CN115755045A - Method for estimating maximum depth reduction of underground water level based on InSAR ground settlement monitoring data - Google Patents

Abstract

The invention provides a method for estimating the maximum underground water level depth reduction based on InSAR ground settlement monitoring data, which comprises the following steps: 1. acquiring annual ground settlement of a research area based on an InSAR coherent target time sequence analysis method; 2. dividing hydrological and geological units and underground water level monitoring data of a research area; 3. establishing a relation model between ground settlement and maximum continuous underground water level depth reduction; 4. the total maximum continuous depth reduction of the underground water level in the region is estimated based on the annual ground settlement obtained by the InSAR coherent target time sequence analysis method. The method is based on water level data of underground water level monitoring points in a limited number of mined water-bearing stratum, and a relation model between annual ground settlement and maximum water head depth reduction of the underground water level is obtained through an InSAR coherent target time sequence analysis technology, so that the total maximum continuous depth reduction of the underground water level of the water-bearing stratum in the same hydrogeological unit of a research area is accurately and quickly estimated, and further, the mining amount of underground water in the hydrogeological unit is effectively guided.

Description

A method for estimating the maximum drawdown of groundwater table based on InSAR land subsidence monitoring data method

technical field

The invention relates to a method for estimating the maximum continuous depth of groundwater level of a regional aquifer group using ground subsidence data obtained by synthetic aperture radar interferometry (InSAR) technology, and belongs to the field of practical application of synthetic aperture radar interferometry technology in the discipline of hydrogeology. It can calculate the relevant parameters reflecting soil deformation characteristics based on the land subsidence obtained by InSAR technology and the groundwater level data at a limited number of groundwater level monitoring points in different aquifers in the same period. The total maximum continuous drawdown of the groundwater level of the aquifer group can effectively guide the extraction of groundwater in the same hydrogeological unit, thereby realizing the scientific management of groundwater and the precise prevention and control of land subsidence.

Background technique

Land subsidence, as a slowly changing geological disaster, is widely distributed in the world and has become a global geological environmental problem.

The overexploitation of groundwater and the continuous decline of groundwater level lead to the continuous compaction of the skeleton of the soil aquifer, which in turn causes land subsidence. The land subsidence consists of three parts: the first is the main subsidence accompanied by the gradual seepage of water in the pores, which is called elastic deformation. , the second is the unrecoverable deformation of the soil due to the readjustment of the soil skeleton structure under the effective load, which is called plastic deformation; the third is the hysteresis deformation of the cohesive soil. Due to the thick cohesive soil layer in the soil, the weak permeability of the cohesive soil layer makes the pore water pressure decrease first in the part close to the aquifer at the beginning of the water level drop, correspondingly causing this part of the cohesive soil to compress first, and The change of pore water pressure far away from the aquifer lags behind, and correspondingly, the deformation of this part of the cohesive soil also lags behind. Therefore, there is a hysteresis in the release and deformation of the cohesive soil layer in the soil, and the length of the lag time is related to the cohesive soil layer. It is proportional to the thickness and inversely proportional to the vertical permeability coefficient of the cohesive soil layer. In soil mechanics, there are three calculation models of land subsidence: classical elastic land subsidence model, quasi-elastic land subsidence model and rheology-based land subsidence model. The classic elastic land subsidence model is based on the Terzaghi theory, and it is generally assumed that the compression deformation of the aquifer skeleton is proportional to the decrease in pore water pressure. This model only considers the linear elastic deformation of the soil and ignores the readjustment of the aquifer skeleton structure The quasi-elastic land subsidence model still assumes that the compaction of the soil conforms to the law of elasticity, but considers that the parameters such as the permeability coefficient and water storage coefficient of the aquifer are not constant, but are functions of the soil void ratio, effective stress and time. The model can explain the nonlinear elastic compaction of soil, and its calculation accuracy and prediction accuracy of land subsidence are better than classical elastic models. Both the classical elastic land subsidence model and the quasi-elastic land subsidence model do not consider the plastic deformation and deformation hysteresis of the soil, and the error will be large when using these two models to calculate the land subsidence in areas with thick cohesive soil layers. The land subsidence model based on rheology can more comprehensively explain the process and law of land subsidence, and predict land subsidence more accurately, but its calculation requires many formation parameters, and its practical application has certain limitations. In addition, groundwater level monitoring data is also crucial when calculating land subsidence. The subsidence of soil is caused by the decline of groundwater levels in all aquifer groups below it. However, in actual work, hydrologists deploy The groundwater level monitoring points in China usually only focus on one or two aquifer groups, and the monitoring data on groundwater level changes in all aquifer groups is very small, so the groundwater level data in this area cannot completely and accurately reflect the groundwater in the whole area. Therefore, the established relationship model between land subsidence and groundwater level has deviations.

In order to overcome the shortcomings of the above-mentioned land subsidence calculation model, based on the groundwater level change data at the groundwater level monitoring points in the limited number of all aquifer groups in the study area, and to more quickly describe the relationship between land subsidence and groundwater level drawdown Relationship, based on Terzaghi’s one-dimensional consolidation theory, assuming that the soil satisfies: 1. The compression of the soil is entirely the result of the deformation of the soil skeleton (soil volume deformation) due to the reduction of the pore volume, while the soil particle itself Compression (shape deformation) is negligible; 2. The soil only produces vertical deformation without lateral deformation; 3. Under the basic assumptions that the soil layer is homogeneous and the pressure is uniformly distributed within the thickness of the soil layer, the soil The compressive deformation s _j of the body can be expressed as the sum of the land subsidence of the exploited aquifer group and the hysteresis deformation of the soil:

Among them, i represents the circulation variable. Quaternary strata in the North China Plain usually have four aquifer groups, denoted by Ⅰ, Ⅱ, Ⅲ and Ⅳ respectively. s _j is the compressive deformation at any point j in the soil, and Δσ _i is the The effective stress increment acting on the soil particles caused by the continuous decrease of the effective water head in the i aquifer group; E _{s, i} is the compressive modulus of the soil in the i aquifer group; H _i is the i aquifer group The thickness of the inner soil; c is the hysteresis deformation of the soil related to time.

Based on the calculation model of soil compression deformation in the above formula (1), using the InSAR coherent target time series analysis method to obtain the land subsidence data of a certain year in the study area and the groundwater level monitoring data of each aquifer group in the same period, the same hydrogeological The relevant parameters that can reflect the deformation characteristics of the soil in the unit, and then deduce the total maximum continuous drawdown of the groundwater level of the aquifer group in the hydrogeological unit.

Contents of the invention

1. Purpose: the purpose of the present invention is to provide a kind of method for estimating the total maximum continuous drawdown of the aquifer group groundwater level in the same hydrogeological unit, it is based on the water level data at the groundwater level monitoring point place in the aquifer group that has exploited limitedly, Through the relationship model between the annual land subsidence and the maximum water head drawdown obtained based on the InSAR coherent target time series analysis technology, the maximum sustained maximum groundwater level of the aquifer group in the same hydrogeological unit in the study area can be accurately and quickly estimated. Drawdown, and then effectively guide the extraction of groundwater in the hydrogeological unit.

