσ= arccos(h/R)Near end distance of beamR 0 =h/cos(σ-θ r /2)Distance of beam from far endR 1 =h/cos(σ+θ r /2)Width of irradiationΔR=R 1 -R 0 WhereinhIn order to ensure the operation height of the platform,Ris the distance of the platform to the target area. The smaller the distance dimension is, the larger the beam width is, and the larger the amplitude is, so that the pulse repetition frequency is reduced on the premise of not generating distance ambiguity; in addition, the antenna gain is reduced, resulting in reduced radar power. Therefore, the distance dimension is preferably selected according to the minimum width index.
Further, when the antennas of multiple bands are designed uniformly, the relationship between the scattering intensity and the frequency point needs to be considered: the scattering intensity of the ground target is in direct proportion to the size of the frequency point. The lower the frequency point is, the smaller the target reflection intensity is, and in order to make the echo intensities of a plurality of frequency bands equivalent, the antenna gain of the low frequency band needs to be increased. According to the principle of radar,G=4πA/λ 2 wherein A is the effective area of the radar. The antenna gain is increased only by increasing the effective area of the antenna, namely the aperture of the antenna is increased.
3. And (4) designing an interference baseline.
The baseline is a parameter unique to interferometric radar systems. On one hand, the longer the base line is, the denser the interference fringes caused by the same height change are, the more sensitive the system is to the reflecting capability of the height change, and the smaller the height measurement error caused by the uncertainty of the phase difference and the length of the base line is; on the other hand, the longer the baseline, the lower the coherence between the two acquired signals, and the lower the interference phase estimation accuracy. There is therefore a baseline, i.e., an optimal baseline, at which the interferometric system operates optimally with minimal altimetric error.
The distance of the interference SAR system is limited to the signal bandwidth, when the spectral offset of two received signals exceeds the bandwidth, the two received signals are incoherent, and an effective interference phase cannot be obtained, wherein the baseline at the moment is called as a limit baseline:
Also closely related to baseline magnitude in polarimetric interferometric SAR is volume scattering decoherenceγ Vol ：
. And is
，p=2σ 0 /cosθ，p 1 =p+jk z ，k z =2kπB ⊥ /（λhtanθ）. Wherein the content of the first and second substances,μthe earth volume amplitude ratio tends to infinity to indicate that the earth scattering is dominant and tends to zero to indicate that the volume scattering is dominant;γ v is the volume scattering coefficient;h v is the vegetation height;k z to a high degree of sensitivity, the inverse number thereof1/k z Is a high blur number;σ 0 is an extinction coefficient; b is ⊥ Is a vertical baseline;kfor parameters relating to the mode of operation, single shotk=1Ping-pong launcherk=2. Meanwhile, the system performance of the polarization interference SAR is measured by the distinguishing accuracy of the phase centers of different scattering mechanisms, and is related to the measurement accuracy of the phase center position and the phase center under each polarization mode. The former can be expressed and the latter can be expressed by the standard deviation of the phase estimationσ φ Represents:
，
. Wherein the content of the first and second substances,φis composed ofγ Vol The phase angle of (a) is determined,P φ is a phase ofThe bit estimates the probability density function of the bit,nin order to be an equivalent view number,Fis a gaussian hypergeometric function, and Γ is a gamma function. Defining the variation of the amplitude ratio of the earthΔμThen, thenΔμThe variation of phase center in the range is equal to the midpointμ 0 2 times the standard deviation of the phase: 2 sigma φ =φ 1 (μ 0 -Δμ/2)-φ 2 (μ 0 +Δμ/2). Solving the optimal baseline by solving the equationΔμWith respect to B ⊥ Then let its partial derivative be 0 to get the optimal baseline value.
