Method for generating correction information in a satellite navigation system and program for generating correction information

Abstract

Improve the availability of WADGPS. [Solution] In satellite navigation systems, including the US GPS and Japan's Quasi-Zenith Satellite System, when a Wide Area Differential Correction System (WADGPS) is configured by setting up multiple reference stations, for each grid point to which an ionospheric propagation delay is given, if there is one or fewer navigation satellites using that grid point in any user station within the service area, a constant or a linear function of the latitude of the grid point position is set as the confidence interval for the ionospheric propagation delay, thereby reducing the confidence interval for the calculation result of the user station position and improving the availability of the navigation system.

Description

Technical Field

[0001] The present invention relates to generation of correction information in a satellite navigation system.

Background Art

[0002] A satellite navigation system that measures position via artificial satellites is collectively referred to as GNSS (Global Navigation Satellite System), a typical example of which is GPS (Global Positioning System) developed by the United States. In general, in GNSS, a satellite navigation receiver receives positioning signals transmitted by artificial satellites called navigation satellites, measures the distance between the navigation satellites and the receiver, and calculates the position at which the receiver received the positioning signal. The position at which the receiver receives the positioning signal is simply referred to as the position of the receiver. A receiver whose position is to be obtained is called a user receiver or a user station. An error of a position obtained by calculation relative to the true position is called a positioning error, and the statistical behavior of the positioning error is called positioning accuracy. Measuring a position is called positioning, and the calculation processing therefor is called positioning calculation.

[0003] To calculate the position of a satellite navigation receiver, it is necessary to know the positions of the navigation satellites transmitting the positioning signals, and the orbit information of the navigation satellites required for this purpose is superimposed on the positioning signals and transmitted by the navigation satellites themselves. Since the orbit information is created by prediction, the position of a navigation satellite calculated based on this information includes an error of up to several meters, which becomes a factor of positioning error as a position error of the navigation satellite when the receiver calculates its position.

[0004] The timing of navigation satellites transmitting positioning signals is predetermined, and these signals are transmitted based on the time on their own clocks. High-precision atomic clocks are used for this purpose, but very slight time discrepancies are unavoidable, so satellite navigation receivers require information on the time indicated by the navigation satellite's clock. This clock information is transmitted by the navigation satellite itself, superimposed on the positioning signal. Since the clock information is created by prediction, the timing of the positioning signal transmission calculated using this information contains an error equivalent to several meters in distance, and this becomes a factor in positioning errors when calculating the receiver's position as a clock error of the navigation satellite.

[0005] During the journey of a positioning signal to the ground, it passes through the ionosphere and troposphere, and delays occur as the radio signal passes through each region. These delays are called ionospheric propagation delay and tropospheric propagation delay, respectively. Therefore, when using a radio signal as a positioning signal, these ionospheric and tropospheric propagation delays become factors in positioning errors. The magnitudes of ionospheric and tropospheric propagation delays, converted to distance, are called ionospheric propagation delay amount and tropospheric delay amount, respectively.

[0006] In a satellite navigation system, the distance measurement obtained by the receiver to the navigation satellite is the sum of the true distance and the measurement errors caused by all these error factors.

[0007] Navigation messages are the orbital information and clock information that navigation satellites transmit superimposed on their positioning signals. Navigation messages may also include information about ionospheric propagation delay, but their accuracy is generally insufficient. Tropospheric propagation delay is typically corrected using mathematical models.

[0008] A receiver is installed at a fixed ground-based reference station, and the distance measured by this receiver is used to create correction information for distance measurement errors. This information is then provided to the user, thereby correcting the distance measured at the user station based on the correction information and improving the positioning accuracy at the user station. This method is called Differential GPS (DGPS). To distinguish it from DGPS, the method of calculating the position of the user station without applying correction information is called standalone positioning. The positioning performance obtained by DGPS is called the correction performance of that DGPS. Similarly, the positioning performance obtained by applying correction information in DGPS is called the correction performance of that correction information.

[0009] There are several specific DGPS methods, but the most common method involves a single base station measuring the distance to generate distance correction values ​​for each navigation satellite, and then providing these correction values ​​to the user station as correction information for multiple navigation satellites. In this method, sometimes called Local Area DGPS (LADGPS), correction information is not created separately for each factor of positioning error. Therefore, as the distance between the user station and the base station increases, the common component of the positioning error decreases, and positioning accuracy tends to deteriorate. It is generally understood by those skilled in the art that it can be used within a range of approximately several hundred kilometers from the base station, or up to several tens of kilometers depending on the ionosphere conditions.

