Altitude measurement method, device, and storage medium based on multi-frequency linear combination InSAR

Abstract

The application relates to a height measurement method and device based on a multi-frequency linear combination InSAR and a storage medium, wherein the method comprises the following steps: segmenting a large-bandwidth signal used to extract different center frequencies, then linearly combining the center frequencies to generate various synthetic multiple measurement frequencies, measuring from small to large based on all the measurement frequencies, and updating the measurement phase difference of the next measurement result based on the product invariance principle by using the result of the previous measurement frequency, and gradually guiding phase unwrapping through hierarchical classification, so that the highest precision is achieved, compared with the prior art, the application simultaneously realizes the maximum measurement range and the highest measurement precision of an extremely steep terrain (EST), through single large-bandwidth signal acquisition, the application realizes real-time measurement without time error, and meanwhile, the large bandwidth provides superior distance resolution.

Description

Technical Field

[0001] This invention relates to InSAR altitude measurement, and more particularly to an altitude measurement method, apparatus, and storage medium based on multi-frequency linear combination InSAR. Background Technology

[0002] Interferometric Synthetic Aperture Radar (InSAR) is an important remote sensing technology that can reconstruct digital elevation models (DEMs) with high accuracy. High-precision DEMs have wide applications in geological, geomorphological, and geophysical analysis.

[0003] However, when measuring extremely steep terrain (EST), including man-made structures such as skyscrapers and steep natural terrain such as cliffs and valleys, traditional InSAR techniques cannot measure the DEM. This is due to the limitation of the Itoh condition. The Itoh condition states that the phase gradient (PG) between adjacent pixels should not exceed π to avoid phase blurring. But for EST, abrupt changes in elevation can easily lead to abrupt phase changes, meaning that the PG between adjacent pixels exceeds π. This violates the Itoh condition, therefore, traditional InSAR techniques cannot obtain the DEM of EST.

[0004] Therefore, multi-baseline InSAR (MB-InSAR) and multi-frequency InSAR (MF-InSAR) were proposed. For extreme terrain (EST), MB-InSAR uses baselines of different lengths to smooth abrupt phase changes, thus satisfying the Iton condition. MF-InSAR achieves the same goal by using different frequencies. The former is more difficult to design and implement in hardware, while the latter is easier to implement in hardware.

[0005] MF-InSAR typically requires information from two or more frequencies; higher frequencies enhance measurement accuracy, while lower frequencies expand the measurement range. By integrating this multi-frequency information, DEMs with large topographic variations can be measured with high precision. Specifically, signal processing of this multi-frequency information can be categorized into three methods. The first method uses maximum likelihood estimation (MLE) to directly estimate the DEM from the wrapped phase at different frequencies, thus avoiding the need to solve for the phase gradient and overcoming the limitations of the Itō condition. The second method utilizes algorithms such as the Chinese Remainder Theorem (CRT) and cluster analysis (CA) to establish a system of mathematical equations, ultimately obtaining a unique solution for the phase gradient, thereby overcoming the limitations of the Itō condition. The third method linearly combines different frequencies to obtain a synthetic frequency, which is much lower than any single frequency used. Theoretically, when the synthetic frequency is sufficiently low, the phase gradient will not exceed π, thus satisfying the Itō condition.

[0006] However, the methods described above still exhibit limitations when measuring ESTs. First, most methods require information from at least two frequency bands to balance measurement range and accuracy, such as the C-band and X-band. This necessitates at least two radar system runs, preventing real-time measurements and introducing time errors. These errors primarily stem from temporal abrupt changes in atmospheric conditions and terrain between runs, such as earthquakes and debris flows. Second, the low-frequency bands selected by the first two methods (such as the C-band) determine the measurable range, while the third method generates a synthetic frequency much lower than the actual low frequencies used, thus achieving a larger measurement range than the other two methods. For example, Klaus Schmitt and Werner Wiesbeck linearly combined 30 GHz and 37 GHz into a lower 7 GHz frequency, significantly expanding the measurement range. However, by using two even closer frequencies, the synthetic frequency can be further reduced, further expanding the measurement range. However, they have not yet explored this aspect in depth. Furthermore, they neglected the linear superposition of noise caused by the linear combination, leading to reduced measurement accuracy. Summary of the Invention