2. Technical solution: the present invention is a method for estimating the total maximum continuous depth of groundwater level of regional aquifer groups based on InSAR land subsidence monitoring data. The specific steps of the method are as follows:

Step 1: Obtain the annual land subsidence in the study area based on the time series analysis method of InSAR coherent targets

(1) InSAR coherent target timing analysis technology method

The InSAR coherent target time series analysis method is based on a series of SAR image data in a long time series. By selecting pixels that maintain high coherence in the time series as the research object, their scattering characteristics have good stability over a long period of time. Then the phase information on the highly coherent pixel is obtained. When selecting an interference image pair, when the amount of data is small (less than 10 scenes), select an interference image with a short baseline (generally less than 300m), and combine the short baseline interference image pair to increase the single difference interference pattern. Obtain the time span of deformation information, and obtain as many observations as possible. Based on the obtained differential interference fringe atlas, the phase information on the differential interference fringe atlas is extracted by using highly coherent pixels, and then the point set of differential interferometric phase is obtained. At this time, the differential interferometric phase δφ _diff on any high coherence pixel point x (x) can be expressed as:

where λ is the radar wavelength, R is the slant distance between the radar satellite and the monitoring target, B _⊥ is the vertical baseline, T is the time baseline, θ is the incident angle of the radar satellite, v(x) and ε _error (x) are respectively Linear velocity (annual subsidence) and elevation error between adjacent highly coherent pixels; δφ _nonlinear (x) is the nonlinear deformation phase, δφ _atm (x) is the error phase caused by atmospheric fluctuations, δφ _noise (x) is Noise phase caused by factors such as decoherence.

In the whole interferogram atlas, the linear rate and digital elevation (DEM) error of any highly coherent pixel point are constant, which is the linear component in the model. Using the two-dimensional spectrum estimation model, the differential interferometric phase is regarded as the observation value, and the deformation sequence of the highly coherent pixel point target is an unknown number. Through formula (3), the estimated model coherence coefficient γ _{x, 0} exceeds a certain threshold, such as greater than 0.85 The deformation sequence value of the highly coherent pixel point target in the study area can be solved in time, and the deformation sequence value of the high coherence pixel point target in the study area can be converted into a vertical deformation sequence value, and the high coherence pixel point target in the study area can be obtained annual land subsidence data.

为第k个差分干涉纹图中第x个高相干像素点处差分干涉相位与线性形变相位、高程误差相位之差，T^k为第k个差分干涉纹图的时间基线，

为第k个差分干涉纹图的垂直基线，

为第k个差分干涉纹图中任意一高相干像素点x上的差分干涉相位，

为第k个差分干涉纹图中第x个高相干像素点的非线性形变相位，

为第k个差分干涉纹图中第x个高相干像素点的大气波动引起的误差相位，

为第k个差分干涉纹图中第x个高相干像素点的失相干等因素引起的噪声相位，λ为雷达波长，R为雷达卫星与监测目标之间的斜距，θ为雷达卫星的入射角，v(x)、ε_error(x)分别为高相干像素点x处的线性速率(年度沉降量)和高程误差。Where γ _x is the coherence coefficient of the two-dimensional spectrum estimation model, N is the number of differential interferograms, k represents the circular variable, and j represents the imaginary unit,

is the difference between the differential interference phase, the linear deformation phase, and the elevation error phase at the xth high-coherence pixel point in the k-th differential interferogram, T ^k is the time baseline of the k-th differential interferogram,

is the vertical baseline of the kth differential interferogram,

is the differential interference phase on any high-coherence pixel x in the k-th differential interferogram,

is the nonlinear deformation phase of the xth highly coherent pixel in the kth differential interferogram,

is the error phase caused by the atmospheric fluctuation of the xth highly coherent pixel in the kth differential interferogram,

is the noise phase caused by factors such as the decoherence of the xth highly coherent pixel in the kth differential interferogram, λ is the radar wavelength, R is the slant distance between the radar satellite and the monitoring target, and θ is the incidence of the radar satellite angle, v(x) and ε _error (x) are the linear velocity (annual settlement) and elevation error at the highly coherent pixel point x, respectively.

(2) The splicing of land subsidence data in adjacent maps

When the research area is large, the radar data of multiple maps are needed to completely cover, but the reference datum position of the ground subsidence data of each map obtained based on the InSAR coherent target timing analysis technology is different, so it is necessary to The reference datum of each map frame is used for overall deviation compensation.

In order to reduce the overall deviation of land subsidence parameters between adjacent map frames, one of the map frames is selected as a reference (the reference map frame is selected based on prior knowledge), based on the deformation of the highly coherent pixel point target in the overlapping part of adjacent map frames Parameters, statistical analysis is carried out according to formulas (4) and (5), and then the overall deviation of deformation between adjacent map sheets is calculated.

ρ′ _s = ρ _s +Δρ _off (5)

Among them, M represents the reference frame and the number of high-coherence pixel targets in the overlapping area of the frame to be adjusted, i represents the cycle variable, Δρ _off is the reference deviation between adjacent frames; ρ _{m, i} is the overlap in the reference frame ρ _{s, i} is the deformation of the coherent target i in the overlapping area in the frame to be adjusted, and ρ′ _s is the corrected deformation of all highly coherent pixel targets in the frame to be adjusted vector; ρ _s is the deformation vector of all highly coherent pixel targets in the frame to be adjusted before correction.

After compensating for the overall deviation of the reference datum between the map sheets, the external DEM data is used to geocode the land subsidence data of each map sheet, and finally the annual land subsidence within the study area is obtained.

Step 2: Division of hydrogeological units and groundwater level monitoring data in the study area

Large-scale regional land subsidence in my country is mainly distributed in the North China Plain. The North China Plain is flat, with an altitude of no more than 100m, and slopes toward the Bohai Bay from the north, west, and south-west directions. The Quaternary strata in the North China Plain can be horizontally divided into piedmont alluvial-diluvial slope plains, central-eastern alluvial plains, and coastal alluvial-marine plains according to their origin and morphological characteristics. Among them, in the central-eastern alluvial plains, the Quaternary The strata can be further subdivided into the alluvial-diluvial hydrogeological sub-region of the Luan River, the alluvial-diluvial hydrogeological sub-region of the Chaobai River, the alluvial-diluvial hydrogeological sub-region of the Yongding River, and the alluvial-diluvial hydrogeological sub-region of the Hutuo River. Because of the different causes, the floor depth, thickness and hydraulic connection of the underlying aquifer groups are different. Therefore, it is necessary to clearly divide the hydrogeological characteristics of the study area on the basis of a detailed analysis of the hydrogeological characteristics of the study area. In this way, it can be considered that the same hydrogeological unit and the same aquifer group have basically the same hydrogeological parameters such as burial depth and groundwater connectivity.

