Dual-star formation sar high-keeping imaging method and device

Abstract

The application discloses a kind of double-star formation SAR high-keeping imaging method and device, first to the main star raw echo and auxiliary star raw echo of double-star formation SAR system is carried out spectrum pre-filtering processing, filter out the phase error between main and auxiliary images caused by non-overlapping range beam spectrum and azimuth beam spectrum;Establish the relationship equation set of Doppler characteristics and transmission slant range, solve the accurate value of target point and transmission slant range component, calculate main and auxiliary star imaging parameters;Using hyperbolic equivalent method and ECS imaging algorithm, main and auxiliary stars are simultaneously imaged, and high-keeping main and auxiliary star SAR images are obtained simultaneously, to realize double-star integrated SAR imaging.The above-mentioned method and device can realize high-keeping imaging to double-star formation SAR raw echo, reduce development cost and can realize good focusing effect, ensure timeliness, suitable for engineering application double-star SAR data fast imaging processing.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of synthetic aperture radar imaging, in particular to a dual-satellite formation SAR high-ambiguity-preserving imaging method and device. BACKGROUND

[0002] Dual-satellite formation refers to two satellites flying in very close orbit planes in coordination. By adjusting the eccentricity, perigee angle and ascending node right ascension of the satellite flight orbit, the dual-satellite can have a flexible working mode. Dual-satellite formation SAR is a configuration of dual-baseline SAR system, in which one satellite acts as a pulse transmitting satellite, and two satellites receive echo signals simultaneously, i.e. one transmitting and two receiving mode, in which the self-transmitting and self-receiving is the primary satellite, and the only receiving is the auxiliary satellite. The relative positions of the primary and auxiliary satellites remain unchanged during imaging time. The dual-satellite formation SAR system can simultaneously obtain a pair of SAR images of the same area, and can subsequently use the synthetic aperture radar interferometry (InSAR) to process the images, generate digital elevation model (DEM), monitor terrain deformation and realize three-dimensional reconstruction. It is one of the most effective observation technologies for global large-scale terrain mapping, and therefore the dual-satellite formation SAR system has great significance for improving satellite remote sensing observation capability.

[0003] Most of the existing dual-satellite formation SAR imaging technologies derive the dual-baseline echo spectrum from the dual-root distance, study the dual-baseline imaging algorithm, and need to accurately know the target point position to obtain the transmitting and receiving components of the range history. However, the above method has not been applied to the actual engineering to obtain the transmitting and receiving components of the range history under the condition that the accurate coordinates of the target point are unknown. In addition, there are inevitable along-track baseline and vertical baseline between the primary and auxiliary satellites in formation flight, i.e. mixed baseline. The mixed baseline will cause the azimuth Doppler spectrum shift and the range beam spectrum shift between the primary and auxiliary satellite echo data, resulting in reduced coherence between the primary and auxiliary SAR images and interferometric phase error, etc., which affects the phase preserving property of the dual-satellite SAR image. The existing dual-satellite formation SAR imaging technology does not consider the phase error problem caused by the mixed baseline. SUMMARY

[0004] The purpose of the present application is to provide a dual-satellite formation SAR high-ambiguity-preserving imaging method and device, which can realize high-ambiguity-preserving imaging of dual-satellite formation SAR raw echo, reduce development cost and realize good focusing effect, ensure timeliness, and is suitable for fast imaging processing of dual-satellite SAR data in engineering application.

[0005] The purpose of the present application is achieved by the following technical solutions:

[0006] A dual-satellite formation SAR high-ambiguity-preserving imaging method, the method comprising:

[0007] Step 1, the original echo of the main star and the original echo of the auxiliary star of the dual-star formation SAR system are subjected to spectrum pre-filtering processing, and the phase error between the main and auxiliary images caused by the non-overlapping range beam spectrum and azimuth beam spectrum is filtered out;

[0008] Step 2, a relationship equation set of Doppler characteristics and transmit-receive slant range is established, the accurate values of the target point and the transmit-receive slant range component are solved, and the main and auxiliary star imaging parameters are calculated;

[0009] Step 3, the main and auxiliary stars are simultaneously imaged by using the hyperbolic equivalent method and the ECS imaging algorithm, the main and auxiliary star SAR images with high phase preservation are simultaneously obtained, and the dual-star integrated SAR imaging is realized.