[0010] Another type of DGPS is called Wide Area Differential GPS (WADGPS). In this method, multiple reference stations (called a group of reference stations) measure distances and use that distance to generate correction information for each factor of positioning error, such as the clock error of the navigation satellites, the position error of the navigation satellites, the ionospheric propagation delay, and the tropospheric propagation delay, and provide this information to the user station. Since the way each of these error factors manifests as distance measurement errors differs depending on the user station's location, the user station calculates the correction value it should use from the correction information based on its approximate location and uses it for correction.

[0011] The clock error of the navigation satellite manifests as a uniform distance measurement error regardless of the user station's position. The position error of the navigation satellite manifests as a distance measurement error as the dot product component of the line of sight direction when the navigation satellite is viewed from the user station. The ionospheric propagation delay manifests as a distance measurement error as the integral of the free electron density distribution (total number of electrons) in the ionospheric atmosphere along the path from the navigation satellite's transmitted ranging signal to the user station. The tropospheric propagation delay manifests as a distance measurement error as the integral of the refractive index of the neutral atmosphere along the path from the navigation satellite's transmitted ranging signal to the user station. In other words, with the exception of the navigation satellite's clock error, the distance measurement error manifests differently depending on the user station's position.

[0012] It is known that the ionospheric propagation delay is proportional to the total number of electrons in the ionospheric atmosphere through which the positioning signal passes, and inversely proportional to the square of the frequency of the positioning signal. Therefore, at a base station, if distance measurements are performed using positioning signals of multiple frequencies, the ionospheric propagation delay can be calculated from the difference between those distances. Alternatively, at a base station or user station, if distance measurements are performed using positioning signals of multiple frequencies, the distance with the ionospheric propagation delay removed can be obtained as a linear combination of the measurement results. The position where a positioning signal passes through the ionosphere is called the IPP (Ionospheric Pierce Point).

[0013] Furthermore, tropospheric propagation delay can be estimated with sufficient accuracy using a simple tropospheric propagation delay model, and corrections can be made at both the base station and the user station. Therefore, in WADGPS, tropospheric propagation delay does not need to be included in the correction information.

[0014] In WADGPS, it is necessary to define not only the physical meaning of correction information, but also how to use it, that is, the procedure for applying correction information at user stations. Without knowing the processing details of user stations, it is impossible to generate appropriate correction information. Therefore, when the master station generates correction information, the procedure for applying the generated correction information at user stations is known. On the other hand, the method for generating correction information is not specifically defined.

[0015] One practical example of WADGPS is the SBAS (Satellite-Based Augmentation System) standardized for aircraft.

[0016] One example of a SBAS (Sub-Satellite Augmentation System) is the MSAS (Michibiki-Based Satellite Augmentation System) operated by the Japan Civil Aviation Bureau, which is currently in practical use. More recently, South Korea has begun operating the KASS (Korea Augmentation Satellite System).

[0017] The SBAS standard allows user stations to not only determine their position but also obtain a confidence interval for the positioning error at any given moment. This confidence interval is called the protection level (in meters), and its confidence level is very high at 1 - 10^(-7) / h (^ represents exponentiation). Providing a protection level is the most important function of SBAS, an aeronautical navigation system.

[0018] Since the confidence level of the protection level is sufficiently high, the protection level is essentially the value presented by the navigation system as the maximum positioning error, and the navigation system can ensure safety as long as there is a distance corresponding to the protection level from obstacles around the route. Therefore, the feasibility of navigating a given route is determined by the magnitude of the protection level, and the smaller the protection level, the better the performance of the navigation system. The protection level is a function of time and the user station position, and the percentage of time during which navigation for a given route is possible at a given position is called availability.

[0019] In the SBAS standard, correction information regarding ionospheric propagation delay is expressed as the vertical ionospheric propagation delay amount (called vertical delay) at multiple grid points (IGP: Ionosphere Grid Point) and an index value (GIVEI: Grid Ionosphere Vertical Error Index) indicating its confidence interval (GIVE: Grid Ionosphere Vertical Error). Grid points are set every 5 degrees of latitude and longitude to sufficiently cover the entire service area.