In the same hydrogeological unit in the North China Plain, the Quaternary strata can usually be divided into four aquifer groups vertically from top to bottom, and I, II, III, and IV can be used to represent the four different aquifer groups. If this hydrogeological unit belongs to the alluvial-diluvial inclined plain in the piedmont, the I and II aquifer groups have been exploited together, and they are collectively referred to as shallow groundwater, and the III and IV aquifer groups are deep-layer groundwater; if this The hydrogeological unit belongs to the central and eastern alluvial plain or the coastal alluvial marine plain. The shallow groundwater mainly occurs in the first aquifer group, and brackish water and salt water are widely distributed. The deep groundwater mainly occurs in the II, III, and IV aquifers. Group.

At present, the monitoring of groundwater level data in the North China Plain is based on the existing mining wells in rural areas and enterprises in the study area, and there are few or almost no wells dug specifically for groundwater level monitoring. Therefore, groundwater level monitoring in the North China Plain The geographic location, monitoring depth, and number of monitoring wells are all random, so the monitoring data of the existing groundwater level monitoring wells need to be analyzed according to the characteristics of the hydrogeological units in the study area and the buried depths of the roof and floor of the four water-bearing groups. The groundwater level monitoring data at different monitoring locations and depths are used to represent the changes in groundwater levels in different aquifer groups. On this basis, it is analyzed whether the monitoring data of groundwater levels in different aquifer groups in this hydrogeological unit are complete, that is, whether there are groundwater level monitoring data in the exploited aquifer groups in this hydrogeological unit. It is possible to establish the relationship model between land subsidence and groundwater level in this area only when there are groundwater level monitoring data in the layer group.

Step 3: Establishment of the relationship model between land subsidence and the maximum sustained groundwater level drawdown

The large-scale land subsidence in the North China Plain is mainly due to the shortage of groundwater resources caused by the overexploitation of groundwater, and the depth of the water table has increased significantly, which has increased the effective stress acting on the soil and caused the soil to compress and deform. The deformation mechanism of soil is very complicated. It is not an ideal elastic-plastic body, but a product of natural history with elasticity and plasticity. However, according to Terzaghi’s one-dimensional consolidation theory, we believe that soil is an ideal soil. The amount of compression deformation s _j can be expressed by formula (1). The compression deformation at any point of the soil is the sum of the compression of each aquifer group below it, and the compression of each aquifer group is determined by the decrease of the groundwater level in the aquifer group and the increase of the effective stress acting on the soil. However, under the premise of the same groundwater head drawdown, the effective stress increment acting on the soil in different aquifer groups is different. If the groundwater head drawdown is Δh (under ideal conditions, the difference between the initial groundwater level at the beginning of monitoring and the groundwater level at the end of monitoring in an aquifer group), then in unconfined aquifers and confined water aquifers, The effective stress increment acting on the soil respectively can be expressed by the following formula:

Δσ _pw ＝(γ _nat -γ _eff )Δh (6)

Δσ _cw = γ _w Δh (7)

In the formula, Δσ _pw is the increment of effective stress in unconfined aquifer; Δσ _cw is the increment of effective stress in confined aquifer; γ _nat is the natural weight of soil; γ _eff is the effective weight of soil (buoyant weight ); γ _w is the weight of water.

It is worth noting that the actual underground aquifer group is composed of layers of clay and sand superimposed on each other. The groundwater level in the aquifer group drops, and the effective water acting on the soil (soil body composed of clay and sand interlayers) When the stress increases, the pore water in the sand is immediately discharged, but the pore water in the clay takes a long time to discharge, and correspondingly, the clay deformation in the aquifer group also needs a certain duration to make the ground reach the final settlement; when the groundwater When the water level rises, the groundwater level in the sandy soil in the aquifer rises rapidly, but the groundwater level in the cohesive soil remains unchanged or is still falling due to the impact of the previous water level drop, and the cohesive soil is still compressively deformed accordingly. Land subsidence continues. Therefore, the drawdown of the groundwater head in the above formulas (6) and (7) is actually the effective average value of the drawdown of the groundwater head in the clay and sandy soils in the aquifer. However, in the process of actual groundwater level monitoring, the change data of the groundwater level in the sandy soil in the aquifer group is usually obtained, and it is difficult to obtain the effective average value of the groundwater head drawdown in the clay and sandy soil in the aquifer. Here we introduce the maximum continuous drawdown of the groundwater table and the coefficient of the cohesive soil deformation characteristics related to the cohesive soil layer thickness, permeability coefficient and other parameters to replace the groundwater head drop in formulas (6) and (7). Depth Δh, where the maximum continuous drawdown of the groundwater table refers to the difference between the lowest elevation of the groundwater level of a certain aquifer group and the initial elevation of the groundwater level within a period of monitoring. At this time, based on the directly obtained groundwater level elevation data of each aquifer group in the study area, we can obtain the maximum continuous drawdown data of each aquifer group within a monitoring period, and use this maximum continuous drawdown Δh _max The compressive deformation of the soil can be calculated by multiplying the product Δh _max f(t) of the cohesive soil deformation coefficient f(t) related to the cohesive soil layer thickness, permeability coefficient and other parameters, so the formula (1) can be further expressed for:

(1) In the central and eastern alluvial plains and coastal alluvial marine plains:

(2) In the alluvial and diluvial sloping plain in front of the mountain:

分别为为第Ⅰ层、第i层含水层土体内地下水位持续下降一个有效单位引起含水层组的压缩变形量，其中在在潜水含水层组内，

在承压含水层组内，

a_Ⅰ，a_i分别表示为

值得注意的是，在上述Ⅰ、Ⅱ、Ⅲ、Ⅳ4个含水层组的任意一含水层组中，γ_nat、γ_eff、γ_w均为常量，E_s为含水层组的压缩模量，通常随着土体有效应力的增大，压缩模量是变化的。In formulas (8) and ( ₉ ), i represents the cycle variable, Ⅰ, _Ⅱ , Ⅲ, and Ⅳ respectively represent the four aquifer groups from top to bottom in the North China Plain; The natural weight of the i-th aquifer soil; γ _{eff, Ⅰ} , γ _{eff, i} are the effective weight (buoyant weight) of the I-th aquifer and the i-th aquifer soil respectively; γ _w is the weight of water; E _{s , i} is the _{compressive modulus of the soil in the i-th aquifer group; H i is the} thickness of the soil in the i-th aquifer group; ; Δh _Ⅰ , Δh _i are the groundwater head drawdowns of the aquifer layer I and i respectively; c is the hysteresis deformation of the soil related to time; f _Ⅰ (t), f _i (t) are respectively is the coefficient representing the deformation of cohesive soil related to the cohesive soil layer thickness, permeability coefficient and other parameters in the aquifer soil body of layer I and i;

are respectively the compressive deformation of the aquifer group caused by the continuous drop of groundwater level in the soil of the first layer and the i-th layer by one effective unit, in which, in the phreatic aquifer group,

Within a confined aquifer group,

a _Ⅰ , a _i are expressed as

It is worth noting that in any one of the above-mentioned 4 aquifer groups I, II, III, and IV, γ _nat , γ _eff , and γ _w are all constants, and E _s is the compressive modulus of the aquifer group, usually As the effective stress of the soil increases, the compressive modulus changes.

