GNSS occultation open-loop forecasting method based on cubic spline interpolation algorithm

Abstract

The invention discloses a GNSS occultation open-loop forecasting method based on a cubic spline interpolation algorithm, and relates to the field of occultation open-loop forecasting. The method comprises the following steps: judging whether a current navigational star is atmospheric occultation or not through an occultation event forecasting algorithm; acquiring position and speed information of atmospheric occultation and a low earth orbit; carrying out occultation forecast calculation on atmospheric occultation by adopting an atmospheric model to obtain model Doppler caused by satellite motion and model pseudo-range caused by neutral atmosphere; the method comprises the following steps: caching n-second model Doppler, model pseudo-range and open-loop forecast time of occultation in a 1HZ task, and obtaining interpolation parameters of the model Doppler and the model pseudo-range by using cubic spline interpolation; through the interpolation parameters, carrying out interpolation to obtain a 100HZ model Doppler and a 100HZ model pseudo-range; through the model pseudo-range, signal emission time is obtained through calculation; through signal emission time of a 100HZ task period, a signal emission time deviation value is obtained through calculation and converted into a hardware adjustment count, and the hardware adjustment count is transmitted into FGPA adjustment so as to carry out open-loop tracking of atmospheric occultation.

Description

Technical Field

[0001] The present invention relates to a field, and in particular to a GNSS occultation open-loop prediction method based on a cubic spline interpolation algorithm. Background Art

[0002] At present, with the continuous increase of human activities, carbon emissions continue to rise, exacerbating the trend of global warming. With global warming, extreme weather events such as high temperature heat waves, floods, low temperature cold waves, typhoons, etc. pose serious threats to human life and property safety. Global warming destroys the balance of the ecosystem, leading to serious consequences such as species extinction and biodiversity reduction. The climate environment faces many severe challenges, which not only affect the natural environment, but also pose a threat to the sustainable development of human society. In the face of major climate changes, it is necessary to strengthen international cooperation and coordination to promote the realization of emission reduction targets and the implementation of climate adaptation measures. At the same time, it is also necessary to strengthen scientific research and technological innovation to improve human cognition and response capabilities to climate change. Accurately capture the changes and development trends of the atmosphere, and give early warnings for natural disasters to obtain sufficient time to take response measures and reduce the loss of human life and property. Occultation open-loop tracking technology has been widely used in the field of atmospheric detection. By receiving GPS or GNSS navigation satellite GNSS signals through low-orbit satellites to conduct occultation observations, the atmospheric refractive index, temperature, pressure and other parameters from the surface to an altitude of 80km can be inverted. These data are of great significance for weather forecasting, scientific research, military applications, etc. In atmospheric occultation observations, the Doppler and amplitude fluctuations of the received occultation GNSS signal model increase dramatically due to the rapid change of the atmospheric refractive index gradient.

[0003] In the existing technology, open-loop occultation tracking is developed based on the traditional phase-locked loop technology. Compared with the traditional phase-locked loop, the open-loop tracking algorithm uses the orbit prediction model, the atmospheric refractive index climate Doppler model, and the pseudo-range model to track the GNSS signal. Therefore, it is not affected by the changes in the GNSS signal and has the ability to track multiple phases and amplitudes.

[0004] However, due to the phenomenon of significant attenuation of GNSS signals and rapid changes in Doppler frequency in open-loop tracking, it is impossible to stably track atmospheric occultation at a lower point during the process of tracking ascending occultation, and it is impossible to obtain atmospheric parameters such as atmospheric refractive index, temperature, humidity, and pressure within the altitude range of 0 to 5 km, thereby making it impossible to ensure high-precision and stable tracking of atmospheric occultation. Summary of the invention

[0005] Based on this, it is necessary to provide a GNSS occultation open-loop prediction method based on the cubic spline interpolation algorithm to address the above technical problems.