[0010] A dual-star formation SAR high-phase-preservation imaging device, the device comprises:

[0011] A pre-filtering processing module is configured to perform spectrum pre-filtering processing on the original echo of the main star and the original echo of the auxiliary star of the dual-star formation SAR system, and filter out the phase error between the main and auxiliary images caused by the non-overlapping range beam spectrum and azimuth beam spectrum;

[0012] An imaging parameter calculation module is configured to calculate the main and auxiliary star imaging parameters by establishing a relationship equation set of Doppler characteristics and transmit-receive slant range, and solving the accurate values of the target point and the transmit-receive slant range component;

[0013] An imaging algorithm module is configured to simultaneously image the main and auxiliary stars by using the hyperbolic equivalent method and the ECS imaging algorithm, simultaneously obtain the main and auxiliary star SAR images with high phase preservation, and realize the dual-star integrated SAR imaging.

[0014] The embodiment of the present application also provides an electronic device comprising a memory and a processor, the memory stores a computer program, and the processor is configured to run the computer program to perform the following steps:

[0015] The original echo of the main star and the original echo of the auxiliary star of the dual-star formation SAR system are subjected to spectrum pre-filtering processing, and the phase error between the main and auxiliary images caused by the non-overlapping range beam spectrum and azimuth beam spectrum is filtered out;

[0016] A relationship equation set of Doppler characteristics and transmit-receive slant range is established, the accurate values of the target point and the transmit-receive slant range component are solved, and the main and auxiliary star imaging parameters are calculated;

[0017] The main and auxiliary stars are simultaneously imaged by using the hyperbolic equivalent method and the ECS imaging algorithm, the main and auxiliary star SAR images with high phase preservation are simultaneously obtained, and the dual-star integrated SAR imaging is realized.

[0018] The embodiment of the present application also provides a computer storage medium, the computer storage medium stores a plurality of instructions, and the instructions are suitable for being loaded by a processor and performing each step in the above method.

[0019] From the technical solutions provided by the application, the method and the device can realize high-keeping imaging of the dual-satellite formation SAR original echo, reduce development cost, realize good focusing effect, ensure timeliness, and are suitable for fast imaging processing of dual-satellite SAR data in engineering application. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0021] Figure 1 The flowchart of the dual-satellite formation SAR high-keeping imaging method provided by the embodiment of the present application is shown.

[0022] Figure 2 The azimuth pre-filtered Doppler spectrum segment diagram described in the embodiment of the present application is shown. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, but not all the embodiments. This does not constitute a limitation on the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0024] As Figure 1 The flowchart of the dual-satellite formation SAR high-keeping imaging method provided by the embodiment of the present application is shown. The method comprises:

[0025] Step 1, performing spectrum pre-filtering processing on the main satellite original echo and the auxiliary satellite original echo of the dual-satellite formation SAR system, and filtering out the phase error between the main and auxiliary images caused by the non-overlapping range beam spectrum and azimuth beam spectrum;

[0026] In this step, the range pre-filtering technology is used to filter out the non-overlapping range beam spectrum of the main and auxiliary satellite echoes, that is, according to the reflectivity spectrum movement amount, the common range wave spectrum of the main and auxiliary satellite echoes is intercepted, and then the signals with the common range wave spectrum are subjected to range compression processing;

[0027] The explanation of the range wave spectrum offset caused by the vertical direction baseline is as follows: the echo data received by the SAR antenna is the convolution of the ground reflectivity and the incident signal. From the frequency domain, it is the product of the ground reflectivity spectrum and the signal spectrum, and the expression is as follows:

[0028]

[0029] wherein S T (ω) and S R (ω) represent the wave number spectrum of the primary star signal and the wave number spectrum of the secondary star signal respectively; R(ω) is the Fourier transform of the ground reflectivity; ω0 is the radar center frequency; c represents the speed of light; R T,c and R R,c represent the primary star center slant range and the secondary star center slant range respectively; θ1 and θ2 are the primary and secondary star's depression angles respectively, θ=(θ1+θ2) / 2; β is the ground slope; W(ω) is the band-pass filter of the SAR system transmission and reception, and the bandwidth thereof is B;