[0007] The purpose of this invention is to provide a height measurement method, device, and storage medium based on multi-frequency linear combination InSAR.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] A height measurement method based on multi-frequency linear combination InSAR includes:

[0010] Step S1: Initialize the buffer wavelength and buffer phase difference to be empty;

[0011] Step S2: Sort all measurement frequencies from smallest to largest, and select the measurement frequency with the smallest frequency value among all measurement frequencies as the current measurement frequency;

[0012] Step S3: Use the current measurement frequency to perform SAR imaging of the target terrain to obtain two phase images;

[0013] Step S4: After registering and subtracting the two phase maps, an interferometric phase map is obtained. Based on the interferometric phase map, the measurement height corresponding to the current measurement frequency and the measurement phase difference are obtained. The measurement phase difference is the phase difference between the dynamic phase at the high point and the reference phase at the low point.

[0014] Step S5: Determine whether the buffer phase difference is empty. If it is, update the buffer phase difference to the current measurement phase difference of the measurement frequency and update the buffer wavelength to the wavelength corresponding to the current measurement frequency. Select the next measurement frequency as the current measurement frequency and return to step S3. Otherwise, execute step S6.

[0015] Step S6: Correct the measurement phase difference based on the buffer phase difference, buffer wavelength, and wavelength corresponding to the current measurement frequency, and update the measurement height of the current measurement frequency based on the corrected measurement phase difference;

[0016] Step S7: Update the buffer phase difference to the current measurement phase difference of the measurement frequency, and update the buffer wavelength to the wavelength corresponding to the current measurement frequency. Determine whether all measurement frequencies have been traversed. If yes, proceed to step S8. Otherwise, select the next measurement frequency as the current measurement frequency and return to step S3.

[0017] Step S8: Use the measured height at the current frequency as the measurement result.

[0018] The measured frequency is a synthesized frequency obtained by combining two reference frequencies, and at least some of the reference frequencies are obtained by dividing the same frequency band.

[0019] The frequency of the measurement is the absolute value of the frequency difference between the two reference frequencies.

[0020] The relationship between the wavelengths corresponding to two adjacent measurement frequencies satisfies the following equation:

[0021] Λ i >Λ i-1 / 5

[0022] Among them: Λ i For the wavelength of the next measurement frequency, Λ i-1 The wavelength of the previous measurement frequency.

[0023] The process of correcting the phase difference in step S6 is specifically implemented based on the principle that the product of the wavelength corresponding to the measured frequency and the phase difference of the side face remains unchanged.

[0024] Step S6 specifically includes:

[0025] Step S6-1: Correct the first phase difference based on the buffer phase difference, buffer wavelength, and the current measurement frequency;

[0026] Step S6-2: Correct the measurement phase difference corresponding to the current measurement frequency based on the quotient of the first phase difference correction amount divided by π.

[0027] △φ i-update =n*π+△φ i MODπ

[0028] Where: △φ i-update The measurement phase difference Δφ corresponds to the updated measurement frequency i. i The measurement phase difference corresponding to the measurement frequency i before the update is given, and n is the quotient of the first phase difference correction divided by π.

[0029] Step S6-3: Obtain the measurement height of the updated current measurement frequency based on the measurement phase difference corresponding to the updated current measurement frequency.

[0030] The first phase difference correction amount is specifically:

[0031] △φ i-re =(Λ) cache *△φ cache ) / Λ i

[0032] Where: △φ i-re For the first phase difference, Δφ cache To buffer the phase difference, Λ cache For buffered wavelengths.

[0033] The relationship between the measured height and the measured phase difference is as follows:

[0034]

[0035] Where: △h is the measurement height, c is the speed of light, R is the slant distance, f is the measurement frequency, θ is the downward angle, and △φ is the measurement frequency difference.

