A power-law model InSAR tropospheric delay correction method
By correcting the InSAR tropospheric delay using a power-law model based on ERA-5 reanalysis data, the problem of insufficient monitoring accuracy caused by the lack of radiosonde data was solved, enabling high-precision monitoring of surface deformation in areas with large topographic relief.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- KUNMING UNIV OF SCI & TECH
- Filing Date
- 2023-02-07
- Publication Date
- 2026-07-17
Smart Images
Figure CN115980751B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of InSAR technology, specifically relating to a power-law model InSAR tropospheric delay correction method based on ERA-5 reanalysis data. Background Technology
[0002] InSAR technology is an interferometric diagram obtained by subtracting the phase values of two SAR image data acquired from repeated orbital observations covering the same area at different times. The resulting phase difference information represents the surface deformation. Compared with traditional leveling methods, InSAR technology can measure surface deformation in all weather conditions, over a wide area, and with high precision. It has gradually become one of the main technical means for monitoring the health of urban infrastructure and is widely used around the world to monitor surface deformation. It has successfully identified and monitored deformation signals that endanger urban safety, such as subsidence funnels caused by groundwater extraction, uneven deformation caused by fault activity, and surface subsidence caused by infrastructure construction.
[0003] Whether it's optical remote sensing or radar remote sensing, the influence of the atmosphere is unavoidable in satellite-based Earth monitoring systems. In radar remote sensing monitoring, the microwave signals emitted by the satellite at the two SAR imaging moments are affected by factors such as temperature, humidity, air pressure, and wind speed as they pass through the atmosphere, resulting in varying degrees of phase delay, or atmospheric effects. This atmospheric effect limits the accuracy of InSAR in surface monitoring and is one of the main sources of error.
[0004] For urban deformation monitoring in mid- and low-latitude regions, the tropospheric effect is one of the main sources of error in InSAR observations due to the relatively small ionospheric effect. The tropospheric effect can be divided into vertical stratification delay and turbulent mixing delay. Vertical stratification delay is caused by the different vertical refraction profiles of two SAR images acquired at different times, mainly affecting areas with large topographic relief, and it shows a strong spatial correlation with the terrain. Turbulent mixing delay is caused by the turbulent flow of atmospheric water vapor, resulting in inconsistent spatial distribution of atmospheric refractive index in the horizontal and vertical directions between the two observations.
[0005] Currently, in InSAR tropospheric delay correction methods, models such as spectrometer (MERIS, MODIS) atmospheric correction models and the Weather Research and Forecasting (WRF) model can effectively correct turbulent mixing delay. In areas with significant topographic relief, although traditional linear models and power-law models can correct vertical stratification delay, they both have their disadvantages. Traditional linear model correction methods are based on single interferograms, assuming a simple phase-elevation relationship and a constant scale factor, thus failing to estimate spatially varying tropospheric delay. Power-law model correction methods use sounding data to estimate power-law parameters to correct vertical stratification delay, but they cannot be used in areas without sounding data.
[0006] Therefore, a power-law model InSAR tropospheric delay correction method based on ERA-5 is proposed. Summary of the Invention
[0007] To address the issue of the inability to use power-law model methods due to the lack of radiosonde data, this invention provides a power-law model InSAR tropospheric delay correction method based on ERA-5 reanalysis data.
[0008] To achieve the above-mentioned technical objectives, the present invention is implemented through the following technical solution:
[0009] A power-law model InSAR tropospheric delay correction method based on ERA-5 reanalysis data is implemented through the following steps:
[0010] S1: Collect a dataset of N SAR single-look complex images, select one of them as the main image, and the remaining N-1 images as auxiliary images.
[0011] S2: Register and resample N-1 auxiliary images with the main image, preprocess them, and generate n interferograms; process them using an external DEM, remove the topographic phase, and finally generate differential interferograms.
