(19)
(11)EP 3 086 138 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
17.02.2021 Bulletin 2021/07

(21)Application number: 16164340.8

(22)Date of filing:  07.04.2016
(51)International Patent Classification (IPC): 
G01S 19/07(2010.01)

(54)

USING CODE MINUS CARRIER MEASUREMENTS TO MITIGATE SPATIAL DECORRELATION ERRORS CAUSED BY IONOSPHERE DELAYS

VERWENDUNG VON CODE-MINUSTRÄGERMESSUNGEN ZUR ABSCHWÄCHUNG VON RÄUMLICHEN DEKORRELATIONSFEHLERN INFOLGE VON IONOSPHÄRENVERZÖGERUNGEN

MESURES DE PORTEUSE À L'AIDE D'UN CODE NÉGATIF AFIN D'ATTÉNUER LES ERREURS DE DÉCORRÉLATION SPATIALE PROVOQUÉES PAR DES RETARDS IONOSPHÉRIQUES


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 20.04.2015 US 201514691455

(43)Date of publication of application:
26.10.2016 Bulletin 2016/43

(73)Proprietor: Honeywell International Inc.
Morris Plains, NJ 07950 (US)

(72)Inventors:
  • JAKEL, Tom
    Morris Plains, NJ 07950 (US)
  • MCDONALD, James Arthur
    Morris Plains, NJ 07950 (US)

(74)Representative: Houghton, Mark Phillip 
Patent Outsourcing Limited 1 King Street
Bakewell, Derbyshire DE45 1DZ
Bakewell, Derbyshire DE45 1DZ (GB)


(56)References cited: : 
  
  • LEE J ET AL: "Enhancements of Long Term Ionospheric Anomaly Monitoring for the Ground-Based Augmentation System", ITM 2011 - PROCEEDINGS OF THE 2011 INTERNATIONAL TECHNICAL MEETING OF THE INSTITUTE OF NAVIGATION, THE INSTITUTE OF NAVIGATION, 8551 RIXLEW LANE SUITE 360 MANASSAS, VA 20109, USA, 26 January 2011 (2011-01-26), pages 930-941, XP056000116,
  • JIYUN LEE ET AL: "Assessment of Nominal Ionosphere Spatial Decorrelation for LAAS", POSITION, LOCATION, AND NAVIGATION SYMPOSIUM, 2006 IEEE/ION CORONADO, CA APRIL 25-27, 2006, PISCATAWAY, NJ, USA,IEEE, 25 April 2006 (2006-04-25), pages 506-514, XP010924966, DOI: 10.1109/PLANS.2006.1650638 ISBN: 978-0-7803-9454-4
  • ZHAO P ET AL: "Detecting Ionospheric Threat for GBAS Using a Spatial-temporal Method", GNSS 2013 - PROCEEDINGS OF THE 26TH INTERNATIONAL TECHNICAL MEETING OF THE SATELLITE DIVISION OF THE INSTITUTE OF NAVIGATION (ION GNSS+ 2013), THE INSTITUTE OF NAVIGATION, 8551 RIXLEW LANE SUITE 360 MANASSAS, VA 20109, USA, 20 September 2013 (2013-09-20), pages 1428-1434, XP056007345,
  • MURPHY T ET AL: "More Ionosphere Anomaly Mitigation Considerations for Category II/III GBAS", GNSS 2007 - PROCEEDINGS OF THE 20TH INTERNATIONAL TECHNICAL MEETING OF THE SATELLITE DIVISION OF THE INSTITUTE OF NAVIGATION (ION GNSS 2007), THE INSTITUTE OF NAVIGATION, 8551 RIXLEW LANE SUITE 360 MANASSAS, VA 20109, USA, 28 September 2007 (2007-09-28), pages 438-452, XP056010333,
  
Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


Description

BACKGROUND



[0001] A Ground Based Augmentation System (GBAS) is used to assist aircraft during approach and landing operations. The ground station of a GBAS broadcasts pseudorange corrections and integrity information to aircraft, which helps to remove Global Navigation Satellite System (GNSS) errors impacting satellite measurements that are processed by the aircraft GNSS receivers. By using GBAS, aircraft have improved continuity, availability, and integrity performance for precision approaches, departure procedures, and terminal area operations.

[0002] A major source of error for an aircraft GNSS receiver is caused by the ionosphere, which delays GNSS signals that pass through it. The error due to ionosphere delay can almost be completely mitigated by a GBAS under nominal conditions when the ionosphere is uniform between the GBAS ground station and the aircraft GNSS receiver because the ionosphere delay for signals received by the GBAS ground station and the GNSS receiver will be similar. However, when ionosphere disturbances (e.g., ionosphere storms or other anomalous ionosphere activity) produce a non-uniform ionosphere (referred to as an ionosphere gradient), the ionosphere delay for the signals received by the GBAS ground station and the aircraft GNSS receiver can be different. This difference in ionosphere delay can cause the pseudorange corrections broadcast by the GBAS ground station and applied by the aircraft to be less accurate. When there are large distances between the GBAS ground station and the aircraft, it is possible for the variation in ionosphere delay to result in unacceptably large position errors in the aircraft navigation position solution. Mitigation of large ionosphere gradients can be accomplished via (1) cooperative mitigation between the aircraft and GBAS ground station; or (2) conservative screening based on worst case GNSS satellite geometries combined with assuming the worst case ionosphere gradient. Option 1 requires costly equipment for both the ground and airborne systems, while option 2 results in degraded system continuity and availability.