4. And designing a polarization mode and a transmitting and receiving time sequence.
The invention designs a working mode of variable polarization transmission and simultaneous dual polarization reception. The quasi-real-time acquisition of the four kinds of polarization information of the system is realized through the polarization conversion switch during transmission and through different control and region division of the array surface during receiving. The method compromises the complexity of the system and the real-time performance of the system, is easy to realize, and most of the foreign polarized SAR adopt the method. The antenna of each band is divided into two channels, namely a channel 1 and a channel 2. The signal is transmitted by a full array surface when being transmitted, the channel 1 is received by H polarization when being received, and the channel 2 is received by V polarization. Therefore, the recording of the full polarization echo signal can be completed in two continuous pulse repetition periods.
The invention designs the time sequence of simultaneous receiving and transmitting of three wave bands. If the transmitting and receiving time sequence is not restricted, the receiving and transmitting time windows of the three wave bands are overlapped, harmonic waves generated during the transmitting of the low wave band can be modulated to the high wave band, the problem of serious interference is generated during the receiving of the high wave band, and the receiver can be saturated or components can be damaged when the problem is serious. Firstly, in order to simplify the design, the system uses a uniform pulse repetition frequency, six sets of antennas simultaneously transmit and receive signals, and the problem of disordered receiving and transmitting is avoided in the system design; then, the timing sequence of the system is uniformly controlled by a timing module in the digital single machine. In a pulse repetition period, the active transmitting antennas trigger the transmitting signals at the same time, and the receiving triggering leading edges of all the antennas are set according to the actual requirements of each wave band, but the receiving trailing edges are ensured not to exceed the leading edge of the next transmitting pulse.
The invention designs two receiving and transmitting time sequences and expands the number of base lines. The first mode is a single-transmitting and double-receiving mode, the L1, X1 and Ku1 antennas of the left array surface actively transmit signals, and the reflected echo waves are received by the corresponding antennas of the right array surface simultaneously; the second mode is a ping-pong mode, wherein the L1, X1 and Ku1 antennas of the left array surface and the L2, X2 and Ku2 antennas of the right array surface alternately transmit signals, and the two antennas simultaneously receive reflected echoes. The ping-pong mode is equivalent to doubling the effective baseline length relative to the single-transmit-double-receive mode. The two modes can be switched by controlling a single machine, and data recorded in the two modes can be mutually corrected, so that the accuracy of target elevation inversion is improved.
5. And (4) designing an external scaling.
In the invention, the distance measurement error of the system is corrected by paving an angle inverse on a test site. Firstly, recording the real coordinates of the lower corner inverse, and calculating the distance between the corner inverse and the aperture center platform
(ii) a Then, through an angle inverse image in the SAR image, calculating an angle inverse slope distance measurement value according to the position of a wave gate and a pixel pointR meas =R 0 +c/(2f s )*N(ii) a Difference between the twoR meas -R real Namely the systematic ranging error. Wherein the content of the first and second substances, (ii) (x 0 ,y 0 ,z 0 ），（x 1 ,y 1 ,z 1 ) The real coordinates of the angular reflection and the aperture center point respectively,R 0 is a wave gate, and is characterized in that,Nfor the pixel position of the angular inversion in the SAR image,f s is the sampling frequency.
6. And (4) designing a real-time imaging function.
When the system is designed, the acquired original echo is divided into two same paths, one path transmits a signal to a recorder through an optical fiber, the other path transmits the signal to a signal processing module through an interface for real-time processing, and a coarse imaging result is transmitted to a display control interface for displaying after the processing. The echo of any antenna, any polarization and any channel can be selected on the display and control interface for real-time processing and display. The function can present a beam irradiation area in real time, and adjust a beam angle in time if pointing deviation occurs; secondly, whether parameter settings such as MGC are reasonable or not can be judged through images, and the parameter settings are adjusted in time when signals are saturated or small, so that the quality of the acquired signals is ensured; thirdly, the running state of the system can be monitored through the speed or the existence of image updating, and the system can be reset or restarted in time when unknown errors occur; and fourthly, corresponding parameters of the image, such as bandwidth, pulse width, pulse repetition frequency, imaging time and the like, can be displayed in real time, so that the phenomenon that the radar parameters are changed through display control without response of the system is prevented.