Step 4: Based on the annual land subsidence obtained by the InSAR coherent target time series analysis method, estimate the total maximum continuous depth of the regional groundwater level

According to formula (8) or (9), based on the annual land subsidence data obtained by the InSAR coherent target time series analysis method and the maximum continuous drawdown data of the groundwater level of each aquifer group at typical points, by solving the linear equations, we can get The coefficient and hysteresis deformation c representing the compressibility of each aquifer group are calculated. It is worth noting that the hysteresis deformation c is related to the maximum continuous drawdown of the groundwater level. Assuming that the hysteresis deformation c is a linear function of the total maximum continuous drawdown of the groundwater level, the linear equations in equation (8) or (9) exist 5 unknowns, in theory, at least 5 groundwater level monitoring points of the maximum continuous groundwater level drawdown data of the 4 aquifer groups are required to accurately solve the correlation coefficients a _I , a _Ⅱ , a of the soil mass of the 4 aquifer groups _Ⅲ , a _Ⅳ and lagged deformation c, but because there is a certain time deviation between the groundwater level monitoring data and the ground subsidence data in the monitoring process, the groundwater level monitoring data we usually obtain deviates from the real data, so we use the iterative method Find the optimal solution to a system of linear equations. On this basis, based on the land subsidence data in the study area obtained by InSAR coherent target time series analysis technology and the correlation coefficients a _I , a _II , a _III , a _IV of the corresponding aquifer groups, and the lagged deformation c, the research area can be estimated. The total maximum continuous drawdown of the groundwater level in the region. When the groundwater level monitoring data in some research areas are incomplete, the linear equations need to be simplified to effectively estimate the total maximum continuous drawdown data of the groundwater level in the research area.

3. Advantages and effects: the present invention provides a method for estimating the maximum continuous drawdown of groundwater levels in aquifer groups based on InSAR land subsidence monitoring data, and its advantages are:

(1) This method comprehensively considers the water head drawdown of sandy soil and cohesive soil in the aquifer group, and introduces the maximum water head continuous drawdown of the groundwater level of the aquifer group and the characterization of the parameters related to the thickness of the cohesive soil, permeability coefficient, time, etc. The cohesive soil deformation coefficient is used to replace the groundwater head drawdown of the aquifer group under ideal conditions, and the relationship between the annual land subsidence and the maximum groundwater head drawdown obtained based on the InSAR coherent target time series analysis technology within a certain period of time can be accurately established Model.

(2) This method can quickly estimate the total groundwater level of the aquifer group in the same hydrogeological unit in the study area based on the amount of land subsidence in the study area and the groundwater level data at a limited number of groundwater level monitoring points of the exploited aquifer group. The maximum continuous drawdown can effectively guide the extraction of groundwater in the hydrogeological unit, realize the scientific management of groundwater and the precise prevention and control of land subsidence.

(3) This method points out that the land subsidence is a comprehensive reflection of the groundwater level decline of all exploited aquifer groups. On the premise of fully considering the groundwater exploitation status of all aquifer groups in the study area, an accurate relationship model between land subsidence and groundwater can be established. This paper The method provides new ideas for hydrogeologists in the deployment of groundwater level monitoring points and the interpretation of the cause of land subsidence.

Description of drawings

Figure 1 Radar data coverage in Hengshui area

Figure 2 shows the land subsidence in Hengshui area in 2019 based on InSAR coherent target timing analysis technology.

Fig. 3 is a hydrogeological profile crossing the entire Hengshui area from northwest to southeast.

Fig. 4 The distribution map of the maximum continuous drawdown of groundwater level at different monitoring depths in Hengshui area in 2019, where (a) is the distribution map of the maximum continuous drawdown of groundwater level at each monitoring point at the groundwater monitoring depth of -6.37 ~ -74.5m; ( b) is the distribution map of the maximum continuous drawdown of the groundwater level at each monitoring point at the groundwater monitoring depth of -69 to -197m; (c) is the maximum continuous drawdown of the groundwater level at each monitoring point at the groundwater monitoring depth of -150 to -270m Distribution map; (d) is the distribution map of the maximum continuous drawdown of groundwater level at each monitoring point at the groundwater monitoring depth of -248 ~ -330m.

Figure 5. The distribution map of the total maximum continuous drawdown of the groundwater level in the alluvial-diluvial hydrogeological units of the Fuyang River and Zhangwei River in the central and southern Hengshui area.

Detailed ways

Taking the radar data and groundwater level monitoring data covering the Hengshui area as an example, the specific operation steps of the present invention in practical application are described. The invention is a method for estimating the total maximum continuous depth of groundwater level of a regional aquifer group based on InSAR land subsidence monitoring data. The specific steps of the method are as follows:

Step 1: Obtain the annual land subsidence in the study area based on the time series analysis method of InSAR coherent targets

(1) Radar data selection

Select the Radarsat-2 radar data with a resolution of 3m, a width of 125km, and an image acquisition mode of Extra-fine. The acquisition time is from September 2018 to September 2019. There are a total of 2 image frames and 26 scenes of radar data. Covering the entire Hengshui area (Figure 1). The RADARSAT-2 satellite was successfully launched on December 14, 2007 at the Baikonur space base in Kazakhstan, and is the follow-up satellite of RADARSAT-1. The RadarSAT-2 satellite has a revisit period of 24 days, C-band, and the incident angle varies between 20°-60°. scene application. The main parameters of Radarsat-2 radar data are shown in Table 1.

Table 1 selects the main parameter list of Radarsat-2 radar

(2) Extraction of annual land subsidence in Hengshui area

Based on the coherent target InSAR time series analysis method, for the radar data of two adjacent maps in the Hengshui area from September 2018 to September 2019, the radar data fine registration, the generation of differential interferograms, and the extraction of coherent target points were respectively carried out 1. Use the two-dimensional periodogram to perform parameter inversion to extract the linear deformation in 2019 on the coherent target points within each map frame; on this basis, select one of the map frames as a benchmark (select the benchmark based on prior knowledge map frame), statistically analyze the deformation parameters of the coherent target in the overlapping part of another map frame, calculate the overall deviation of annual deformation between the two adjacent map frames, and add the overall deviation from the reference map frame to the other map frame. All the coherent target points in one map frame are used to obtain the corrected 2019 annual deformation of the map frame; finally, the annual deformation values of the two map frames are converted into vertical deformation values, and then the external DEM data is used for radar image data analysis. Geocoding, and then realized the transformation of the vertical deformation in the Hengshui area in 2019 from the radar coordinate system to the plane coordinate system, and obtained the distribution of the vertical deformation in the Hengshui area in 2019 (Figure 2), where "-" indicates land subsidence, "+" indicates ground lift.

