Method and program for measuring ionospheric propagation delay at satellite navigation receiving station

Abstract

The ionospheric propagation delay is measured using a single-frequency satellite navigation receiving station. [Solution] Ionospheric propagation delay is measured using satellite navigation systems, including the US GPS and Japan's Quasi-Zenith Satellite System. Since ionospheric propagation delay depends on the signal frequency, a receiving station that receives positioning signals at two frequencies has traditionally been required. However, by performing a calculation process to estimate two parameters using the receiver clock error and the vertical component of the ionospheric propagation delay as unknowns, it is now possible to measure ionospheric propagation delay using a satellite navigation receiving station that receives positioning signals at only one frequency.

Description

[Technical Field]

[0001] The present invention relates to a method and program for measuring the amount of ionospheric propagation delay at a satellite navigation receiving station. [Background technology]

[0002] Satellite navigation systems that use satellites to measure position are collectively called GNSS (Global Navigation Satellite Systems), and a representative example is the US-based GPS (Global Positioning System). GNSS generally uses a receiver to receive positioning signals transmitted by radio from satellites called navigation satellites, and measures the distance between the navigation satellite and the receiver to calculate the receiver's position. The distance between the navigation satellite measured by the receiver is called the pseudo-distance. A receiver that uses GNSS to determine its position is called a satellite navigation receiver, GNSS receiver, or user receiver. Equipment that combines a GNSS receiver and a receiving antenna is called a satellite navigation receiving station, GNSS receiving station, user station, or simply a receiving station. The error between the determined position and the true position is called the positioning error. The accuracy with which the position is measured is called the positioning precision.

[0003] To calculate the receiver's position, it is necessary to know the position of the navigation satellite that is transmitting the positioning signal, and the orbital information required for this is transmitted by the navigation satellite itself by superimposing it on the positioning signal. Because the orbital information is created by prediction, it contains an error of several meters, and this position error becomes a factor in positioning error when calculating the receiver's position.

[0004] The timing at which a navigation satellite transmits a positioning signal is predetermined, and the navigation satellite transmits the positioning signal based on the time on its own clock. This clock uses a highly accurate atomic clock, but it contains an error equivalent to a few meters in distance, and this clock error becomes a factor in positioning error when calculating the receiver's position.

[0005] Before reaching the ground, a positioning signal passes through the ionosphere and troposphere above, and delays occur as the radio signal passes through each of these regions. These delays are called the ionospheric propagation delay and the troposphere propagation delay, respectively. Therefore, when this radio signal is used as a positioning signal, these ionospheric propagation delay and troposphere propagation delay become a cause of positioning errors. The magnitude of the ionospheric propagation delay and the troposphere propagation delay converted into distance is called the ionospheric propagation delay and the troposphere delay, respectively.

[0006] Various tropospheric propagation delay models are known, which can estimate the tropospheric propagation delay with relatively good accuracy.

[0007] The amount of ionospheric propagation delay is proportional to the total number of free electrons in the ionospheric atmosphere along the signal propagation path (the integral of the ionospheric electron density over the signal propagation path), and has the property of being inversely proportional to the square of the signal frequency. Since the signal path is the same for the same navigation satellite and receiving station, there is a difference between pseudoranges obtained using positioning signals of multiple frequencies that is inversely proportional to the square of the signal frequency due to ionospheric propagation delay. Since there are no error factors with this property for pseudoranges other than ionospheric propagation delay, the amount of ionospheric propagation delay along the signal propagation path between the navigation satellite and the receiving station can be calculated by using positioning signals of multiple frequencies.

[0008] A satellite navigation receiving station that receives only one frequency of positioning signals cannot use multiple frequencies of positioning signals. For this reason, satellite navigation systems generally transmit ionospheric propagation delays in navigation messages, but the resolution and accuracy of such messages are usually insufficient.

[0009] While navigation satellites transmit positioning signals based on the time of a highly accurate atomic clock, receivers do not normally have a highly accurate clock. For this reason, the usual method of calculating position in GNSS is to assume that the receiver's clock has an error and treat this as an unknown. There are a total of four unknowns: the three-dimensional coordinates of the receiver's position and the receiver's clock error, so in order for the receiver to determine its position, pseudoranges between it and four or more navigation satellites are required. If the receiver's position is known, the only unknown is the receiver's clock error. [Prior art documents] [Non-patent literature]

