A high-precision fast network solution method for GNSS in high-altitude mountainous areas based on tropospheric prior information constraints

Abstract

The present invention provides a high-precision rapid network solution method for GNSS in high-drop mountainous areas based on tropospheric prior information constraints, comprising the following steps: step one, solving the three-dimensional spatial coordinates of ground points with long observation time and hourly zenith tropospheric delay information; step two, estimating the zenith tropospheric delay parameters of large-drop high points in double-difference equations of a synchronous time period with drop high points based on an ionosphere-free combination; step three, taking the tropospheric zenith delay values ​​of large-drop high points and ground points as initial values, and compiling a constraint condition equation information file; step four, constraining the initial values ​​of step three, solving and fixing integer ambiguities; step five, estimating the position parameters of large-drop high points and the zenith tropospheric delay parameter values; step six, adjusting the baseline information file solved in step five; the method improves the accuracy of the rapid positioning results of drop high points, and meets the centimeter-level requirements of GNSS rapid positioning of high points in high-drop areas.

Description

Technical Field

[0001] The invention belongs to the technical field of geodetic measurement, and in particular relates to a GNSS high-precision rapid network solution method for high-drop mountainous areas based on tropospheric prior information constraints. Background Art

[0002] With the rapid progress and popularization of GNSS technology, its application in traditional geodetic and engineering surveying in my country has become increasingly important. At present, rapid measurement using satellites such as GPS, Beidou, Galileo, and GLONASS has become an important application for urban and mountainous surveying. With the rapid development of satellite navigation and positioning base stations, the scale of base stations jointly built by the state, provinces, cities, and industries in my country has reached about 6,000 stations. Satellite navigation and positioning base stations have become modern infrastructure for establishing and maintaining regional high-precision, dynamic, geocentric three-dimensional coordinate frameworks, and are the dynamic maintenance of my country's modern surveying and mapping benchmarks. The data from these GNSS continuously operating base stations provide relatively accurate atmospheric information for regional fast and high-precision data processing.

[0003] In the high-precision GNSS data processing in mountainous areas with high elevation, in order to ensure a certain positioning accuracy, various space-related error sources must be eliminated, such as atmospheric delay bias and orbit bias. With the increase of ground tracking station data, the satellite dynamics model is more scientific, and the influence of orbit on positioning in double-difference positioning has become smaller and smaller. In the post-positioning rapid positioning in high-elevation mountainous areas, the main influencing factor is the influence of the troposphere. How to deal with the influence of the troposphere is the premise of GNSS precise and rapid positioning.

[0004] At present, the main technical methods for tropospheric delay correction are: First, directly use empirical models for estimation. Tropospheric models include Sasstamoninen, etc., which are based on measured meteorological parameters, and GPT series and IGGtrop series, which are based on atmospheric numerical models. Second, use parameter estimation, take tropospheric wet delay as the parameter to be estimated, and solve it using equations. Third, directly use sounding data to obtain high-precision tropospheric delay values ​​as the true value of the parameter. When positioning based on the double-difference model, parameter estimation methods are often used to eliminate or weaken the impact of tropospheric delay.

[0005] Due to the complex climatic conditions in high-altitude areas and the lack of measured meteorological data, traditional empirical models are mainly constructed based on numerical atmospheric models, and the calculated zenith tropospheric delay (ZTD) also has a certain overall model deviation. Therefore, the GNSS double-difference network solution at the high point of the drop requires a longer observation time to improve the accuracy of the tropospheric delay estimation and determine the geodetic height of the high point of the drop. However, the observation environment at the top of the mountain is harsh, making it difficult to conduct long-term GNSS observations. At the same time, the high drop causes a large difference in tropospheric delay at both ends of the baseline, and the traditional double-difference observations cannot be used to weaken the tropospheric delay to meet centimeter-level positioning requirements. Summary of the invention

[0006] The purpose of the present invention is to provide a high-precision rapid network solution method for GNSS in high-rise mountainous areas based on tropospheric prior information constraints, comprising the following steps:

[0007] Step 1: Calculate the three-dimensional spatial coordinates of ground points with long observation time and hourly zenith tropospheric delay information based on the double-difference network solution mode or the precise point positioning (PPP) mode;

[0008] Step 2: Using the high-precision prior zenith tropospheric delay information and the three-dimensional spatial coordinates of the ground point as constraints, the zenith tropospheric delay parameters of the large drop point in the double difference equation in the synchronous time period with the drop point are estimated based on the ionosphere-free combination;

[0009] Step 3: Taking the tropospheric zenith delay values ​​of the high point with large drop height and the ground point as initial values, compile the constraint condition equation information file;

[0010] Step 4: Constrain the initial value of step 3, and solve and fix the integer ambiguity based on the ambiguity search strategy (usually select a suitable ambiguity resolution strategy based on the average edge length of the control, commonly used are SIGMA and QIF strategies);

[0011] Step 5: Substitute the fixed integer ambiguity back into the equation to estimate the position parameters of the high point of the large drop and the zenith tropospheric delay parameter values;

[0012] Step 6: Adjust the baseline information file solved in the previous step, that is, use the constrained adjustment method to constrain the ground point coordinates to obtain the final three-dimensional spatial coordinates and point accuracy of the high point with a large drop.