[0030] The offset amount Δf of the ground reflectivity spectrum between different depression angles is:

[0031]

[0032] In the formula, Δθ is the depression angle difference; f0 is the radar carrier frequency; the non-overlapping spectrum (non-coherent spectrum) is equivalent to the noise of the overlapping spectrum (coherent spectrum), and the coherence is reduced, so the non-overlapping spectrum must be cut off while the overlapping spectrum is retained;

[0033] In view of the problems of the reduced coherence between the primary and secondary images and the interference phase error caused by the Doppler spectrum offset caused by the along-track baseline, the azimuth pre-filtering technology is used to filter the non-overlapping azimuth Doppler spectrum, and the specific process is as follows:

[0034] According to the Doppler spectrum center frequency and the Doppler bandwidth of the primary and secondary star echo data, the overlapping Doppler spectrum is determined, and the non-overlapping Doppler spectrum is filtered out;

[0035] If f dc1 and f dc2 are the Doppler center frequencies of the primary and secondary star echo data respectively, and f dc1 ≥f dc2 , the Doppler bandwidths of the primary and secondary star echo data are both B d , then the overlapping Doppler spectrum is As shown in Fig. Figure 2 is the azimuth pre-filtering Doppler spectrum segment according to the embodiment of the application, and then the common Doppler spectrum in the spectrum segment is cut out from the primary and secondary star echo data, so as to filter out the non-overlapping azimuth Doppler spectrum.

[0036] Step 2, a Doppler characteristic and a relationship equation set of the transmission and reception slant range are established, the accurate values of the target point and the transmission and reception slant range components are solved, and the primary and secondary star imaging parameters are calculated;

[0037] In this step, the azimuth time η c, the main star antenna wave velocity center and the auxiliary star antenna beam center irradiate the target point p at the same time, and the bistatic echo distance history is R b ' i ; R S,C and R M,C respectively represent the distance between the auxiliary star and the main star antenna and the target point p at η c ; V M and V S respectively represent the equivalent velocity of the main star and the auxiliary star; θ M and θ S respectively represent the equivalent squint angle of the main star and the auxiliary star;

[0038] Let V'=(V M +V S ) / 2, the relationship equation group between the Doppler characteristics and the transmitting-receiving slant range is established and expressed as:

[0039]

[0040] where f dc and f dr respectively represent the Doppler center frequency and the Doppler frequency modulation of the satellite relative to the target point p; λ represents the wavelength;

[0041] Since V M ≈V S under the double-star formation configuration, the equations (4) and (5) can be considered as accurate, let the intersection orbit baseline length between the main star and the auxiliary star be d1, and the in-orbit baseline length be d2, according to the geometric relationship, there are:

[0042]

[0043] Substituting equation (6) into equations (4) and (5), the following equation can be obtained:

[0044] c2(R M,c ) 2 +c1R M,c +c0=0 (7)

[0045] wherein:

[0046]

[0047] The transmitting slant range R M,C can be obtained by solving the equation, and then the coordinates of the target point p can be obtained according to the antenna pointing or the distance Doppler positioning method, so as to complete the accurate calculation of the position of the target point p in the actual engineering;

[0048] Through the above geometric relationship analysis and modeling, the coordinates of the target point p and the transmitting-receiving slant range component R b ' i can be solved under the condition that the bistatic echo distance history R b ' i is known.S,C and R M,C ;

[0049] Then the primary star imaging parameter V M and θ M is solved according to the primary star orbit parameter and the target point position;

[0050] For the secondary star, the hyperbolic equivalent method is used to calculate the secondary star imaging parameter, including the equivalent slant range R eq,c , the equivalent velocity V eq and the equivalent squint angle θ eq , that is:

[0051]

[0052] In the specific implementation, after the hyperbolic equivalence, there is no double root in the secondary star echo, and then the ECS imaging algorithm can be used to image the secondary star echo.

[0053] Step 3, using the hyperbolic equivalent method and the ECS (Extended Chirp-Scaling) imaging algorithm to simultaneously image the primary and secondary stars, and simultaneously obtaining the high-keeping-phase primary and secondary star SAR images, realizing the integrated SAR imaging of the double stars.