[0010] [Non-Patent Document 1] Sonosuke Fukushima, "Chapter 5: Estimation of PVT (Position, Velocity, and Time)," A Detailed Explanation of GPS: Basic Concepts, Positioning Principles, Signals and Receivers, Seiyo Bunko, 2004 [Non-patent document 2] Nobuaki Kubo, Easy-to-understand Illustrated Guide to Satellite Positioning and Location Information, Nikkan Kogyo Shimbun, 2018 [Non-patent document 3] Yuichi Otsuka et al., "A new technique for mapping of total electron content using GPS network in Japan," Earth, Planets and Space, vol. 54, pp. 63-70, 2002. [Non-patent document 4] Takeyasu Sakai, "Bias Error Estimation Method for GPS Ionospheric Total Electron Content Observation," IEICE Transactions on Electronics, Information and Communication Engineers, Vol. J88-B, pp. 2382-2389, 2005. Summary of the Invention [Problem to be solved by the invention]

[0011] Since the ionospheric propagation delay is inversely proportional to the square of the signal frequency, it is possible to measure the ionospheric propagation delay by using positioning signals of multiple frequencies. However, this method cannot be used at satellite navigation receiving stations that receive positioning signals of only one frequency. Therefore, navigation satellites transmit the ionospheric propagation delay in their navigation messages. However, the resolution and accuracy of this information is usually insufficient, and it does not measure the ionospheric propagation delay at the receiver location.

[0012] In other words, a satellite navigation receiving station that receives a positioning signal of only one frequency has no method for measuring the amount of ionospheric propagation delay at the receiver position. The object of the present invention is to make it possible to measure the amount of ionospheric propagation delay using a satellite navigation receiving station that receives a positioning signal of only one frequency. [Means for solving the problem]

[0013] The prediction errors contained in the navigation satellite's orbit information and the navigation satellite's clock error are both on the order of a few meters, which is much smaller than the ionospheric propagation delay. Tropospheric propagation delay can be estimated with relatively good accuracy using various tropospheric propagation delay models and can be removed. When these are removed from the pseudorange measured by the satellite navigation receiver, the receiver clock error and ionospheric propagation delay remain.

[0014] This will be explained using a formula. The pseudorange P(i, k) measured by receiving station k using the positioning signal of navigation satellite i can be written as follows:

[0015] (Number 1) P(i,k)=R(i,k)-B(i)+I(i,k)+T(i,k) +S(k)

[0016] Here, R(i, k) is the geometric distance between the navigation satellite and the receiving station, B(i) is the clock error of the navigation satellite i, I(i, k) is the ionospheric propagation delay, T(i, k) is the tropospheric propagation delay, and S(k) is the receiver clock error of the receiving station. Clock errors are considered to be ahead or ahead.

[0017] Assuming that the density distribution of the ionosphere is uniform around receiving station k, the vertical component of the ionospheric propagation delay (called the vertical delay) can be considered constant, and can be written as V(k). The vertical delay and line-of-sight component can be converted using the following equation via an obliquity factor:

[0018] (Number 2) I(i,k)=F(i,k)×V(k)

[0019] The tilt coefficient F(i, k) is calculated by the following equation using the thin-film ionospheric model: where r is the Earth's radius, h is the ionospheric altitude, and E(i, k) is the elevation angle of the navigation satellite i. h may be set to 350 km, for example.

[0020] (Number 3) F(i,k)=(1-(r×cos(E(i,k)) ÷(r+h))^2)^(-0.5)

[0021] The clock error B(i) of navigation satellite i is corrected by the navigation message transmitted by the navigation satellite, and the tropospheric propagation delay T(i,k) can be calculated using any tropospheric propagation delay model. By subtracting these and R(i,k) from the measured pseudorange, the measurement residual can be written as follows:

[0022] (Number 4) Δ(i,k)=P(i,k)-R(i,k)+B(i)-T(i,k) =I(i,k)+S(k) =F(i,x)×V(x)+S(x)

[0023] The correction information in the navigation message allows the clock error B(i) to be corrected to within a few meters. The satellite position from the navigation message contains a predicted error of within a few meters, which becomes a calculation error in R(i, k). Both of these are included as noise in (Equation 4).

[0024] If the receiver clock error S and the vertical delay V are unknowns, the following simultaneous equations can be constructed for N navigation satellites using an N×2 matrix G that represents the relationship between the receiver clock error S and the vertical delay V and the measurement residuals.

[0025] (Number 5) G[SV]'=[Δ(1,x) Δ(2,x) … Δ(N,x)]'

[0026] The symbol "'" means transpose. Since all elements of the first column of matrix G are 1, and the second column is the tilt coefficient for each of the N navigation satellites, the element G(i,j) in the ith row and jth column of matrix G is as follows:

[0027] (Number 6) G(i,1)=1 G(i,2)=F(i,x)

[0028] When the receiver's position is known, the only unknown is the receiver's clock error. However, in the simultaneous equations expressed by (Equation 5) and (Equation 6), the receiver's clock error S and the vertical delay V are also unknown, estimating two parameters. By solving this simultaneous equation, it is possible to determine the receiver's clock error as well as the vertical delay around the receiving station. At least two navigation satellites are required to solve this simultaneous equation, but the least-squares method can be applied using a larger number of navigation satellites.