[0006] The present invention adopts the following technical solutions:

[0007] A GNSS occultation open-loop prediction method based on a cubic spline interpolation algorithm comprises the following steps:

[0008] The GNSS occultation event prediction algorithm is used to determine whether the currently tracked navigation star is an atmospheric occultation, and the position and velocity information of the currently tracked atmospheric occultation is calculated using the GNSS navigation ephemeris; and the positioning module of the navigation receiver is used to obtain the position and velocity information of the low earth orbit;

[0009] Through the velocity and position information of atmospheric occultation and the velocity and position information of low earth orbit, the atmospheric model is used to calculate the atmospheric occultation prediction, and the model Doppler caused by the satellite motion and the model pseudorange caused by the neutral atmosphere are obtained;

[0010] In the 1HZ mission cycle, the model Doppler, model pseudorange and open-loop prediction time of the atmospheric occultation for n seconds are obtained through the atmospheric model, and the interpolation parameters of the model Doppler and model pseudorange are obtained by using the cubic spline interpolation method; and the model Doppler, model pseudorange and open-loop prediction time of the atmospheric occultation for n seconds and the interpolation parameters of the model Doppler and model pseudorange are cached into an array;

[0011] In the 100 Hz mission cycle, the cubic spline interpolation method is used to interpolate the 100 Hz model Doppler and model pseudorange based on the model Doppler, model pseudorange, open-loop prediction time, and interpolation parameters of the model Doppler and model pseudorange cached in the array for n seconds of atmospheric occultation; and the 100 Hz model pseudorange is used to calculate the GNSS signal transmission time.

[0012] According to the difference between the 100HZ GNSS signal transmission time and the GNSS signal transmission time calculated by hardware, the deviation value of the GNSS signal transmission time is obtained and converted, and the hardware adjustment count is obtained and transmitted to the FPGA for adjustment. The atmospheric parameters are inverted in combination with the 100HZ model Doppler and model pseudorange to capture open-loop atmospheric occultation and realize atmospheric forecasting.

[0013] Preferably, the predicting whether the currently tracked navigation star is an atmospheric occultation by using a GNSS occultation event prediction algorithm comprises:

[0014] Obtain the altitude angle, azimuth angle and tangent point height of the navigation star through the navigation star position and velocity information and the low earth orbit satellite position and velocity information;

[0015] If the azimuth and tangent point height of the navigation star at the current moment meet the first and second conditions of occultation, then extrapolate for 40 seconds. If the current navigation star still meets the first and second conditions of occultation, then it is determined that the current navigation star is atmospheric occultation.

[0016] Preferably, the satisfaction of the first condition and the second condition for occultation includes:

[0017] The satisfaction of the first condition for occultation includes: (absaz < 35°) || ((180° - absaz) < 35°)); where absaz is the absolute value of the azimuth angle of the low Earth orbit satellite, and || represents logical OR operation;

[0018] The satisfaction of the second condition for occultation includes: abot < h < atop; where h is the tangent height of the current navigation star, abot is the lowest tangent height, atop is the highest tangent height, and abot = -125 km, atop = 150 km.

[0019] Preferably, the obtaining of the model Doppler caused by satellite motion and the model pseudorange caused by neutral atmosphere includes:

[0020] Through the atmospheric occultation and the position and velocity information of the low Earth orbit, the model Doppler and the model pseudorange caused by satellite motion are predicted and calculated using an atmospheric model. The formulas are:

[0021] OLFrq = c × ((c / 1000.0 - vw2) / (c / 1000.0 - vw1) - 1);

[0022] OLRange = PseNeo + PseDeion + r2abs;

[0023] where OLFrq is the model Doppler caused by satellite motion, c is the speed of light, vw1 is the speed of the atmospheric occultation, vw2 is the speed of the low Earth orbit; OLRange is the model pseudorange caused by neutral atmosphere, PseNeo is the phase delay that occurs when the GNSS signal passes through the atmosphere, PseDeion is the phase delay that occurs when the GNSS signal passes through the ionosphere, and r2abs is the straight-line distance from the GNSS signal to the GNSS receiver.

[0024] Preferably, the obtaining of the GNSS signal emission time includes the following steps:

[0025] Through the cached model Doppler, model pseudorange, open-loop prediction time of the atmospheric occultation for n seconds, and the interpolation parameters of the model Doppler and the model pseudorange, the model Doppler and the model pseudorange of 100 HZ are interpolated using the cubic spline interpolation method. The formulas are:

[0026] Cur_OLFrq = y 1 [n] + c 1 [0][n] × d + c 1 [1][n] × d 2 + c 1 [2][n] × d3 ;

[0027] Cur_OLRange=y 2 [n]+c 2 [0][n]×d+c 2 [1][n]×d 2 +c 2 [2][n]×d 3 ;