[0020] The user station is required to obtain the necessary ionospheric propagation delay and its confidence interval by linear interpolation of the vertical delay amount at the IGP surrounding the IPP corresponding to the positioning signal. Along with the selection criteria for the IGP and the bilinear interpolation formula used for linear interpolation, a conversion formula for converting the vertical delay amount to the line-of-sight direction is also defined. The selection criteria for the IGP is to select four grid points in a rectangular shape surrounding the IPP.

[0021] The ionosphere is formed when atmospheric molecules are turned into plasma by sunlight, and therefore, it generally grows to a high density during the day and declines at night. However, as it is a natural phenomenon, it fluctuates greatly depending on the time of day, whether it is day or night, and the season. In general, it is influenced by the approximately 11-year cycle of solar activity, and tends to be denser above low magnetic latitude regions. The latter is due to the influence of the Earth's magnetic field on ionospheric phenomena, and it is important to note that in the vicinity of Japan, the magnetic equator is located north of the equator, so magnetic latitude is lower than geographic latitude. [Prior art documents] [Patent Documents]

[0022] [Patent Document 1] Patent No. 7868834 [Non-patent literature]

[0023] [Non-Patent Document 1] T. Walter et al., "Robust Detection of Ionospheric Irregularities", NAVIGATION: Journal of the Institute of Navigation, Vol. 48, No. 2, pp. 89-199, 2001 [Non-Patent Document 2] D. Kim et al., "Performance Analysis of Ionospheric Delay Estimation for Multi-Constellation WA-DGNSS According to the Number of Reference Stations", Journal of Advanced Navigation Technology, Vol. 18, No. 4, pp. 260-267, 2014 Summary of Invention Problem to be Solved by the Invention

[0024] A user station of SBAS is configured to obtain a required ionospheric propagation delay amount and its confidence interval as linear interpolation of vertical delay amounts at IGPs located in the vicinity of an IPP corresponding to a positioning signal, and a conversion formula for converting a vertical delay amount into a line-of-sight direction is defined together with a grid point selection criterion and a bilinear interpolation formula used for linear interpolation. From the GIVE represented by the GIVEI of an IGP, a confidence interval for a correction residual that still remains after applying correction information related to ionospheric propagation delay can be obtained through an interpolation process similar to that for the ionospheric propagation delay amount. This confidence interval is used for calculation of a protection level.

[0025] In Japan, since the Nansei Islands fall under a low geomagnetic latitude region, the ionosphere in the sky tends to have a high density, and a user station using MSAS tends to have a large protection level particularly in this region. This means that the availability of MSAS (the proportion of time that a user station can use MSAS) decreases in the region, resulting in a state where it is difficult to use as a navigation system.

[0026] Since MSAS is a navigation system based on the SBAS standard, it transmits the vertical delay amount at multiple grid points and its GIVEI as correction information for ionospheric propagation delay. The reason the protection level increases is that this GIVEI is large. The magnitude of GIVE, which corresponds to GIVEI, is not proportional to GIVEI, but it is monotonically increasing.

[0027] In the SBAS standard, correction information regarding ionospheric propagation delay is expressed as the vertical ionospheric propagation delay at an IGP. Therefore, in actual SBAS systems, the ionospheric propagation delay at the location of each IGP is estimated using the ionospheric propagation delay measured in the vicinity of that IGP.

[0028] Patent Document 1 describes a method for generating correction information regarding ionospheric propagation delay that conforms to the SBAS standard transmission format, using distance measured by a single-frequency positioning signal at a reference station. However, the calculation method for GIVEI is not described.

[0029] Non-Patent Document 1 describes a method for generating correction information regarding ionospheric propagation delay that conforms to the SBAS standard transmission format, using distances from positioning signals of multiple frequencies measured at a base station. Non-Patent Document 1 also describes the GIVEI calculation method, and the following equation is presented as the basic relationship.

