A micro GNSS occultation detector open loop data compression method

Abstract

The present application relates to a kind of micro GNSS occultation detector open loop data compression method, the signal required for positioning and the signal required for predicting occultation event are received by antenna on the detector in the method;The signal required for positioning is processed to obtain the position of detector and each GNSS satellite;Combining the position of detector and each GNSS satellite obtained, calculate and list the GNSS satellite meeting the occultation event, process the signal required for predicting occultation event, predict and track the occultation event;The relevant parameters of each GNSS satellite are calculated using open loop model, and the continuous tracking of the occultation event is realized based on the calculated parameters;The carrier-to-noise ratio of the occultation event is calculated, and compared with the set threshold, and high-quality occultation signal and low-quality occultation signal are obtained according to the comparison result;Actual carrier phase recovery is carried out on high-quality occultation signal, actual carrier phase is compressed and cached, low-quality occultation signal is cached using traditional method, and the compression of detector open loop data is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of GNSS radio occultation atmospheric sounding technology, and particularly relates to a micro GNSS occultation sounding instrument open loop data compression method and system. BACKGROUND

[0002] GNSS occultation sounding is a kind of radio occultation sounding. In the process of relative motion between a low-orbit satellite carrying an occultation sounding instrument and a GNSS satellite, the GNSS satellite signal received by the occultation sounding instrument will penetrate the atmosphere and ionosphere and be refracted, resulting in a change in the measured signal carrier phase. By solving and analyzing the carrier phase change, physical quantities such as atmospheric temperature, humidity and pressure can be obtained, which has important research significance and value in climatology and meteorology.

[0003] At present, GNSS occultation sounding instruments have developed towards miniaturization, low cost and commercialization. The traditional sounding instrument does not judge the quality of occultation events, and uniformly processes the received occultation events. The I / Q path integral results, model carrier phase, carrier-to-noise ratio and occultation satellite information are received and transmitted down. Actual carrier phase recovery and data inversion are performed in the ground post-processing system. Due to the limited data transmission capability of the low-cost commercialized sounding instrument, if the traditional method is used for data transmission, it will cause excessive pressure on the transmission system and incomplete occultation event transmission, resulting in that the sounding instrument cannot truly play its maximum detection performance. SUMMARY

[0004] In order to improve the above-mentioned defects in the original method, the present application provides a micro GNSS occultation sounding instrument open loop data compression system. The open loop occultation signal quality is judged in real time by the on-board sounding instrument. The high-quality occultation data is directly preprocessed on the satellite to complete carrier phase recovery, and the recovered real carrier phase is packed and cached. The poor-quality signals are packed and cached according to the model carrier phase and I / Q path integral results. Finally, the cached data is transmitted down to the ground receiving station through the satellite service system to complete subsequent inversion calculation. The real carrier phase can be directly used when the high-quality data is processed on the ground. The poor-quality data is processed separately. The method has low complexity, improves the resource utilization rate of the sounding instrument, reduces the data transmission amount of the satellite service transmission link, and can run on the original micro GNSS sounding instrument without hardware modification.

[0005] The present application provides a micro GNSS occultation sounding instrument open loop data compression method, which comprises the following steps:

[0006] S1. receiving the signals required for positioning through the positioning antenna on the sounding instrument, and receiving the signals required for predicting the occultation event through the occultation antenna on the sounding instrument;

[0007] processing the received positioning required signals to obtain the positions of the probe and each GNSS satellite;

[0008] combining the obtained positions of the probe and each GNSS satellite, calculating and listing the GNSS satellites meeting the occultation event, processing the received prediction required signals of the occultation event to predict and track the occultation event;

[0009] calculating the related parameters of each GNSS satellite by using the open loop model, and realizing the continuous tracking of the occultation event based on the calculated parameters;

[0010] calculating the carrier-to-noise ratio of the occultation event, and comparing with the set threshold, and judging the high-quality occultation signal and the low-quality occultation signal according to the comparison result;

[0011] S2. performing the actual carrier phase recovery on the high-quality occultation signal, compressing and buffering the actual carrier phase, and buffering the low-quality occultation signal in a traditional way, to realize the compression of the open loop data of the probe.