[0028] Where Cur_OLFrq is the model Doppler of atmospheric occultation in the 100 Hz mission period, Cur_OLRange is the model pseudorange of atmospheric occultation in the 100 Hz mission period, and y 1 [n] is the interval [x i , x i+1 ] n seconds model Doppler cubic polynomial, open loop prediction time i = 1, 2, ..., n, y 2 [n] is the interval [x i +x i+1 ] is the cubic polynomial of the n-second model pseudorange, c 1 [0], c 1 [1] and c 1 [2] is the interpolation parameter of the model Doppler, c 2 [0], c 2 [1] and c 2 [2] is the interpolation parameter of the model pseudorange, d = t tic -x[n],t tic It is a moment in the 100HZ task cycle;

[0029] The model pseudorange Cur_OLRange corresponding to the 100HZ GNSS signal is used to calculate the GNSS signal transmission time using the model pseudorange value corresponding to the 100HZ GNSS signal. The formula is:

[0030]

[0031] Among them, Cur_S_time is the GNSS signal transmission time, Cur_OLRange is the model pseudorange value corresponding to the 100HZ GNSS signal, t tic is the time of 100HZ task cycle, and c is the speed of light.

[0032] Preferably, the obtaining of the hardware adjustment count includes:

[0033] The hardware adjustment count includes: a code cycle count, a code chip count and a code phase count corresponding to the GNSS signal transmission time deviation.

[0034] For GPS atmospheric occultation, the conversion formula for hardware adjustment count is:

[0035]

[0036] Among them, Z_GPS is the time conversion value of atmospheric occultation of the global positioning system, is the GNSS signal transmission time deviation value, code cycle_GPS is the code week count corresponding to the global positioning system atmospheric occultation, code chip_GPS is the chip count corresponding to the atmospheric occultation of the global positioning system, chip Phase_GPS The code phase counts corresponding to the atmospheric occultation of the global positioning system;

[0037] For the atmospheric occultation of the BeiDou satellite system, the conversion formula for the hardware adjustment count is:

[0038]

[0039] Among them, Z_BD is the time conversion value corresponding to the atmospheric occultation of the Beidou satellite system, code cycle_BD is the code week count corresponding to the atmospheric occultation of the Beidou satellite system, code chip_BD Chip count corresponding to atmospheric occultation of Beidou satellite system, chip Phase_BD It is the code phase count corresponding to the atmospheric occultation of the Beidou satellite system.

[0040] At least one of the above technical solutions adopted by the present invention can achieve the following beneficial effects:

[0041] The present specification provides a GNSS occultation open-loop prediction method based on a cubic spline interpolation algorithm. The interpolation parameters of the model Doppler and model pseudorange of a low-frequency mission cycle are obtained by using the cubic spline interpolation algorithm, and the model Doppler, model pseudorange and their interpolation parameters are cached; the cached interpolation parameters are used to participate in a high-frequency mission cycle, and the model Doppler and model pseudorange of the atmospheric occultation in the high-frequency mission are interpolated; the accurate high-frequency GNSS signal transmission time is calculated through the model pseudorange, and the GNSS signal transmission time deviation value is obtained through the difference between the GNSS signal transmission time and the signal transmission time calculated by the hardware and converted into a hardware adjustment count, and the model Doppler and model pseudorange of the high-frequency mission cycle are combined to invert the atmospheric parameters, so as to perform stable open-loop tracking of the lower point of the atmospheric occultation during the ascent process.

[0042] In summary, the method proposed in the present invention is aimed at the phenomenon of large attenuation of GNSS signals and rapid change of Doppler frequency in open-loop tracking. The atmospheric occultation open-loop prediction tracking algorithm is optimized by a cubic spline interpolation algorithm, and the atmospheric occultation model Doppler and model pseudorange of the open-loop prediction are changed from 1HZ to 100HZ, and the stable tracking of the atmospheric occultation at a lower point (0km-5km) during the ascent process is achieved, which effectively increases the number of captured occultations, improves the open-loop prediction accuracy of atmospheric occultation, and provides more accurate and rich data resources for atmospheric detection. In addition, the present invention does not involve hardware changes, is easy to operate, and provides favorable technical support for the acquisition of atmospheric parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0044] Figure 1 A schematic flow chart of a GNSS occultation open-loop prediction method based on a cubic spline interpolation algorithm provided by the present invention;