[0013] Further, in the step 1, the three-dimensional spatial coordinates and hourly zenith tropospheric delay information of ground points with long-term observation time are solved based on the double-difference network solution mode or the precise point positioning (PPP) mode. First, an IGS reference station or a stable national or provincial continuously operating reference station 500 km away from the area is selected, and it is combined with the long-term observation ground points in the area as the basic meteorological parameter control network for obtaining tropospheric information in the area; secondly, the reference stations in the area are solved by the high-precision GNSS double-difference model solution software GAMIT software or BERNESE to solve the hourly zenith tropospheric delay values ​​and corresponding accuracy information of the long-term observation ground points;

[0014] When the double-difference model is used to solve the zenith tropospheric delay, the observation equation uses the observation equation that eliminates the ionosphere. The specific solution model is shown in formula (1) to formula (2);

[0015] When the GNSS synchronous observation network adopts the double difference model baseline solution, the double difference equation can be expressed as:

[0016]

[0017] When the ionosphere-free combination is used, the double difference observation equation can be expressed as:

[0018]

[0019] In equations (1) and (2), superscripts i and j and subscripts r and s represent the given receiver and satellite, respectively; f1 and f2 are the frequencies of carriers L1 and L2, respectively; λ1 and λ2 are the wavelengths of carriers L1 and L2, respectively; n1 and n2 are the double difference ambiguities of carriers L1 and L2, respectively; is the station-satellite geometric distance; is the double difference ionospheric delay; is the double-difference tropospheric delay; is the ionospheric-free combined carrier and pseudorange double difference observation value of satellites i and j observed by stations r and s; is the double-difference ionospheric-free combined ambiguity; IF is the wavelength of the ionosphere-free combined observation.

[0020] When calculating the zenith tropospheric delay at the ground point, the main parameter settings for baseline solution are:

[0021] (1) Satellite orbit: Use the IGS hybrid precise ephemeris or the hybrid precise ephemeris of other international analysis centers;

[0022] (2) Satellite cut-off elevation angle: 10°;

[0023] (3) Epoch interval: Based on the observation duration, the minimum sampling interval is an integer multiple of 5 s;

[0024] (4) Observation type: combined observation after eliminating the ionosphere;

[0025] (5) Tropospheric model correction model: the Sasstamoninen model and the global pressure and temperature model are used for correction;

[0026] (6) Solar radiation pressure correction: BERNE model;

[0027] (7) Tropospheric delay model: The first-order Gauss-Markov model is used for parameter estimation;

[0028] (8) Baseline solution coordinate constraints: The starting point is given a constraint of 5 cm in the horizontal direction and 10 cm in the vertical direction, and the point to be solved is given a constraint of 10 m in the horizontal and vertical directions;

[0029] (9) Solid tide model: IERS2010;

[0030] (10) Ocean tide model: FES2004 ocean tide model;

[0031] (11) Tropospheric mapping function model: VMF1;

[0032] (12) Number of zenith delay parameters: 25.

[0033] Furthermore, in step 2, the high-precision prior zenith tropospheric delay information and the three-dimensional spatial coordinates of the ground point are used as constraints, and the zenith tropospheric delay parameters of the large drop point in the double difference equation of the synchronous time period with the drop point are estimated based on the ionosphere-free combination;

[0034] The main process is:

[0035] (1) First, the synchronous observation data of ground points with long-term observation and mountain top points in high-altitude mountainous areas are combined into a regional joint observation network;

[0036] (2) Secondly, the regional network data is processed with the parameter settings of the first step baseline solution. When the ionosphere-free combined equation is used for parameter estimation, additional condition constraints are introduced for the ground points where the zenith tropospheric delay has been obtained, and then the three-dimensional spatial position coordinate parameters and tropospheric parameters of the high point with a large drop are estimated;

[0037] The additional constraint model in parameter estimation is:

[0038] ΔZTD r =ZTD r +ε r，VZTD (3)

[0039] In formula (3), the ground point r is the zenith tropospheric delay parameter ZTD r , the random model is The zenith tropospheric delay ZTD of the long-term observation data at the ground point r As a virtual observation, ε r，VZTD is the zenith tropospheric delay virtual value noise.

