A method and system for obtaining open-loop prediction parameters of a micro GNSS occultation detector

Abstract

The present invention provides a method and system for obtaining open-loop prediction parameters of a micro-miniature GNSS occultation sounder. By using the overlapping time period of closed-loop tracking and open-loop tracking for the same occultation event, the open-loop prediction parameters are fitted and corrected using the closed-loop occultation tracking results within this time period, so as to improve the accuracy of the open-loop event prediction parameters, increase the success rate of open-loop tracking, and ultimately enhance the inversion accuracy of the occultation event. The present invention has low complexity and small resource consumption, and does not require hardware modification compared with traditional receivers.

Description

Technical Field

[0001] The present invention relates to a micro GNSS occultation detector, and particularly to a method and system for obtaining open-loop prediction parameters of a micro GNSS occultation detector. Background Art

[0002] With the rapid development of major navigation systems, GNSS occultation detection has become a hot spot in the field of radio remote sensing detection. When a GNSS occultation detector conducts occultation event detection, a single occultation event observation usually has two stages: a closed-loop occultation tracking stage and an open-loop occultation tracking stage. Closed-loop tracking often has higher accuracy than open-loop tracking, but its adaptable dynamic range is smaller; open-loop tracking has a stronger ability to withstand dynamic changes than closed-loop tracking, but since it uses prediction parameters for tracking, the tracking accuracy depends on the prediction accuracy, and unbiased tracking like in the closed-loop cannot be achieved.

[0003] When the tangent point height of the GNSS satellite relative to the occultation detector is relatively high and the elevation angle is relatively high, it is less affected by the atmosphere and ionospheric refraction. At this time, the Doppler change rate is weak, and it can be successfully captured and precisely tracked using a closed-loop (phase-locked loop, frequency-locked loop) loop to obtain accurate occultation observation data; however, as the tangent point height decreases, the Doppler change rate intensifies, the closed-loop tracking quickly loses lock, and it is difficult to capture successfully again. At this time, only open-loop tracking can be relied on for subsequent tracking to obtain occultation observation values. Therefore, open-loop tracking is very important for observing occultation events of the underlying atmosphere.

[0004] The performance of open-loop tracking depends on the prediction of various tracking parameters. The two most critical parameters are the predicted pseudorange and the predicted carrier frequency. For example, for the GPS L1C / A signal, its pseudocode length is 300 meters. When the difference between the predicted pseudorange error and the true pseudorange exceeds 300 meters, the relevant peak cannot be obtained and correct open-loop tracking cannot be performed; when the predicted carrier frequency value is close to the respective measured true values of the pseudorange prediction value, its open-loop tracking accuracy is high and the subsequent inversion effect is better. Therefore, how to provide high-quality open-loop occultation prediction parameters is very important for occultation inversion.

[0005] It can be found from the actual signal reception statistics that when the tangent point altitude is relatively low, due to the refraction effect of the atmosphere, the GNSS satellite signals received by the observatory are bent. At this time, there will be a large deviation between the GNSS pseudorange directly deduced from the position of the observatory and the GNSS satellite position and the true signal pseudorange. This deviation is often greater than 300 meters, and it becomes even larger as the tangent point altitude decreases, resulting in the inability to correctly track occultation events. Therefore, a correction algorithm needs to be used to correct it. The traditional method uses the CIRA86-Q atmospheric model to compensate the predicted pseudorange results. This algorithm has a good compensation effect when the tangent point altitude is greater than 0 km, and the deviation between the predicted pseudorange and the true pseudorange can be controlled within 150 meters (half a chip). However, as the tangent point altitude decreases, the compensation ability of this method also decreases, and the error after compensation will exceed 300 meters (one chip) at the lowest tangent point altitude, resulting in the inability to perform normal open-loop tracking and correctly obtain the measurement results of occultation events. Therefore, a new method is needed to correct the open-loop predicted pseudorange at low tangent point altitudes (especially below 0 km) to minimize the deviation between the true pseudorange and the open-loop predicted pseudorange and improve the open-loop tracking ability of the detector.