[0029] Once the vertical delay is calculated, the ionospheric propagation delay for each navigation satellite can be obtained by multiplying it by a gradient coefficient. This allows the ionospheric propagation delay to be measured by a satellite navigation receiving station that receives positioning signals at only one frequency.

[0030] Non-Patent Documents 1 and 2 explain the procedure for calculating the receiver position in a satellite navigation receiver. However, they do not mention a method for calculating the amount of ionospheric propagation delay.

[0031] Non-patent documents 3 and 4 describe methods for calculating the amount of ionospheric propagation delay from distance measurements made by satellite navigation receivers. However, these methods both use two-frequency positioning signals and are not applicable to single-frequency receiving stations.

[0032] The invention of claim 1 is a method for measuring ionospheric propagation delay in a satellite navigation receiving station, comprising: a satellite navigation receiver that receives positioning signals transmitted by multiple navigation satellites and measures the distances between them; a receiving antenna fixed to a known point on the ground for receiving the positioning signals; and an information processing device that calculates ionospheric propagation delay using the distance measurements obtained by the satellite navigation receiver, wherein the information processing device considers the distance measurement error to be composed of a clock error of the satellite navigation receiver, an ionospheric propagation delay that occurs in each of the multiple navigation satellites, and a tropospheric propagation delay, calculates and removes the tropospheric propagation delay using a tropospheric propagation delay model, considers the ionospheric propagation delay to be the product of a constant vertical delay and a tilt coefficient according to the elevation angle of each of the multiple navigation satellites, and then estimates the two parameters of the clock error and the vertical delay to obtain the ionospheric propagation delay corresponding to each of the multiple navigation satellites.

[0033] The invention of claim 2 is a program for measuring ionospheric propagation delay in a satellite navigation receiving station, which is equipped with a satellite navigation receiver that receives positioning signals transmitted by multiple navigation satellites and measures the distance between them, a receiving antenna fixed to a known point on the ground for receiving the positioning signals, and an information processing device that calculates ionospheric propagation delay using the distance measurements obtained by the satellite navigation receiver, the program operating on the information processing device is characterized in that the distance measurement error is considered to be composed of a clock error of the satellite navigation receiver, an ionospheric propagation delay that occurs in each of the multiple navigation satellites, and a tropospheric propagation delay, the tropospheric propagation delay is calculated and removed using a tropospheric propagation delay model, and the ionospheric propagation delay is considered to be the product of a constant vertical delay and a tilt coefficient according to the elevation angle of each of the multiple navigation satellites, and the program obtains the ionospheric propagation delay corresponding to each of the multiple navigation satellites by estimating two parameters, the clock error of the satellite navigation receiver and the vertical delay. [Effects of the Invention]

[0034] The inventions according to claims 1 and 2 are configured as described above, so that the amount of ionospheric propagation delay can be measured by a satellite navigation receiving station that receives positioning signals of only one frequency. [Brief explanation of the drawings]

[0035] [Figure 1] 1 is a schematic diagram illustrating a method for generating correction information in a satellite navigation system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0036] Specific embodiments of the present invention will be described in detail below with reference to the drawings. [Example]

[0037] An embodiment of the present invention will be described in detail with reference to FIG.

[0038] Each of the navigation satellites 1 (1a, 1b, etc.) transmits a positioning signal.

[0039] The satellite navigation receiving station 2 has the function of receiving the positioning signals transmitted by the navigation satellites 1 (1a, 1b, etc.) using a satellite navigation receiver and measuring the distance from each navigation satellite. The measured distance is called a pseudorange.

[0040] The pseudorange measured by the satellite navigation receiving station 2 includes, in addition to the geometric distance between the navigation satellite and the receiving station, the clock error and position error of the navigation satellite i, the ionospheric propagation delay 4 (4a, 4b...), which is the delay when the positioning signal passes through the ionosphere 3, the tropospheric propagation delay 7 (7a, 7b...), which is the delay when the positioning signal passes through the troposphere 6, and the clock error of the satellite navigation receiver. Of these, the clock error and position error of the navigation satellite i are small, within a few meters, and the tropospheric propagation delay 7 (7a, 7b...) can be estimated with relatively good accuracy using various tropospheric propagation delay models. When these are removed from the pseudorange measured by the satellite navigation receiver, the receiver clock error and ionospheric propagation delay remain as residuals.