[0030] (Math 1) σGIVE^2=σFIT^2+σTHREAT^2+σTEMP^2

[0031] σGIVE represents the confidence interval at the IGP and is converted to GIVEI to become part of the augmentation information. σFIT represents the estimation accuracy of the calculation process that estimates the ionospheric propagation delay at the IGP's location using ionospheric propagation delays measured in the vicinity of the IGP, and is determined based on the chi-squared distribution. σTHREAT is a term that reflects the fact that when using ionospheric propagation delays measured in the vicinity of the IGP in the calculation process that estimates the ionospheric propagation delay at the IGP's location, the observation (sampling) of these ionospheric propagation delays is not performed spatially uniformly and with sufficient density. σTEMP is a term to address the time variation of the ionospheric propagation delay and sets a constant based on knowledge from previous ionospheric observations.

[0032] In equation (1), σFIT, one of the terms that make up σGIVE, is determined by the number of ionospheric propagation delays measured in the vicinity of the IGP. Therefore, increasing the density of reference stations is effective in reducing σFIT. Increasing the density of reference stations increases the sampling density, which can also be expected to have the effect of reducing σTHREAT.

[0033] However, there are inherent limitations on the number and placement of reference stations, and it is impossible to install reference stations at sea. Therefore, simply increasing the density of reference stations does not necessarily guarantee a sufficient sampling density.

[0034] Another way to increase sampling density is to increase the number of navigation satellites. Non-patent document 2 suggests that using new satellite navigation systems such as Galileo in addition to GPS may improve the correction performance for ionospheric propagation delay in WADGPS.

[0035] However, there are inherent limitations on the navigation satellites that can be used, and the placement of these satellites cannot be chosen according to the needs of WADGPS. Therefore, simply increasing the number of navigation satellites does not necessarily guarantee a sufficient sampling density.

[0036] As described above, in WADGPS, which provides a confidence interval for ionospheric propagation delay in correction information related to ionospheric propagation delay, the confidence interval tends to be large, especially when a level of safety required for aviation applications is needed. This has the disadvantage of also resulting in a large confidence interval for the user station position calculation results. The present invention solves this problem by changing the method of generating correction information in WADGPS. [Means for solving the problem]

[0037] For WADGPS, a formula is provided for calculating the IPP (Integrated Point Position) where the positioning signal passes through the ionosphere. In SBAS, the ionosphere is approximated by a single-layer thin-film model, and the IPP is calculated as a thin spherical shell at an altitude of 350 km. In other words, the IPP is a single point in space and is a function of the position of the navigation satellite and the position of the receiver (base station or user station).

[0038] In the SBAS standard, when receiver k receives a positioning signal from navigation satellite i, the ionospheric propagation delay I(i,k) is expressed by the following equation:

[0039] (Math 2) I(i,k) = F(ELi) × Z(IPP(i,k))

[0040] ELi is the elevation angle of the navigation satellite i at the receiver k position, IPP(i,k) is the IPP position, and Z(X) is the ionospheric vertical delay at position X. F(EL) is a gradient coefficient that converts the ionospheric vertical delay to a delay in the line of sight direction, and is defined by the SBAS standard along with the formula for calculating the IPP position. SBAS transmits the vertical delay at the IGP position, i.e., Z(X), as correction information for ionospheric propagation delay.

[0041] The actual ionosphere has a vertical structure, with the highest density often occurring at an altitude of around 300-350 km. However, the ionosphere exists continuously above and below this altitude, with decreasing density, and it is said that significant density exists particularly in the upper regions up to an altitude of about 1,000 km.

[0042] Such a vertical structure of the ionosphere cannot be adequately represented by the single-layer thin-film model employed by SBAS. For example, consider the case where the positioning signal passes through the ionosphere from the east in the combination of navigation satellite i and receiver k, and from the west in the combination of navigation satellite j and receiver h.

[0043] In this case, the IPPs may coincide, i.e., IPP(i,k) = IPP(j,h). Even though the IPP locations are the same, the portion of the ionosphere through which the positioning signal actually passes and the direction of its passage are different. Therefore, if there is a bias in the electron density distribution within the ionosphere, the ionospheric propagation delay will differ. In other words, even at the same IPP location, the measured ionospheric propagation delay will differ, resulting in a larger apparent measurement noise for the ionospheric propagation delay.

[0044] When the apparent measurement noise for ionospheric propagation delay increases, σFIT and σTHREAT in (Equation 1) become excessively large. This was the reason why GIVEI tended to be large in SBAS.