[0006] In a complete occultation event, it usually includes closed-loop occultation tracking detection at high tangent point altitudes and open-loop occultation tracking detection at low tangent point altitudes. Open-loop tracking has a stronger ability to withstand dynamic changes than closed-loop tracking. However, since it uses predicted parameters for tracking, the tracking accuracy depends on the prediction accuracy, and unbiased tracking as in the closed-loop case cannot be achieved. Summary of the Invention

[0007] The purpose of the present invention is to solve the above problems and overcome the problem that inaccurate open-loop prediction parameters lead to incorrect open-loop tracking, thereby providing a method and system for obtaining open-loop prediction parameters of a micro GNSS occultation detector.

[0008] To solve the above technical problems, the present invention proposes a method and system for obtaining open-loop prediction parameters of a micro GNSS occultation detector. By using the overlapping time period of closed-loop tracking and open-loop tracking in the same occultation event, the closed-loop occultation tracking results during this time period are used to fit and correct the open-loop prediction parameters, improve the accuracy of open-loop event prediction parameters, increase the success rate of open-loop tracking, and ultimately improve the inversion accuracy of occultation events. The present invention has low complexity and small resource consumption, and no hardware modification is required compared to traditional receivers.

[0009] The present invention proposes a method for obtaining open-loop prediction parameters of a micro GNSS occultation detector, including the following steps:

[0010] Step 1) In the overlapping stage of closed-loop occultation tracking and open-loop occultation tracking, collect the unbiased pseudorange of the occultation event through the closed-loop occultation tracking channel;

[0011] Step 2) Estimate the predicted carrier frequency and predicted pseudorange of the open-loop occultation tracking channel based on the velocity, position, and time information of the GNSS satellite, the velocity, position, and time information of the GNSS occultation sounder, and the CIRA86-Q atmospheric model.

[0012] Step 3) In the open-loop occultation tracking channel, use the corrected open-loop pseudorange module. Taking the elevation angle, relative azimuth angle, and tangent height of the GNSS satellite as inputs, and taking the pseudorange deviation between the unbiased pseudorange and the predicted pseudorange as the target, call the curve fitting algorithm to perform curve fitting on the pseudorange deviation until the iteration end condition is satisfied, obtain the fitted pseudocode phase and pseudocode carrier frequency control word, and transmit them into the pseudocode generator of the open-loop occultation tracking channel to correct the predicted pseudorange.

[0013] As an improvement of the above method, the method further includes:

[0014] During the closed-loop occultation tracking phase, track the occultation event through the closed-loop occultation tracking channel to obtain closed-loop occultation data.

[0015] During the open-loop occultation tracking phase, the open-loop occultation tracking channel tracks the occultation event based on the corrected predicted pseudorange and the open-loop model carrier frequency calculated in Step 2), and obtains open-loop occultation data.

[0016] As an improvement of the above method, the method further includes: After caching and packing the closed-loop occultation data and the open-loop occultation data, transmit them to the ground receiving device.

[0017] As an improvement of the above method, the method further includes a preprocessing step: Based on the GNSS satellite ephemeris or almanac information received by the GNSS occultation sounder, obtain the velocity, position, and time information of the GNSS satellite, and calculate the velocity, position, and time information of the GNSS occultation sounder; Based on the velocity, position, and time information of the GNSS satellite and the velocity, position, and time information of the GNSS occultation sounder, calculate the elevation angle, azimuth angle, relative azimuth angle, and tangent height of the GNSS satellite to determine the current occultation event type, where the occultation event type includes: ascending closed-loop occultation event, ascending open-loop occultation event, descending closed-loop occultation event, and descending open-loop occultation event.