[0012] S3: Select coherent points and filter out highly coherent target points;
[0013] S4: Unwrap the selected coherent point targets to obtain the differential interference phase after unwrapping each coherent point;
[0014] S5: Tropospheric delay correction was performed using the ERA-5 meteorological reanalysis data dataset, and the dry and wet delays of the troposphere in the study area were calculated.
[0015] S6: Analyze the relationship between the corrected tropospheric delay phase and topographic elevation in the ERA-5 reanalysis dataset, and use the obtained relationship between the tropospheric delay phase and elevation to fit the required power-law parameter α and reference elevation h.c Finally, a power-law model was used to correct the tropospheric delay.
[0016] S7: After correcting for vertical stratification delay, InSAR time series results are generated.
[0017] Preferably, the specific technical method in S5 is as follows:
[0018] Use the following expression: Calculate the atmospheric refractive index caused by dry delay in the study area. Calculate the atmospheric refractive index caused by the moisture delay in the study area. Calculate the refractive index N of the troposphere; where K1 = 0.776 kPa. -1 K2 = 0.716 kPa -1 K3 = 3.75 * 10 5 K 2 pa -1 P is the total air pressure, T is the temperature, and e is the partial pressure of water vapor.
[0019] By integrating the above refractive index, we obtain the dry and wet tropospheric delays:
[0020] Use the following expression: Calculate the radar line-of-sight tropospheric dry delay within the study area.
[0021] Calculate the radar line-of-sight wet tropospheric delay within the study area.
[0022]
[0023] Calculate the total radar line-of-sight delay into the troposphere within the study area. Calculate the tropospheric delay of the interferogram; where, The conversion factor from pseudorange increase to phase delay is given by θ, where θ is the incident angle and h is the phase delay. top h is the tropospheric zenith, and h is the Earth's surface elevation.
[0024] Preferably, the expression used in step S6 is: h <h c K is the scaling factor for estimating the tropospheric delay phase and the reference elevation. The constant deviation term is the height h. c The delayed phase at that time.
[0025] The beneficial effects of this invention are:
[0026] The InSAR tropospheric delay correction method provided by this invention takes advantage of the global free availability of EAR-5 reanalysis dataset data. The power-law model can be applied in different time periods and under different atmospheric conditions, effectively correcting the vertical stratification delay caused by large topographic relief and improving the accuracy of surface deformation detection. Attached Figure Description
[0027] Figure 1 This is a flowchart of the time series InSAR technique method in this invention.
[0028] Figure 2 The flowchart of the InSAR tropospheric delay correction method based on the power-law model of ERA-5 provided by this invention is shown. Detailed Implementation
[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0030] This invention proposes a power-law model InSAR tropospheric correction method based on ERA-5, which is an atmospheric delay correction method used when there are large topographic reliefs and a high correlation between tropospheric delay and elevation. It involves incorporating a tropospheric delay correction method into the time-series InSAR data processing, removing vertical stratification delays based on the relationship between tropospheric delay and elevation. Specifically, it uses ERA-5 meteorological reanalysis data to estimate the tropospheric phase of the studied area. If a power-law relationship exists between the estimated tropospheric delay and elevation, the parameters α and h in the power-law model are then estimated using the tropospheric delay. c Finally, a power-law model correction method was used to correct the atmospheric delay in vertical stratification.
[0031] Example 1
[0032] Reference Figure 1 This invention proposes a time-series InSAR technique processing flowchart based on the power-law model tropospheric delay correction method of ERA-5, which includes the following steps:
[0033] S1: Collect a dataset of N SAR single-look complex images, select one of them as the main image, and the remaining N-1 images as auxiliary images.
[0034] S2: Register and resample N-1 auxiliary images with the main image, preprocess them, and generate n interferograms; process them using an external DEM, remove the topographic phase, and finally generate differential interferograms.