[0003] A real-time screen of all possible GNSS satellite geometries is performed, which removes measurements that may lead to unacceptable position errors in the presence of the worst case ionosphere gradient. More specifically, a GBAS could automatically assume that the worst case ionosphere gradient is always present. When a GBAS ground station checks the possible geometry configurations that an aircraft may be using, any GNSS satellite geometries that produce an error larger than a tolerable error limit, assuming the worst case ionosphere gradient is present, are broadcast to the aircraft with the indication that they should not be used.

[0004] The set of available geometries may also be restricted by inflating integrity-related parameters (e.g., broadcast sigmas) such that only usable geometries are available to the aircraft. In exemplary embodiments, this includes: (1) identifying all credible satellite geometries; (2) computing a Maximum Ionosphere Error in Vertical Position (MIEV); (3) computing the smallest possible Vertical Protection Limit (VPL) for this potentially hazardous subset of credible geometries; (4) when any geometries in this subset have a VPL less than the Vertical Alert Limit (VAL) for the desired category of precision approach, begin a search to find the smallest inflation factors that include the VPL above the VAL for all geometries in the subset of credible geometries.

[0005] One such integrity related parameter is the Vertical Ionosphere Gradient (VIG) standard deviation, referred to herein as sigma-vig (σvig). Typically, σvig is calculated for a future time based on the GNSS satellites that will be in view of the GBAS at a future time. Since GNSS satellites orbit the earth twice each sidereal day, over time, different GNSS satellites rise and set from the perspective of the GBAS. For every cycle, the calculation of σvig is performed for a subsequent epoch for all predicted GNSS satellites that will be in view of the GBAS at the future time on all predicted sub-geometries. The larger of the values between the σvig calculated for one time step in the future and the σvig value previously computed for the current time step is broadcast to the aircraft.

[0006] Lee et al, in both "Enhancements of Long Term Ionospheric Anomaly Monitoring for the GBAS" (ION 2011) and "Assessment of Nominal Ionosphere Spatial Decorrelation for LAAS" (ION 2006) disclose the monitoring of the ionosphere delay using SBAS systems for broadcasting the vertical ionosphere gradient standard deviation.

SUMMARY



[0007] The embodiments of the present disclosure provide methods and systems for using code minus carrier measurements to mitigate spatial decorrelation errors caused by ionosphere delays.

[0008] A Ground Based Augmentation System (GBAS) includes a plurality of Global Navigation Satellite System (GNSS) reference receivers configured to receive and process GNSS satellite signals. The GBAS further includes at least one processing module communicatively coupled to the plurality of GNSS reference receivers, wherein the at least one processing module is configured to determine a respective ionosphere quality metric along a line of sight of at least one GNSS satellite of a plurality of observable GNSS satellites using code minus carrier measurements from the at least one GNSS satellite. The at least one processing module is further configured to set at least one overbounded Vertical Ionosphere Gradient standard deviation (σvig) for the at least one GNSS satellite if the respective ionosphere quality metric meets a threshold. The at least one processing module is further configured to define one or more valid ionosphere regions where the at least one overbounded σvig is applicable. The at least one processing module is further configured to determine which GNSS satellites of the plurality of observable GNSS satellites have an ionosphere pierce point within the one or more valid ionosphere regions where the at least one overbounded σvig is applicable. The at least one processing module is further configured to output the at least one overbounded σvig and an indication of which GNSS satellites have an ionosphere pierce point within the one or more valid ionosphere regions.

DRAWINGS



[0009] Understanding that the drawings depict only exemplary embodiments and are not therefore to be considered limiting in scope, the exemplary embodiments will be described with additional specificity and detail through the use of the accompanying drawings, in which:

Figure 1A is an example ground-based augmentation system (GBAS) according to one embodiment of the present disclosure.

Figure 1B is an example GBAS processing module according to one embodiment of the present disclosure.

Figure 2 is a chart of the sky illustrating example valid ionosphere regions defined using code minus carrier measurements from GNSS satellites according to one embodiment of the present disclosure.

Figure 3 is a flow diagram illustrating one example method of selecting a GBAS ionosphere threat mitigation technique using GNSS satellites according to one embodiment of the present disclosure.



[0010] In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize specific features relevant to the exemplary embodiments.

DETAILED DESCRIPTION



[0011] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments. However, it is to be understood that other embodiments may be utilized and that logical, mechanical, and electrical changes may be made. Furthermore, the method presented in the drawing figures and the specification is not to be construed as limiting the order in which the individual steps may be performed.

[0012] By using the geometric screening and inflation techniques discussed above to mitigate the spatial decorrelation errors caused by the large ionosphere gradients, GBAS continuity and availability performance is significantly degraded. Further, since the worst case ionosphere gradients in the United States have historically been present only about once every ten years, making the worst case assumption often results in the unnecessary underutilization of resources.

[0013] The embodiments described below address the above issues associated with ionosphere gradients by implementing a Ground-Based Augmentation System (GBAS) that uses code minus carrier measurements from observable GNSS satellites to define regions of the sky where the ionosphere is healthy. The regions are deemed to be valid ionosphere regions for a finite period of time. For GNSS satellites having ionosphere pierce points within the valid ionosphere regions, a simple overbound mitigation technique can be applied to the satellite measurements instead of the techniques discussed above. Differential corrections based on measurements from any observable GNSS satellites having ionosphere pierce points within the valid ionosphere regions during the finite period of time can be integrity-protected using the overbound technique and used by a vehicle utilizing the GBAS.

[0014] Figure 1A is an example Ground-Based Augmentation System (GBAS) ground station 100 according to one embodiment of the present disclosure. As shown in Figure 1, the GBAS ground station 100 includes a processing module 102, a plurality of reference receivers 104, and a broadcast module 108.