[0018] As an improvement of the above method, Step 3) specifically includes:

[0019] Step 3-1) Take the difference between the unbiased pseudorange and the predicted pseudorange as the pseudorange deviation Pd err ;

[0020] Step 3-2) Use the elevation angle, relative azimuth angle, and tangent height of the GNSS satellite to perform a preliminary curve fitting on the pseudorange deviation to obtain several parameter terms:

[0021]

[0022] wherein, Elev is the elevation angle of the GNSS satellite, T ph is the tangent height of the GNSS satellite, R AZM is the azimuth angle of the GNSS satellite, p 1 ~p 11 are parameter terms respectively;

[0023] Step 3-3) Substitute the Elev, T ph , R AZM collected from multiple occultation events into the above formula for iteration, and solve through a global optimization algorithm until the result evaluation reaches the iteration condition, then stop the iteration, so that the several parameter terms p 1 ~p 11 tend to a fixed value; after the parameter terms tend to be stable, directly use the parameter terms p 1 ~p 11 and the current moment Elev, T ph , R AZM to substitute into the above formula to obtain the pseudorange deviation Pd err , and compensate this difference into the open-loop model pseudorange, so as to realize the correction of the open-loop model pseudorange;

[0024] The iteration condition is: the coefficient of determination is greater than 0.996, the correlation coefficient is greater than 0.998, and the certainty coefficient is greater than 0.996.

[0025] As an improvement of the above method, the overlapping stage of the closed-loop occultation tracking and the open-loop occultation tracking is the stage when the open-loop occultation tracking channel and the closed-loop occultation tracking channel are both turned on; wherein, the open-loop occultation tracking channel is turned on when the tangent height of the GNSS satellite is N, and N is stored in the non-volatile storage space of the open-loop occultation tracking channel, and the closed-loop occultation tracking channel is turned off when the tangent height of the GNSS satellite is M, and M is stored in the non-volatile storage space of the closed-loop occultation tracking channel; the values of N and M can be modified on orbit to increase or shorten the overlapping stage.

[0026] As an improvement of the above method, the method further includes: before the step 1), increasing the opening height of the open-loop occultation tracking channel to increase the overlapping stage of the closed-loop occultation tracking and the open-loop occultation tracking, so that the curve fitting converges quickly; before the step 3), reducing the opening height of the open-loop occultation tracking channel to narrow the overlapping stage of the closed-loop occultation tracking and the open-loop occultation tracking to the interval with the largest curvature change of the difference between the true pseudorange obtained by the closed-loop tracking and the pseudorange of the open-loop prediction model, so as to improve the accuracy of the curve fitting.

[0027] To achieve another object of the present invention, the present invention also provides a system for obtaining open-loop prediction parameters of a micro-miniature GNSS occultation detector based on the above method for obtaining open-loop prediction parameters of a micro-miniature GNSS occultation detector, including: a closed-loop occultation tracking channel and an open-loop occultation tracking channel, characterized in that the system further includes: a prediction module and a module for correcting the open-loop pseudorange; wherein,

[0028] The closed-loop occultation tracking channel is used to track the occultation event in the closed-loop occultation tracking stage to obtain closed-loop occultation data; and is used to collect the unbiased pseudorange of the occultation event in the overlapping stage of the closed-loop occultation tracking and the open-loop occultation tracking;

[0029] The prediction module estimates the predicted carrier frequency and predicted pseudorange of the open-loop occultation tracking channel based on the velocity, position, and time information of the GNSS satellite, the velocity, position, and time information of the GNSS occultation detector, and the CIRA86-Q atmospheric model;

[0030] The module for correcting the open-loop pseudorange is used to take the elevation angle, relative azimuth angle, and tangent point height of the GNSS satellite as inputs, take the pseudorange deviation between the unbiased pseudorange and the predicted pseudorange as the target, call a curve fitting algorithm to perform curve fitting on the pseudorange deviation until the iteration end condition is met, obtain the fitted pseudocode phase and pseudocode carrier frequency control word, and transmit them into the pseudocode generator of the open-loop occultation tracking channel to correct the predicted pseudorange;

[0031] The open-loop occultation tracking channel is used to track the occultation event based on the corrected predicted pseudorange and carrier frequency in the open-loop occultation tracking stage and obtain open-loop occultation data.