[0040] Furthermore, in step three, the tropospheric zenith delay values ​​of the large drop height point and the ground point are used as initial values ​​to compile a constraint condition equation information file;

[0041] First, the zenith tropospheric delay value of the height difference point obtained in the second step and the zenith tropospheric delay value of the ground point obtained in the first step are used as initial values ​​to prepare the zenith tropospheric delay initial value constraint file for the synchronous observation period;

[0042] Secondly, since the starting time of the mountain top may not be an integer observation, and the high-precision GNSS data processing software uses integer estimation in data processing, it is necessary to establish a connection between the observation time corresponding to the initial value of the troposphere at the ground point and the observation time of the mountain top;

[0043] Assuming that the change of the troposphere is stable and can be described linearly during the synchronous observation time, the zenith tropospheric delay value and accuracy at the average time during the synchronous observation time are used as the basic information of the constraint file; the zenith tropospheric delay is calculated by linear interpolation, see formula (4);

[0044] Assume that the start and end time of the synchronous observation period are t1 and t2, and the zenith tropospheric delay values ​​at the corresponding time of the station are ZTD1 and ZTD2. Then the zenith tropospheric delay value ZTD at any time t of the station is calculated as shown in formula (4):

[0045] ZTD=ZTD1+(t-t1)×(ZTD1-ZTD2) / (t2-t1) (4)

[0046] Furthermore, in step 4, the initial value of step 3 is constrained, and based on the ambiguity search strategy (usually a suitable ambiguity resolution strategy is selected according to the average side length of the control, and the commonly used strategies are SIGMA and QIF), the integer ambiguity is resolved and fixed;

[0047] (1) First, the wide-lane combined equations are adopted and the SIGMA ambiguity resolution strategy is used;

[0048] (2) Secondly, the zenith tropospheric delay constraint information obtained in the third step is introduced, and the site coordinates and ionosphere initial values ​​are fixed, and the wide lane ambiguity values ​​are estimated and saved.

[0049] Furthermore, in step five, the fixed integer ambiguity is substituted back into the equation to estimate the position parameters of the large drop high point and the zenith tropospheric delay parameter value; the specific process is: the wide lane ambiguity solved in step four is substituted into the equation, the narrow lane ambiguity is estimated using the SIGMA ambiguity resolution strategy, and the spatial position coordinates of the ground joint measurement point and the zenith tropospheric delay constraints are given to estimate the spatial position coordinate parameters and tropospheric parameters of the large drop high point.

[0050] Further, in step 6, the baseline information file solved in step 5 is adjusted, that is, the constrained adjustment method is used to constrain the ground point coordinates to obtain the final three-dimensional space coordinates and point accuracy of the high point with a large drop;

[0051] The synchronous solution file uses the constraint adjustment method to calculate the three-dimensional position parameters of the drop height point. The synchronous solution file contains the site location parameters and the covariance information of all estimated parameters.

[0052] The general model of constrained adjustment based on station coordinates is:

[0053]

[0054] When adjusting ground points, the prior constraints on ground points are given, and the adjustment model is:

[0055]

[0056] The covariance matrix of the observations can be expressed as:

[0057]

[0058] The parameter estimates are

[0059]

[0060] Where: V is the observation residual; A is the observation equation coefficient design matrix; L is the actual observation vector; σ is the unit priori mean error; P and Pc are the observation weight matrix and the ground point priori constraint weight matrix respectively; H c is the coefficient matrix of the prior constraint equation; is the parameter to be estimated.

[0061] The advantages of the present invention are as follows: the present invention provides a tropospheric delay solution scheme for a high-precision rapid network solution method of GNSS in a high-drop mountainous area based on tropospheric prior information constraints, which can effectively improve the accuracy of the tropospheric delay estimation parameters of the short-term observed mountain top in the high-drop area, thereby improving the accuracy of the rapid positioning results of the high-drop high point, and meeting the centimeter-level requirements of GNSS rapid positioning of high points in the high-drop area; based on the shortcomings of the insufficient accuracy of tropospheric delay correction in the traditional positioning scheme in the short-term positioning of the high-drop mountainous area, a correction method that takes into account the high-precision tropospheric delay constraints of the ground point is proposed. The high-precision tropospheric delay correction and positioning coordinates calculated by long-term ground station observation data are used as constraints to achieve a dual-constraint solution of the synchronous observation network of the mountain top point and the ground point. This method effectively improves the accuracy of the tropospheric delay correction of the high-drop high point, significantly improves the accuracy of the rapid positioning of the mountain top, and the improvement result in the elevation direction is particularly obvious, so as to achieve rapid centimeter-level positioning of the high point in the high-drop area.

[0062] The present invention is described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 It is a flowchart for rapid positioning of high-drop high points taking into account the prior tropospheric delay of ground points.

[0064] Figure 2 This is the distribution map of the observation network in a certain high mountain area in Yunnan.

[0065] Figure 3 This is the IGS joint solution site distribution map.

[0066] Figure 4 This is a schematic diagram comparing the solution results of different solutions. DETAILED DESCRIPTION

[0067] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined purpose, the specific implementation methods, structural features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and embodiments.