[0015] The reference receivers 104 are ground reference receivers with precisely known positions. Each reference receiver 104 is a radio frequency receiver with an antenna. In the embodiment shown in Figure 1A, GBAS ground station 100 includes four reference receivers. In other embodiments, a greater or fewer number of reference receivers are used. The reference receivers 104 are communicatively coupled to the processing module 102 through a wired or wireless link.

[0016] The reference receivers 104 are each configured to receive and process GNSS signals from a plurality of observable GNSS satellites 110. In exemplary embodiments, the GNSS satellites 100 are single-frequency or multi-frequency GNSS satellites. The GNSS signals transmitted by the GNSS satellites 110 include, but are not limited to, information such as the signal's time of transmission and the position of the GNSS satellite at the time of transmission. This information is also referred to herein as GNSS data.

[0017] Each reference receiver 104 calculates its own position using the transmission time of the GNSS signals for GNSS satellites 110 from which it receives GNSS signals. The transmission time is the difference between the time the GNSS signals were transmitted from the respective GNSS satellite 110 and the time the reference receiver 104 received the GNSS signals. Each reference receiver104 sends its calculated position to the processing module 102 to be used for the differential corrections.

[0018] The reference receivers 104 are also configured to receive and process code and carrier measurements from the plurality of observable GNSS satellites 110. The reference receivers 104 calculate the difference between the two measurements to obtain the code minus carrier measurement, which is essentially a measure of the rate of change of ionosphere delay. The reference receivers 104 send the code minus carrier measurements of the plurality of observable GNSS satellites 110 to the processing module 102.

[0019] As shown in Figure 1B, the processing module includes one or more processing devices 114. The one or more processing devices 114 can include any suitable processing device such as a digital signal processor (DSP), central processing unit (CPU), microcontroller, arithmetic logic unit (ALU), Field Programmable Gate Array (FPGA), or others known to those having skill in the art.

[0020] The one or more processing devices 114 may include or function with software programs, firmware, or other computer readable instructions, such as instructions 117, for carrying out various methods, process tasks, calculations, and control functions, used in the functionality described herein. In exemplary embodiments, the instructions 117 can include a differential correction module 118 and an ionosphere health module 120 to implement the functionality described herein. In exemplary embodiments, the differential correction module 118 and the ionosphere health module 120 can be the same module.

[0021] These instructions 117 are stored on one or more data storage devices 116. In exemplary embodiments, the one or more data storage devices 116 can include any appropriate computer readable medium used for storage of computer readable instructions or data structures. The computer readable medium can be implemented as any available media that can be accessed by a general purpose or special purpose computer or processor, or any programmable logic device. Suitable processor-readable media may include storage or memory media such as magnetic or optical media. For example, storage or memory media may include conventional hard disks, Compact Disk - Read Only Memory (CD-ROM), volatile or non-volatile media such as Random Access Memory (RAM) (including, but not limited to, Synchronous Dynamic Random Access Memory (SDRAM), Double Data Rate (DDR) RAM, RAMBUS Dynamic RAM (RDRAM), Static RAM (SRAM), etc.), Read Only Memory (ROM), Electrically Erasable Programmable ROM (EEPROM), and flash memory, etc. Suitable processor-readable media may also include transmission media such as electrical, electromagnetic, or digital signals, conveyed via a communication medium such as a network and/or a wireless link.

[0022] The differential correction module 118 is configured to receive the position calculations from the reference receivers 104. The differential correction module 118 uses the position calculations, as well as the precisely known positions of the reference receivers 104, to determine an estimation of the error in the GNSS based calculations. In exemplary embodiments, these errors in the GNSS based calculations are used to provide differential corrections to GNSS receivers on aircraft 112 using the broadcast module 108. In other embodiments, differential corrections may also be provided to other vehicles, objects, things, or people.

[0023] Residual errors remain after application of differential correction terms. The GBAS ground station also broadcasts integrity-related parameters with the differential corrections, such as βvig, that enable the position error of the aircraft112 to be statistically bound. In exemplary embodiments, the position is bound by a cylindrical shaped boundary, referred to as a protection limit, around the aircraft 112 having a vertical component and a lateral component. In other embodiments, boundaries having other shapes are used. In exemplary embodiments, the vertical component is bound to less than 10 meters such that the aircraft is actually within 10 meters of where it thinks it is with a high probability (such as 1 - 10-7).

[0024] The ionosphere health module 120uses the code minus carrier measurements from the reference receivers 104 to determine the quality of the ionosphere. In exemplary embodiments, the ionosphere health module 120determines a respective ionosphere quality metric along a line of sight of a first GNSS satellite of a plurality of observable GNSS satellites 110 using the code minus carrier measurements provided by the reference receivers 104. In exemplary embodiments, determining the respective ionosphere quality metric along a line of sight of the first GNSS satellite 110 includes determining the rate of change of a total electron count along the respective line of sight of the first GNSS satellites 110. The ionosphere health module 120 then uses the rate of change of the total electron count to determine a respective ionosphere quality metric for the line of sight. In exemplary embodiments, the ionosphere quality metric relates inversely to the rate of change of the total electron count. In exemplary embodiments, the ionosphere quality metric can be defined using a numerical range that corresponds to a scale from a healthy ionosphere to an ionosphere storm.

[0025] If the ionosphere quality metric along the line of sight of the first GNSS satellite meets a threshold, then the first GNSS satellite is considered safe for mitigation using an overbounded σvig. That is, the complex geometric screening and σvig inflation techniques used by the GBAS processing module 102 can be suspended for the first GNSS satellite and a simpler technique of overbounding the σvig can be used. In exemplary embodiments, overbounding of σvig can be accomplished by increasing the error bounding distance from the aircraft 112 by adding a K factor and/or sigma multiplier. For example, a one meter one-sigma error indicates that 67% of the time the aircraft 112 is within one meter and this is Gaussian distributed. The one-sigma can be statistically overbound to 95% by multiplying it by two and broadcasting to a user that there is a two meter σvig overbound on this ranging source. This assures that 95% of the time, the range error is not going to exceed 2 meters during fault free conditions.