[0045] Figure 2 A flow chart of GNSS occultation open-loop tracking adjustment after cubic spline interpolation of a GNSS occultation open-loop prediction method based on a cubic spline interpolation algorithm provided by the present invention;

[0046] Figure 3 A geometrical plane diagram of GPS radio occultation events for a GNSS occultation open-loop prediction method based on a cubic spline interpolation algorithm provided by the present invention;

[0047] Figure 4 A schematic diagram of the GPS radio occultation tangent point height of a GNSS occultation open-loop prediction method based on a cubic spline interpolation algorithm provided by the present invention. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. 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 making creative work are within the scope of protection of the present invention.

[0049] The technical solutions provided by various embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0050] Figure 1Schematic diagram of the GNSS occultation open-loop prediction method based on the cubic spline interpolation algorithm in the present invention, specifically including the following steps:

[0051] S101: Determine whether the currently tracked navigation star is an atmospheric occultation through the GNSS occultation event prediction algorithm, and calculate the position and velocity information of the currently tracked atmospheric occultation through the GNSS navigation ephemeris; and use the positioning module of the navigation receiver to obtain the position and velocity information of the low Earth orbit, specifically including:

[0052] Obtain the altitude angle, azimuth angle, and tangent height of the navigation star through the navigation star position and velocity information and the low Earth orbit satellite position and velocity information;

[0053] If the azimuth angle and tangent height of the navigation star at the current moment satisfy the first condition and the second condition of occultation, extrapolate for 40 s. If the current navigation star still satisfies the first condition and the second condition of occultation, determine that the current navigation star is an atmospheric occultation;

[0054] Among them, the first condition includes: (absaz < 35°) || ((180° - absaz) < 35°)); where absaz is the absolute value of the azimuth angle of the low Earth orbit satellite, and || represents logical OR operation; the second condition includes: abot < h < atop; where h is the tangent height of the current navigation star, abot is the lowest tangent height, atop is the highest tangent height, and abot = -125 km, atop = 150 km.

[0055] S102: Through the velocity and position of the atmospheric occultation and the low Earth orbit, use the atmospheric model to perform occultation prediction calculations on the atmospheric occultation to obtain the model Doppler caused by satellite motion and the model pseudorange caused by the neutral atmosphere, specifically including:

[0056] Through the position and velocity information of the atmospheric occultation and the low Earth orbit, use the atmospheric model to predict and calculate the model Doppler and model pseudorange caused by satellite motion. The formula is:

[0057] OLFrq = c × ((c / 1000.0 - vw2) / (c / 1000.0 - vw1) - 1);

[0058] OLRange = PseNeo + PseDeion + r2abs;

[0059] Among them, OLFrq is the model Doppler caused by satellite motion, c is the speed of light, vw1 is the speed of atmospheric occultation, and vw2 is the speed of low Earth orbit; OLRange is the model pseudorange caused by the neutral atmosphere, PseNeo is the phase delay caused by the GNSS signal passing through the atmosphere, PseDeion is the phase delay caused by the GNSS signal passing through the ionosphere, and r2abs is the straight-line distance from the GNSS signal to the GNSS receiver.

[0060] S103: In the 1 Hz task cycle, the model Doppler, model pseudorange and open-loop prediction time of the atmospheric occultation for n seconds are obtained through the atmospheric model, and the interpolation parameters of the model Doppler and model pseudorange are obtained by using the cubic spline interpolation method; and the model Doppler, model pseudorange and open-loop prediction time of the atmospheric occultation for n seconds and the interpolation parameters of the model Doppler and model pseudorange are cached into an array, specifically including:

[0061] Cache the model Doppler, model pseudorange, and open-loop prediction time of the atmospheric occultation for n seconds. In the one-second task, use the cubic spline interpolation method to interpolate the model Doppler interpolation parameter c 1 , interpolation parameter c of the model pseudorange 2 ;

[0062] For each interval [x i , x i+1 ], the expression is:

[0063] S i (x) = a i +b i (xx i )+c i (xx i ) 2 +d i (xx i ) 3 ;

[0064] Among them, a i 、b i 、c i and d i is the interpolation parameter, which is determined by the following steps:

[0065] For each i=0,1,…,n, S i (x i )=y i , S i (x i+1 )=y i+1 ; Make the second-order derivative continuous: Si″(x i+1 )=S i+1 ″(x i+1); Select the periodic cubic spline S″(x 0 )=S″(x n ) is the boundary condition, and all interpolation parameters are determined;

[0066] For determining all interpolation parameters a i 、b i 、c i and d i , use matrix representation and Gaussian elimination method to solve the equations and obtain all interpolation parameters, specifically:

[0067] a i =y i ;

[0068]

[0069] Among them, h i =x i+1 -x i , represents an interval of cubic spline polynomial; m i =s” i (x i ), which represents the second-order derivative of each interval expression;

[0070] Furthermore, cubic spline interpolation is performed on the occultation model Doppler, and its interpolation parameter c 1 , specifically: c 1 [0] = b i , c 1 [1] = c i , c 1 [2] = d i ; Perform cubic spline interpolation on the pseudo-range of the occultation model, and its interpolation parameter c 2 , specifically c 2 [0] = b i , c 2 [1] = c i , c 2 [2] = d i ;

[0071] The model Doppler, model pseudorange, open-loop prediction time and interpolation parameters of the model Doppler and model pseudorange of the above atmospheric occultation are cached into an array.

[0072] S104: In the 100HZ duty cycle, see Figure 2 , according to the model Doppler, model pseudorange, open-loop prediction time and interpolation parameters of model Doppler and model pseudorange of n seconds of atmospheric occultation cached in the array, the cubic spline interpolation method is used to interpolate the 100HZ model Doppler and model pseudorange; and the 100HZ model pseudorange is used to calculate the GNSS signal transmission time, which specifically includes:

[0073] The model Doppler and model pseudorange of the 100 Hz mission period are obtained by interpolating the model Doppler and model pseudorange of the cached atmospheric occultation model of n seconds, open-loop prediction time, and interpolation parameters of the model Doppler and model pseudorange, using the cubic spline interpolation method. The formula is:

[0074] Cur_OLFrq=y 1 [n]+c 1 [0][n]×d+c 1 [1][n]×d 2 +c 1 [2][n]×d 3 ;

[0075] Cur_OLRange=y 2 [n]+c 2 [0][n]×d+c 2 [1][n]×d 2 +c 2 [2][n]×d 3 ;

[0076] Among them, Cur_OLFrq is the model Doppler of the 100HZ mission, Cur_OLRange is the model pseudorange of the 100HZ mission, and y 1 [n] is the interval [x i , x i+1 ] n seconds model Doppler cubic polynomial, open loop prediction time i = 1, 2, ..., n, y 2 [n] is the interval [x i +x i+1 ] is the cubic polynomial of the n-second model pseudorange, c 1 [0], c 1 [1] and c 1 [2] is the interpolation parameter of the model Doppler, c 2 [0], c 2 [1] and c 2 [2] is the interpolation parameter of the model pseudorange, d = t tic -x[n],t tic It is a moment in the 100HZ task cycle;

[0077] The model pseudorange Cur_OLRange corresponding to the GNSS signal with a 100 Hz task cycle is used to calculate the GNSS signal transmission time using the model pseudorange value corresponding to the GNSS signal with a 100 Hz task cycle. The formula is:

[0078]

[0079] Among them, Cur_S_time is the GNSS signal transmission time, Cur_OLRange is the model pseudorange value corresponding to the 100HZ mission period GNSS signal, t tic is the time of 100HZ task cycle, and c is the speed of light.

[0080] S105: According to the difference between the 100 Hz GNSS signal transmission time and the GNSS signal transmission time calculated by hardware, the deviation value of the GNSS signal transmission time is obtained and converted, and the hardware adjustment count is obtained and transmitted to the FPGA for adjustment, and the atmospheric parameters are inverted in combination with the 100 Hz model Doppler and model pseudorange to capture the open-loop atmospheric occultation to realize the atmospheric forecast, which specifically includes:

[0081] The hardware adjustment count includes: a code cycle count, a code chip count and a code phase count corresponding to the GNSS signal transmission time deviation.