[0012] As one of the improvements of the above technical solutions, the S1 specifically comprises:

[0013] receiving the double-frequency radio frequency signals for positioning through the positioning antenna located at the top end of the probe, and receiving the radio frequency signals for predicting the occultation event through the occultation antenna located at the front and rear sides of the probe; the frequency points of the radio frequency signals received by the occultation antenna are the same as the frequency points of the signals received by the positioning antenna;

[0014] processing the received radio frequency signals through the low-noise amplifier to obtain the analog intermediate frequency signals of each frequency point of the positioning antenna and the occultation antenna, and using the AD sampler to sample and process each analog intermediate frequency signal to obtain the corresponding digital intermediate frequency signal;

[0015] using the digital intermediate frequency signals obtained after the processing of the positioning antenna to position the probe and each GNSS satellite, and to predict the occultation; combining the obtained positions of the probe and each GNSS satellite, calculating and listing the GNSS satellites meeting the occultation event;

[0016] using the digital intermediate frequency signals obtained after the processing of the occultation antenna to track the predicted occultation event;

[0017] after obtaining the position of the probe, using the relative positions between each GNSS satellite and the probe to solve the elevation angle, the relative azimuth angle and the tangent height of each GNSS satellite having received the ephemeris / almanac every second, predicting the GNSS satellite meeting the open loop occultation condition, determining the occultation event type of the GNSS satellite and tracking the GNSS satellite using the corresponding occultation antenna, to obtain the occultation tracking data;

[0018] The open loop model is used to calculate the pseudo-range and Doppler frequency of the GNSS satellite in the next second, further to convert the pseudo-range and Doppler frequency into the pseudo-code phase and carrier phase of the GNSS satellite, and to calculate the intra-second pseudo-range and Doppler difference, and to compensate the intra-second pseudo-range and Doppler difference into the loop to ensure the continuous tracking of the open loop;

[0019] After the pseudo-code phase and carrier frequency calculated by the open loop model are input into the open loop tracking loop and continuously tracked stably, the I / Q channel integration results of the occultation tracking channel in a set coherent integration time are obtained every fixed time, the noise floor is measured, the occultation event carrier-to-noise ratio is calculated, and the carrier-to-noise ratio is compared with a threshold value, and the quality of the occultation signal is judged according to the comparison result.

[0020] As one of the improvements of the above technical solutions, the dual-frequency signal includes: GPS L1 of 1575.42Mhz±1.023Mhz and GPS L5 of 1176.45Mhz±10.23Mhz, or Beidou B1C signal of 1575.42Mhz±16.368Mhz and Beidou B2A signal of 1176.45Mhz±10.23Mhz, or GAL E1 frequency point signal of 1575.42Mhz±12.276Mhz and GAL E5A frequency point signal of 1176.45Mhz±10.23Mhz.

[0021] As one of the improvements of the above technical solutions, the GNSS satellite satisfying the open loop occultation condition is predicted, and the specific prediction method includes:

[0022] After the GNSS detector is positioned, all GNSS satellites whose relative positions have been calculated are judged, and if the ranges of the cut point height, relative azimuth angle and elevation angle height set under the forward open loop and backward open loop conditions are met at the same time, it is considered that the GNSS satellites are in the occultation state.

[0023] As one of the improvements of the above technical solutions, the range of the cut point height set under the forward open loop and backward open loop conditions is-160km~0km.

[0024] The range of the relative azimuth angle set under the forward open loop condition is-45°~45°.

[0025] The range of the relative azimuth angle set under the backward open loop condition is-180°~-135° or 135°~180°.

[0026] The range of the elevation angle height set under the forward open loop and backward open loop conditions is-33°~5°.

[0027] As one of the improvements of the above technical solutions, the positioning antenna processing digital intermediate frequency signal is used for positioning of the probe instrument and each GNSS satellite, specifically including:

[0028] The digital intermediate frequency signal of the positioning antenna is used for capturing and tracking GNSS satellites within the visual range of the positioning antenna, and the positions of each GNSS satellite and the probe instrument are calculated through ephemeris / almanac and time information.