[0054] Among them, the primary and secondary star echoes are processed according to the ECS imaging algorithm in the prior art, including the steps of CS factor multiplication, range migration correction and distance compression, azimuth compression and residual phase compensation.

[0055] Based on the above method embodiment, the embodiment of the application further provides a double-star formation SAR high-keeping-phase imaging device, the device comprising:

[0056] A pre-filtering processing module is configured to perform frequency spectrum pre-filtering processing on the primary star original echo and the secondary star original echo of the double-star formation SAR system, and filter out the phase error between the primary and secondary images caused by the non-overlapping distance beam spectrum and azimuth beam spectrum.

[0057] An imaging parameter calculation module is configured to solve the accurate values of the target point and the transmission-reception slant range component by establishing a relationship equation group of Doppler characteristics and transmission-reception slant range, and calculate the primary and secondary star imaging parameters.

[0058] An imaging algorithm module is configured to use the hyperbolic equivalent method and the ECS imaging algorithm to simultaneously image the primary and secondary stars, and simultaneously obtain the high-keeping-phase primary and secondary star SAR images, realizing the integrated SAR imaging of the double stars.

[0059] The implementation process of each module in the above device is described in the above method embodiment.

[0060] The embodiment of the present application also provides an electronic device, comprising a memory and a processor, the memory has stored a computer program, and the processor is arranged to run the computer program to perform the following steps:

[0061] The original echo of the primary satellite and the original echo of the secondary satellite of the dual-satellite formation SAR system are subjected to spectrum pre-filtering processing, and phase errors between the primary and secondary images caused by non-overlapping range beam spectrum and azimuth beam spectrum are filtered out.

[0062] A set of equations of Doppler characteristics and transmission-reception slant range are established, accurate values of target points and transmission-reception slant range components are solved, and imaging parameters of the primary and secondary satellites are calculated.

[0063] The hyperbolic equivalent method and the ECS imaging algorithm are used to simultaneously image the primary and secondary satellites, and high-keeping SAR images of the primary and secondary satellites are simultaneously obtained, so that dual-satellite integrated SAR imaging is realized.

[0064] The embodiment of the present application also provides a computer storage medium, which stores a plurality of instructions, and the instructions are suitable for being loaded by a processor and performing each step in the above method embodiment.

[0065] It is worth noting that the contents not described in detail in the embodiment of the present application belong to the prior art known to those skilled in the art.

[0066] In summary, the method and device in the embodiment of the present application have the following advantages:

[0067] 1. The present application extracts the common range wave spectrum and azimuth Doppler spectrum of the primary and secondary satellite echoes from the signal filtering level, cuts off the non-overlapping spectrum while retaining the overlapping spectrum, and reduces the SAR image phase error caused by the mixed baseline;

[0068] 2. The traditional dual-satellite formation SAR imaging method is realized based on the condition that the target point position is known, but in actual engineering application, the target point position cannot be predicted in advance, so the corresponding imaging method cannot be directly applied for processing. The present application solves the transmission-reception slant range components by establishing the Doppler parameter and distance history equation, and further obtains the target point coordinates according to the antenna pointing or distance Doppler positioning method, so as to complete the calculation of the accurate coordinates of the target point in the actual engineering application, which belongs to the method innovation in the actual engineering application;

[0069] 3. After completing the spectrum filtering and the imaging parameter calculation of the primary and secondary satellites, the present application simultaneously images the primary and secondary satellites by using the same set of traditional ECS imaging programs, so that high-keeping SAR images of the primary and secondary satellites are simultaneously obtained, the development cost is reduced, good focusing effect can be realized, the timeliness is ensured, and the present application is suitable for the rapid imaging processing of dual-satellite SAR data in engineering application.

[0070] Those skilled in the art can understand that all or part of the steps in the methods of the above embodiments can be instructed by programs to related hardware, and the corresponding programs can be stored in a computer readable storage medium. The storage medium mentioned above can be a read-only memory, a magnetic disk or an optical disk, etc.