[0068] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0069] In the description of the present invention, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "aligned", "overlap", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0070] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features; in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0071] Example 1

[0072] This embodiment provides a Figure 1 The high-precision rapid network solution method of GNSS in high-rise mountainous areas based on tropospheric prior information constraints shown in the figure includes the following steps:

[0073] Step 1: Calculate the three-dimensional spatial coordinates of ground points with long observation time and hourly zenith tropospheric delay information based on the double-difference network solution mode or the precise point positioning (PPP) mode;

[0074] Step 2: Using the high-precision prior zenith tropospheric delay information and the three-dimensional spatial coordinates of the ground point as constraints, the zenith tropospheric delay parameters of the large drop point in the double difference equation in the synchronous time period with the drop point are estimated based on the ionosphere-free combination;

[0075] Step 3: Taking the tropospheric zenith delay values ​​of the high point with large drop height and the ground point as initial values, compile the constraint condition equation information file;

[0076] Step 4: Constrain the initial value of step 3, and solve and fix the integer ambiguity based on the ambiguity search strategy (usually select a suitable ambiguity resolution strategy based on the average edge length of the control, commonly used are SIGMA and QIF strategies);

[0077] Step 5: Substitute the fixed integer ambiguity back into the equation to estimate the position parameters of the high point of the large drop and the zenith tropospheric delay parameter values;

[0078] Step 6: Adjust the baseline information file solved in the previous step, that is, use the constrained adjustment method to constrain the ground point coordinates to obtain the final three-dimensional spatial coordinates and point accuracy of the high point with a large drop.

[0079] Further, in the step 1, the three-dimensional spatial coordinates and hourly zenith tropospheric delay information of ground points with long-term observation time are solved based on the double-difference network solution mode or the precise point positioning (PPP) mode. First, an IGS reference station 500 km away from the area and a stable national or provincial continuously operating reference station are selected, and they are combined with the long-term observation ground points in the area as the basic meteorological parameter control network for obtaining tropospheric information in the area; secondly, the reference stations in the area are solved by the high-precision GNSS double-difference model solution software GAMIT software or BERNESE to solve the hourly zenith tropospheric delay values ​​and corresponding accuracy information of the long-term observation ground points;

[0080] When the double-difference model is used to solve the zenith tropospheric delay, the observation equation uses the observation equation that eliminates the ionosphere. The specific solution model is shown in formula (1) to formula (2);

[0081] When the GNSS synchronous observation network adopts the double difference model baseline solution, the double difference equation can be expressed as:

[0082]

[0083] When the ionosphere-free combination is used, the double difference observation equation can be expressed as:

[0084]

[0085] In equations (1) and (2), superscripts i and j and subscripts r and s represent the given receiver and satellite, respectively; f1 and f2 are the frequencies of carriers L1 and L2, respectively; λ1 and λ2 are the wavelengths of carriers L1 and L2, respectively; n1 and n2 are the double difference ambiguities of carriers L1 and L2, respectively; is the station-satellite geometric distance; is the double difference ionospheric delay; is the double-difference tropospheric delay; is the ionospheric-free combined carrier and pseudorange double difference observation value of satellites i and j observed by stations r and s; is the double-difference ionospheric-free combined ambiguity; IF is the wavelength of the ionosphere-free combined observation.

[0086] When calculating the zenith tropospheric delay at the ground point, the main parameter settings for baseline solution are:

[0087] (1) Satellite orbit: Use the IGS hybrid precise ephemeris or the hybrid precise ephemeris of other international analysis centers;

[0088] (2) Satellite cut-off elevation angle: 10°;

[0089] (3) Epoch interval: Based on the observation duration, the minimum sampling interval is an integer multiple of 5 s;

[0090] (4) Observation type: combined observation after eliminating the ionosphere;

[0091] (5) Tropospheric model correction model: the Sasstamoninen model and the global pressure and temperature model are used for correction;

[0092] (6) Solar radiation pressure correction: BERNE model;

[0093] (7) Tropospheric delay model: The first-order Gauss-Markov model is used for parameter estimation;

[0094] (8) Baseline solution coordinate constraints: The starting point is given a constraint of 5 cm in the horizontal direction and 10 cm in the vertical direction, and the point to be solved is given a constraint of 10 m in the horizontal and vertical directions;

[0095] (9) Solid tide model: IERS2010;

[0096] (10) Ocean tide model: FES2004 ocean tide model;

[0097] (11) Tropospheric mapping function model: VMF1;

[0098] (12) Number of zenith delay parameters: 25.