The specific operation method of the present application is described by taking a certain system as an example, and the flight altitude of the carrying platform used in the present embodimenth=7000mAt a flying speed ofv=130m/s。
The radar parameters are shown in table 1:
TABLE 1 Radar parameter Table
By the formulaD a =2ρ a It can be seen that the azimuth dimension D of the tri-band antenna aL ≤0.8m，D aX ≤0.4m，D aKu ≤0.4m。
Taking the X-band antenna as an example, the distance dimension D can be obtained from the width calculation formula rX ≦ 0.3m, and the dimension of the distance may not be too small, taking into account factors of the pulse repetition frequency and antenna gain. The distance dimension D of the Ku-band antenna can be obtained in the same way rKu Less than or equal to 0.2m, and the distance dimension D of the L-band antenna rL Less than or equal to 2.0m. Meanwhile, the design result also accords with the constraint condition caused by the scattering intensity factor of the ground object, namely the antenna aperture is larger as the frequency point is lower. In addition, the design L needs to be designed by considering the limitation of the size of a pod for placing the antenna array and combining various factorsThe size of the wave band antenna is as follows: d aL =0.8m，D rL =0.6m, x-band antenna size: d aX =0.4m，D rX =0.3m, ku band antenna size: d aKu =0.4m，D rKu =0.2m. The installation diagram of the antenna of each band is shown in fig. 3.
When the length of the base line is designed, the X wave band is located among the three, so the constraint condition is based on the X wave band. The baseline design parameters are shown in table 2.
TABLE 2 Baseline design parameters Table
Due to the complexity of the phase estimation probability density function, it is difficult to directly solve the optimal baseline. Since the dichotomy is the information query mode with the fastest finite concentration convergence and has lower computational complexity and time complexity, the dichotomy search is used to change the ground body radiation ratioΔμReach the minimum baseline, i.e. the optimal baseline B ⊥ . According to the relationship graph of the two, when B is ⊥ When the particle size is within 2m to 8m,Δμat a smaller value, and is flatter, indicates B ⊥ System performance still remains good at slight deviations from the optimal baseline value. And in B ⊥ When the grain size is not larger than 4.1m,Δμat a minimum value. In addition, due to the constraint of the distance between the pod hanging points on the two sides of the platform, B is selected in the invention ⊥ =3.75m. A schematic of the baseline spatial geometry is shown in fig. 3.
In the mode of variable polarization transmission and simultaneous dual polarization receiving, the quasi-real-time acquisition of four kinds of polarization information of the system is realized through a polarization conversion switch during transmission and through different control and area division of a wave front during receiving. Taking the first two frames of the system as an example, the first frame signal is transmitted in H polarization, the echo of the channel 1 is HH polarization, and the echo of the channel 2 is VH polarization; the second frame signal is transmitted in V polarization, with the echo for channel 1 being in HV polarization and the echo for channel 2 being in VV polarization. Therefore, recording of the complete polarization interference signal is completed in two continuous pulse repetition periods.
The timing sequence of the single-transmit-double-receive mode of the system is shown in fig. 4, the solid line represents the transmit window, the curve represents the receive window, and the dashed line represents the absence of a pulse. Taking two-frame work in a cycle as an example, three antennas on the left side of a first frame simultaneously transmit H polarized signals, namely an L1 antenna transmits L-band H polarized signals, an X1 antenna transmits X-band H polarized signals, a Ku1 antenna transmits Ku-band H polarized signals, antennas on the left side and the right side in the same frequency band complete receiving at the same time, and receiving wave gates of the antennas in different frequency bands are set according to specific conditions; three antennas on the left side of the second frame transmit V polarization signals simultaneously, namely an L1 antenna transmits L-band V polarization signals, an X1 antenna transmits X-band V polarization signals, a Ku1 antenna transmits Ku-band V polarization signals, and so on, H polarization and V polarization pulses are alternated. The ping-pong mode is similar in the receiving and sending timing, but the four frames of data are used as a cycle, and the details are not repeated here.