[0029] As one of the improvements of the above technical solutions, the open loop model refers to, after the relative positions of the GNSS satellite and the probe instrument are determined, the pseudorange and Doppler frequency are calculated by using the dynamic model; and on this basis, the CIRA86-Q model is used to interpolate and calculate the atmospheric physical parameters of different time and latitude regions according to the geographical position band division mode, so as to obtain the refraction angle of the GNSS satellite and the probe instrument at the current time, and the additional influence of atmospheric refraction on pseudorange and carrier frequency is calculated according to the refraction angle, so as to finally determine the predicted model code phase and carrier frequency required for open loop tracking.

[0030] As one of the improvements of the above technical solutions, the carrier-to-noise ratio is compared with the threshold value, and the quality of the occultation signal is judged according to the judgment result, including:

[0031] If the carrier-to-noise ratio is greater than the threshold value, the occultation signal is marked as a high-quality occultation signal;

[0032] If the carrier-to-noise ratio is less than the threshold value, the occultation signal is marked as a low-quality occultation signal;

[0033] The threshold value is a modifiable parameter, and is dynamically adjusted according to subsequent on-orbit observation results.

[0034] As one of the improvements of the above technical solutions, the high-quality and low-quality occultation signals obtained by judgment are compressed and buffered respectively, including:

[0035] For the high-quality occultation signal obtained by judgment, the actual carrier phase recovery on the satellite is performed by using the I / Q path integral result and the open loop model carrier phase, and the actual carrier phase result is buffered;

[0036] For the low-quality occultation signal obtained by judgment, the I / Q path integral result and the open loop model carrier phase are directly buffered on the satellite according to the traditional method;

[0037] The traditional method refers to buffering all the measured I / Q two-path integral results and the predicted information obtained by using the open loop model, and the predicted information obtained by using the open loop model includes: predicted carrier frequency, predicted pseudorange and current time signal strength information, and data transmission is performed by using the satellite bus for subsequent ground inversion calculation.

[0038] As one of the improvements of the above technical solutions, the high-quality occultation signal obtained by the judgment is used to recover the actual carrier phase on the satellite by using the I / Q path integral result and the model carrier phase, and the actual carrier phase result is cached, including:

[0039] Reading the open-loop model carrier phase CarPh MOD (t);

[0040] Reading the I / Q path integral result, and calculating the model additional carrier phase CarPh ODD (t) by using a phase discriminator, and the expression is:

[0041] CarPh ODD (t) = arctan 2 (I(t) / Q(t))

[0042] Recovering the additional carrier phase CarPh ODD (t) to the model phase, so as to obtain the real carrier phase CarPh(t), and the expression is:

[0043] CarPh(t) = CarPh MOD (t) + CarPh ODD (t);

[0044] Caching the recovered real carrier phase.

[0045] The present application has the following advantages:

[0046] The method for judging the quality of the occultation event signal and the method for pre-processing the high-quality occultation data on the satellite provided by the present application can fully utilize the operation performance of the probe, compress the open-loop occultation data volume, reduce the data transmission burden of the satellite system, and is simple and effective without the need for hardware modification, compared with the traditional occultation data direct transmission. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is a whole flow chart of a micro GNSS occultation probe provided by the present application;

[0048] Figure 2 is an open-loop data judgment and compression processing flow chart. DETAILED DESCRIPTION

[0049] The technical solutions provided by the present application are further illustrated below by combining with the embodiments.

[0050] The application provides an open loop data compression system for a micro GNSS (Global Navigation Satellite System) occultation detector. Compared with the past occultation detector, the new generation detector has stronger performance and has sufficient resources for occultation data on-board preprocessing. The method fully utilizes the data processing capacity of the on-board detector, directly calculates the additional carrier phase by using the open loop I / Q path integral energy value when the signal is strong, restores the open loop measurement model carrier phase, and thus calculates the real carrier phase. The method of directly packaging and downloading the restored carrier phase reduces the occupied space compared with the method of packaging the model carrier phase and I / Q path information in the traditional method, reduces the actual data amount of the detector when the occultation signal is strong, realizes data compression, reduces the data transmission burden of the link, is suitable for the micro GNSS occultation detection equipment, and has a wide application prospect. The method has simple structure and low calculation complexity, and can be implemented on the basis of the original FPGA+ARM (Field Programmable Gate Array; Advanced RISC Machine) micro GNSS receiver without hardware modification.

[0051] Specific description:

[0052] The method provided by the application comprises the following steps:

[0053] (1) Radio frequency signal down conversion

[0054] The radio frequency signals received by the positioning antenna and the occultation antenna are filtered and down-converted to obtain intermediate frequency signals of the antennas for subsequent acquisition and tracking observation.