[0032] As an improvement of the above system, the system further includes: a preprocessing module; wherein,

[0033] The preprocessing module is used to obtain the velocity, position, and time information of the GNSS satellite based on the GNSS satellite ephemeris or almanac information received by the GNSS occultation sounder, and calculate the velocity, position, and time information of the GNSS occultation sounder; and is used to calculate the satellite elevation angle, azimuth angle, relative azimuth angle, and tangent height of the GNSS satellite based on the velocity, position, and time information of the GNSS satellite and the velocity, position, and time information of the GNSS occultation sounder to determine the current occultation event type, where the occultation event types include: ascending closed-loop occultation event, ascending open-loop occultation event, descending closed-loop occultation event, and descending open-loop occultation event.

[0034] The open-loop parameter curve fitting algorithm proposed and adopted in the present invention utilizes the characteristic that the true pseudorange changes smoothly during the observation process of an open-loop occultation event, as well as the correspondence between the GNSS satellite pseudorange and the elevation angle, azimuth angle, relative azimuth angle, and tangent height. The deviation between the true pseudorange and the open-loop predicted pseudorange is fitted using the above parameters to obtain an open-loop model pseudorange deviation compensation polynomial. After the fitting is completed, the open-loop tracking pseudorange below 0 km of the tangent height can be better predicted during the actual tracking process, making up for the deficiencies of the traditional atmospheric model pseudorange algorithm, reducing the error between the open-loop pseudorange and the true pseudorange, improving the open-loop tracking accuracy, and enhancing the open-loop detection ability of the occultation sounder for the lower atmosphere. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Shown is a schematic diagram of the system design for obtaining the open-loop prediction parameters of a micro GNSS occultation sounder;

[0036] Figure 2 Shown is a flowchart of the method for obtaining the open-loop prediction parameters of a micro GNSS occultation sounder;

[0037] Figure 3 Shown is a schematic diagram of the overlapping stage between closed-loop occultation tracking and open-loop occultation tracking. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The technical solutions provided by the present invention are further described below in conjunction with embodiments.

[0039] The present invention provides a method and a system for obtaining open-loop prediction parameters of a micro GNSS occultation detector for GNSS (Global Navigation Satellite System) occultation detection. This method uses parameters such as precise pseudorange and carrier phase measured by a closed-loop tracking loop during the same occultation time to fit and correct the predicted pseudorange in open-loop tracking, thereby improving the success rate of open-loop tracking and the subsequent inversion carrier phase accuracy, and enhancing the working performance of the occultation detector. This method has a simple structure and a fast calculation speed, and can be carried out based on the original micro receiver without hardware modification.

[0040] The purpose of the method proposed by the present invention is to more precisely fit and calculate the predicted pseudorange during the open-loop tracking process, and improve the open-loop model tracking accuracy. As Figure 1-2 shown, the specific steps are as follows:

[0041] (1) Detector positioning, occultation prediction

[0042] The GNSS occultation detector uses a positioning antenna to receive a positioning signal and perform down-conversion. After obtaining an intermediate-frequency signal, it realizes receiver positioning through acquisition and tracking, and collects GNSS satellite ephemeris / almanac, thereby realizing occultation prediction and determining the tracking satellite of the occultation event and the type of occultation event at the current moment.

[0043] (2) Closed-loop occultation tracking, collecting closed-loop occultation data

[0044] Use the acquisition engine and the closed-loop occultation tracking channel to acquire and track the closed-loop occultation event confirmed in step (1). After stable tracking, collect information such as the pseudorange, carrier, elevation angle, tangent point height, and I / Q path energy integration value of the occultation event.

[0045] (3) Predicting open-loop carrier and pseudorange using an atmospheric model

[0046] According to the PVT (Position, Velocity, Time) information of the receiver after positioning and the PVT information of the GNSS satellite, use an atmospheric model to estimate the carrier frequency and model pseudorange required for open-loop tracking.

[0047] Estimate the predicted carrier frequency and predicted pseudorange of the open-loop occultation tracking channel based on the velocity, position, and time information of GNSS satellites, the velocity, position, and time information of the GNSS occultation sounder, and the CIRA86-Q (COSPAR international reference atmosphere) atmospheric model; the CIRA86-Q model adopts a geographical location zone differentiation mode, and looks up the corresponding atmospheric physical parameter storage table through the time and position information obtained by the positioning and resolution of the sounder and performs interpolation calculations to obtain the signal refraction angle α at the current moment at the position of the sounder, and uses this refraction angle to calculate the additional Doppler frequency (carrier frequency) and code phase correction amount in the open-loop signal propagation path based on the geometric relationship between the refraction angle, the satellite, and the sounder, so as to obtain the predicted frequency and predicted pseudorange.