Step 2: Division of hydrogeological units and groundwater level monitoring data in the study area

(1) Division of aquifer groups in the Hengshui area

Horizontally, the Hengshui area is located in the central and eastern alluvial plain. According to the genesis of the Quaternary strata, the strata in this area can be subdivided into the Hutuo River alluvial hydrogeological subregion, the Fuyang River alluvial hydrogeological subregion, and the Zhangwei River subregion. Alluvial-diluvial hydrogeological sub-region; from a vertical perspective, referring to the standard for dividing aquifer groups in the North China Plain, the aquifer groups in the Hengshui area are divided into I, II, III and IV aquifer groups from top to bottom, as shown in Figure 3 Show.

The first aquifer group: this aquifer group gradually transitions from northwest to southeast to the channel belt in the central plain area, the thickness of the aquifer becomes larger, and the thickness of some sections can reach 40m~50m, and the lithology is mainly silty sandstone, which is permeable Strong water conductivity and high precipitation infiltration coefficient. However, in the alluvial-diluvial hydrogeological subregion of the Hutuo River, the aquifer group is a thin-layered multi-layered aquifer structure with a small thickness. Since there are many clay layers with different thicknesses between the aquifers, the water permeability and conductivity of the aquifer The water property is poor, and the precipitation infiltration coefficient is small, which is the whole freshwater zone in the study area.

The second aquifer group: In the alluvial-diluvial hydrogeological subregion of the Hutuo River, there is an unstable and thin clay layer between this aquifer group and the above first aquifer group, and the lateral recharge conditions are good and the hydraulic pressure between the groundwater Contact is better. In the Fuyang River alluvial-diluvial hydrogeological sub-region and the Zhangwei River alluvial-diluvial hydrogeological sub-region, the aquifer formation is formed by fluvial alluvial and lake sediments, and the lithology is mainly medium-fine sand and fine sand. Between 6 and 12m ³ /h·m.

The third aquifer group (Ⅲ1 and Ⅲ ² ): this aquifer group is a set of fluvial alluvial-diluvial sediments, the floor is buried at a depth of 250-350m, and the aquifer is thicker and further subdivided into upper and lower aquifers subgroup. The lithology of this aquifer group is mainly muddy and sandy, and the grain size of the sand layer presents a trend of being finer in the middle and thicker on both sides. Correspondingly, the water permeability and conductivity of the aquifer group also show the same trend. The cohesive soil layer overlying this aquifer group is relatively thick, with a local thickness of up to 10 m and a large continuous distribution. It is worth noting that in the alluvial-diluvial hydrogeological sub-region of the Hutuo River, the aquifer is discontinuous, the water-richness is weak, and there is a good hydraulic connection with the second aquifer group in some sections.

The fourth aquifer group: the burial depth of this aquifer group is 450-600m, and its bottom boundary is the Quaternary basement. The central part of the aquifer group has a shallow burial depth and a small thickness, while the two sides have a large burial depth and a large thickness; the lithology presents a change from coarse to fine from west to east, with medium-fine sand in the middle and medium-coarse sand on both sides Mainly. The cohesive soil layer of this aquifer group is also relatively developed, and its water permeability and water conductivity are also poor. In the alluvial-diluvial hydrogeological subregion of the Hutuo River, it is composed of medium-fine sand and gravel-containing medium-coarse sand formed by alluvial-diluvial and glacier accumulation. The aquifer is not developed, and the vertical and lateral recharge conditions are poor. In the alluvial-diluvial hydrogeological sub-area of Fuyang River and the alluvial-diluvial hydrogeological sub-area of Zhangwei River, it is composed of thick clay, silty clay and water-bearing sand layers, with weak water permeability and water-richness. Runoff conditions are weak.

(2) Spatial division of groundwater level monitoring data

According to the division of aquifer groups in Hengshui area and the monitoring depth of groundwater level, the groundwater level data is divided into 4 groups, and the monitoring depths are -6.37～-74.5m, -69～-197m, -150～-270m and - 248~-330m, respectively corresponding to the I, II, III ¹ and III ² aquifer groups in the Hengshui area (Fig. 4). The amount of groundwater level monitoring data at each depth is different. There are 19 groundwater level monitoring points at the groundwater level monitoring depth of -6.37 to -74.5m, and 8 groundwater level monitoring points at the depth of -69 to -197m. There are 10 groundwater level monitoring points at -150～-270m, and 7 groundwater level monitoring points at -248～-330m. Among them, there are more groundwater level monitoring points at the monitoring depth of -6.37～-74.5m. Only 10 of these monitoring points have groundwater level monitoring data at the monitoring depths of -69 to -197m, -150 to -270m and -248 to -330m, so only these 10 monitoring points are shown in Figure 4 (a ), and the labels are completely consistent with the labels at the monitoring depths of -69~-197m, -150~-270m and -248~-330m, and the other monitoring points are not labeled.

Groundwater level monitoring points ①, ②, ③, and ④ belong to the alluvial-diluvial hydrogeological subregion of the Hutuo River, except for monitoring point ③ which has monitoring data at three monitoring depths (-6.37～-74.5m, -69～-197m and -150m ~-270m), other monitoring points only have monitoring data at one or two monitoring depths. In addition, in the alluvial-diluvial hydrogeological unit of the Hutuo River, because the first aquifer group has a thin-layered multi-layered aquifer structure and its thickness is small, there is an unstable and thinner aquifer group between this aquifer group and the second aquifer group. The hydraulic connection between the clay layer and the groundwater is good, but the aquifer in the third aquifer group is discontinuous and the water-richness is weak, and it only has a good hydraulic connection with the second aquifer group in some areas. Therefore, in the Hutuo River In the alluvial hydrogeological unit, not only the groundwater level monitoring data at the four monitoring depths are incomplete, but the aquifer is also in a discontinuous state, and the land subsidence is locally developed. Based on the current groundwater level monitoring data, it is impossible to establish a hydrogeological unit for this hydrogeological unit. Its model of the relationship between land subsidence and groundwater level.

Groundwater level monitoring points ⑤, ⑥, ⑦, ⑧, ⑨, ⑩, ⑾, ⑿, ⒀, ⒁, ⒂, ⒃, ⒄ are located in or near the Fuyang River and Zhangwei River basins, and they may all belong to the Fuyang River Pluvial hydrogeological sub-area and Zhangwei River alluvial-diluvial hydrogeological sub-area, in which monitoring points ⑩ and ⒀ are at -6.37～-74.5m, -69～-197m, -150～-270m and -248～-330m4 There are groundwater level monitoring data at each monitoring depth. At the same time, in the Fuyang River alluvial hydrogeological sub-region and the Zhangwei River alluvial hydrogeological sub-region, groundwater exploitation is mainly concentrated in the II and III aquifer groups, and these two aquifer groups are formed by alluvial rivers, lakes and swamps. Formed by deposits, the lithology is mainly ^mud sand and fine sand, and the water permeability and water conductivity are relatively large ^. Large-scale and regional characteristics, the monitoring points ⑩ and ⒀ are located in the middle of this hydrogeological unit, so based on the groundwater level monitoring data at the monitoring points ⑩ and ⒀, the alluvial and flood hydrogeological units of the Fuyang River and Zhangwei River can be accurately established. A model of the relationship between land subsidence and groundwater level.