[0099] Furthermore, in step 2, the high-precision prior zenith tropospheric delay information and the three-dimensional spatial coordinates of the ground point are used as constraints, and the zenith tropospheric delay parameters of the large drop point in the double difference equation of the synchronous time period with the drop point are estimated based on the ionosphere-free combination;

[0100] The main process is:

[0101] (1) First, the synchronous observation data of ground points with long-term observation and mountain top points in high-altitude mountainous areas are combined into a regional joint observation network;

[0102] (2) Secondly, the regional network data is processed with the parameter settings of the first step baseline solution. When the ionosphere-free combined equation is used for parameter estimation, additional condition constraints are introduced for the ground points where the zenith tropospheric delay has been obtained, and then the three-dimensional spatial position coordinate parameters and tropospheric parameters of the high point with a large drop are estimated;

[0103] The additional constraint model in parameter estimation is:

[0104] ΔZTD r =ZTD r +ε r，VZTD (3)

[0105] In formula (3), the zenith tropospheric delay parameter at ground point r is ZTD r , the random model is The zenith tropospheric delay ZTD of the long-term observation data at the ground point r As a virtual observation, ε r，VZTD is the zenith tropospheric delay virtual value noise.

[0106] Furthermore, in step three, the tropospheric zenith delay values ​​of the large drop height point and the ground point are used as initial values ​​to compile a constraint condition equation information file;

[0107] First, the zenith tropospheric delay value of the height difference point obtained in the second step and the zenith tropospheric delay value of the ground point obtained in the first step are used as initial values ​​to prepare the zenith tropospheric delay initial value constraint file for the synchronous observation period;

[0108] Secondly, since the starting time of the mountain top may not be an integer observation, and the high-precision GNSS data processing software uses integer estimation in data processing, it is necessary to establish a connection between the observation time corresponding to the initial value of the troposphere at the ground point and the observation time of the mountain top;

[0109] Assuming that the change of the troposphere is stable and can be described linearly during the synchronous observation time, the zenith tropospheric delay value and accuracy at the average time during the synchronous observation time are used as the basic information of the constraint file; the zenith tropospheric delay is calculated by linear interpolation, see formula (4);

[0110] Assume that the start and end time of the synchronous observation period are t1 and t2, and the zenith tropospheric delay values ​​at the corresponding time of the station are ZTD1 and ZTD2. Then the zenith tropospheric delay value ZTD at any time t of the station is calculated as shown in formula (4):

[0111] ZTD=ZTD1+(t-t1)×(ZTD1-ZTD2) / (t2-t1) (4)

[0112] Furthermore, in step 4, the initial value of step 3 is constrained, and based on the ambiguity search strategy (usually a suitable ambiguity resolution strategy is selected according to the average side length of the control, and the commonly used strategies are SIGMA and QIF), the integer ambiguity is resolved and fixed;

[0113] (1) First, the wide-lane combined equations are adopted and the SIGMA ambiguity resolution strategy is used;

[0114] (2) Secondly, the zenith tropospheric delay constraint information obtained in the third step is introduced, and the site coordinates and ionosphere initial values ​​are fixed, and the wide lane ambiguity values ​​are estimated and saved.

[0115] Furthermore, in step five, the fixed integer ambiguity is substituted back into the equation to estimate the position parameters of the large drop high point and the zenith tropospheric delay parameter value; the specific process is: the wide lane ambiguity solved in step four is substituted into the equation, the narrow lane ambiguity is estimated using the SIGMA ambiguity resolution strategy, and the spatial position coordinates of the ground joint measurement point and the zenith tropospheric delay constraints are given to estimate the spatial position coordinate parameters and tropospheric parameters of the large drop high point.

[0116] Further, in step 6, the baseline information file solved in step 5 is adjusted, that is, the constrained adjustment method is used to constrain the ground point coordinates to obtain the final three-dimensional space coordinates and point accuracy of the high point with a large drop;

[0117] The synchronous solution file uses the constraint adjustment method to calculate the three-dimensional position parameters of the drop height point. The synchronous solution file contains the site location parameters and the covariance information of all estimated parameters.

[0118] The general model of constrained adjustment based on station coordinates is:

[0119]

[0120] When adjusting ground points, the prior constraints on ground points are given, and the adjustment model is:

[0121]

[0122] The covariance matrix of the observations can be expressed as:

[0123]

[0124] The parameter estimates are

[0125]

[0126] Where: V is the observation residual; A is the observation equation coefficient design matrix; L is the actual observation vector; σ is the unit priori mean error; P and Pc are the observation weight matrix and the ground point prior constraints respectively; H c is the coefficient matrix of the prior constraint equation; is the parameter to be estimated.

[0127] Example 2

[0128] A mountain in China was selected for measurement experiment. The mountain is located in Yunnan Province. The stations are distributed as follows: Figure 2 As shown. Among them, the maximum height difference between the peak and the ground point is 2156m. The observation time in Yunnan region is the observation data on March 1, 2019, the observation time is 24h, the satellite cut-off elevation angle is set to 10°, and the data sampling interval is 30s. GNSS dual-frequency receivers are set up at the peak and ground points for continuous observation, and the ground points are evenly distributed around the peak.