[0082] For GPS atmospheric occultation, the conversion formula for hardware adjustment count is:

[0083]

[0084] Among them, Z_GPS is the time conversion value of atmospheric occultation of the global positioning system, is the GNSS signal transmission time deviation value, code cycle_GPS is the code week count corresponding to the global positioning system atmospheric occultation GNSS signal transmission time deviation value, code chip_GPS is the chip count corresponding to the global positioning system atmospheric occultation GNSS signal transmission time deviation value, chip Phase_GPS It is the code phase count corresponding to the global positioning system atmospheric occultation GNSS signal transmission time deviation value;

[0085] For the atmospheric occultation of the BeiDou satellite system, the conversion formula for the hardware adjustment count is:

[0086]

[0087] Among them, Z_BD is the time conversion value corresponding to the atmospheric occultation of the Beidou satellite system, code cycle_BD is the code week count corresponding to the time deviation value of the atmospheric occultation GNSS signal transmission of the Beidou satellite system, code chip_BD It is the chip count corresponding to the time deviation value of the atmospheric occultation GNSS signal transmission of the Beidou satellite system. Phase_BD It is the code phase count corresponding to the transmission time deviation value of the atmospheric occultation GNSS signal of the Beidou satellite system.

[0088] This embodiment takes a GPS occultation open-loop prediction as an example. The low-orbit satellite is running at an altitude of 500km, with an orbital inclination of 55 degrees, an attitude designed to be oriented to the earth, and a three-axis stable elliptical orbit. The geometric structure diagram of the GPS radio occultation event can be found in Figure 3 When the GPS is predicted to be an atmospheric occultation, the above steps are used to start predicting the model Doppler and model pseudorange values ​​of the GPS star, and data caching is performed. When the cached model pseudorange and model Doppler exceed 4s, a cubic spline interpolation operation is performed to calculate the cubic spline interpolation coefficient a of the star. i 、b i 、c i and d i , that is, the model Doppler parameter c 1 [0][3], c 1 [1][3] and c 1 [2][3],c 2 [0][3], c 2 [1][3], c 2 [2][3], that is, the cubic spline model Doppler Cur_OLFrq and model pseudorange Cur_OLRange are obtained in each interval [x i ,x i +1]:

[0089] Cur_OLFrq=y 1 [3]+c 1 [0][3]×d+c 1 [1][3]×d 2 +c 1 [2][3]×d 3 ;

[0090] Cur_OLRange=y 2 [3]+c 2 [0][3]×d+c 2 [1][3]×d 2 +c 2 [2][3]×d 3 ;

[0091] Among them, Cur_OLFrq is the model Doppler of the 100HZ mission, Cur_OLRange is the model pseudorange of the 100HZ mission, and y 1 [n] is the interval [x i , x i+1 ] is the cubic polynomial of the n-second model Doppler, y 2 [n] is the interval [x i +x i+1 ] is the cubic polynomial of the n-second model pseudorange, c 1 [0], c1 [1] and c 1 [2] is the interpolation parameter of the model Doppler, c 2 [0], c 2 [1] and c 2 [2] is the interpolation parameter of the model pseudorange, d = t tic -x[n],t tic It is a moment in the 100HZ task cycle.

[0092] The model Doppler and model pseudorange values ​​of GPS atmospheric occultation at the current moment in the 100HZ mission cycle obtained by the above method steps are used to further calculate the transmission time Cur_S_time of the current TIC signal through the model pseudorange value. The signal transmission time t calculated by the hardware is subtracted from Cur_S_time. hw The obtained difference Δt, the model Doppler value corresponding to the current tic moment and Δt are converted into the code week, code chip, and code phase counts corresponding to the signal transmission time deviation and placed into the FPGA for adjustment to accurately complete the open-loop tracking of the GPS atmospheric occultation signal.

[0093] Take a GPS ascending occultation as an example, see Figure 4 , OQ is the height from the occultation tangent point to the center of the earth, and the tangent point height h = HR, where R is the radius of the earth. Using the occultation prediction method of this patent, GPS atmospheric occultation stable tracking can be completed at a tangent point height of about 1 km, breaking the defect that the existing method cannot stably track atmospheric occultation at a lower point, greatly increasing the atmospheric parameters such as atmospheric refractive index, temperature, humidity, pressure, etc. within the altitude range of 0 to 5 km, and the inventive method does not involve hardware changes, and the operation is easy to implement, providing favorable technical support for the acquisition of atmospheric parameters.