[0026] In exemplary embodiments, the processing module 102 can switch between the overbounding technique and the more complicated screening techniques based on the circumstances. In exemplary embodiments, greater or fewer GNSS satellites 110 can be used depending on which technique is used. In exemplary embodiments, the processing module 102 can switch between the overbounding technique and the screening techniques and switch the number of GNSS satellites 110 used seamlessly.

[0027] When the technique of overbounding the σvig can be used, the ionosphere health module 120 sets an overbounded σvig for the respective line of sight and a region of the sky surrounding the ionosphere pierce point for the first GNSS satellite. The point at which a satellite's line of sight from a respective reference receiver intersects a two-dimensional shell defined for the ionosphere is the pierce point for the particular satellite. The region of the sky surrounding the ionosphere pierce point where the ionosphere quality metric meets a threshold is defined as a valid ionosphere region for a finite period of time. In exemplary embodiments, the area of the valid ionosphere region varies depending on the quality of the ionosphere at the pierce point. For example, if the ionosphere is determined to be healthy, then the valid ionosphere region may extend 50 nautical miles from the pierce point. However, if the ionosphere is less than healthy, the area of the valid ionosphere region will be proportionately less depending on the severity of the degraded quality of the ionosphere.

[0028] In exemplary embodiments, this process is repeated for one or more additional observable GNSS satellites 110 where the respective ionosphere quality metric meets the threshold. In exemplary embodiments, the one or more additional observable GNSS satellites 110 is less than half of the total amount of observable GNSS satellites 110. In some embodiments, the same overbounded σvig set for the first GNSS satellite is applicable to the valid ionosphere regions for each of the GNSS satellites 110 that has a respective ionosphere quality metric meet the threshold. In other embodiments, two or more different overbounded σvig values are applicable to subsets of the valid ionosphere regions.

[0029] Figure 2 is chart of the sky illustrating example valid ionosphere regions for a first GNSS satellite track seen from the perspective of a GBAS ground station, such as GBAS ground station 100. In the example shown in Figure 2, a first GNSS satellite travels along track 220. The GBAS ground station observes this GNSS satellite and the processing module determines whether the ionosphere surrounding track 220 is healthy using code minus carrier measurements from the GNSS satellite as discussed above. If the ionosphere quality metric meets a threshold at time interval T1, then ionosphere region 201 is defined as valid ionosphere region for the finite period of time T1. The first GNSS satellite, traveling along its orbital path, will subsequently move along track 220.The processing module checks if the ionosphere is healthy at each time interval along track 220. In Figure 2, the processing module determines that the ionosphere is healthy at each time interval (T1-T6); therefore, regions 201-206 are defined as valid ionosphere regions for the respective time intervals. In exemplary embodiments, the time intervals are approximately 20 minutes in length. In other embodiments, the time intervals can have shorter or greater length depending on the conditions of the ionosphere. In exemplary embodiments, the region is only considered valid for the finite period in time in which the first GNSS satellite has a pierce point falling within that ionosphere region.

[0030] In addition to defining the valid ionosphere regions as discussed above, the code minus carrier measurements for each of the plurality of GNSS satellites 110 can also be used by the ionosphere health module 120 to define further valid ionosphere regions. In exemplary embodiments, the ionosphere health module 120 analyzes the ionosphere quality metric for pierce points of the GNSS satellites 110 to determine if an ionosphere gradient may be present between them. In one embodiment, the ionosphere health module 120 compares the ionosphere quality metrics of pierce points of GNSS satellites 110 that are within a threshold distance of one another. In exemplary embodiments, the threshold distance can be a straightline distance or a radial distance. In exemplary embodiments, the threshold distance is approximately 100 km. In other embodiments, the threshold distance can be shorter or longer depending on the condition of the ionosphere. If the difference between the ionosphere quality metrics at pierce points for GNSS satellites 110 within the threshold distance to one another is below a threshold, then the ionosphere health module 120 may assume that an ionosphere gradient is not present in the regions of the sky between the pierce points. Thus, these regions between the pierce points are also defined as valid ionosphere regions. This process can be repeated for all GNSS satellites 110 having an ionosphere quality metric that meets the threshold. In exemplary embodiments, the valid ionosphere regions are rectangular (as shown in Figure 2). In other embodiments, the valid ionosphere regions are circular or any other geometric shape.

[0031] It is likely that not all of the observable GNSS satellites 110 will be used to define the valid ionosphere regions. Therefore, after the valid ionosphere regions are defined, the ionosphere health module 120 can further analyze which additional GNSS satellites 110 have ionosphere pierce points that fall within the valid ionosphere regions. Any GNSS satellite 110 having an ionosphere pierce point within a valid ionosphere region will be considered safe for mitigation via an overbounded σvig. That is, the complex geometric screening and σvig inflation techniques used by the GBAS processing module 102 can be suspended for these GNSS satellites 110 and the simpler technique of overbounding the σvig can be used. By conducting this analysis, the ionosphere health module 120 can leverage the valid ionosphere regions and determine which differential corrections from additional GNSS satellite measurements can also be broadcast to the aircraft 112. If a GNSS satellite 110 does not have a pierce point within a valid ionosphere region, then the measurements from that GNSS satellite 110 will be considered unsafe for mitigation via an overbounded σvig. In exemplary embodiments, each of the plurality of observable GNSS satellites 110 are evaluated to determine if their respective ionosphere pierce point is within a valid ionosphere region.