[0055] (2) Detector positioning

[0056] The positioning antenna signal is used to position the receiver, and the positions of the GNSS satellites are calculated through ephemeris / almanac.

[0057] (3) Open loop occultation event prediction and tracking

[0058] After the detector is positioned, the elevation angle, relative azimuth angle and tangent height of the GNSS satellites are calculated every second, the GNSS satellites satisfying the open loop occultation condition are predicted, and the GNSS satellites are tracked and observed.

[0059] (4) Open loop model tracking parameter calculation

[0060] Through the open loop prediction model, the Doppler frequency and the predicted pseudo-range of the current second prediction model are obtained, and the tracking loop parameters are updated in real time to adapt to the open loop tracking.

[0061] (5) Occultation event quality judgment

[0062] The I / Q path integration results are obtained, the current tracking signal noise floor is obtained, the real-time carrier-to-noise ratio of the current occultation satellite is calculated, and the threshold is judged, and the signal quality at this time is judged according to the result.

[0063] (6) Occultation data preprocessing

[0064] For the occultation event with good signal quality judged in step (5), the actual carrier phase recovery on the satellite is performed using the I / Q path integration results and the model carrier phase, and the actual carrier phase results at this time are cached. For the occultation event with poor signal quality, the I / Q path integration results and the model carrier phase are cached respectively according to the traditional method.

[0065] (7) Occultation data packaging and sending

[0066] The occultation event observation values cached in step (6) are packaged by time, and the quality of the package and various information used for inversion are attached, and they are sent to the satellite system, so as to be forwarded to the ground receiving station for subsequent inversion.

[0067] In the above process:

[0068] In step (1), the positioning antenna receives the radio frequency signal centered at 1575.42 MHz, thereby obtaining the GPS L1, Beidou B1C, and GAL E1 signals, and simultaneously receives the radio frequency signal centered at 1174.45 MHz, thereby obtaining the GPS L5, Beidou B2A, and GALE5A frequency point signals; the forward and backward occultation antennas located at the front and rear ends of the receiver receive the same frequency points as the positioning antenna. The radio frequency front end down-converts, filters, and obtains the intermediate frequency signals of each frequency point, and converts the analog intermediate frequency signals into digital intermediate frequency signals using an AD sampling module.

[0069] In step (2), the detector captures and tracks the GNSS satellites in the visible range of the positioning antenna, and collects the ephemeris, and then calculates the GNSS satellite position and the detector position using the ephemeris / almanac and time information.

[0070] The step (3) comprises: using the relative positions between GNSS satellites and the receiver satellites, calculating the elevation, relative azimuth and cut height of the GNSS satellites every second, listing the GNSS satellites satisfying the open-loop occultation conditions, determining the types of the occultation events and tracking the satellites using the corresponding occultation antennas, so as to obtain the occultation tracking data.

[0071] The step (4) comprises: calculating the pseudo-range and Doppler frequency of the GNSS satellites in the next second by using the open-loop prediction model, further converting the pseudo-code phase and carrier phase of the satellites, and calculating the pseudo-range and Doppler difference in the second, and compensating them into the loop to ensure the continuous open-loop tracking.

[0072] The step (5) comprises: obtaining the I / Q channel integration results of the occultation tracking channel in a set coherent integration time, measuring the noise floor at the time, and calculating the carrier-to-noise ratio of the occultation event. The calculated carrier-to-noise ratio is compared with a preset threshold value. If the carrier-to-noise ratio is greater than the threshold value, the occultation event at this time is marked as a high-quality occultation event; if the carrier-to-noise ratio is less than the threshold value, the occultation event at this time is marked as a poor-quality occultation event. The comparison threshold value is a modifiable parameter, which can be dynamically adjusted according to subsequent on-orbit observation results.

[0073] The step (6) comprises: for the high-quality occultation event obtained in the step (5), a real carrier phase recovery is performed, and the recovery method is:

[0074] · reading the carrier phase CarPh MOD (t) of the open-loop tracking model at this time;

[0075] · reading the I / Q channel integration results at this time, and calculating the model additional carrier phase CarPh ODD (t) = arctan 2 (I(t) / Q(t));

[0076] · restoring the additional carrier phase to the model phase, so as to obtain the real carrier phase CarPh(t) = CarPh MOD (t) + CarPh ODD (t);

[0077] The recovered real carrier phase is cached. For the low-quality occultation event, the model carrier phase and the I / Q channel integration value are cached respectively.