[0036] A height measurement device based on multi-frequency linear combination InSAR includes a memory, a processor, and a program stored in the memory, wherein the processor executes the program to implement the method described above.

[0037] A storage medium having a program stored thereon, which, when executed, implements the method described above.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. By measuring frequencies from smallest to largest and hierarchically classifying them to guide phase unwrapping, the highest accuracy is achieved. This application's method simultaneously achieves the maximum measurement range and the highest measurement accuracy for EST.

[0040] 2. The measurement frequency is a composite frequency obtained by synthesizing two reference frequencies, and at least some of the reference frequencies are obtained by dividing the same frequency band. This can result in a sufficiently small minimum frequency, ensuring that the phase difference of the first measurement does not exceed π, while reducing costs and ensuring measurement accuracy.

[0041] 3. Using the quotient of the first phase difference and the remainder of its own phase difference as the updated measurement phase difference can ensure that the result is accurate enough. Attached Figure Description

[0042] Figure 1 A schematic diagram illustrating the failure of single-frequency InSAR in EST measurements;

[0043] Figure 2 This is a schematic diagram illustrating the principle of this application;

[0044] Figure 3 A schematic diagram illustrating the process of obtaining the synthesized wavelength;

[0045] Figure 4 This is a schematic diagram of a darkroom.

[0046] Figure 5 SAR intensity map;

[0047] Figure 6 The parameter range required by a certain prior art 3 and the method of this application;

[0048] Figure 7 This is a schematic diagram of the main steps of the method of the present invention; Detailed Implementation

[0049] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0050] Existing failure issues of single-frequency InSAR in EST measurements, such as Figure 1 As shown. The simulated 3D scene in the Cartesian coordinate system is as follows. Figure 1As shown in part (a), S1(x1,y1,z1) is the main antenna, and S2(x2,y2,z2) is the auxiliary antenna. The baseline length and antenna operating height are d = x2 - x1 = 5m and H = z1 = z2 = 10000m, respectively. Both S1 and S2 move along the y-axis, and y1 = y2 at all times. The antenna's downward angle of view is θ = 60°, and the center frequency of the radar system is f = 9CHz. The target is a mountain, and its left foot is located at point A(x1,y1,z1). A ,y A ,z A The mountaintop is located at point B(x). B ,y B ,z B The height difference dh between points A and B is...

[0051] S1 and S2 simultaneously perform SAR imaging of the target, generating phase images respectively. Figure 1 Parts (b) and (c) are shown. After registering and subtracting the two phase maps, an interferometric phase map is generated as shown. Figure 1 As shown in part (d). The corresponding height h can be calculated as:

[0052]

[0053] Where c is the speed of light, and R is the slant range corresponding to h. Figure 1 The x-coordinates of (b), (c), and (d) are given. Taking the derivative of φ with respect to h, we can obtain the relationship between dh and the phase difference dφ, expressed as:

[0054]

[0055] exist Figure 1 In (d), point A(R) A1 ,y A ,φ A ) and point B(R) B1 ,y B ,φ B The dφ between ) is dφ AB =φ A -φ B .

[0056] According to formula (2), we know that in dh AB If R, d, and θ remain constant and are relatively large, then the larger f is, the larger dφ will be. AB The larger the value, the greater the value. Under single-frequency InSAR measurement conditions, a larger value for f implies a larger value for dφ. AB .exist Figure 1 In part (d), for very close R A1 and R B1 This large dφAB This can lead to phase ambiguity. Therefore, for terrain with abrupt elevation changes (EST), it is difficult for single-frequency InSAR to reconstruct its digital elevation model (DEM).

[0057] To address the aforementioned problems, this application proposes a method that can simultaneously expand the measurement range and improve measurement accuracy.

[0058] Specifically, it manifests as a height measurement method based on multi-frequency linear combination InSAR, such as... Figure 2 and Figure 7 As shown, it includes:

[0059] Step S1: Initialize the buffer wavelength and buffer phase difference to be empty;

[0060] Before each measurement, the buffer wavelength and buffer phase difference need to be initialized to empty.