[0032] Figure 2 shows this process with a second GNSS satellite as viewed by the GBAS ground station 100 along track 210. The GBAS ground station 100 may broadcast differential corrections for the second GNSS satellite signals during the given finite period in which the pierce point of the second GNSS satellite falls within a valid ionosphere region. That is, when the pierce point of the second GNSS satellite exists within an ionosphere region currently co-occupied by the first GNSS satellite, and the ionosphere health module 120 has determined the ionosphere region to be a valid ionosphere region based on the quality metric for the first GNSS satellite, then processing module 102 may leverage that determination when broadcasting differential corrections associated with the second GNSS satellite. For example, the signals for the second GNSS satellite shown in Figure 2, are most reliable at time intervals T1 and T2 (within the valid ionosphere regions 201 and 202) when the second GNSS satellite has a pierce point nearest to the pierce point of the first GNSS satellite's track 210. By time interval T6, track 210 of the pierce point of the second GNSS satellite has significantly traveled away from the first GNSS satellite track 220 so that the pierce point of the second GNSS satellite is no longer in the valid ionosphere region.

[0033] In exemplary embodiments, after determining which of the plurality of observable GNSS satellites 110 have ionosphere pierce points within the valid ionosphere regions, the processing module 102 can then determine if the number of GNSS satellites 110 considered safe for mitigation via an overbounded σvig will be able to produce a Vertical Protection Limit (VPL) that would meet the Vertical Alert Limit (VAL) required for the desired precision approach. In exemplary embodiments, the VAL for a Category I approach is 10 meters. In exemplary embodiments, if the computed VPL is less than the VAL, then the GBAS ground station 100 broadcasts the overbounded σvig as well as an indication of the GNSS satellites 110 having ionosphere pierce points within the valid ionosphere regions. In exemplary embodiments, the GBAS ground station 100 broadcasts an indication of the GNSS satellites 110 having ionosphere pierce points within the valid ionosphere regions and those that do not regardless of the VPL determination. In such embodiments, the GNSS satellites 110 having ionosphere pierce points within the valid ionosphere regions will be marked as safe for use and GNSS satellites 110 having ionosphere pierce points outside the valid ionosphere regions will be marked as unsafe for use.

[0034] In exemplary embodiments, if the processing module 102 determines that there is currently an ionosphere storm (or other ionosphere interference) at a certain level, the processing module 102 applies a hysteresis by waiting a certain timeout period (such as a number of minutes and/or hours) before resuming operation of the ionosphere health module 120. In exemplary embodiments, the timeout period is determined by looking at data from a number of stations over a number of days to determine how increasing and/or decreasing this timeout period affects the gradient distribution. In exemplary embodiments, a sensitivity analysis is performed to the timeout period to select a timeout period where the gradient distribution collapsed to be similar to what the gradient distribution was under a quiet day without these ionosphere storms present. Accordingly, in exemplary embodiments the timeout period is selected to be a duration when the distribution of ionosphere gradients for a particular geographic area has historically collapsed to what would be expected on a normal day with a particular decreased ionosphere quality metric. In exemplary embodiments, the processing module 102 determines that the system is not able to function adequately once a certain threshold of ionosphere gradients is met and the hysteresis using the timeout period allows the GBAS ground station 100 to reach a more normal state before it is considered to be functioning adequately enough to provide valid data.

[0035] The GBAS ground station discussed above provides many advantages over conventional GBAS ground stations. By mapping regions of the sky where the ionosphere is healthy, GBAS ground station is able to leverage GNSS satellite measurements to avoid having to use the computationally intensive geometric screening and inflation processes. Also, the GBAS will have greater continuity and availability because assuming the worst case ionosphere gradient is not necessary in circumstances where the overbounded σvig mitigation is possible.

[0036] Further, the GBAS ground station does not require a modification to the reference receivers as with other proposed solutions. Specifically, the reference receivers do not need to be configured to receive and process multi-frequency satellite signals or Space Based Augmentation System (SBAS) satellite signals. Also, the embodiments of the present disclosure can utilize signals from all GNSS satellites when defining the valid ionosphere regions, rather than being limited to using just multi-frequency satellites or just SBAS satellites. Thus, the embodiments of the present disclosure address the problem with ionosphere gradients in a manner that is cheaper than other proposed solutions and provide greater continuity and availability as well.

[0037] In exemplary embodiments, the GBAS ground station 100 can be further modified to utilize the code minus carrier measurements from observable GNSS satellites 110 of multiple GNSS constellations when defining the valid ionosphere regions, not just the constellation for which the GBAS is broadcasting corrections. This modification of the GBAS ground station 100 requires that the reference receivers 104 be configured to receive GNSS data from multiple GNSS constellations. In exemplary embodiments, the GNSS constellations may include the United States' Global Positioning System (GPS), Russia's Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS), China's Beidou and Compass, and the European Union's Galileo. In exemplary embodiments, the GBAS ground station 100 will only broadcast differential corrections for GNSS satellites 110 from a single GNSS constellation. For example, when configured for GPS, the processing module 102 may utilize the code minus carrier measurements from GNSS satellites from the GPS, GLONASS, and Galileo constellations when defining the valid ionosphere regions, but would only broadcast differential corrections for GPS satellites. By using the code minus carrier measurements from GNSS satellites 110 of multiple GNSS constellations, a greater area of the sky may be defined using the above techniques. This increases the likelihood that the GBAS ground station 100 can utilize the less complex overbounded σvig mitigation technique.