[0078] The step (7) comprises: for the two types of occultation event observation data in step (6), packaging is performed. For a good quality occultation event, the real carrier phase is packaged, and various additional information such as the length of the package, the data quality type and the pseudo-range is stated in the package; for a poor quality occultation event, the I / Q road integral information and the model carrier phase are put into the package, and various additional information such as the length of the package, the data quality type and the pseudo-range is stated in the package. Finally, the two types of package information are transmitted to the satellite service system, and are forwarded to the ground through the ground receiving station for subsequent inversion calculation.

[0079] The open loop occultation signal quality is judged in real time by the detector, and specifically comprises:

[0080] The positioning antenna located at the top of the detector is used to receive the GPS L1 / Beidou B1 / GAL E1 signal of 1575.42 Mhz and the GPS L5 / Beidou B2A / GAL E5A signal of 1176.45 Mhz required for positioning, and the double-frequency signal can be used to eliminate ionospheric errors; the high-sensitivity occultation antenna located on the front and rear sides of the detector is used to receive the predicted radio frequency signal of the occultation event, and the radio frequency point received by the occultation antenna is the same as that of the positioning antenna;

[0081] The received radio frequency signal is amplified, filtered and down-converted by a low-noise amplifier to obtain analog intermediate frequency signals of each frequency point of the positioning antenna and the occultation antenna, and an AD sampler is used to sample each signal to obtain corresponding digital intermediate frequency signals. The intermediate frequency signal obtained after processing of the positioning antenna is input into the positioning module of the detector baseband board, which is used for subsequent positioning and occultation prediction of the detector; the intermediate frequency signal obtained after processing of the occultation antenna is input into the occultation signal processing module of the detector baseband board, which is used for subsequent tracking of the predicted occultation event;

[0082] The GNSS satellites in the visible range of the positioning antenna are captured and tracked based on the intermediate frequency signal of the positioning antenna, and the positions of the GNSS satellites and the position of the detector are solved through ephemeris / almanac and time information;

[0083] After the position of the detector is obtained, the relative positions between the GNSS satellites and the detector are used to solve the elevation, relative azimuth and cut height of each system GNSS satellite that has received ephemeris / almanac every second, to predict the GNSS satellites that meet the open loop occultation condition, to determine the occultation event type and to track them using the corresponding occultation antenna, so as to obtain occultation tracking data;

[0084] The judgment method for predicting the GNSS satellites that meet the open loop occultation condition is as follows: after the GNSS detector is positioned, all the GNSS satellites whose relative positions have been calculated are judged, and if the following conditions are met at the same time, it is considered that the GNSS satellites are in the occultation state:

[0085]

[0086] The open loop prediction model is used to calculate the pseudorange and Doppler frequency of the GNSS satellite in the next second, further convert the pseudorange and Doppler frequency into the pseudocode phase and carrier phase of the satellite, and calculate the pseudorange and Doppler difference in the second, and compensate the pseudorange and Doppler difference into the loop to ensure the continuous tracking of the open loop.

[0087] The open loop model refers to that after the relative position between the GNSS satellite and the detector is determined, the pseudorange and Doppler frequency are calculated by using a dynamic model; and on this basis, the CIRA86-Q model is used to calculate the atmospheric physical parameters in different time and latitude regions according to the geographical position area division mode, so as to obtain the refraction angle of the GNSS satellite and the detector at the current time, and calculate the additional influence of the atmospheric refraction on the pseudorange and carrier frequency at this time according to the refraction angle, so as to finally determine the predicted model pseudocode phase and carrier frequency required for the open loop tracking.

[0088] After the pseudocode phase and carrier frequency calculated by the open loop model are input into the open loop tracking loop and continuously and stably tracked, the I / Q channel integration results of the occultation tracking channel in a set coherent integration time are obtained every fixed time, the noise floor at the time is measured, the carrier-to-noise ratio of the occultation event is calculated, and the carrier-to-noise ratio is judged with a threshold value, and the signal quality of the occultation at this time is judged according to the judgment result.