[0045] Incidentally, when considering individual IGPs, it becomes clear that for some IGPs, the navigation satellites that can be corrected are limited when a user station at any given location performs ionospheric propagation delay correction. For example, an IGP located north of a service area may only be used for navigation satellites in the northern sky.

[0046] Here, since WADGPS does not provide service outside its service area, we do not need to consider cases where the user station is outside the service area. In other words, we can limit the location of the user station to within the service area.

[0047] If a navigation satellite using a given IGP is limited to 1, then the IPP position is determined solely by the receiver position and does not change drastically with respect to changes in the receiver position. Therefore, (Equation 2) changes roughly linearly with respect to changes in the receiver position.

[0048] In this case, even though the IPP (Integrated Point) location is the same, the portion of the ionosphere through which the positioning signal actually passes will not differ significantly. Therefore, the apparent measurement noise for the ionospheric propagation delay will not increase. If the apparent measurement noise for the ionospheric propagation delay does not increase, the measurement noise for the ionospheric propagation delay can be kept low.

[0049] Reflecting this, a constant can be set for GIVEI. Alternatively, reflecting the general tendency for ionospheric activity to be more active at lower magnetic latitudes, GIVEI can be a linear function of the latitude of the IGP location (either geographical or magnetic latitude). This allows for a smaller confidence interval for the ionospheric propagation delay, and consequently, a smaller confidence interval for the user station position calculation.

[0050] Furthermore, if there are no navigation satellites that use a particular IGP, any value can be set for GIVEI for that IGP. Therefore, in such cases, the same processing as when the number of navigation satellites used is limited to one may be applied.

[0051] Patent Document 1 describes a method for generating correction information regarding ionospheric propagation delay that conforms to the transmission format of the SBAS standard, but it does not describe the calculation method for GIVEI.

[0052] Non-patent document 1 describes a method for generating correction information regarding ionospheric propagation delay that conforms to the transmission format of the SBAS standard, and also describes a method for calculating GIVEI, but it does not suggest that GIVEI be a constant or a linear function of the latitude of the IGP location.

[0053] Non-patent document 2 suggests the possibility of improving the correction performance for ionospheric propagation delay in WADGPS by using new satellite navigation systems such as Galileo in addition to GPS, but the specific processing procedure is not specified, nor is the calculation method of GIVEI explained. [Effects of the Invention]

[0054] According to the present invention, in a WADGPS that provides a confidence interval for ionospheric propagation delay for correction information relating to ionospheric propagation delay, if, for each grid point to which the ionospheric propagation delay is given, there is one or fewer navigation satellites using that grid point in any user station within the service area, the confidence interval for the ionospheric propagation delay can be kept small, and thereby the confidence interval for the calculation result of the user station position can also be kept small. [Brief explanation of the drawing]

[0055] [Figure 1] This is a schematic diagram illustrating an embodiment of the present invention. [Modes for carrying out the invention]

[0056] Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. [Examples]

[0057] Embodiments of this invention will be described in detail with reference to Figure 1. Note that while Figure 1 illustrates two user stations, the number of user stations is not limited to two. Similarly, while Figure 1 illustrates two navigation satellites, the number of navigation satellites is not limited to two.

[0058] Navigation satellites 11 and 12 each transmit positioning signals.

[0059] The positioning signals transmitted by navigation satellites 11 and 12 are received by user stations 31 and 32, respectively, which are within the service area 2.

[0060] The positioning signal transmitted by navigation satellite 11 is received by user station 31 after passing through IPP position 411, and by user station 32 after passing through IPP position 412. The positioning signal transmitted by navigation satellite 12 is received by user station 31 after passing through IPP position 421, and by user station 32 after passing through IPP position 422.

[0061] In Figure 1, the locations of the IGPs are shown as 51-56.

[0062] According to the SBAS standard, for the positioning signal of navigation satellite 11 received by user station 31, the IPP position is 411, so the vertical delay is calculated as bilinear interpolation of the vertical delay amounts at IGPs 51, 52, 54, and 55 in the vicinity. For the positioning signal of navigation satellite 12 received by user station 31, the IPP position is 421, so the vertical delay is calculated as bilinear interpolation of the vertical delay amounts at IGPs 52, 53, 55, and 56 in the vicinity.