Obtaining the true slope distance of the angle reversal according to the laid angle reversal true coordinates and the coordinates of the center point of the synthetic aperture; the angular inversion position and the wave gate parameter in the SAR image are positioned to obtain the slope distance measured by the system, and the difference value of the angular inversion position and the wave gate parameter is the slope distance error of the systemΔR. When data processing is carried out subsequently, the slope distance error needs to be considered, and the inversion accuracy of vegetation elevation information is improved. The schematic diagram of the corner array is shown in FIG. 5.
The test system selects the frequency band of the test system for measuring the vegetation elevation based on the scattering characteristic of the electromagnetic wave; based on the consideration of the minimized system measurement error, the design of an interference optimal baseline is developed; designing a unified transceiving time sequence and two transceiving working modes based on the requirements of three-waveband full-polarization interference data; performing external calibration design based on the ranging error correction of the system; and designing an onboard real-time imaging function based on the judgment of the data recording effectiveness in the test process, and monitoring the working states of the six sets of antennas in real time. Compared with the prior art, the test system can work in three wave bands simultaneously and can image the targets in the same area simultaneously. In addition, the antenna can transmit a single-polarization signal and can also transmit a full-polarization signal; the single-transmitting single-receiving mode can be realized, the single-transmitting multi-receiving mode can also be realized, and the working mode is more flexible and richer.
In the previous description, numerous specific details were set forth in order to provide a thorough understanding of the present invention. The foregoing description is that of the preferred embodiment of the invention only, and the invention can be practiced in many ways other than as described herein, so that the invention is not limited to the specific implementations disclosed above. And that those skilled in the art may, using the methods and techniques disclosed above, make numerous possible variations and modifications to the disclosed embodiments, or modify equivalents thereof, without departing from the scope of the claimed embodiments. Any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are within the scope of the technical solution of the present invention.
Claims (8)
1. The utility model provides a high low frequency polarization interference test system of inversion vegetation elevation which characterized in that: the all-polarization antenna system comprises two sets of all-polarization antennas with L, X and Ku wave bands, wherein each set of excitation source, each set of inner calibrator, each set of receiver, one set of reference source, one set of control unit, and two sets of wave control machine, servo and position attitude measurement systems are respectively corresponding to the antenna with each wave band; the L1, X1 and Ku1 antennas are respectively fixed on the left side of the array surface, the L2, X2 and Ku2 antennas are respectively fixed on the right side of the corresponding positions of the array surface, and certain intervals exist among the array surfaces to form an intersection-rail interference baseline;
the reference source provides reference signals for the excitation source and the receiver, the excitation source converts the frequency of the reference signals to corresponding wave bands, and then the reference signals are radiated to a specific space through the full-polarization antenna; the electromagnetic wave reflected by the ground object is received by the corresponding antenna, the analog echo signal is converted into a digital signal through the down-conversion, filtering and sampling of the receiver, the single control unit is responsible for controlling the mode and the time sequence of the whole system, the wave control unit and the servo unit are responsible for adjusting the beam direction of the antenna, and the system inverts the elevation information of the target area through the phase difference of the data of the two antennas.
2. The high and low frequency polarization interference testing system for inversion of vegetation elevation of claim 1, wherein: the method for calculating the vegetation height comprises the following steps: calculating the vegetation height according to the difference value of the high-low frequency phase center by utilizing a high-low frequency interference SAR, or obtaining two states with the maximum phase difference under all polarization scattering states by utilizing a polarization SAR, and calculating the vegetation height according to the difference value of the two states; the test system records high-low frequency full-polarization interference data required by the two methods by radiating full-polarization signals of three high-low frequency bands of L, X and Ku.