[0094] As shown in the table below, the atmospheric occultation events of GPS26 were captured and tracked by open-loop forecasting within about 24 hours. The lowest altitude of atmospheric occultation detection was about 1 km, which greatly improved the detection capability of the occultation receiver and solved the problem of difficulty in obtaining ascending occultation events. The above examples fully illustrate that the invention method can be widely used in the field of atmospheric detection. By receiving GPS or GNSS navigation satellite signals from low-orbit satellites for occultation observation, the atmospheric refractive index, temperature, pressure and other parameters from the surface to 80 km altitude can be inverted. These data are of great significance for weather forecasting, scientific research, early warning of natural disasters, military applications, etc.

[0095]

[0096] In summary, the present embodiment provides a GNSS occultation open-loop prediction method based on a cubic spline interpolation algorithm. Aiming at the phenomenon of large attenuation of GNSS signals and rapid change of Doppler frequency in open-loop tracking, the open-loop prediction tracking algorithm is optimized by optimizing the open-loop prediction algorithm through the cubic spline interpolation algorithm, so that the atmospheric model Doppler and atmospheric model pseudorange of the open-loop prediction are changed from 1 Hz to 100 Hz. In the process of tracking the ascending occultation, the stable tracking of the atmospheric occultation at a lower point is guaranteed, so as to obtain atmospheric parameters such as atmospheric refractive index, temperature, humidity, pressure and the like in the altitude range of 0 km to 5 km, effectively increase the number of captured occultations, improve the open-loop prediction accuracy of atmospheric occultation, and provide more accurate and rich data resources for atmospheric detection.

[0097] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. All technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A GNSS occultation open-loop prediction method, characterized in that: The method includes the following steps: Judge whether the currently tracked navigation star is an atmospheric occultation through the GNSS occultation event prediction algorithm, and calculate the position and velocity information of the currently tracked atmospheric occultation through the GNSS navigation ephemeris; and use the positioning module of the navigation receiver to obtain the position and velocity information of the low Earth orbit; Through the velocity and position information of the atmospheric occultation and the velocity and position information of the low Earth orbit, use the atmospheric model to perform occultation prediction calculations on the atmospheric occultation to obtain the model Doppler caused by satellite motion and the model pseudorange caused by the neutral atmosphere; In the 1HZ task cycle, obtain the model Doppler, model pseudorange, and open-loop prediction time of the atmospheric occultation for n seconds through the atmospheric model, and use the cubic spline interpolation method to obtain the interpolation parameters of the model Doppler and model pseudorange; and cache the model Doppler, model pseudorange, and open-loop prediction time of the atmospheric occultation for n seconds and the interpolation parameters of the model Doppler and model pseudorange into an array; In the 100HZ task cycle, according to the model Doppler, model pseudorange, open-loop prediction time of the atmospheric occultation for n seconds, and the interpolation parameters of the model Doppler and model pseudorange cached in the array, use the cubic spline interpolation method to interpolate and obtain the model Doppler and model pseudorange at 100HZ; and calculate the GNSS signal emission time through the model pseudorange at 100HZ; According to the difference between the GNSS signal emission time at 100HZ and the GNSS signal emission time calculated by hardware, obtain the deviation value of the GNSS signal emission time and convert it, obtain the hardware adjustment count and pass it into the FPGA for adjustment, and combine the model Doppler and model pseudorange at 100HZ to invert the atmospheric parameters to capture the open-loop atmospheric occultation and achieve atmospheric prediction.

2. A GNSS occultation open-loop prediction method as claimed in claim 1, characterized in that: The prediction of whether the currently tracked navigation star is an atmospheric occultation through the GNSS occultation event prediction algorithm includes: Obtain the elevation angle, azimuth angle, and tangent height of the navigation star through the position and velocity information of the navigation star and the position and velocity information of the low Earth orbit satellite; If the azimuth angle and tangent height of the navigation star at the current moment satisfy the first condition and the second condition of occultation, extrapolate for 40s. If the current navigation star still satisfies the first condition and the second condition of occultation, determine that the current navigation star is an atmospheric occultation.