[0035] S3: Select coherent points and filter out highly coherent target points;
[0036] S4: Unwrap the selected coherent point targets to obtain the differential interference phase after unwrapping each coherent point;
[0037] S5: Tropospheric delay correction was performed using the ERA-5 meteorological reanalysis data dataset, calculating the dry and wet tropospheric delays in the study area, including:
[0038] Use the following expression: Calculate the atmospheric refractive index caused by dry delay in the study area. Calculate the atmospheric refractive index caused by the moisture delay in the study area. Calculate the refractive index N of the troposphere; where K1 = 0.776 kPa. -1 K2 = 0.716 kPa -1 K3 = 3.75 * 10 5 K 2 pa -1 P is the total air pressure, T is the temperature, and e is the partial pressure of water vapor.
[0039] By integrating the above refractive index, we obtain the dry and wet tropospheric delays:
[0040] Use the following expression: Calculate the tropospheric dry delay within the study area.
[0041] Calculate the tropospheric wet delay within the study area.
[0042]
[0043] Calculate the total tropospheric delay within the study area. Calculate the tropospheric delay in the interferogram. Among them, The conversion factor from pseudorange increase to phase delay is given by θ, where θ is the incident angle and h is the phase delay. top h represents the tropospheric zenith, and h represents the Earth's surface elevation.
[0044] S6: Analyze the relationship between the corrected tropospheric delay phase and topographic elevation in the ERA-5 reanalysis dataset, and use the obtained relationship between the tropospheric delay phase and elevation to fit the required power-law parameter α and reference elevation h. c Finally, a power-law model was used to correct the tropospheric delay.
[0045] Using the expression: Δφ tropo =K(h) c -h) α +Φ c ,h <h c K is the scaling factor for estimating the tropospheric delay phase and the reference elevation, and φ is the scaling factor. c The constant deviation term (height h) c (Time delay phase).
[0046] S7: After correcting for vertical stratification delay, InSAR time series results are generated.
[0047] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0048] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.
Claims
1. A power-law model InSAR tropospheric delay correction method based on ERA-5 reanalysis data, characterized in that, This can be achieved through the following steps: S1: Collect a dataset of N SAR single-look complex images, select one of them as the main image, and the remaining N-1 images as auxiliary images. S2: Register and resample N-1 auxiliary images with the main image, preprocess them, and generate n interferograms; process them using an external DEM, remove the topographic phase, and finally generate differential interferograms. S3: Select coherent points and filter out highly coherent target points; S4: Unwrap the selected coherent point targets to obtain the differential interference phase after unwrapping each coherent point; S5: Tropospheric delay correction was performed using the ERA-5 meteorological reanalysis data dataset, and the dry and wet delays of the troposphere in the study area were calculated. S6: Analyze the relationship between the corrected tropospheric delay phase and topographic elevation in the ERA-5 reanalysis dataset. Use the obtained relationship between the tropospheric delay phase and elevation to fit the required power-law parameter α and reference elevation hc. Finally, use the power-law model to perform tropospheric delay correction. S7: After correcting for vertical stratification delay, InSAR time series results are generated; The specific technical method in S5 is as follows: Use the following expression: Calculate the atmospheric refractive index caused by dry delay in the study area. Calculate the atmospheric refractive index caused by the moisture delay in the study area. Calculate the refractive index N of the troposphere; where K1 = 0.776 kPa. -1 K2 = 0.716 kPa -1 K3 = 3.75 * 10⁵ K² Pa -1 P is the total air pressure, T is the temperature, and e is the partial pressure of water vapor. By integrating the above refractive index, we obtain the dry and wet tropospheric delays: Use the following expression: Calculate the radar line-of-sight tropospheric dry delay within the study area. Calculate the radar line-of-sight wet tropospheric delay within the study area. Calculate the total radar line-of-sight delay into the troposphere within the study area. Calculate the tropospheric delay of the interferogram; where, The conversion factor from pseudorange increase to phase delay is given by θ, where θ is the incident angle and h is the phase delay. top h represents the tropospheric zenith, and h represents the Earth's surface elevation. The expression used in S6 is: K is the scaling factor for estimating the relationship between the tropospheric delay phase and the reference elevation. The constant deviation term is the height. The delayed phase at that time.