[0089] In order to make the purpose and technical scheme of the present application clearer, a micro GNSS occultation detector open loop data compression system is described in detail below in combination with the drawings and examples.

[0090] The overall flowchart of the method in the embodiment of the present application is shown in Figure 1 Taking the Beidou third-generation B2A signal as an example, the carrier frequency of the signal is 1174.45Mhz, and after being received by a positioning antenna, filtered and down-converted, an intermediate frequency signal r IF is obtained. IF The r IF is correlated with a local carrier and a local code to obtain a correlation peak, so as to realize the positioning channel acquisition, tracking and message decryption, and complete the positioning of the detector.

[0091] After the detector is positioned, the elevation angle, relative azimuth angle and cut point height of the GNSS satellite are calculated according to the position of the detector and the position of the GNSS satellite. For the satellites satisfying the open loop occultation range in Table 1, the open loop occultation event is predicted, and the specified forward / backward occultation antenna is used for occultation tracking, and the tracking loop integration time is set to 10 ms. This range in the table is an empirical value, and data beyond this range has little value in subsequent ground processing. This range can also be expanded and reduced, and the specific value is related to the satellite orbit height of the satellite carrying the detector.

[0092]

[0093]

[0094] After predicting and tracking the open loop occultation event, the open loop parameter calculation is performed. According to the open loop prediction model, the carrier and pseudorange model values per second are predicted, and the open loop loop parameters are updated every 10 ms. The carrier frequency model value calculation method is:

[0095]

[0096] where f OL_pre (n) is the initial carrier frequency of the current second predicted according to the relative relationship of the GNSS satellite position, velocity and detector position and velocity, f OL_diff (n) is the 10 ms carrier frequency change in the predicted second, i is the 10 ms count value in the second, f OL_model (n) is the carrier frequency difference between seconds, and f OL (n) is set to f OL_pre (n) of the next second, so that the open loop carrier frequency is dynamically updated and kept within the trackable range; the pseudorange model calculation is performed by the atmospheric prediction model. After obtaining the predicted open loop satellite auxiliary information, the relative position of the receiver and the satellite ephemeris are used to predict the pseudorange, and the atmospheric bending angle information is added to obtain the open loop pseudorange at this time. The open loop pseudorange is differentiated from the existing pseudorange in the loop to obtain the open loop pseudorange offset pd err , which is compensated to the open loop code loop. The carrier loop update parameter is:

[0097]

[0098] where STD_CAR_NCO(n) is the standard carrier NCO value, f OL (n) is the open loop tracking carrier frequency at the current time, STD_NCO_RATIO is the NCO resolution, and FPGA_FREQ is the baseband frequency.

[0099] The code loop update parameter is:

[0100]

[0101] where pd err is the pseudo-range offset, STD_CODE_NCO is the standard code NCO value, c v is the speed of light, taking 299792458 m / s.

[0102] After the open loop stable tracking and parameter calculation are implemented, the I / Q path integration result reading and noise floor measurement reading are performed according to a 10 ms integration time, and the carrier-to-noise ratio is calculated:

[0103]

[0104] where T coh is the coherent integration time, which is 10 ms in this example, I and Q are the open loop tracking integration results, and noise is the noise measurement path integration result.

[0105] The calculated CNR result is compared with a preset carrier-to-noise ratio judgment threshold CNR ol If CNR≥CNR ol , it is considered that the occultation event at this time is a high-quality occultation event, otherwise it is a low-quality occultation event. For the high-quality occultation event, the on-board carrier phase preprocessing is implemented:

[0106] According to the model carrier frequency f OL predicted at this time, (i) the predicted carrier phase CarPh MOD (t) at this time is calculated, and the integral results of the I path and the Q path are used to calculate the attached carrier phase:

[0107] CarPh ODD (t) = arctan 2 (I(t) / Q(t))

[0108] Finally, the real carrier phase at this time is calculated in the probe instrument:

[0109] CarPh(t) = CarPh MOD (t) + CarPh ODD (t)

[0110] The real carrier phase is stored and used for subsequent packaging. For the occultation event with a carrier-to-noise ratio lower than the threshold CNR ol , the I / Q path integration value at this time is stored together with the model carrier phase, which is used for subsequent packaging.