[0129] IGS stations in and around China were selected, and the high-precision GNSS data processing software BERNESE was used to calculate the coordinates of the ground points in the ITRF2014 framework and the 1-hour zenith tropospheric delay value. The station distribution is as follows: Figure 3 Then, the ground point coordinates are used as the starting point to obtain the long-term observation positioning results and tropospheric zenith delay parameters of the peak vertex, and use them as reference values. Finally, the peak measurement data is divided into 1-hour observation data at the whole point, and the following three tropospheric delay data processing schemes are used to compare and analyze the short-term mountain network solution experimental results.

[0130] Scheme 1: Use the Saastamoinen+VMF1 model value as the tropospheric delay correction;

[0131] Scheme 2: All stations perform tropospheric delay estimation, the prior value uses the Saastamoinen model tropospheric dry delay, the mapping function is VMF1, and the tropospheric wet delay estimation interval is 1h;

[0132] Scheme 3: The tropospheric delay correction and positioning results obtained from long-term observations at ground points are used as prior constraints, combined with the peak synchronous observation period for 1h segmented solution to estimate the peak tropospheric delay and position parameter values ​​for each period.

[0133] In order to compare the spatiotemporal characteristics of the zenith relative tropospheric delay deviation under the three schemes, the baselines with the largest height difference in three different regions were selected, and the baseline zenith relative tropospheric delay results calculated over a long period of time and the peak position results were used as reference values. The estimated values ​​of the three schemes were compared with the reference values.

[0134]

[0135] In formula (4), X i is the estimated value of the relative tropospheric zenith delay parameter between the peak position estimated at each time period of different schemes and the maximum height difference baseline; It is the reference value of the tropospheric zenith delay parameter between the estimated peak position in each time period and the maximum height difference baseline; N represents the total number of time periods involved in the statistics; the average deviation bias can measure the average deviation degree of different schemes, and the root mean square error RMS can measure the solution accuracy and stability of different schemes.

[0136] Depend on Figure 4It can be seen that the zenith relative tropospheric delay of Scheme 1 is the largest and has an obvious systematic deviation, which indicates that directly using the tropospheric model cannot effectively weaken the influence of the tropospheric delay of the large height difference baseline, and the model correction can only weaken part of the influence. The systematic deviation of the tropospheric delay has a greater impact on the estimation of parameters; Schemes 2 and 3 have no obvious systematic deviation, and the correlation with the height difference is weak, indicating that the use of parameter estimation for tropospheric delay can effectively eliminate the tropospheric delay error; Scheme 2 has a large zenith tropospheric delay in some periods, with a maximum deviation of 2.85cm. On the one hand, this shows that there is uncertainty in the short-term tropospheric estimation method, and on the other hand, it shows that the tropospheric parameters are highly correlated with the elevation parameters, and reliable estimated parameter values ​​cannot be obtained in a short time; The zenith relative tropospheric delay deviation obtained by Scheme 3 has a weak correlation with the height difference between the two segments of the baseline, the tropospheric delay deviation value is the smallest and has high stability, and the zenith relative tropospheric delay deviation is less than 1cm, indicating that Scheme 3 effectively weakens the influence of the residual tropospheric delay error of the large height difference baseline.

[0137] Table 1 Statistics of peak positioning and zenith tropospheric delay errors of three schemes (m)

[0138]

[0139] From the above statistical analysis, we can conclude that:

[0140] (1) Scheme 3 has the highest positioning accuracy and reliability and is less affected by height differences. The average accuracy of N and E is better than 0.4 cm, the accuracy of U direction is better than 1.1 cm, and the average accuracy is 1.0 cm.

[0141] (2) Scheme 1 directly reflects the accuracy of the tropospheric delay model. From the correction number of the tropospheric zenith delay, it can be concluded that the accuracy of the Saastamoinen+VMF1 model at the peak reaches the millimeter level, but the positioning accuracy in the elevation direction is the worst among the three schemes. This shows that the absolute tropospheric delay has little effect on the elevation positioning result, and the error in the relative tropospheric delay will affect the accuracy of the positioning result at the peak.

[0142] (3) The reliability and accuracy of the tropospheric zenith delay parameter estimation results of Scheme 2 are poor, but the positioning results are better than those of Scheme 1. The reason is that the absolute tropospheric delay error affects the baseline scale and has little impact on the elevation positioning results.

[0143] (4) Scheme 3 reduces the dimension of the observation equation by constraining the prior tropospheric parameters and estimates the effective parameters. The estimated peak ZTD accuracy reaches the mm level, which is better than that of Scheme 2. In mountainous areas with a height difference greater than 2000m, the average peak elevation positioning accuracy is better than 1.1cm, indicating that this method eliminates the influence of height difference on elevation positioning accuracy and can be used for high-precision rapid positioning of short-term GNSS observation networks in mountainous areas with high drop differences.