[0061] Step S2: Sort all measurement frequencies from smallest to largest, and select the measurement frequency with the smallest frequency value among all measurement frequencies as the current measurement frequency;

[0062] The measured frequency is the composite frequency obtained by combining two reference frequencies, and at least some of the reference frequencies are obtained by dividing the same frequency band. Specifically, the measured frequency is the absolute value of the frequency difference between the two reference frequencies.

[0063] Specifically, according to formula (2), in order to use a smaller dφ AB Measure larger dh AB A smaller f can be used. For terrain with abrupt elevation changes (ESTs) that cannot be measured, a smaller f can make dφ AB It decreases proportionally. When dφ AB When reduced to a certain extent, the R caused by EST... A1 and R B1 In cases where frequencies are close together, phase ambiguity will not occur, thus resolving the aforementioned problem. Based on this concept, the measurement frequency f is generated by combining two close reference frequencies f1 and f2. min That is, f min = |f1-f2|, and design f min The value of f is used to ensure that it does not cause phase blurring. min The theoretical design is as follows. For Figure 1 For points A and B in (a), we first need to estimate the approximate dh. AB The requirement is to use f. min When, dφ nB <π satisfies the Itō condition. Let dφ AB <π and formula (2), f min The following conditions should be met:

[0064]

[0065] Specifically, to solve the aforementioned problems, a signal with a central frequency of 9 GHz and a bandwidth of 2 GHz is adopted. It is selected to split out f1 = 8.5 GHz and f2 = 9.1 GHz from this large-bandwidth signal to form f min = 9.1 - 8.5 = 0.6 GHz < Q = 1.5 GHz. The interference phase diagrams of f1 and f2, that is, Figure 2 parts (e) and (f) in, both have phase ambiguities on the left side, while the interference phase diagram of f min is, that is, Figure 2 part (g) in, avoids phase ambiguity. Therefore, f min can be used to reconstruct the digital elevation model (DEM), as shown in part (h) of Figure 2 , and this model is roughly consistent with the true DEM in part (a) of Figure 1 . However, due to the expansion of the measurement range, it inevitably has relatively large measurement errors. The measured peak dh min using f AB is 630 m, while the true is 600 m. In addition, the DEM measured using f min is generally rough overall.

[0066] In order to simultaneously expand the measurement range and improve the measurement accuracy, one cannot rely solely on the single f formed by f1 and f2 min . A series of reference frequencies f1 < f2 < f3... < f[[ID=3?]] n are needed to generate a series of synthetic frequencies, that is, the measurement frequencies f sy1 < f sy2 < f sy3 ... < f syn , where f sy1 = f min . The synthetic frequencies can be expressed in terms of synthetic wavelengths, and the relationship between them is:

[0067]

[0068] Therefore, a series of synthetic frequencies arranged from the smallest to the largest can be expressed as a series of synthetic wavelengths, that is, Λ1 > Λ2 > Λ3... > Λ n , where Λ1 = c / f min . According to formula (2), for the same dφ AB , the larger the wavelength (i.e., the smaller the frequency), the larger the corresponding dh AB measurement range, but the lower the measurement accuracy, and vice versa. The relationship between the measurement ranges and accuracies of Λ1, Λ2, Λ3, λ is as shown in Figure 2The (j) part is shown, where λ = c / f1. In Figure 2 In part (i), by using gradually decreasing wavelengths Λ1, Λ2, Λ3, λ to guide the phase unwrapping process, the measurement accuracy gradually improves, as evidenced by the measured dh AB The values ​​change from 630, 621, 609, and 602m, gradually approaching the true value. This demonstrates that the method proposed in this application can simultaneously achieve the largest measurement range and the highest measurement accuracy.