[0038] Figure 3 is a flow chart illustrating an example method 300 of one embodiment of the present disclosure. In one implementation, one or more elements of method 300 are implemented within a GBAS ground station, such as GBAS ground station 100 discussed above with respect to any of Figures 1A-1B and Figure 2. Method 300 is implemented using GNSS satellite measurements to mitigate spatial decorrelation errors caused by ionosphere gradients. For some embodiments, the method of Figure 3 may be implemented using any embodiment of a GBAS ground station or elements thereof described above.

[0039] The method starts at block 302 with determining a quality metric of the ionosphere along a line of sight of at least one GNSS satellite of a plurality of GNSS satellites using code minus carrier measurements from the at least one GNSS satellite. In some embodiments, determining the quality metric of the ionosphere includes computing a rate of change of the total electron count along the line of sight of the at least one GNSS satellite.

[0040] The method proceeds to block 303 with checking if the quality metric of the ionosphere meets a threshold. When the quality metric of the ionosphere does not meet the threshold, the method proceeds to block 305 with utilizing an alternative method of mitigation, which in some embodiments, may include geometric screening and inflation techniques used by the GBAS ground station to assist the aircraft to compensate for the ionosphere delay. In exemplary embodiments, the quality metric of the ionosphere can be severe enough that the measurements of the GNSS satellites have to be excluded from broadcast.

[0041] When the quality metric of the ionosphere meets the threshold, the method proceeds to block 304 with setting at least one overbounded Vertical Ionosphere Gradient (VIG) standard deviation (σvig) for measurements from at least one GNSS satellite. In exemplary embodiments, the overbound can be set by increasing the error bounding distance from the aircraft by adding a K factor and/or a sigma multiplier.

[0042] The method proceeds to block 306 with defining one or more valid ionosphere regions at a given period in time where the at least one overbounded σvig is applicable. In some implementations of this method, valid ionosphere regions may be defined by utilizing GNSS satellites from multiple constellations.

[0043] The method proceeds to block 308 with determining which satellites of the plurality of GNSS satellites have an ionosphere pierce point in the one or more valid ionosphere regions where the at least one overbounded σvig is applicable. In some implementations, method 300 further comprises computing differential corrections using measurements from GNSS satellites that have an ionosphere pierce point in the one or more valid ionosphere regions.

[0044] The method proceeds to block 310 with outputting the at least one overbounded σvig and a list of GNSS satellites having an ionosphere pierce point in the one or more valid ionosphere regions. In an implementation of this method, outputting the at least one overbounded σvig and a list of GNSS satellites having an ionosphere pierce point in the one or more valid ionosphere regions includes broadcasting this information to a vehicle (e.g., an aircraft). In exemplary embodiments, outputting the at least one overbounded σvig and a list of GNSS satellites having an ionosphere pierce point in the one or more valid ionosphere regions occurs if the number of GNSS satellites considered safe for mitigation via an overbounded σvig will be able to produce a Vertical Protection Limit (VPL) that would meet the Vertical Alert Limit (VAL) required for the desired precision approach.

[0045] It is manifestly intended that this invention be limited only by the claims.


Claims

1. A Ground Based Augmentation System, GBAS (100), comprising:

a plurality of Global Navigation Satellite System, GNSS, reference receivers (104) configured to receive and process GNSS satellite (110) signals;

at least one processing module (102) communicatively coupled to the plurality of GNSS reference receivers (104), wherein the at least one processing module (102) is configured to:

determine at least one respective ionosphere quality metric along a line of sight between at least one GNSS reference receiver (104) and at least one GNSS satellite (110) of a plurality of observable GNSS satellites (110) using code minus carrier measurements from the at least one GNSS satellite (110);

the Ground Based Augmentation System characterised in that the at least one processing module is further configured to: set

at least one overbounded Vertical Ionosphere Gradient standard deviation σvig for the at least one GNSS satellite (110) if the respective ionosphere quality metric meets a threshold of ionosphere health; define one or more respective valid ionosphere regions where the at least one respective overbounded σvig is applicable as the region in the sky surrounding the ionosphere pierce point of the at least one GNSS satellite (110) where the at least one respective ionosphere quality metric meets the threshold;

determine which additional GNSS satellites (110) of the plurality of observable GNSS satellites (110) have an ionosphere pierce point within the one or more valid ionosphere regions where the at least one overbounded σvig is applicable, wherein the additional GNSS satellites (110) have not been used to define the one or more valid ionosphere regions; and

output the at least one overbounded σvig and an indication of which GNSS satellites (110) have an ionosphere pierce point within the one or more valid ionosphere regions.


 
2. The GBAS (100) of claim 1, wherein output the at least one overbounded σvig and the indication of which GNSS satellites (110) have an ionosphere pierce point within the one or more valid ionosphere regions comprises broadcasting the at least one overbounded σvig and the indication of which GNSS satellites (110) have an ionosphere pierce point within the one or more valid ionosphere regions with a broadcast module.
 
3. The GBAS (100) of claim 1, wherein the processing module (102) is further configured to compute and broadcast differential corrections for measurements from the GNSS satellites (110) having an ionosphere pierce point within the one or more valid ionosphere regions.
 
4. The GBAS (102) of claim 3, wherein the plurality of observable GNSS satellites (110) include satellites from multiple GNSS constellations; and
wherein the differential corrections are broadcast for GNSS satellites (110) from only one GNSS constellation.
 
5. The GBAS (100) of claim 1, wherein the at least one processing module is further configured to output an indication of which GNSS satellites (110) do not have an ionosphere pierce point within the one or more valid ionosphere regions, wherein the indication includes a notice that signals from GNSS satellites (110) that do not have an ionosphere pierce point within the one or more valid ionosphere regions are not safe for mitigation using the overbounded σvig.
 