[0048] (4) Close-loop extract parameters to correct the open-loop pseudorange

[0049] Judge whether the current occultation event is in the overlapping stage of the closed loop and the open loop. If they overlap, judge the error between the closed-loop unbiased pseudorange and the open-loop model predicted pseudorange at this moment, and use the elevation angle, azimuth angle, and tangent height of the GNSS satellite at this moment to fit the error of the predicted pseudorange to correct the open-loop model predicted pseudorange.

[0050] (5) Open-loop tracking pseudorange and carrier update

[0051] Use the carrier frequency and the corrected open-loop pseudorange calculated in step (4) to calculate the carrier NCO (carrier frequency control word), pseudocode NCO, and pseudocode phase at the current moment of this open-loop event, and place them into the open-loop tracking loop according to the set integration time to achieve open-loop tracking.

[0052] (6) Collect occultation observation data

[0053] Cache, pack, and transmit the above-mentioned closed-loop and open-loop occultation data to the ground receiving device for post-processing pseudorange fitting verification on the ground.

[0054] Step (1) also includes: after positioning, determine the open-loop and closed-loop occultation events through the occultation prediction module, and determine the movement trend of the occultation event (rising occultation / falling occultation) according to the movement trend of the GNSS satellite, so as to calculate the overlapping time of the open and closed loops.

[0055] Step (4) also includes: the overlapping time period of the open-loop occultation and the closed-loop occultation is identified by the tangent height (T ph ) This parameter is set separately for the open loop and the closed loop and stored in the non-volatile storage space (MRAM), so the overlapping time of the open loop and the closed loop can be modified by modifying the open-loop maximum height and the closed-loop minimum height on orbit, which is more conducive to fitting the open-loop parameters during the overlapping time.

[0056] Step (4) further includes: in the initial fitting stage of the fitting method, the open-loop T ph height increase value can coincide with the closed-loop, so as to further increase the overlapping time between the open-loop and the closed-loop, enabling the curve fitting to converge quickly; after the fitting curve converges, lower the highest height of the open-loop and reduce the overlapping height to the interval with a large curvature change, making the curve fitting more accurate.

[0057] Lower the opening height of the open-loop occultation tracking channel, so that the overlapping stage between the closed-loop occultation tracking and the open-loop occultation tracking is reduced to the interval with the largest curvature change of the difference between the true pseudorange obtained by the closed-loop tracking and the pseudorange of the open-loop prediction model, in order to improve the accuracy of the curve fitting.

[0058] Step (4) further includes: the fitting method is: taking the GNSS satellite elevation angle, azimuth angle and tangent point height as inputs, and taking the difference between the actual closed-loop tracking unbiased pseudorange and the open-loop model pseudorange as the target, using the quasi-Newton method combined with the general global optimization algorithm to perform approximation calculations, and calling the curve fitting algorithm to iterate during each occultation event overlapping time period until the iteration end condition is met.

[0059] The iteration end condition is:

[0060] Determination Coef. > 0.996

[0061] Correlation Coef. > 0.998

[0062] R-Suqare > 0.996

[0063] Step (5) further includes: the carrier frequency is placed using a linear interpolation algorithm, and after the specified coherent integration time arrives, the carrier phase is restored according to the I / Q path integration result to obtain the final true carrier frequency and carrier phase.

[0064] To make the purpose and technical solution of the present invention clearer, the following will combine the accompanying drawings and embodiments to elaborate in detail on a micro-miniature GNSS occultation detector open-loop prediction parameter correction system proposed by the present invention.