3. A GNSS occultation open-loop prediction method as claimed in claim 2, characterized in that: The satisfaction of the first condition and the second condition of occultation includes: The satisfaction of the first condition of occultation includes: (absaz < 35°) || ((180° - absaz) < 35°)); where absaz is the absolute value of the azimuth angle of the low Earth orbit satellite, and || represents the logical OR operation; The satisfaction of the second condition of occultation includes: abot < h < atop; where h is the tangent height of the current navigation star, abot is the lowest tangent height, atop is the highest tangent height, and abot = -125km, atop = 150km.

4. A GNSS occultation open-loop prediction method as claimed in claim 1, characterized in that: The obtaining of the model Doppler caused by satellite motion and the model pseudorange caused by the neutral atmosphere includes: Through the position and velocity information of the atmospheric occultation and the low Earth orbit, use the atmospheric model to predict and calculate the model Doppler and model pseudorange caused by satellite motion. The formula is: OLFrq=c×((c / 1000.0-vw2) / (c / 1000.0-vw1)-1); OLRange=PseNeo+PseDeion+r2abs; Among them, OLFrq is the model Doppler caused by satellite motion, c is the speed of light, vw1 is the speed of atmospheric occultation, and vw2 is the speed of low Earth orbit; OLRange is the model pseudorange caused by the neutral atmosphere, PseNeo is the phase delay caused by the GNSS signal passing through the atmosphere, PseDeion is the phase delay caused by the GNSS signal passing through the ionosphere, and r2abs is the straight-line distance from the GNSS signal to the GNSS receiver.

5. A GNSS occultation open-loop prediction method as claimed in claim 1, characterized in that: The acquisition of the GNSS signal transmission time includes the following steps: The model Doppler and model pseudorange of 100 Hz are interpolated by using the cached atmospheric occultation model Doppler, model pseudorange, open-loop prediction time, and interpolation parameters of model Doppler and model pseudorange for n seconds, and the cubic spline interpolation method is used. The formula is: Cur_OLFrq=y1[n]+c1[0][n]×d+c1[1][n]×d 2 +c1[2][n]×d 3 ; Cur_OLRange=y2[n]+c2[0][n]×d+c2[1][n]×d 2 +c2[2][n]×d 3 ; Where Cur_OLFrq is the model Doppler of atmospheric occultation in the 100 Hz mission cycle, Cur_OLRange is the model pseudorange of atmospheric occultation in the 100 Hz mission cycle, and y1[n] is the interval [x i , x i+1 ], the open-loop prediction time i=1,2,…,n, y2[n] is the interval [x i +x i+1 ] is a cubic polynomial of the n-second model pseudorange, c1[0], c1[1] and c1[2] are the interpolation parameters of the model Doppler, c2[0], c2[1] and c2[2] are the interpolation parameters of the model pseudorange, d = t tic -x[n],t tic It is a moment in the 100HZ task cycle; The model pseudorange Cur_OLRange corresponding to the 100HZ GNSS signal is used to calculate the GNSS signal transmission time using the model pseudorange value corresponding to the 100HZ GNSS signal. The formula is: Among them, Cur_S_time is the GNSS signal transmission time, Cur_OLRange is the model pseudorange value corresponding to the 100HZ GNSS signal, t tic is the time of 100HZ task cycle, and c is the speed of light.

6. A GNSS occultation open-loop prediction method as claimed in claim 1, characterized in that: The obtaining of the hardware adjustment count includes: The hardware adjustment count includes: code cycle count, code chip count and code phase count corresponding to the GNSS signal transmission time deviation; For GPS atmospheric occultation, the conversion formula for hardware adjustment count is: Among them, Z_GPS is the time conversion value of atmospheric occultation of the global positioning system, is the GNSS signal transmission time deviation value, code cycle_GPS is the code week count corresponding to the global positioning system atmospheric occultation, code chip_GPS is the chip count corresponding to the atmospheric occultation of the global positioning system, chip Phase_GPS The code phase counts corresponding to the atmospheric occultation of the global positioning system; For the atmospheric occultation of the BeiDou satellite system, the conversion formula for the hardware adjustment count is: Among them, Z_BD is the time conversion value corresponding to the atmospheric occultation of the Beidou satellite system, code cycle_BD is the code week count corresponding to the atmospheric occultation of the Beidou satellite system, code chip_BD Chip count corresponding to atmospheric occultation of Beidou satellite system, chip Phase_BD It is the code phase count corresponding to the atmospheric occultation of the Beidou satellite system.

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