6. A method of mitigating spatial decorrelation errors in a Ground Based Augmentation System, GBAS, caused by ionosphere gradients (300), the method comprising:

determining at least one respective quality metric of the ionosphere along a line of sight between at least one Global Navigation Satellite System, GNSS, reference receiver (104) of a plurality of GNSS reference receivers (104) and at least one GNSS satellite (110) of a plurality of GNSS satellites (110) using code minus carrier measurements from the at least one GNSS satellite (110) (302);

the method being characterised in that it further comprises:

setting at least one overbounded Vertical Ionosphere Gradient standard deviation (σvig) for measurements from the at least one GNSS satellite (110) when the quality metric of the ionosphere along the line of sight of the at least one GNSS satellite (110) meets a threshold of ionosphere health (304);

defining one or more respective valid ionosphere regions at a given period in time where the at least one respective overbounded σvig is applicable as the region of the sky surrounding the ionosphere pierce point of the at least one respective GNSS satellite (110) along the line of sight where the at least one respective quality metric of the ionosphere (306) meets the threshold;

determining which additional GNSS satellites (110) of the plurality of GNSS satellites (110) have an ionosphere pierce point in the one or more valid ionosphere regions where the at least one overbounded σvig is applicable (308), wherein the additional GNSS satellites (110) have not been used to define the one or more valid ionosphere regions;

outputting the at least one overbounded σvig and a list of GNSS satellites (110) having an ionosphere pierce point in the one or more valid ionosphere regions (310).


 
7. The method (300) of claim 6, wherein defining the one or more valid ionosphere regions at a given period in time where the overbounded σvig is applicable includes comparing the quality metrics of the ionosphere along multiple lines of sight for a plurality of GNSS satellites (110) that are within a threshold distance of one another and determining whether the difference between the quality metrics is below a threshold.
 
8. The method (300) of claim 6, further comprising determining whether the number of GNSS satellites (110) having ionosphere pierce points in the one or more valid ionosphere regions will be able to produce a Vertical Protection Limit, VPL, that would meet a Vertical Alert Limit, VAL, required for a desired precision approach.
 
9. The method (300) of claim 8, further comprising waiting a timeout period before resuming operation when the number of GNSS satellites (110) having ionosphere pierce points in the one or more valid ionosphere regions would not be able to produce the VPL that would be able to meet the VAL required for the desired precision approach.
 
10. The method (300) of claim 6, further comprising marking the GNSS satellites (110) having an ionosphere pierce point in the one or more valid ionosphere regions as safe for mitigation using the overbounded σvig; and
marking the GNSS satellites (110) that have an ionosphere pierce point outside the one or more valid ionosphere regions as unsafe for mitigation using the overbounded σvig.
 


Ansprüche

1. Bodengestütztes Ergänzungssystem (GBAS; Ground Based Augmentation System) (100), umfassend:
eine Mehrzahl von Referenzempfängern (104) eines globalen Navigationssatellitensystems (GNSS; Global Navigation Satellite System), die zum Empfangen und Verarbeiten von GNSS-Satellitensignalen (110) konfiguriert sind;
mindestens ein Verarbeitungsmodul (102), das kommunikativ mit der Mehrzahl von GNSS-Referenzempfängern (104) gekoppelt ist, wobei das mindestens eine Verarbeitungsmodul (102) konfiguriert ist zum:

Bestimmen mindestens einer jeweiligen lonosphärenqualitätsmetrik entlang einer Sichtlinie zwischen mindestens einem GNSS-Referenzempfänger (104) und mindestens einem GNSS-Satelliten (110) einer Mehrzahl von beobachtbaren GNSS-Satelliten (110) unter Verwendung von Code-Minusträgermessungen von dem mindestens einen GNSS-Satelliten (110);

wobei das bodengestützte Ergänzungssystem dadurch gekennzeichnet ist, dass das mindestens eine Verarbeitungsmodul ferner konfiguriert ist zum:
Einstellen von mindestens einer zu weit begrenzten vertikalen lonosphärengradienten-Standardabweichung σvig für den mindestens einen GNSS-Satelliten (110), wenn die jeweilige lonosphärenqualitätsmetrik einen Schwellenwert der lonosphärengesundheit erfüllt;
Definieren einer oder mehrerer jeweils gültiger lonosphärenregionen, in denen die mindestens eine zu weit begrenzte σvig als die Region am Himmel anwendbar ist, die den lonosphären-Durchstoßpunkt des mindestens einen GNSS-Satelliten (110) umgibt, in der die mindestens eine jeweilige lonosphärenqualitätsmetrik den Schwellenwert erfüllt;
Bestimmen, welche zusätzlichen GNSS-Satelliten (110) der Mehrzahl von beobachtbaren GNSS-Satelliten (110) einen lonosphären-Durchstoßpunkt innerhalb einer oder mehrerer gültiger lonosphärenregionen aufweisen, in denen die mindestens eine zu weit begrenzte σvig anwendbar ist, wobei die zusätzlichen GNSS-Satelliten (110) nicht verwendet wurden, um eine oder mehrere gültige lonosphärenregionen zu definieren; und
Ausgeben der mindestens einen zu weit begrenzten σvig und Angabe, welche GNSS-Satelliten (110) einen lonosphären-Durchstoßpunkt innerhalb der einen oder mehreren gültigen lonosphärenregionen aufweisen.