3. The high and low frequency polarization interference testing system for inversion of vegetation elevation of claim 1, wherein: azimuth dimension of antennaD a Is composed of
D a =2ρ a (1)
Wherein the content of the first and second substances,ρ a the radar azimuth resolution is obtained;
dimension in the direction of distanceD r Determined according to the following equation:
wherein the content of the first and second substances,ΔRin order to be able to irradiate a wide range, hin order to obtain the running height of the platform,Ris the distance of the platform to the target area,λis a function of the wavelength of the light, D r is taken to beΔRThe minimum width index is met.
4. The high and low frequency polarization interference testing system for inversion of vegetation elevation of claim 3, wherein: for the antenna of the low frequency band, the antenna gain is increased by increasing the antenna aperture, so that the echo intensities of a plurality of frequency bands are equivalent.
5. The high and low frequency polarization interference testing system for inversion of vegetation elevation of claim 1, wherein: the optimal baseline value for the cross-rail interference of the test system is calculated as follows:
wherein, the first and the second end of the pipe are connected with each other,σ φ in order to estimate the standard deviation of the phase,φis composed ofγ Vol The phase angle of (a) is determined, P φ estimating a probability density function for a phase ，nIn order to be an equivalent view number,Fis a Gaussian hypergeometric function, and gamma is a gamma function;μthe earth volume amplitude ratio tends to infinity to indicate that the ground scattering is dominant and tends to zero to indicate that the volume scattering is dominant;γ v is the volume scattering coefficient; h v is the vegetation height; k z the sensitivity is high, and the reciprocal is a high fuzzy number;σ 0 is an extinction coefficient; b is ⊥ Is a vertical baseline;kfor parameters relating to the mode of operation, in a single transmission modek=1In ping-pong launch modek=2；
When determining the optimal baseline, solve from equation (3)ΔμWith respect to B ⊥ Then let its partial derivative be 0 to get the optimal baseline value.
6. The high and low frequency polarization interference testing system for inversion of vegetation elevation of claim 1, wherein: the system adopts the working mode of variable polarization transmission and simultaneous dual polarization reception: the antenna of each wave band is divided into a front channel and a rear channel, and the front channel and the rear channel are marked as a first channel and a second channel, wherein the signal is transmitted in a full array surface mode during transmission, the first channel is received in H polarization during reception, and the second channel is received in V polarization;
the system designs a time sequence for simultaneously receiving and transmitting three wave bands, the timing time sequence is controlled by a timing module in a digital single machine, the receiving and transmitting time sequences comprise two types, one type is a single-transmitting and double-receiving mode, L1, X1 and Ku1 antennas of a left array surface actively transmit signals, and the signals and corresponding antennas of a right array surface simultaneously receive reflected echoes; the second mode is a ping-pong mode, wherein the L1, X1 and Ku1 antennas of the left array surface and the L2, X2 and Ku2 antennas of the right array surface alternately transmit signals, the two antennas simultaneously receive reflected echoes, and the two modules are switched by a single controller.