[0069] In order to execute correctly, as follows Figure 2 The stepwise cascaded phase unwrapping shown in part (j) requires these wavelengths to satisfy Λ i The measurement range is greater than Λ i-1 The measurement accuracy. Λ i The measurement accuracy can be roughly estimated based on experience. Using Λ i One-fifth as Λ i The measurement accuracy is required. Therefore, for cascading to be performed, the wavelength must meet the following conditions:

[0070] Λ i >Λ i-1 / 5 (5)

[0071] Among them: Λ i For the wavelength of the next measurement frequency, Λ i-1 The wavelength of the previous measurement frequency.

[0072] In the simulation, a series of synthesized wavelengths were designed, namely Λ1 = 0.5m, Λ2 = 0.3m, Λ3 = 0.16m, and λ = 0.034m, where Λ1 satisfies formula (3), and the relationship between them satisfies formula (5). These wavelengths were obtained by combining a series of wavelengths segmented from a broadband signal, such as... Figure 3 As shown. The center frequencies of the segments are f1 = 8.1 GHz, f2 = 8.5 GHz, f3 = 9.1 GHz, and f4 = 9.9 GHz.

[0073] In summary, the method proposed in this application achieves both the largest elevation measurement range and the highest elevation measurement accuracy. Simulation results verify the effectiveness of the method proposed in this application.

[0074] Step S3: Use the current measurement frequency to perform SAR imaging of the target terrain to obtain two phase images;

[0075] Step S4: After registering and subtracting the two phase maps, an interferometric phase map is obtained. Based on the interferometric phase map, the measurement height corresponding to the current measurement frequency and the measurement phase difference are obtained. The measurement phase difference is the phase difference between the dynamic phase at the high point and the reference phase at the low point.

[0076] Step S5: Determine whether the buffer phase difference is empty. If it is, update the buffer phase difference to the current measurement phase difference of the measurement frequency and update the buffer wavelength to the wavelength corresponding to the current measurement frequency. Select the next measurement frequency as the current measurement frequency and return to step S3. Otherwise, execute step S6.

[0077] Step S6: Correct the measurement phase difference based on the buffer phase difference, buffer wavelength, and wavelength corresponding to the current measurement frequency, and update the measurement height of the current measurement frequency based on the corrected measurement phase difference. Specifically, the process of correcting the phase difference is implemented based on the principle that the product of the wavelength corresponding to the measurement frequency and the side phase difference remains unchanged.

[0078] Step S6 specifically includes:

[0079] Step S6-1: Based on the buffer phase difference, buffer wavelength, and the first phase difference correction amount corresponding to the current measurement frequency, the first phase difference correction amount is specifically as follows:

[0080] △φ i-re =(Λ) cache *△φ cache ) / Λ i

[0081] Where: △φ i-re For the first phase difference, Δφ cache To buffer the phase difference, Λ cache For buffered wavelengths.

[0082] Step S6-2: Correct the measurement phase difference corresponding to the current measurement frequency based on the quotient of the first phase difference correction amount divided by π.

[0083] △φ i-update =n*π+△φ i MODπ

[0084] Where: △φ i-update The measurement phase difference Δφ corresponds to the updated measurement frequency i. i The measurement phase difference corresponding to the measurement frequency i before the update is given, and n is the quotient of the first phase difference correction divided by π.

[0085] Step S6-3: Obtain the measurement height of the updated current measurement frequency based on the measurement phase difference corresponding to the updated current measurement frequency.

[0086] Step S7: Update the buffer phase difference to the current measurement phase difference of the measurement frequency, and update the buffer wavelength to the wavelength corresponding to the current measurement frequency. Determine whether all measurement frequencies have been traversed. If yes, proceed to step S8. Otherwise, select the next measurement frequency as the current measurement frequency and return to step S3.

[0087] Step S8: Take the measured height at the current frequency as the measurement result. As shown in Equation 5, the relationship between the measured height and the measured phase difference is:

[0088]

[0089] where: Δh is the measured height, c is the speed of light, R is the slant range, f is the frequency value of the measured frequency, θ is the depression angle, and Δφ is the measured frequency difference.