Step 3: Establishment of the relationship model between land subsidence and the maximum sustained groundwater level drawdown

(1) Calculate the maximum continuous drawdown of the groundwater level of the aquifer group

The maximum continuous drawdown of the groundwater table refers to the difference between the lowest elevation of the groundwater level of the aquifer group and the initial elevation of the groundwater level within a certain period of time. The calculation period of land subsidence in Hengshui area is from September 2018 to September 2019, so the initial elevation of the groundwater level is the elevation of the groundwater level in each aquifer group in September 2018, and the lowest elevation of the groundwater level is September 2018 The minimum value of the groundwater level elevation in each aquifer group between September and September 2019, the minimum value of the groundwater level elevation in this period minus the initial elevation of the groundwater level in September 2018 can be calculated for each water content in the Hengshui area The maximum continuous drawdown of groundwater level at each groundwater level monitoring position in the layer group. Figure 4 shows the groundwater level monitoring depths of -6.37~-74.5m, -69~-197m, -150~-270m and -248~ The maximum continuous depth of groundwater level at each monitoring point at -330m.

(2) The relationship model between land subsidence and maximum continuous depth drop in Hengshui area

The Hengshui area is located in the south-central part of the North China Plain, and belongs to the central-eastern alluvial plain on the plane. The first aquifer group is an unconfined aquifer, and the second, third, and fourth aquifer groups are confined aquifers. The groundwater exploitation in the Hengshui area is concentrated in In the second and third aquifer groups, the land subsidence s _j at any point in the Hengshui area can be expressed by the following formula:

通常根据土体的物理、力学参数，土体各个含水层组的压缩模量、天然重度、有效重度及水的重度都可以获得，进而可以计算出

和

如在衡水地区承压含水层组内，土体为半干硬的砂粘土，根据有关土的经验参数附表《土的压缩模量一般范围值》(表2)，可获得衡水地区承压含水层土体压缩模量为16～39MPa，同时基于承压含水层Ⅱ、Ⅲ¹、Ⅲ²的厚度(分别为128m、120m和82m)，则可计算出衡水地区承压含水层Ⅱ、Ⅲ¹、Ⅲ²内地下水位分别持续下降一个有效单位引起各含水层组的压缩变形量分别为

但是与粘性土层厚度、渗透系数及渗流时间等参数相关的表征粘性土体变形的系数f_Ⅱ(t)，

通常无法由土体的基本物理力学参数来确定且其数值并不是一常量。因此，只有基于足够多的各个含水层的地下水位降深数据和地面沉降量，通过求解线性方程组来反算系数a_Ⅰ、a_Ⅱ、

或者f_Ⅰ(t)、f_Ⅱ(t)、

in

Usually, according to the physical and mechanical parameters of the soil, the compressive modulus, natural weight, effective weight and water weight of each aquifer group of the soil can be obtained, and then can be calculated

and

For example, in the confined aquifer group in the Hengshui area, the soil is semi-dry and hard sandy clay, according to the relevant soil empirical parameters attached table "General range of compressive modulus of soil" (Table 2), the pressure of the Hengshui area can be obtained The compressive modulus of the aquifer soil is 16-39MPa, and based on the thickness of the confined aquifer II, III ¹ and III ² (128m, 120m and 82m respectively), the confined aquifer II and III in the Hengshui area can be calculated ¹ , Ⅲ ² , the continuous drop of groundwater level by one effective unit respectively causes the compressive deformation of each aquifer group to be

However, the cohesive soil deformation coefficient f _Ⅱ (t), which is related to the cohesive soil layer thickness, permeability coefficient and seepage time, is

Usually it cannot be determined by the basic physical and mechanical parameters of the soil and its value is not a constant. Therefore, based on enough groundwater table drawdown data and land subsidence of each aquifer, the coefficients a _Ⅰ , a _Ⅱ ,

or f _Ⅰ (t), f _Ⅱ (t),

Table 2 The general range of compressive modulus of soil

In the actual aquifer group, with the fluctuation of the groundwater level of the aquifer group, the compressive modulus of each aquifer group, and the coefficients representing the deformation of cohesive soil related to the thickness of the cohesive soil layer, the permeability coefficient and the seepage time are all different. is not a constant, but we assume that the compressive modulus of the aquifer group and the coefficient representing the deformation of the cohesive soil are constant when we establish the relationship model between the land subsidence and the maximum continuous drawdown of the groundwater table in a certain period of time, then based on this One assumption can be considered that the land subsidence at any point is a linear function of the continuous maximum drawdown of the groundwater level of the aquifer group. At present, the monitoring of groundwater level data is based on existing water wells in rural areas and enterprises in the research area, and the number of specially dug wells for groundwater level monitoring is small or almost non-existent. Therefore, the geographical location and monitoring depth of groundwater level monitoring And the number of monitoring wells is random. According to statistics, there are 18 groundwater level monitoring points in the confined aquifer group in Hengshui area. ¹ ) and 31.06m (Ⅲ ² )) and ⒀ (0.34m (Ⅰ), 9.08m (Ⅱ), 7.18m (Ⅲ ¹ ) and 16.38m (Ⅲ ² )) there are groundwater in four aquifer groups at different depths Therefore, the land subsidence at groundwater level monitoring points ⑩ and ⒀ in Hengshui area in 2019 can be expressed as a linear combination of the maximum continuous drawdown of groundwater levels in each aquifer group, namely

c1，c2>0，c1，c2可以改写为地下水位总持续降深的线性函数(12)where a _Ⅰ , a _Ⅱ ,

c1, c2>0, c1, c2 can be rewritten as a linear function of the total continuous drawdown of groundwater level (12)

Step 4: Based on the annual land subsidence obtained by the InSAR coherent target time series analysis method, estimate the total maximum continuous depth of the regional groundwater level

简化成整个含水层组的综合系数a，各个含水层组内地下水位最大持续降深的和代表整个含水层组的地下水位最大持续降深，同时忽略与时间相关的土体滞后变形量，于是将式(12)可以进一步简化为：Equation (12) is a system of linear equations, with 5 unknowns and 2 equations, and theoretically there are infinitely many solutions. In order to find the unique solution of the 5 unknowns in Equation (12), at least 4 water-bearing Based on the groundwater level monitoring data of the layer group, three linear equations were established between the ground subsidence and the maximum continuous depth of the groundwater level, but there is a lack of groundwater level monitoring data. The aquifer groups are integrated into a whole aquifer group, correspondingly representing the 4 coefficients a _Ⅰ , a _Ⅱ ,