[0111] The open loop occultation tracking adopts 10 ms coherent integration, so 100 Hz frequency can be used for occultation event packaging. For the high-quality occultation event, the packaging mode is:

[0112] High quality package = specific package header + package length + high quality identification + recovered carrier phase + sampling time + other data + package tail + check sum

[0113] For low quality occultation event, the packaging mode is as follows:

[0114] Low quality package = specific package header + package length + low quality identification + I path integral + Q path integral + model carrier phase + sampling time + other data + package tail + check sum

[0115] By using the above packaging mode, the I / Q path integral results in high quality occultation data can be processed in advance, and the space in the package is saved. After the packaging is completed, the two types of package data are transmitted to the satellite service system for storage, and the satellite service system transmits the stored observation data to the ground receiving station during transit for subsequent inversion.

[0116] As can be seen from the above specific description of the present application, the method of the present application compresses the open loop occultation data volume without reducing the quality of the occultation observation data, and reduces the data transmission burden of the satellite service system.

[0117] The above implementation example is only a preferred implementation scheme of the open loop data compression system of the micro GNSS occultation probe provided by the present application, and the preferred implementation scheme is not used to limit the protection scope of the present application. All algorithms disclosed by the present application and their corresponding system designs can be variously combined or replaced by features with the same or similar purposes and effects. It should be pointed out that for ordinary skilled persons in the art, various improvements and changes can be made without departing from the principles and spirits of the present application, for example, adding, deleting, replacing or merging certain steps or functional units / modules, and these improvements and changes are also within the protection scope of the present application.

Claims

1. A method for open loop data compression of a micro GNSS occultation probe, the method comprising: S1.receiving signals required for positioning through a positioning antenna on the probe and receiving signals required for predicting an occultation event through an occultation antenna on the probe; processing the received signals required for positioning to obtain positions of the probe and each GNSS satellite; combining the obtained positions of the probe and each GNSS satellite to calculate and list GNSS satellites meeting the occultation event, processing the received signals required for predicting the occultation event, predicting and tracking the occultation event; calculating relevant parameters of each GNSS satellite using an open loop model, and realizing continuous tracking of the occultation event based on the calculated parameters; calculating a carrier-to-noise ratio of the occultation event and comparing it with a set threshold to determine high-quality occultation signals and low-quality occultation signals according to a comparison result; S2.compressing and caching actual carrier phases of the high-quality occultation signals on the satellite, and caching the low-quality occultation signals in a traditional way to realize compression of open loop data of the probe; compressing and caching the determined high-quality and low-quality occultation signals, including: for the determined high-quality occultation signals, performing actual carrier phase recovery on the satellite using I / Q path integral results and open loop model carrier phases, and caching actual carrier phase results; for the determined low-quality occultation signals, directly caching I / Q path integral results and open loop model carrier phases on the satellite in a traditional way; the traditional way refers to caching all of the measured I / Q two-path integral results and predicted information obtained using the open loop model, the predicted information including predicted carrier frequencies, predicted pseudoranges, and current time signal strength information, and using a satellite bus for data transmission for subsequent ground inversion calculation; for the determined high-quality occultation signals, performing actual carrier phase recovery on the satellite using I / Q path integral results and model carrier phases, and caching actual carrier phase results, including: Read Open-Loop Model Carrier Phase CarPh MOD (t); The I / Q path integration results are read and the model carrier phase CarPh is calculated using a phase discriminator ODD (t), where the expression is: CarPh ODD (t) = arctan 2 (I(t) / Q(t)) Recover the additional carrier phase CarPh ODD (t) to the model phase, so that the real carrier phase CarPh(t) is obtained, expressed as: CarPh(t) = CarPh MOD (t) + CarPh ODD (t); caching the recovered true carrier phases.