[0090] Verification was carried out in a darkroom, and a complete radar interferometric imaging experimental link was established. The darkroom is as Figure 4 shown.

[0091] The radar system uses a one-transmitter and two-receiver operating mode, and the baseline length is d = 0.4 m. The system runs a total of one acquisition. A corner reflector is used as the measurement target to simulate a steep terrain with a sharp height change. Here, two corner reflectors A and B are used, and the height difference between them is A signal with a center frequency of f = 10 GHz and a bandwidth of 2 GHz is used. The SAR intensity image obtained by one of the antennas is as Figure 5 shown, where A and B are magnified on the right. A and B represent discontinuous phases, corresponding to a sudden change in elevation.

[0092] When using traditional single-frequency InSAR for measurement, the dφ calculated by formula (2) AB = 7.4 > π, which violates the Itoh condition, so dh cannot be obtained AB .

[0093] To solve this problem, a lower f is obtained to expand the measurement range. f1 = 9.1 GHz and f2 = 9.3 GHz are selected from the broadband signal to form f min = 9.3 - 9.1 = 0.2 GHz < Q = 3 GHz, which satisfies formula (3). In this case, dφ AB does not exceed π, so dh can be obtained AB = 0.62 m.

[0094] However, compared with , this value still has a relatively large error. Therefore, the cascaded step-by-step phase unwrapping method is performed to improve the measurement accuracy. A series of signals with synthetic wavelengths are designed, namely Λ1 = 1.5 m, Λ2 = 0.75 m, Λ3 = 0.15 m, and λ = c / f1 = 0.034 m, where Λ1 = c / f minThey satisfy formula (3), and the relationship between them satisfies formula (5). These wavelengths are obtained by combining a series of bands segmented from a broadband signal, such as... Figure 3 As shown in the figure, the center frequencies of the segments are f1 = 9.1 GHz, f2 = 9.3 GHz, f3 = 9.7 GHz, and f4 = 10.9 GHz. The results recovered from this series of wavelengths are shown in Table 1.

[0095] Table 1 Experimental Results

[0096]

[0097]

[0098] In Table 1, as the wavelength decreases, the measurement accuracy gradually increases, with the error changing from 0.28, 0.06, 0.05 to 0.02 m, and dh AB Gradually approaching the true value via f min The measurement range was expanded, and the measurement accuracy was improved by using Λ1, Λ2, Λ3, and λ. Ultimately, both large-range and high-precision measurements were achieved. Experimental results demonstrate the effectiveness of the method proposed in this application.

[0099] To address the limitation of single-frequency InSAR in measuring ESTs, a linear combination multi-frequency InSAR (MF-InSAR) method is proposed. This method not only expands the measurement range but also improves measurement accuracy, while eliminating the error superposition caused by linear combination. Simulations and experiments demonstrate the effectiveness of the proposed method.

[0100] Furthermore, the performance of the method presented in this application was compared with that of some prior art, and the results are shown in Table 2. Under the same set of hardware conditions, the parameters were the same as those used in the simulation. The method presented in this application not only requires only one run but also achieves a larger measurement range while maintaining high accuracy.

[0101] Table 2. Comparison of theoretical performance of the method in this application with three existing methods.

[0102]

[0103] In other words, when measuring the same height, the method of this application imposes fewer hardware constraints on the radar system parameters d, H, and θ. Taking method 3 as an example, in Figure 6 In the comparison, green indicates that the method can measure within that set of parameters, while red indicates that it cannot be measured. Clearly, for EST measurements, the method in this application covers a wider range of parameters.