Simplified into the comprehensive coefficient a of the whole aquifer group, the sum of the maximum continuous drawdown of the groundwater level in each aquifer group represents the maximum continuous drawdown of the groundwater level of the entire aquifer group, while ignoring the time-related hysteresis deformation of the soil, so Formula (12) can be further simplified as:

47.85mm＝a×41.45×10 ³⁺ +1.26×c

35.08mm＝a×32.98×10 ³ +c, where a, c>0 (13)

Theoretically, the equation group (13) should have a unique solution, but because there is a certain time delay between the groundwater level monitoring data and the land subsidence data, it is not completely accurate, and there is a certain deviation from the real value, so the iterative method is used The optimal solution for the comprehensive coefficients of the entire aquifer group in the alluvial-diluvial hydrogeological units of the Fuyang River and Zhangwei River in the Hengshui area is successively approximated as a=1.11×10 ^-3 and c=0.3. On this basis, based on the timing analysis of InSAR coherent targets The land subsidence data in Hengshui area in 2019 obtained by technology can be used to obtain the total maximum continuous depth of groundwater level in the alluvial-diluvial hydrogeological units of Fuyang River and Zhangwei River in Hengshui area, as shown in Figure 5.

Claims (9)

1. A method for estimating the maximum drawdown of groundwater table based on InSAR land subsidence monitoring data, is characterized in that: the specific steps of the method are as follows: Step 1: Obtain the annual land subsidence in the study area based on the InSAR coherent target timing analysis method; (1) InSAR coherent target timing analysis method When selecting an interference image pair, in the case of a small amount of data, select an interference image with a shorter baseline, combine the short baseline interference image pair, increase the time span for obtaining deformation information of a single differential interference fringe image, and obtain the observation value. number; based on the obtained differential interferogram atlas, the phase information on the differential interferogram atlas is extracted by using highly coherent pixels, and then the point set of differential interferometric phase is obtained; (2) Mosaic of land subsidence data in adjacent maps When the research area is large, the radar data of multiple maps are required to completely cover, but the reference datum position of the ground subsidence data of each map obtained based on the InSAR coherent target timing analysis method is different, so it is necessary to The reference datum of each map frame is used for overall deviation compensation; Step 2: Division of hydrogeological units and groundwater level monitoring data in the study area; In the central and eastern alluvial plain, the Quaternary strata are subdivided into the alluvial hydrogeological subregion of Luan River, the alluvial hydrogeological subregion of Chaobai River, the alluvial hydrogeological subregion of Yongding River and the alluvial hydrogeological subregion of Tuohe River. , these different hydrogeological units have different causes of formation, resulting in different floor depths, thicknesses of aquifer groups, and hydraulic connections of the underlying aquifer groups. The hydrogeological units of the study area are divided geographically, so that the same hydrogeological unit and the same aquifer group have the same burial depth and groundwater connectivity hydrogeological parameters; Step 3: Establishment of the relationship model between land subsidence and the maximum sustained groundwater level drawdown; Land subsidence is not an ideal elastic-plastic body, but a product of natural history with elasticity and plasticity. According to Terzaghi's one-dimensional consolidation theory, the soil is considered to be an ideal soil, and the compression deformation at any point s _j is expressed by the formula (1) Expression; the compressive deformation at any point of the soil is the sum of the compression of each aquifer group below it, and the compression of each aquifer group is caused by the decline of the groundwater level in the aquifer group, acting on the soil However, under the premise of the same groundwater head drawdown, the effective stress increments acting on the soil in different aquifer groups are different;

Among them, i represents the circulation variable. There are four aquifer groups in the Quaternary strata in the North China Plain, denoted by I, II, III, and IV respectively; s _j is the compressive deformation at any point j in the soil; Δσ _i is the The effective stress increment acting on the soil particles caused by the continuous decrease of the effective water head in the i aquifer group; E _{s, i} is the compressive modulus of the soil in the i aquifer group; H _i is the i aquifer group The thickness of the inner soil; c is the hysteresis deformation of the soil related to time; Step 4: Based on the annual land subsidence obtained by the InSAR coherent target time series analysis method, estimate the total maximum continuous depth of the regional groundwater level; Based on the annual land subsidence data obtained by the InSAR coherent target time-series analysis method and the maximum continuous groundwater depth data of each aquifer group at typical points, the coefficients representing the compression characteristics of each aquifer group are calculated by solving the linear equations. Hysteresis deformation. 2. A kind of method for estimating the maximum groundwater level drawdown based on InSAR ground subsidence monitoring data according to claim 1, is characterized in that: in step 1, the differential interference phase δφ _diff (x ) is expressed as:

Among them, λ is the radar wavelength, R is the slant distance between the radar satellite and the monitoring target, B _⊥ is the vertical baseline, T is the time baseline, θ is the incident angle of the radar satellite, v(x) and ε _error (x) are respectively is the linear velocity (annual settlement) and elevation error between adjacent highly coherent pixels; δφ _nonlinear (x) is the nonlinear deformation phase, δφ _atm (x) is the error phase caused by atmospheric fluctuations, δφ _noise (x) is the noise phase caused by decoherence factors. 3. A method for estimating the maximum groundwater level drawdown based on InSAR land subsidence monitoring data according to claim 1 or 2, characterized in that: in the entire interference fringe atlas, the linear velocity and digital elevation of any highly coherent pixel point The DEM error is a constant, which is a linear component in the model; the two-dimensional spectrum estimation model is used, and the differential interferometric phase is regarded as an observation value, and the deformation sequence of the high-coherence pixel target is an unknown number. Through formula (3), the estimated model coherence coefficient When γ _{x, 0} exceeds a certain threshold, the deformation sequence value of the highly coherent pixel point target in the study area can be solved, and the deformation sequence value of the high coherence pixel point target in the study area is converted into a vertical deformation sequence value, and the research Annual land subsidence data of high-coherence pixel targets in the region;

in

Among them, γ _x is the coherence coefficient of the two-dimensional spectrum estimation model, N is the number of differential interferograms, k represents the circular variable, j represents the imaginary number unit,

is the difference between the differential interference phase, the linear deformation phase, and the elevation error phase at the xth high-coherence pixel point in the k-th differential interferogram, T ^k is the time baseline of the k-th differential interferogram,

is the vertical baseline of the kth differential interferogram,

is the differential interference phase on any high-coherence pixel x in the k-th differential interferogram,

is the nonlinear deformation phase of the xth highly coherent pixel in the kth differential interferogram,

is the error phase caused by the atmospheric fluctuation of the xth high-coherence pixel in the k-th differential interferogram, δφ _noise (x) is the decoherence of the x-th high-coherence pixel in the k-th differential interferogram λ is the radar wavelength, R is the slant distance between the radar satellite and the monitoring target, θ is the incident angle of the radar satellite, v(x) and ε _error (x) are the high coherence pixel point x respectively Linear rate and elevation errors. 4. a kind of method for estimating the maximum groundwater level drawdown based on InSAR land subsidence monitoring data according to claim 3 is characterized in that: for reducing the integral deviation of ground subsidence parameter between adjacent map sheets, select one of them As a benchmark, based on the deformation parameters of the high-coherence pixel target in the overlapping part of adjacent frames, statistical analysis is carried out according to formulas (4) and (5), and then the overall deviation of deformation between adjacent frames is calculated;