[0071] The above description is merely preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any changes or replacements easily conceived by those skilled in the art within the technical scope disclosed by the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims. The information disclosed in the background section of the present application is merely intended to deepen the understanding of the overall background of the present application, and should not be regarded as acknowledging or implying in any form that the information constitutes the prior art known by those skilled in the art.

Claims

1. A method for high-coherent imaging of a bistatic satellite formation SAR, characterized in that, The method comprises: Step 1, performing spectrum pre-filtering processing on the primary satellite original echo and the auxiliary satellite original echo of the dual-satellite formation SAR system, and filtering out the phase error between the primary satellite image and the auxiliary satellite image caused by the non-overlapping range beam spectrum and azimuth beam spectrum; Step 2, establishing a relationship equation group of Doppler characteristics and transmission-reception slant range, solving the accurate values of the target point and the transmission-reception slant range component, and calculating the imaging parameters of the primary satellite and the auxiliary satellite; The process of step 2 is specifically as follows: At azimuth time η c , the main and auxiliary antenna beam centers simultaneously illuminate the target point p, and the bistatic echo distance history is R' bi ; R S,C and R M,C respectively represent the distances between the auxiliary and main antennas and the target point p at time η c ; V M and V S respectively represent the equivalent speeds of the main and auxiliary antennas; θ M and θ S respectively represent the equivalent squint angles of the main and auxiliary antennas; Let V' = (V M + V S ) / 2, the relationship between Doppler characteristics and the transmitting-receiving slant range is established, expressed as: where f dc and f dr respectively represent the Doppler center frequency and Doppler frequency rate of the satellite relative to the target point p; and λ represents the wavelength. Since V M ≈V S , let the intersection orbit baseline length between the primary star and the secondary star be d1, and the in-orbit baseline length be d2, according to the geometric relationship, there are: By substituting formula (6) into formula (4) and formula (5), the following formula can be obtained: c2(R M,c ) 2 +c1R M,c +c0= 0 (7) Wherein: The slant range R is solved by solving the equation M,C Then, the coordinates of the target point p are obtained according to the antenna pointing or the range-doppler positioning method, and the accurate position of the target point p in the actual project is obtained. Through the above geometric relationship analysis and modeling, the coordinates of the target point p, the transmitting-receiving slant range components R bi and R S,C and R M,C are solved under the condition that the double-station echo distance history R bi is known. Then the main star imaging parameter V M and θ M According to the main star orbit parameter and the target point position For the secondary star, the hyperbolic equivalent method is used to calculate the imaging parameters of the secondary star, including the equivalent slant distance R eq,c , the equivalent velocity V eq and the equivalent angle of view θ eq , that is: Step 3, simultaneously imaging the primary satellite and the auxiliary satellite by using the hyperbolic equivalent method and the ECS imaging algorithm, simultaneously obtaining the high phase-preserving primary satellite SAR image and the auxiliary satellite SAR image, and realizing the dual-satellite integrated SAR imaging.

2. The dual-star formation SAR high-precision phase imaging method according to claim 1, characterized in that, In step 1, the distance pre-filtering technology is used to filter out the non-overlapping range beam spectrum of the primary satellite echo and the auxiliary satellite echo, that is, according to the reflectivity spectrum shift, the common range wave spectrum of the primary satellite echo and the auxiliary satellite echo is intercepted, and then the signals with the common range wave spectrum are subjected to range compression processing; The echo data received by the SAR antenna is the convolution of the ground reflectivity and the incident signal, and from the frequency domain, it is the product of the ground reflectivity spectrum and the signal spectrum, and the expression is as follows: where S T (ω) and S R (ω) represent the wave number spectrum of the primary star signal and the wave number spectrum of the secondary star signal, respectively; R(ω) is the Fourier transform of the ground reflectivity; ω0is the radar center frequency; c represents the speed of light; R T,c and R R,c represent the primary star central slant range and the secondary star central slant range, respectively; θ1and θ2are the primary and secondary star's angles of depression, respectively, θ = (θ1+ θ2) / 2; and β is the ground slope. W(ω) is a band-pass filter for transmitting and receiving of the SAR system, and the bandwidth is B; The shift amount Δf of the ground reflectivity spectrum between different downward angles is as follows: In the formula, Δθ is the angle difference; f0 is the radar carrier frequency; the non-overlapping spectrum segment is equivalent to the noise of the overlapping spectrum segment, and the coherence is reduced, so it is necessary to cut off the non-overlapping spectrum segment while keeping the overlapping spectrum segment; In order to solve the problem that the Doppler spectrum shift caused by the along-track baseline reduces the coherence between the primary satellite image and the auxiliary satellite image and causes the interference phase error, the azimuth pre-filtering technology is used to filter out the non-overlapping azimuth Doppler spectrum, and the specific process is as follows: According to the Doppler spectrum center frequency and the Doppler bandwidth of the primary satellite echo data and the auxiliary satellite echo data, the overlapping Doppler spectrum is determined, and the non-overlapping Doppler spectrum is filtered out; If f dc1 and f dc2 are the Doppler center frequencies of the primary and secondary star echo data, respectively, and f dc1 ≥ f dc2 , the Doppler bandwidths of the primary and secondary star echo data are both B d , then the overlapping Doppler spectrum is Then, spectral segments were extracted from the primary and secondary star echo data. The common Doppler spectrum within the spectrum is used to filter out non-overlapping azimuth Doppler spectra.