[0065] The overall structure diagram of the open-loop parameter correction system of the present invention is as Figure 1As shown, the positioning antenna of the GNSS occultation detector receives the signal, obtains the GNSS satellite ephemeris or almanac information, solves the speed, position and time information of the GNSS satellite, uses the above information to perform real-time positioning of the detector, and calculates the speed, position and time information of the GNSS occultation detector; based on the speed, position and time information of the GNSS satellite and the speed, position and time information of the GNSS occultation detector, calculates the GNSS satellite elevation (Elev), azimuth (Azm), relative azimuth (R AZM ) and the tangent point height (T ph ), and compare it with the occultation prediction conditions in Table 1 to determine the type of occultation event (open loop / closed loop, rising / falling), where each threshold range can be adaptively modified through the injection command.

[0066] Table 1 Occultation range judgment table

[0067]

[0068] After the occultation event is determined, each occultation event can be placed in the occultation tracking channel for tracking. In the early stage of the receiver's on-orbit operation, due to the small number of observation data samples, the correction system error is large at this time, so the open-loop end condition is first raised to 100km, and the overlap time of the open-loop and closed-loop is lengthened, which is conducive to better convergence of the data during the parameter correction process.

[0069] For closed-loop occultation events, the capture engine is called to capture them, obtain the initial carrier information and pseudo code information, and convert the carrier information into carrier NCO:

[0070] Car NCO =(IF GNSS +IF Dop ) / CarNco Res

[0071] Where IF GNSS It is the standard intermediate frequency after the GNSS signal is down-converted, in Hz; IF Dop The Doppler shift frequency measured for the capture engine, in Hz; CarNco Res The code phase information in the capture result is converted into code NCO and the code initial phase is written into the carrier generator and pseudo code generator of the closed-loop tracking channel, and closed-loop feedback adjustment is performed through the I / Q phase detector to concentrate the energy on the I path to achieve stable tracking.

[0072] For open-loop occultation events, a prediction model is used to predict the carrier frequency and pseudo-code phase. Each time when the preset integration time of 10 ms arrives, the open-loop carrier frequency and pseudo-code phase are placed into the open-loop loop. Among them, the carrier frequency is predicted by using linear interpolation within seconds, and the pseudo-code phase is obtained by resolving the pseudo-range calculated according to the atmospheric model and the open-loop parameter correction system.

[0073] As Figure 3 shown, when the open-loop tracking and closed-loop tracking of a single occultation event are in the overlapping time period, open-loop parameter correction fitting can be performed. First, the unbiased pseudo-range Pd of the satellite measurement is extracted from the closed-loop loop CL , and the pseudo-range Pd predicted by the atmospheric model at this moment is calculated OL . The elevation angle (Elev), relative azimuth angle (R AZM ) and tangent point height (T ph ) of the satellite are obtained from the stored information of the satellite. As Figure 2 shown, after obtaining the above parameters from the closed-loop loop, they are attached to the open-loop loop. The pseudo-range deviation is fitted in the open-loop pseudo-range correction module, and the fitted pseudo-code phase and pseudo-code NCO are sent into the pseudo-code generator to realize the correction of the open-loop predicted pseudo-range, and the fitted parameter equation is stored. The determination coefficient, correlation coefficient and certainty coefficient are evaluated. If one of the three coefficients does not meet the preset threshold condition, the fitting system keeps running. If it meets, the fitting stops.

[0074] In order to make the above parameter correction system run quickly, before the occultation detector is officially launched, the difference Pd CL between Pd OL and Pd in the ground test data and the satellite parameter information can be used for curve pre-fitting. An equation for setting a fitting curve can be: err

[0075]

[0076] where p 1 ~p 11 are all parameter terms determined during fitting. After multiple iterative fittings, the parameters will tend to fixed values.

[0077] The fitted pseudo-range, satellite information, fitting parameters and occultation detection data are cached, packed and transmitted to the ground receiving station for subsequent ground inversion calculation and subsequent verification and evaluation of the fitting effect.

[0078] By using the above method for open-loop pseudo-range correction, the open-loop predicted pseudo-range can be well approximated to the true pseudo-range, effectively improving the open-loop detection success rate and the working performance of the detector. And the content of the present invention does not need to modify the hardware of the traditional receiver, which is more conducive to the rapid design and layout of micro-miniature receivers.