ρ′ _s = ρ _s +Δρ _off (5) Among them, M represents the number of high-coherence pixel targets in the overlapping area of the reference frame and the frame to be adjusted, i represents the cycle variable, Δρ _off is the reference deviation between adjacent frames; ρ _{m, i} is the Deformation amount of highly coherent pixel point i in the overlapping area; ρ _{s, i} is the deformation amount of the coherent target i in the overlapping area in the image frame to be adjusted, and ρ′ _s is the correction value of all highly coherent pixel point targets in the image frame to be adjusted Deformation vector; ρ _s is the deformation vector of all highly coherent pixel targets in the image frame to be adjusted before correction; After compensating for the overall deviation of the reference datum between the map sheets, the external DEM data is used to geocode the land subsidence data of each map sheet, and finally the annual land subsidence within the study area is obtained. 5. A method for estimating the maximum groundwater level drawdown based on InSAR land subsidence monitoring data according to claim 1, characterized in that: in step 2, in the same hydrogeological unit in the North China Plain, the Quaternary formation is vertically It is divided into 4 aquifer groups from top to bottom, and I, II, III, and IV are used to represent 4 different aquifer groups; Layer groups have been exploited in a mixed manner, and the two are collectively referred to as shallow groundwater, and the third and fourth aquifer groups are deep groundwater; There is Aquifer Group I, brackish water and salt water are widely distributed, and deep groundwater mainly occurs in Aquifer Group II, III, and IV. 6. A kind of method for estimating the maximum groundwater level drawdown based on InSAR surface subsidence monitoring data according to claim 1 or 5, is characterized in that: in step 3, if the groundwater head drawdown is Δh, then in the phreatic aquifer and In the confined water aquifer, the effective stress increment acting on the soil respectively is expressed by the following formula: Δσ _pw ＝(γ _nat -γ _eff )Δh (6) Δσ _cw = γ _w Δh (7) In the formula, Δo _pw is the increment of effective stress in unconfined aquifer; Δσ _cw is the increment of effective stress in confined aquifer; γ _nat is the natural weight of soil; γ _eff is the effective weight of soil; γ _w is the gravity of water; Δh refers to the difference between the initial groundwater level at the beginning of monitoring and the groundwater level at the end of monitoring in an aquifer group under ideal conditions. 7. A method for estimating the maximum groundwater level drawdown based on InSAR land subsidence monitoring data according to claim 6, characterized in that: the underground aquifer group is composed of multilayer clay and sand superimposed on each other, when the groundwater level rises , the groundwater level in the sandy soil in the aquifer rises rapidly, but the groundwater level in the cohesive soil remains unchanged or is still falling due to the impact of the previous water level drop. Correspondingly, the cohesive soil is still undergoing compression deformation and land subsidence is still going on; therefore the drawdown of the groundwater head in the above formulas (6) and (7) is actually the effective average value of the drawdown of the groundwater head in the clay and sandy soils in the aquifer. 8. A method for estimating the maximum groundwater level drawdown based on InSAR land subsidence monitoring data according to claim 6, characterized in that: in the actual groundwater level monitoring process, what is obtained is the groundwater level in the sand layer soil in the aquifer group It is difficult to obtain the effective average value of the groundwater head drawdown in the clay and sandy soils in the aquifer; here, the maximum continuous drawdown of the groundwater level and the cohesive soil deformation related to the thickness of the cohesive soil layer and the parameters of the permeability coefficient are introduced. These two parameters are used to replace the groundwater head drawdown Δh in formulas (6) and (7), where the maximum continuous drawdown of groundwater level refers to the lowest elevation of a certain aquifer group’s groundwater level and The difference of the initial elevation of the groundwater level; at this time, based on the directly obtained groundwater level elevation data of each aquifer group in the study area, the maximum continuous drawdown data of the groundwater level of each aquifer group within a period of monitoring is obtained, and the maximum groundwater level is used to The compressive deformation of the soil is calculated by the product Δh _max f(t) of the continuous drawdown Δh _max and the coefficient f(t) related to the thickness of the cohesive soil layer and the coefficient of permeability that characterizes the cohesive soil deformation, so the formula (1) is further expressed for: In the central and eastern alluvial plains and coastal alluvial marine plains:

In the alluvial and diluvial sloping plains in front of the mountains:

In formulas (8) and ( ₉ ), i represents the cycle variable, and I, _II , III, and IV respectively represent the four aquifer groups from top to bottom in the North China Plain; The natural weight of the i-th aquifer soil; γ _{eff, I} , γ _{eff, i} are the effective weights of the first and i-th aquifer soil respectively; γ _w is the weight of water; E _{s, i} is the The compressive modulus of the soil in the i aquifer group; H _i is the thickness of the soil in the i aquifer group; H _I , H _i are the thicknesses of the soil in the i layer and i layer respectively; Δh _I , Δh _i is the groundwater head drawdown of the aquifer soil in layer I and layer i respectively; c is the hysteresis deformation of the soil related to time; f _I (t) and f _i (t) are the , the cohesive soil deformation coefficient that is related to the thickness of the cohesive soil layer and the permeability coefficient in the i-th aquifer soil body;

are respectively the compressive deformation of the aquifer group caused by continuous drop of the groundwater level in the soil of the first layer and the i-th layer by one effective unit, in which, in the phreatic aquifer group,

Within a confined aquifer group,

a _I , a _i are expressed as

It is worth noting that in any one of the above four aquifer groups I, II, III, and IV, γ _nat , γ _eff , and γ _w are all constants, and E _s is the compressive modulus of the aquifer group. The compressive modulus changes with the increase of the effective stress of the soil. 9. A kind of method for estimating the maximum groundwater level drawdown based on InSAR ground subsidence monitoring data according to claim 8, is characterized in that: in step 4, the hysteresis deformation c is related to the maximum continuous drawdown of groundwater level, and when setting the lag On the premise that the amount of deformation c is a linear function of the total maximum continuous drawdown of the groundwater level, there are 5 unknowns in the linear equation system of formula (8) or (9), and the groundwater levels of 4 aquifer groups at least 5 groundwater level monitoring points are required The correlation coefficient a _I , a _II , a _III , a _IV and the hysteresis deformation c of the four aquifer groups can be accurately calculated only by the maximum continuous drawdown data. There is a certain time deviation in the groundwater level monitoring data, and there is a deviation between the groundwater level monitoring data and the real data. Therefore, the iterative method is used to solve the optimal solution of the linear equation system; on this basis, the land subsidence in the research area obtained based on the InSAR coherent target timing analysis technology The maximum continuous drawdown of the groundwater table in the study area can be estimated based on the volume data and the correlation coefficients a _I , a _II , a _III , a _IV of the corresponding aquifer groups, and the lagged deformation c.

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