[0104] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

Claims

1. A method for height measurement based on multi-frequency linear combination InSAR, characterized in that, The method comprises the following steps: Step S1: initializing a cache wavelength and a cache phase difference as empty; Step S2: sorting all measurement frequencies from small to large, and selecting a measurement frequency with the smallest frequency value as a current measurement frequency from all measurement frequencies; Step S3: performing SAR imaging on a target terrain by using the current measurement frequency to obtain two phase maps; Step S4: obtaining an interference phase map by registering and subtracting the two phase maps, and obtaining a measurement height corresponding to the current measurement frequency and a measurement phase difference based on the interference phase map, wherein the measurement phase difference is a phase difference between a high point dynamic phase and a low point reference phase; Step S5: determining whether the cache phase difference is empty, if yes, updating the cache phase difference as the measurement phase difference of the current measurement frequency, updating the cache wavelength as a wavelength corresponding to the current measurement frequency, selecting a next measurement frequency as the current measurement frequency, and returning to step S3, otherwise, executing step S6; Step S6: correcting the measurement phase difference according to the cache phase difference, the cache wavelength and a wavelength corresponding to the current measurement frequency, and updating the measurement height of the current measurement frequency based on the corrected measurement phase difference; Step S7: updating the cache phase difference as the measurement phase difference of the current measurement frequency, updating the cache wavelength as a wavelength corresponding to the current measurement frequency, and determining whether all measurement frequencies are traversed, if yes, executing step S8, otherwise, selecting a next measurement frequency as the current measurement frequency and returning to step S3; Step S8: taking the measurement height of the current frequency as a measurement result.

2. The height measurement method based on multi-frequency linear combination InSAR according to claim 1, characterized in that, The measurement frequency is a synthetic frequency synthesized by two reference frequencies, and at least part of the reference frequencies is obtained by dividing a same frequency band.

3. The height measurement method based on multi-frequency linear combination InSAR according to claim 2, characterized in that, The measurement frequency is an absolute value of a frequency difference between the two reference frequencies.

4. The height measurement method based on multi-frequency linear combination InSAR according to claim 1, characterized in that, A relationship between wavelengths corresponding to two adjacent measurement frequencies satisfies the following formula: A i >Λ i-1 / 5 where: Λ i is the wavelength of the previous measurement frequency, Λ i-1 is the wavelength of the previous measurement frequency.

5. The height measurement method based on multi-frequency linear combination InSAR according to claim 1, characterized in that, The step S6 is specifically implemented by a principle that a product of a wavelength corresponding to a measurement frequency and a measurement phase difference is invariant.

6. The height measurement method based on multi-frequency linear combination InSAR according to claim 5, characterized in that, The step S6 specifically comprises: Step S6-1: correcting a first phase difference correction amount corresponding to the current measurement frequency according to the cache phase difference, the cache wavelength and the current measurement frequency; Step S6-2: correcting the measurement phase difference corresponding to the current measurement frequency according to a quotient obtained by dividing the first phase difference correction amount by π: △ Step S6-3: obtaining the measurement height of the updated current measurement frequency based on the updated measurement phase difference corresponding to the current measurement frequency. i-update = n *π+△ The first phase difference correction amount is specifically: i MODπ wherein: Δ The relationship between the measurement height and the measurement phase difference is: i-update is the updated measurement frequency i is the corresponding measurement phase difference, Δ The processor implements the method of any one of claims 1-8 when executing the program. i is the updated measurement frequency i is the corresponding measurement phase difference, Δ n is the first phase difference correction divided by π; The program is executed to implement the method of any one of claims 1-8.

7. The height measurement method based on multi-frequency linear combination InSAR according to claim 6, characterized in that, ​ △ ​ i-re =(Λ cache *△ ​ cache ) / Λ i where: Δ ​ i-re is the first phase difference, Δ ​ cache is the cache phase difference, Λ cache is the cache wavelength.

8. The height measurement method based on multi-frequency linear combination InSAR according to claim 6, characterized in that, ​ wherein: is the height of the object, is the speed of light, R is the slant range, f is the frequency value of the measuring frequency, ​ is the lower viewing angle, is the phase difference of the measuring phase, d is the base line length.

9. A height measuring apparatus based on multi-frequency linear combination InSAR, comprising a memory, a processor, and a program stored in the memory, characterized in that, ​ 10. A storage medium having stored thereon a program, characterized by ​

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