[0079] ​It should be noted that the above embodiments are only preferred implementation schemes of a method and system for obtaining open-loop prediction parameters of a micro GNSS occultation detector provided by the present invention. This preferred implementation scheme is not used to limit the scope of protection of the present invention. All algorithms and their corresponding system designs disclosed in the present invention can be combined and intercepted in various ways or replaced by features with the same or similar purposes and effects. It should be pointed out that for those of ordinary skill in the art, without departing from the principles and spirit of the present invention, various improvements and changes can be made, such as adding, deleting, replacing or combining certain steps or functional units / modules, and these improvements and changes are also within the scope of protection of the present invention.

Claims

1. A method for obtaining open-loop prediction parameters of a micro GNSS occultation sounder, comprising the following steps: Step 1) In the overlapping stage of closed-loop occultation tracking and open-loop occultation tracking, collect unbiased pseudorange of the occultation event through the closed-loop occultation tracking channel; Step 2) Estimate the predicted carrier frequency and predicted pseudorange of the open-loop occultation tracking channel based on the velocity, position, and time information of the GNSS satellite, the velocity, position, and time information of the GNSS occultation sounder, and the CIRA86-Q atmospheric model; Step 3) In the open-loop occultation tracking channel, use the corrected open-loop pseudorange module, take the elevation angle, relative azimuth angle, and tangent height of the GNSS satellite as inputs, take the pseudorange deviation between the unbiased pseudorange and the predicted pseudorange as the target, call the curve fitting algorithm to perform curve fitting on the pseudorange deviation until the iteration end condition is satisfied, obtain the fitted pseudocode phase and pseudocode carrier frequency control word, and transmit them into the pseudocode generator of the open-loop occultation tracking channel to correct the predicted pseudorange; The specific content of Step 3) includes: Step 3-1) Use the difference between the unbiased pseudorange and the predicted pseudorange as the pseudorange deviation Pd err ; Step 3-2) Perform preliminary curve fitting on the pseudorange deviation using the elevation angle, relative azimuth angle, and tangent height of the GNSS satellite to obtain several parameter terms: where Elev is the elevation angle of the GNSS satellite, and T ph is the tangent height of the GNSS satellite, and R AZM is the azimuth angle of the GNSS satellite, and p 1 ~p 11 are parameter terms respectively; Step 3-3) Bring the Elev, T ph , R AZM collected from multiple occultation events into the above formula for iteration, and solve through a global optimization algorithm until the result evaluation reaches the iteration condition, then stop the iteration, so that the several parameter terms p 1 ~p 11 tend to a fixed value; after the parameter terms tend to be stable, directly use the parameter terms p 1 ~p 11 and the current moment Elev, T ph , R AZM to substitute into the above formula to obtain the pseudorange deviation Pd err , and compensate this difference into the open-loop model pseudorange, so as to realize the correction of the open-loop model pseudorange; The iteration condition is: the coefficient of determination is greater than 0.996, the correlation coefficient is greater than 0.998, and the certainty coefficient is greater than 0.

996.

2. The method for obtaining open-loop prediction parameters of a micro GNSS occultation sounder according to claim 1, characterized in that, the method further includes: Tracking the occultation event through the closed-loop occultation tracking channel in the closed-loop occultation tracking stage to obtain closed-loop occultation data; The open-loop occultation tracking channel tracks the occultation event based on the corrected predicted pseudorange and the open-loop model carrier frequency calculated in Step 2) in the open-loop occultation tracking stage and obtains open-loop occultation data.

3. The method for obtaining open-loop prediction parameters of a micro GNSS occultation sounder according to claim 2, characterized in that, the method further includes: After caching and packing the closed-loop occultation data and the open-loop occultation data, transmit them to the ground receiving device.

4. The method for obtaining open-loop prediction parameters of a micro GNSS occultation sounder according to claim 1, characterized in that, the method further includes a preprocessing step: Based on the GNSS satellite ephemeris or almanac information received by the GNSS occultation sounder, obtain the velocity, position, and time information of the GNSS satellite, and calculate the velocity, position, and time information of the GNSS occultation sounder; Based on the velocity, position, and time information of the GNSS satellite and the velocity, position, and time information of the GNSS occultation sounder, calculate the elevation angle, azimuth angle, relative azimuth angle, and tangent height of the GNSS satellite to determine the current occultation event type, where the occultation event type includes: rising closed-loop occultation event, rising open-loop occultation event, falling closed-loop occultation event, and falling open-loop occultation event.