2. The method according to claim 1, wherein, the S1 specifically includes: receiving dual-frequency radio frequency signals for positioning through a positioning antenna located at the top of the probe, and receiving radio frequency signals for predicting an occultation event through occultation antennas located at the front and back sides of the probe; the frequency points of the radio frequency signals received by the occultation antennas are the same as those of the signals received by the positioning antenna; processing the received radio frequency signals through a low-noise amplifier to amplify, filter, and down-convert the signals to obtain analog intermediate frequency signals of each frequency point of the positioning antenna and the occultation antennas, and using an AD sampler to sample and process each analog intermediate frequency signal to obtain corresponding digital intermediate frequency signals; obtaining positions of the probe and each GNSS satellite using the digital intermediate frequency signals obtained after processing by the positioning antenna; The digital intermediate frequency signal obtained after the occultation antenna processing is used to track the predicted occultation event, specifically: after obtaining the positions of the probe instrument and each GNSS satellite, the elevation angle, relative azimuth angle and cut point height of each GNSS satellite which has received the ephemeris are solved every second by using the relative positions between each GNSS satellite and the probe instrument, the GNSS satellite satisfying the open loop occultation condition is predicted, the GNSS satellite occultation event type is determined and the GNSS satellite is tracked using the corresponding occultation antenna, so as to obtain the occultation tracking data; The pseudorange and Doppler frequency of the GNSS satellite in the next second are calculated by using the open loop model, the pseudorange and Doppler difference of the GNSS satellite in the second are further converted, and the pseudorange and Doppler difference in the second are compensated into the loop to ensure continuous tracking of the open loop; After the pseudorange and carrier frequency calculated by the open loop model are input into the open loop tracking loop and continuously and stably tracked, the I / Q channel integration results in the set coherent integration time of the occultation tracking channel are obtained every fixed time, the noise floor is measured, the occultation event carrier-to-noise ratio is calculated, and the carrier-to-noise ratio is compared with the threshold value, and the occultation signal quality is judged according to the comparison result.

3. The method according to claim 2, wherein, The double-frequency radio frequency signal includes: GPS L1 of 1575.42Mhz±1.023Mhz and GPS L5 of 1176.45Mhz±10.23Mhz, or Beidou B1C signal of 1575.42Mhz±16.368Mhz and Beidou B2A signal of 1176.45Mhz±10.23Mhz, or GAL E1 frequency point signal of 1575.42Mhz±12.276Mhz and GAL E5A frequency point signal of 1176.45Mhz±10.23Mhz.

4. The method of claim 2, wherein, The GNSS satellite satisfying the open loop occultation condition is predicted, and the specific prediction method includes: After the GNSS probe instrument is positioned, all GNSS satellites whose relative positions have been calculated are judged, if the cut point height, relative azimuth angle and elevation angle height ranges set under the forward open loop and backward open loop conditions are met at the same time, it is considered to be in the occultation state.

5. The method of claim 4, wherein, The cut point height ranges set under the forward open loop and backward open loop conditions are both: -160km~0km; The relative azimuth angle range set under the forward open loop condition is: -45°~45°; The relative azimuth angle range set under the backward open loop condition is: -180°~-135° or 135°~180°; The elevation angle height ranges set under the forward open loop and backward open loop conditions are both: -33°~5°.

6. The method of claim 2, wherein, The positions of the probe instrument and each GNSS satellite are obtained by using the digital intermediate frequency signal obtained after the positioning antenna processing, specifically including: The GNSS satellites in the visible range of the positioning antenna are captured and tracked by using the digital intermediate frequency signal of the positioning antenna, and the positions of each GNSS satellite and the probe instrument are solved through ephemeris / orbits and time information.

7. The method of claim 2, wherein, The open loop model refers to, after the relative position of the GNSS satellite and the probe is determined, the pseudorange and Doppler frequency are calculated by using a dynamic model; and on this basis, the CIRA86-Q model is used, the atmospheric physical parameters of different time and different latitude areas are calculated by interpolation according to the geographical position area division mode, so that the refraction angle of the GNSS satellite and the probe at the current time is obtained, and the additional influence of the atmospheric refraction on the pseudorange and the carrier frequency is calculated according to the refraction angle, so that the predicted model code phase and carrier frequency required for open loop tracking are finally determined.

8. The method of claim 2, wherein, The carrier-to-noise ratio is compared with a threshold value, and the quality of the occultation signal is judged according to the judgment result, including: If the carrier-to-noise ratio is greater than the threshold value, the occultation signal is marked as a high-quality occultation signal; If the carrier-to-noise ratio is less than the threshold value, the occultation signal is marked as a low-quality occultation signal; The threshold value is a modifiable parameter, and is dynamically adjusted according to subsequent in-orbit observation results.

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