[0144] In summary, this tropospheric delay solution scheme based on the high-precision rapid network solution method of GNSS in high-drop mountainous areas based on tropospheric prior information constraints can effectively improve the accuracy of tropospheric delay estimation parameters of short-term observations of mountain tops in high-drop areas, thereby improving the accuracy of rapid positioning results of high-drop high points, and meeting the centimeter-level requirements of GNSS rapid positioning of high points in high-drop areas; Based on the shortcomings of insufficient short-term positioning accuracy of tropospheric delay correction in traditional positioning schemes in high-drop mountainous areas, a correction method that takes into account the high-precision tropospheric delay constraints of ground points is proposed. The high-precision tropospheric delay correction and positioning coordinates calculated using long-term ground station observation data are used as constraints to achieve a dual-constraint solution of the synchronous observation network of mountain top points and ground points. This method effectively improves the accuracy of tropospheric delay correction at high drop points, significantly improves the accuracy of rapid positioning at mountain tops, and the improvement in elevation direction is particularly obvious, achieving rapid centimeter-level positioning of high points in high drop areas.

[0145] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A high-precision rapid network solution method for GNSS in high-rise mountainous areas based on tropospheric prior information constraints, characterized in that: The steps include: Step 1: Calculate the three-dimensional spatial coordinates of ground points with long observation time and hourly zenith tropospheric delay information based on double-difference network solution mode or precise point positioning mode; Step 2: Using the high-precision prior zenith tropospheric delay information and the three-dimensional spatial coordinates of the ground point as constraints, the zenith tropospheric delay parameters of the large drop point in the double difference equation in the synchronous time period with the drop point are estimated based on the ionosphere-free combination; Step 3: Taking the tropospheric zenith delay values ​​of the high point with large drop height and the ground point as initial values, compile the constraint condition equation information file; Step 4: constrain the initial value of step 3, and solve and fix the integer ambiguity based on the ambiguity search strategy; Step 5: Substitute the fixed integer ambiguity back into the equation to estimate the position parameters of the high point of the large drop and the zenith tropospheric delay parameter values; Step 6: Adjust the baseline information file solved in step 5, that is, use the constrained adjustment method to constrain the ground point coordinates to obtain the final three-dimensional spatial coordinates and point accuracy of the high point with a large drop.

2. The high-precision rapid network solution method for GNSS in high-rise mountainous areas based on tropospheric prior information constraints as claimed in claim 1, characterized in that: The step 1, based on the double difference network solution mode or the precise single point positioning mode, solves the three-dimensional spatial coordinates of the ground point with long-term observation time and the hourly zenith tropospheric delay information, firstly selects the IGS reference station outside 500km around the area, the stable national or provincial continuously operating reference station, and combines it with the long-term observation ground points in the area as the basic meteorological parameter control network for obtaining the tropospheric information in the area; secondly, the high-precision GNSS double difference model solution software GAMIT software or BERNESE is used for the reference station in the area to solve the hourly zenith tropospheric delay value and corresponding accuracy information of the long-term observation ground point; When the double-difference model is used to solve the zenith tropospheric delay, the observation equation uses the observation equation that eliminates the ionosphere. The specific solution model is shown in formula (1) to formula (2); When the GNSS synchronous observation network adopts the double difference model baseline solution, the double difference equation can be expressed as: When the ionosphere-free combination is used, the double difference observation equation can be expressed as: In equations (1) and (2), superscripts i and j and subscripts r and s represent the given receiver and satellite, respectively; f1 and f2 are the frequencies of carriers L1 and L2, respectively; λ1 and λ2 are the wavelengths of carriers L1 and L2, respectively; n1 and n2 are the double difference ambiguities of carriers L1 and L2, respectively; is the station-satellite geometric distance; is the double difference ionospheric delay; is the double-difference tropospheric delay; is the ionospheric-free combined carrier and pseudorange double difference observation value of satellites i and j observed by stations r and s; is the double-difference ionospheric-free combined ambiguity; IF is the wavelength of the ionosphere-free combined observation; When calculating the zenith tropospheric delay at the ground point, the main parameter settings for baseline solution are: (1) Satellite orbit: Use the IGS hybrid precise ephemeris or the hybrid precise ephemeris of other international analysis centers; (2) Satellite cut-off elevation angle: 10°; (3) Epoch interval: Based on the observation duration, the minimum sampling interval is an integer multiple of 5 s; (4) Observation type: combined observation after eliminating the ionosphere; (5) Tropospheric model correction model: the Sasstamoninen model and the global pressure and temperature model are used for correction; (6) Solar radiation pressure correction: BERNE model; (7) Tropospheric delay model: The first-order Gauss-Markov model is used for parameter estimation; (8) Baseline solution coordinate constraints: The starting point adopts the constraints of 5 cm in the horizontal direction and 10 cm in the vertical direction, and the points to be solved adopt the constraints of 10 m in the horizontal and vertical directions; (9) Solid tide model: IERS2010; (10) Ocean tide model: FES2004 ocean tide model; (11) Tropospheric mapping function model: VMF1; (12) Number of zenith delay parameters:

25.