7. The high and low frequency polarization interference testing system for inversion of vegetation elevation of claim 1, wherein: systematic ranging error correction by reversing the angle of lay at the test siteΔRThe calculation method is as follows:
recording the real coordinates of the lower angular reflection, and calculating the distance between the angular reflection and the aperture center platformR real The calculation formula is as follows:
wherein the content of the first and second substances, (ii) (x 0 ,y 0 ,z 0 ），（x 1 ,y 1 ,z 1 ) Real coordinates of the angle inverse and the aperture center point are respectively;
calculating the slope distance measurement value of the angle reflection according to the positions of the wave gate and the pixel points through the angle reflection image in the SAR imageR meas The calculation formula is as follows:
wherein the content of the first and second substances, R 0 is a wave gate, N is the position of a pixel point of an angle inversion in the SAR image, f s in order to be able to sample the frequency, cis the speed of light;
the range error of the system is: R meas -R real 。
8. the high and low frequency polarization interference testing system for inversion of vegetation elevation of claim 1, wherein: the system divides the collected original echo into two paths, one path transmits signals to an external recorder through optical fibers, the other path transmits the signals to a signal processing module of the single control unit through an interface for real-time processing, and after the processing, the coarse imaging result is transmitted to an external display control interface for display.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116755093A (en) * | 2023-08-18 | 2023-09-15 | 中国电子科技集团公司第十四研究所 | Method, device and computer medium for improving scanning polarization SAR blurring |
| CN117081660A (en) * | 2023-10-12 | 2023-11-17 | 齐鲁卫星技术(山东)有限责任公司 | Wide-beam hidden transmitting platform for synchronous orbit satellite platform |
| CN117214898A (en) * | 2023-11-09 | 2023-12-12 | 中国电子科技集团公司第十四研究所 | Wide-scale earth surface deformation refined remote sensing method based on multidimensional electromagnetic information depth fusion |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5552787A (en) * | 1995-10-10 | 1996-09-03 | The United States Of America As Represented By The Secretary Of The Navy | Measurement of topography using polarimetric synthetic aperture radar (SAR) |
| CN103376451A (en) * | 2012-04-16 | 2013-10-30 | 中国科学院电子学研究所 | Airborne double-waveband synthetic aperture radar system and method for measuring vegetation thickness utilizing same |
| CN110988879A (en) * | 2019-12-24 | 2020-04-10 | 中南大学 | Vegetation parameter inversion method, terminal equipment and storage medium |
| CN112363161A (en) * | 2020-10-27 | 2021-02-12 | 中南大学 | Vegetation vertical structure and under-forest topography inversion method and device based on scattering mechanism decomposition |
| CN114594478A (en) * | 2022-03-17 | 2022-06-07 | 北京卫星信息工程研究所 | Ship target interference detection method based on satellite-borne Ka-band SAR system |
-
2022
- 2022-10-18 CN CN202211269870.XA patent/CN115343712B/en active Active
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5552787A (en) * | 1995-10-10 | 1996-09-03 | The United States Of America As Represented By The Secretary Of The Navy | Measurement of topography using polarimetric synthetic aperture radar (SAR) |
| CN103376451A (en) * | 2012-04-16 | 2013-10-30 | 中国科学院电子学研究所 | Airborne double-waveband synthetic aperture radar system and method for measuring vegetation thickness utilizing same |
| CN110988879A (en) * | 2019-12-24 | 2020-04-10 | 中南大学 | Vegetation parameter inversion method, terminal equipment and storage medium |
| CN112363161A (en) * | 2020-10-27 | 2021-02-12 | 中南大学 | Vegetation vertical structure and under-forest topography inversion method and device based on scattering mechanism decomposition |
| CN114594478A (en) * | 2022-03-17 | 2022-06-07 | 北京卫星信息工程研究所 | Ship target interference detection method based on satellite-borne Ka-band SAR system |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116755093A (en) * | 2023-08-18 | 2023-09-15 | 中国电子科技集团公司第十四研究所 | Method, device and computer medium for improving scanning polarization SAR blurring |
| CN116755093B (en) * | 2023-08-18 | 2023-10-31 | 中国电子科技集团公司第十四研究所 | Method, device and computer medium for improving scanning polarization SAR blurring |
| CN117081660A (en) * | 2023-10-12 | 2023-11-17 | 齐鲁卫星技术(山东)有限责任公司 | Wide-beam hidden transmitting platform for synchronous orbit satellite platform |
| CN117081660B (en) * | 2023-10-12 | 2024-01-16 | 齐鲁卫星技术(山东)有限责任公司 | Wide-beam hidden transmitting platform for synchronous orbit satellite platform |
| CN117214898A (en) * | 2023-11-09 | 2023-12-12 | 中国电子科技集团公司第十四研究所 | Wide-scale earth surface deformation refined remote sensing method based on multidimensional electromagnetic information depth fusion |
| CN117214898B (en) * | 2023-11-09 | 2024-01-23 | 中国电子科技集团公司第十四研究所 | Wide-scale earth surface deformation refined remote sensing method based on multidimensional electromagnetic information depth fusion |
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