3. A dual-star formation SAR high-coherent imaging device, characterized in that, The device comprises: A pre-filtering processing module is configured to perform spectrum pre-filtering processing on the primary satellite original echo and the auxiliary satellite original echo of the dual-satellite formation SAR system, and filter out the phase error between the primary satellite image and the auxiliary satellite image caused by the non-overlapping range beam spectrum and azimuth beam spectrum; An imaging parameter calculation module is configured to calculate the imaging parameters of the primary satellite and the auxiliary satellite by establishing a relationship equation group of Doppler characteristics and transmission-reception slant range, solving the accurate values of the target point and the transmission-reception slant range component, and the specific calculation process is as follows: At azimuth time η c , the main star antenna beam center and the auxiliary star antenna beam center simultaneously illuminate the target point p, and the bistatic echo distance history is R' bi ; R S,C and R M,C respectively represent the distances between the auxiliary star and the main star antennas and the target point p at time η c ; V M and V S respectively represent the equivalent speeds of the main star and the auxiliary star; θ M and θ S respectively represent the equivalent squint angles of the main star and the auxiliary star; Let V' = (V M + V S ) / 2, the relationship equations between Doppler characteristics and the slant ranges are established, expressed as: where f dc and f dr respectively represent the Doppler center frequency and Doppler frequency rate of the satellite relative to the target point p; and λ represents the wavelength. Since V M ≈V S , let the intersection orbit baseline length between the primary star and the secondary star be d1, and the in-orbit baseline length be d2, according to the geometric relationship, there are: By substituting formula (6) into formula (4) and formula (5), the following formula can be obtained: c2(R M,c ) 2 +c1R M,c +c0= 0 (7) Wherein: The slant range R is solved by solving the equation M,C Then, the coordinates of the target point p are obtained according to the antenna pointing or the range-Doppler positioning method, and the accurate position of the target point p in the actual project is obtained. Through the geometric relationship analysis and modeling above, it was achieved that the bistatic echo distance history R' was known. bi In this case, solve for the coordinates of the target point p and the transmit / receive slant range component R. S,C and R M,C ; Then the main star imaging parameter V M and θ M Solved according to the main star orbit parameters and target point position; For the secondary star, the hyperbolic equivalent method is used to calculate the imaging parameters of the secondary star, including the equivalent slant distance R eq,c , the equivalent velocity V eq and the equivalent angle of view θ eq , that is: An imaging algorithm module is configured to simultaneously image the primary satellite and the auxiliary satellite by using the hyperbolic equivalent method and the ECS imaging algorithm, simultaneously obtain the high phase-preserving primary satellite SAR image and the auxiliary satellite SAR image, and realize the dual-satellite integrated SAR imaging.

4. An electronic device comprising a memory and a processor, characterized in that The memory stores a computer program, and the processor is configured to run the computer program to execute the method in any one of claims 1 to 2.

5. A computer storage medium, characterized in that The computer storage medium stores a plurality of instructions, and the instructions are adapted to be loaded and executed by the processor to execute the method in any one of claims 1 to 2.

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