3. The high-precision rapid network solution method for GNSS in high-rise mountainous areas based on tropospheric prior information constraints as claimed in claim 1, characterized in that: The second step is to use the high-precision prior zenith tropospheric delay information and the three-dimensional spatial coordinates of the ground point as constraints, and estimate the zenith tropospheric delay parameters of the large drop point in the double difference equation of the synchronous time period with the drop point based on the ionosphere-free combination; The main process is: (1) First, the synchronous observation data of ground points with long-term observation and mountain top points in high-altitude mountainous areas are combined into a regional joint observation network; (2) Secondly, the regional network data is processed with the parameter settings of the first step baseline solution. When the ionosphere-free combined equation is used for parameter estimation, additional condition constraints are introduced for the ground points where the zenith tropospheric delay has been obtained, and then the three-dimensional spatial position coordinate parameters and tropospheric parameters of the high point with a large drop are estimated; The additional constraint model in parameter estimation is: ΔZTD r =ZTD r +e r，VZTD (3) In formula (3), the zenith tropospheric delay parameter at ground point r is ZTD r , the random model is The zenith tropospheric delay ZTD of the long-term observation data at the ground point r As a virtual observation, ε r，VZTD is the zenith tropospheric delay virtual value noise.

4. The high-precision rapid network solution method for GNSS in high-rise mountainous areas based on tropospheric prior information constraints as claimed in claim 1, characterized in that: The step three is to use the tropospheric zenith delay values ​​of the large drop height point and the ground point as initial values ​​to compile a constraint condition equation information file; First, the zenith tropospheric delay value of the height difference point obtained in the second step and the zenith tropospheric delay value of the ground point obtained in the first step are used as initial values ​​to prepare the zenith tropospheric delay initial value constraint file for the synchronous observation period; Secondly, since the starting time of the mountain top may not be an integer observation, and the high-precision GNSS data processing software uses integer estimation in data processing, it is necessary to establish a connection between the observation time corresponding to the initial value of the troposphere at the ground point and the observation time of the mountain top; Assuming that the change of the troposphere is stable and can be described linearly during the synchronous observation time, the zenith tropospheric delay value and accuracy at the average time during the synchronous observation time are used as the basic information of the constraint file; the zenith tropospheric delay is calculated by linear interpolation, see formula (4); Assume that the start and end time of the synchronous observation period are t1 and t2, and the zenith tropospheric delay values ​​at the corresponding time of the station are ZTD1 and ZTD2. Then the zenith tropospheric delay value ZTD at any time t of the station is calculated as shown in formula (4): ZTD=ZTD1+(t-t1)×(ZTD1-ZTD2) / (t2-t1) (4) 5. The high-precision rapid network solution method for GNSS in high-rise mountainous areas based on tropospheric prior information constraints as claimed in claim 1, characterized in that: In the step 4, constraining the initial value of step 3, solving and fixing the integer ambiguity based on the ambiguity search strategy; (1) First, the wide-lane combined equations are adopted and the SIGMA ambiguity resolution strategy is used; (2) Secondly, the zenith tropospheric delay constraint information obtained in the third step is introduced, and the site coordinates and ionosphere initial values ​​are fixed, and the wide lane ambiguity values ​​are estimated and saved.

6. The high-precision rapid network solution method for GNSS in high-rise mountainous areas based on tropospheric prior information constraints as claimed in claim 1, characterized in that: The step five is to substitute the fixed integer ambiguity back into the equation to estimate the position parameters of the large drop high point and the zenith tropospheric delay parameter value; the specific process is: the wide lane ambiguity solved in step four is brought into the equation, the narrow lane ambiguity is estimated using the SIGMA ambiguity resolution strategy, and the spatial position coordinates of the ground joint measurement point and the zenith tropospheric delay constraints are given to estimate the spatial position coordinate parameters and tropospheric parameters of the large drop high point.

7. The high-precision rapid network solution method for GNSS in high-rise mountainous areas based on tropospheric prior information constraints as claimed in claim 1, characterized in that: Described step 6, the baseline information file solved in step 5 is adjusted, i.e., the final three-dimensional space coordinates and point position accuracy of the large drop high point are obtained by constraining the ground point coordinates using the constraint adjustment method; The synchronous solution file uses the constraint adjustment method to calculate the three-dimensional position parameters of the drop height point. The synchronous solution file contains the site location parameters and the covariance information of all estimated parameters. The general model of constrained adjustment based on station coordinates is: When adjusting ground points, the prior constraints on ground points are given, and the adjustment model is: The covariance matrix of the observations can be expressed as: The parameter estimates are Where: V is the observation residual; A is the observation equation coefficient design matrix; L is the actual observation vector; σ is the unit priori mean error; P and Pc are the observation weight matrix and the ground point priori constraint weight matrix respectively; H c is the coefficient matrix of the prior constraint equation; is the parameter to be estimated.

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