[0063] Similarly, for the positioning signal of navigation satellite 11 received by user station 32, the IPP position is 412, so the vertical delay is calculated as bilinear interpolation of the vertical delay amounts at IGPs 52, 53, 55, and 56 in the vicinity. For the positioning signal of navigation satellite 12 received by user station 32, the IPP position is 422, so the vertical delay is calculated as bilinear interpolation of the vertical delay amounts at IGPs 52, 53, 55, and 56 in the vicinity.

[0064] IGP51 and 54 are only used in calculating the vertical delay when the user station 31 receives positioning signals from the navigation satellite 11. In other words, IGP51 or 54 are used in calculating the ionospheric propagation delay of positioning signals received by the user station only for the navigation satellite 11.

[0065] In such cases, for IGP51 and 54, either a constant value is set as GIVEI, or the function value of a linear function of the latitude of the IGP position is set. These values ​​should be smaller than the GIVEI that can be set by methods other than those of this invention.

[0066] For IGP52, 53, 55, and 56, the IPP of the positioning signal received by the user station will be located around these IGPs not only from navigation satellite 11, so GIVEI is set using a method other than that of the present invention.

[0067] Next, we will explain the operation.

[0068] In this embodiment, for IGP51 and 54, GIVEI is set to a constant or a function value of a linear function of the latitude of the IGP position. Since these values ​​are set to be smaller than GIVEI that can be set by methods other than the present invention, the effect of reducing GIVEI can be obtained by the present invention.

[0069] Reducing GIVEI means that the confidence interval for the ionospheric propagation delay amount will be kept small for the correction information related to ionospheric propagation delay, and therefore the confidence interval for the calculation result of the user station position will also be kept small. [Industrial applicability]

[0070] WADGPS has been put into practical use as SBAS and is already widespread. According to this invention, in WADGPS, which provides a confidence interval for ionospheric propagation delay for correction information related to ionospheric propagation delay, if the number of navigation satellites using each grid point for which an ionospheric propagation delay is given is one or less for any user station in the service area, the confidence interval for the ionospheric propagation delay can be kept small, and thus the confidence interval for the calculation result of the user station position can also be kept small. This means that the protection level can be reduced, which leads to an improvement in the availability of the navigation system. [Explanation of Symbols]

[0071] 11,12 Navigation Satellites 2 Service Areas 31,32 User Stations 411,412,421,422 IPP 51, 52, 53, 54, 55, 56 IGP

Claims

1. Multiple navigation satellites that transmit positioning signals, A user station that receives positioning signals transmitted by the aforementioned multiple navigation satellites and measures the distance between them, Multiple reference stations that receive positioning signals transmitted by the multiple navigation satellites using satellite navigation receivers fixed on the ground and measure the distance between them, The system includes a master station that generates correction information regarding the clock error, position error, and ionospheric propagation delay of navigation satellites using the distances measured by the aforementioned multiple reference stations, and provides this correction information to the user stations. The correction information regarding the ionospheric propagation delay is expressed as an index value indicating the vertical ionospheric propagation delay amount at multiple grid points arranged to sufficiently cover the geographical area of ​​the service target, and its confidence interval. The user station is to calculate the ionospheric propagation delay and its confidence interval for each positioning signal of the plurality of navigation satellites by interpolating the vertical ionospheric propagation delay and its confidence interval at grid points around the position where the positioning signal passes through the ionosphere, and the selection criteria for the surrounding grid points used in the interpolation process are predetermined. In a satellite navigation system that performs wide-area differential correction, The aforementioned master station, When generating an index value that indicates the confidence interval for the ionospheric propagation delay, Assuming the location of the user station is within the geographical area covered by the service, For each of the plurality of grid points, if, according to the selection criteria, at any position of the user station, only one or fewer of the plurality of navigation satellites will use the confidence interval at that grid point, then the confidence interval for that grid point shall be set to a constant. A method for generating correction information in a satellite navigation system, characterized by the above.