5. The method for obtaining open-loop prediction parameters of a micro GNSS occultation sounder according to claim 1, characterized in that, The overlapping stage of the closed-loop occultation tracking and the open-loop occultation tracking is the stage when the open-loop occultation tracking channel and the closed-loop occultation tracking channel are both turned on; wherein, the open-loop occultation tracking channel is turned on when the tangent height of the GNSS satellite is N, and N is stored in the non-volatile storage space of the open-loop occultation tracking channel, and the closed-loop occultation tracking channel is turned off when the tangent height of the GNSS satellite is M, and M is stored in the non-volatile storage space of the closed-loop occultation tracking channel; the values of N and M can be modified on orbit to increase or decrease the overlapping stage.

6. The method for obtaining the open-loop prediction parameters of a micro-miniature GNSS occultation detector according to claim 1, wherein, the method further includes: increasing the opening height of the open-loop occultation tracking channel before step 1) to increase the overlapping stage of the closed-loop occultation tracking and the open-loop occultation tracking, so that the curve fitting converges quickly; reducing the opening height of the open-loop occultation tracking channel before step 3) to reduce the overlapping stage of the closed-loop occultation tracking and the open-loop occultation tracking to the interval with the largest curvature change of the difference between the true pseudorange obtained by the closed-loop tracking and the pseudorange of the open-loop prediction model, so as to improve the accuracy of the curve fitting.

7. A system for obtaining the open-loop prediction parameters of a micro-miniature GNSS occultation detector based on the method for obtaining the open-loop prediction parameters of a micro-miniature GNSS occultation detector according to any one of claims 1 to 6, comprising: a closed-loop occultation tracking channel and an open-loop occultation tracking channel, wherein the system further includes: a prediction module and a module for correcting the open-loop pseudorange; wherein, the closed-loop occultation tracking channel is used to track the occultation event in the closed-loop occultation tracking stage to obtain closed-loop occultation data; and is used to collect the unbiased pseudorange of the occultation event in the overlapping stage of the closed-loop occultation tracking and the open-loop occultation tracking; the prediction module estimates the predicted carrier frequency and the predicted pseudorange of the open-loop occultation tracking channel based on the velocity, position and time information of the GNSS satellite, the velocity, position and time information of the GNSS occultation detector, and the CIRA86-Q atmospheric model; the module for correcting the open-loop pseudorange is used to take the elevation angle, relative azimuth angle and tangent height of the GNSS satellite as inputs, take the pseudorange deviation between the unbiased pseudorange and the predicted pseudorange as the target, call a curve fitting algorithm to perform curve fitting on the pseudorange deviation until the iteration end condition is met, obtain the fitted pseudocode phase and the pseudocode carrier frequency control word, and transmit them into the pseudocode generator of the open-loop occultation tracking channel to correct the predicted pseudorange; the open-loop occultation tracking channel is used to track the occultation event based on the corrected predicted pseudorange and carrier frequency in the open-loop occultation tracking stage and obtain open-loop occultation data.

8. The system for obtaining the open-loop prediction parameters of a micro-miniature GNSS occultation detector according to claim 7, the system further comprising: a preprocessing module; wherein, The preprocessing module is used to obtain the velocity, position, and time information of the GNSS satellite based on the GNSS satellite ephemeris or almanac information received by the GNSS occultation sounder, and calculate the velocity, position, and time information of the GNSS occultation sounder; and is used to calculate the elevation angle, azimuth angle, relative azimuth angle, and tangent height of the GNSS satellite based on the velocity, position, and time information of the GNSS satellite and the velocity, position, and time information of the GNSS occultation sounder to determine the current occultation event type, where the occultation event type includes: rising closed-loop occultation event, rising open-loop occultation event, falling closed-loop occultation event, and falling open-loop occultation event.

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