[0041] The satellite navigation receiving station 2 assumes that the density distribution of the ionosphere 3 in the vicinity is uniform, and that the vertical component 5 (vertical delay) of the ionospheric propagation delay 4 (4a, 4b...) is constant. The ionospheric propagation delay 4 (4a, 4b...) and the vertical delay 5 can be converted via the tilt coefficient corresponding to each navigation satellite.

[0042] The satellite navigation receiving station 2 uses the residual of

[0040] as measurement data and constructs the simultaneous equations expressed by (Equation 5) and (Equation 6) with two parameters, the receiver clock error and the vertical delay amount 5 around the receiving station, as unknowns. The satellite navigation receiving station 2 solves these simultaneous equations to obtain an estimate of the vertical delay amount 5, and multiplies this by the tilt coefficient corresponding to each navigation satellite to obtain the ionospheric propagation delay amount 4 (4a, 4b...) for each navigation satellite.

[0043] Next, the operation will be explained.

[0044] The simultaneous equations in

[0042] are constructed with two unknown parameters: the receiver clock error and the vertical delay amount 5 around the receiving station. In principle, this equation can be solved if there are two or more navigation satellites, but in the case of GPS, the number of navigation satellites from which a satellite navigation receiving station can receive positioning signals is generally around 6 to 10, so stable calculation processing is possible by using the least squares method or the like.

[0045] Once the vertical delay 5 is calculated, the ionospheric propagation delay 4 (4a, 4b...) of each navigation satellite can be obtained by multiplying it by the tilt coefficient. This allows the ionospheric propagation delay to be measured by a satellite navigation receiving station that receives positioning signals at only one frequency. [Industrial Applicability]

[0046] The method of measuring the amount of ionospheric propagation delay in a satellite navigation receiving station of this invention makes it possible to measure the amount of ionospheric propagation delay using a satellite navigation receiving station that receives a positioning signal of only one frequency, rather than using a satellite navigation receiving station that receives positioning signals of two frequencies as in the past. This simplifies the configuration of the satellite navigation receiving station that measures the amount of ionospheric propagation delay. [Explanation of symbols]

[0047] 1(1a,1b···) Navigation satellite 2 Satellite navigation receiving stations 3. Ionosphere 4(4a,4b···) Ionospheric propagation delay 5 Vertical component of ionospheric propagation delay (vertical delay) 6 Troposphere 7(7a,7b···) Tropospheric propagation delay

Claims

1. a satellite navigation receiver that receives positioning signals transmitted from a plurality of navigation satellites and measures the distances therebetween; a receiving antenna fixed at a known point on the ground for receiving the positioning signal; In a satellite navigation receiving station equipped with an information processing device that calculates an ionospheric propagation delay using the distance measurement value obtained by the satellite navigation receiver, The information processing device includes: The distance measurement error is considered to be composed of a clock error of the satellite navigation receiver, an ionospheric propagation delay amount occurring in each of the plurality of navigation satellites, and a tropospheric propagation delay amount, The tropospheric propagation delay amount is calculated using a tropospheric propagation delay model and removed. The ionospheric propagation delay is considered to be the product of a constant vertical delay and a tilt coefficient according to the elevation angle of each of the plurality of navigation satellites, and By estimating the two parameters of the clock error and the vertical delay, the ionospheric propagation delay corresponding to each of the plurality of navigation satellites is obtained. A method for measuring ionospheric propagation delay at a satellite navigation receiving station, characterized by:

2. a satellite navigation receiver that receives positioning signals transmitted from a plurality of navigation satellites and measures the distances therebetween; a receiving antenna fixed at a known point on the ground for receiving the positioning signal; In a satellite navigation receiving station equipped with an information processing device that calculates an ionospheric propagation delay using the distance measurement value obtained by the satellite navigation receiver, Operated by the information processing device, The distance measurement error is considered to be composed of a clock error of the satellite navigation receiver, an ionospheric propagation delay amount occurring in each of the plurality of navigation satellites, and a tropospheric propagation delay amount, The tropospheric propagation delay amount is calculated using a tropospheric propagation delay model and removed. The ionospheric propagation delay is considered to be the product of a constant vertical delay and a tilt coefficient according to the elevation angle of each of the plurality of navigation satellites, and By estimating two parameters, namely, the clock error of the satellite navigation receiver and the vertical delay amount, the ionospheric propagation delay amount corresponding to each of the plurality of navigation satellites is obtained. A program that measures the amount of ionospheric propagation delay at a satellite navigation receiving station.

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