2. Multiple navigation satellites that transmit positioning signals, A user station that receives positioning signals transmitted by the aforementioned multiple navigation satellites and measures the distance between them, Multiple reference stations that receive positioning signals transmitted by the multiple navigation satellites using satellite navigation receivers fixed on the ground and measure the distance between them, The system includes a master station that generates correction information regarding the clock error, position error, and ionospheric propagation delay of navigation satellites using the distances measured by the aforementioned multiple reference stations, and provides this correction information to the user stations. The correction information regarding the ionospheric propagation delay is expressed as an index value indicating the vertical ionospheric propagation delay amount at multiple grid points arranged to sufficiently cover the geographical area of ​​the service target, and its confidence interval. The user station is to calculate the ionospheric propagation delay and its confidence interval for each positioning signal of the plurality of navigation satellites by interpolating the vertical ionospheric propagation delay and its confidence interval at grid points around the position where the positioning signal passes through the ionosphere, and the selection criteria for the surrounding grid points used in the interpolation process are predetermined. In a satellite navigation system that performs wide-area differential correction, The aforementioned master station, When generating an index value that indicates the confidence interval for the ionospheric propagation delay, Assuming the location of the user station is within the geographical area covered by the service, For each of the plurality of grid points, if, according to the selection criteria, at any position of the user station, only one or fewer of the plurality of navigation satellites will be used for the confidence interval at that grid point, then the confidence interval for that grid point shall be a linear function of the latitude of that grid point. A method for generating correction information in a satellite navigation system, characterized by the above.

3. Multiple navigation satellites that transmit positioning signals, A user station that receives positioning signals transmitted by the aforementioned multiple navigation satellites and measures the distance between them, Multiple reference stations that receive positioning signals transmitted by the multiple navigation satellites using satellite navigation receivers fixed on the ground and measure the distance between them, The system includes a master station that generates correction information regarding the clock error, position error, and ionospheric propagation delay of navigation satellites using the distances measured by the aforementioned multiple reference stations, and provides this correction information to the user stations. The correction information regarding the ionospheric propagation delay is expressed as an index value indicating the vertical ionospheric propagation delay amount at multiple grid points arranged to sufficiently cover the geographical area of ​​the service target, and its confidence interval. The user station is to calculate the ionospheric propagation delay and its confidence interval for each positioning signal of the plurality of navigation satellites by interpolating the vertical ionospheric propagation delay and its confidence interval at grid points around the position where the positioning signal passes through the ionosphere, and the selection criteria for the surrounding grid points used in the interpolation process are predetermined. In a satellite navigation system that performs wide-area differential correction, A program that operates on the aforementioned master station, When generating an index value that indicates the confidence interval for the ionospheric propagation delay, Assuming the location of the user station is within the geographical area covered by the service, For each of the plurality of grid points, if, according to the selection criteria, at any position of the user station, only one or fewer of the plurality of navigation satellites will use the confidence interval at that grid point, then the confidence interval for that grid point shall be set to a constant. A program that generates correction information for a satellite navigation system, characterized by the following:

4. Multiple navigation satellites that transmit positioning signals, A user station that receives positioning signals transmitted by the aforementioned multiple navigation satellites and measures the distance between them, Multiple reference stations that receive positioning signals transmitted by the multiple navigation satellites using satellite navigation receivers fixed on the ground and measure the distance between them, The system includes a master station that generates correction information regarding the clock error, position error, and ionospheric propagation delay of navigation satellites using the distances measured by the aforementioned multiple reference stations, and provides this correction information to the user stations. The correction information regarding the ionospheric propagation delay is expressed as an index value indicating the vertical ionospheric propagation delay amount at multiple grid points arranged to sufficiently cover the geographical area of ​​the service target, and its confidence interval. The user station is to calculate the ionospheric propagation delay and its confidence interval for each positioning signal of the plurality of navigation satellites by interpolating the vertical ionospheric propagation delay and its confidence interval at grid points around the position where the positioning signal passes through the ionosphere, and the selection criteria for the surrounding grid points used in the interpolation process are predetermined. In a satellite navigation system that performs wide-area differential correction, A program that operates on the aforementioned master station, When generating an index value that indicates the confidence interval for the ionospheric propagation delay, Assuming the location of the user station is within the geographical area covered by the service, For each of the plurality of grid points, if, according to the selection criteria, at any position of the user station, only one or fewer of the plurality of navigation satellites will be used for the confidence interval at that grid point, then the confidence interval for that grid point shall be a linear function of the latitude of that grid point. A program that generates correction information for a satellite navigation system, characterized by the following:

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