 
2. GBAS (100) nach Anspruch 1, wobei das Ausgeben der mindestens einen zu weit begrenzten σvig und die Angabe, welche GNSS-Satelliten (110) einen lonosphären-Durchstoßpunkt innerhalb der einen oder mehreren gültigen lonosphärenregionen aufweisen, das Senden der mindestens einen zu weit begrenzten σvig mit einem Sendemodul, und die Angabe umfasst, welche GNSS-Satelliten (110) einen lonosphären-Durchstoßpunkt innerhalb der einen oder mehreren gültigen lonosphärenregionen aufweisen.
 
3. GBAS (100) nach Anspruch 1, wobei das Verarbeitungsmodul (102) ferner zum Berechnen und Senden differenzieller Korrekturen von Messungen von den GNSS-Satelliten (110) mit einem lonosphären-Durchstoßpunkt innerhalb der einen oder mehreren gültigen lonosphärenregionen konfiguriert ist.
 
4. GBAS (102) nach Anspruch 3, wobei die Mehrzahl von beobachtbaren GNSS-Satelliten (110) Satelliten von mehreren GNSS-Konstellationen einschließt; und
wobei die differenziellen Korrekturen für GNSS-Satelliten (110) von nur einer GNSS-Konstellation gesendet werden.
 
5. GBAS (100) nach Anspruch 1, wobei das mindestens eine Verarbeitungsmodul ferner zum Ausgeben einer Angabe konfiguriert ist, welche GNSS-Satelliten (110) keinen lonosphären-Durchstoßpunkt innerhalb des einen oder der mehreren gültigen lonosphärenregionen aufweisen, wobei die Angabe einen Hinweis einschließt, dass Signale von GNSS-Satelliten (110), die keinen lonosphären-Durchstoßpunkt innerhalb der einen oder mehreren gültigen lonosphärenregionen aufweisen, nicht sicher für die Abschwächung unter Verwendung der zu weit begrenzten σvig sind.
 
6. Verfahren zur Abschwächung räumlicher Dekorrelationsfehler in einem bodengestützten Ergänzungssystem (GBAS; Ground Based Augmentation System), die durch lonosphärengradienten (300) verursacht werden, wobei das Verfahren umfasst:

Bestimmen mindestens einer jeweiligen lonosphärenqualitätsmetrik entlang einer Sichtlinie zwischen mindestens einem Referenzempfänger (104) eines globalen Navigationssatellitensystems (GNSS; Global Navigation Satellite System) einer Mehrzahl von GNSS-Referenzempfängern (104) und mindestens einem GNSS-Satelliten (110) einer Mehrzahl von GNSS-Satelliten (110) unter Verwendung von Code-Minusträgermessungen von dem mindestens einen GNSS-Satelliten (110) (302);

wobei das Verfahren dadurch gekennzeichnet ist, dass es ferner umfasst:
Einstellen von mindestens einer zu weit begrenzten vertikalen lonosphärengradienten-Standardabweichung (σvig) für Messungen von dem mindestens einen GNSS-Satelliten (110), wenn die lonosphärenqualitätsmetrik entlang der Sichtlinie des mindestens einen GNSS-Satelliten (110) einen Schwellenwert der lonosphärengesundheit (304) erfüllt;
Definieren einer oder mehrerer jeweils gültiger lonosphärenregionen zu einem bestimmten Zeitpunkt, in denen die mindestens eine, jeweils zu weit begrenzte σvig als die Region des Himmels anwendbar ist, die den lonosphären-Durchstoßpunkt des mindestens einen jeweiligen GNSS-Satelliten (110) entlang der Sichtlinie umgibt, in der die mindestens eine jeweilige lonosphärenqualitätsmetrik (306) den Schwellenwert erfüllt;
Bestimmen, welche zusätzlichen GNSS-Satelliten (110) der Mehrzahl von GNSS-Satelliten (110) einen lonosphären-Durchstoßpunkt in der einen oder den mehreren gültigen lonosphärenregionen aufweisen, in denen die mindestens eine zu weit begrenzte σvig anwendbar ist (308), wobei die zusätzlichen GNSS-Satelliten (110) nicht verwendet wurden, um eine oder mehrere gültige lonosphärenregionen zu definieren;
Ausgeben der mindestens einen zu weit begrenzten σvig und einer Liste von GNSS-Satelliten (110), die einen lonosphären-Durchstoßpunkt innerhalb der einen oder mehreren gültigen lonosphärenregionen aufweisen (310).


 
7. Verfahren (300) nach Anspruch 6, wobei das Definieren der einen oder mehreren gültigen lonosphärenregionen zu einem bestimmten Zeitpunkt, in dem die zu weit begrenzte σvig anwendbar ist, das Vergleichen der lonosphärenqualitätsmetrik entlang mehrerer Sichtlinien für eine Mehrzahl von GNSS-Satelliten (110) einschließt, die sich innerhalb eines Schwellenwertabstands voneinander befinden, und das Bestimmen, ob der Unterschied zwischen den Qualitätsmetriken unter einem Schwellenwert liegt.
 
8. Verfahren (300) nach Anspruch 6, ferner umfassend das Bestimmen, ob die Anzahl von GNSS-Satelliten (110), die lonosphären-Durchstoßpunkte in der einen oder den mehreren gültigen lonosphärenregionen aufweisen, in der Lage sein wird, eine vertikale Schutzgrenze (VPL; Vertical Protection Limit) zu erzeugen, die eine vertikale Alarmgrenze (VAL; Vertical Alert Limit) erfüllen würde, die für einen gewünschten Präzisionsansatz erforderlich ist.
 
9. Verfahren (300) nach Anspruch 8, ferner umfassend das Abwarten einer Zeitüberschreitung vor Wiederaufnahme des Betriebs, wenn die Anzahl von GNSS-Satelliten (110), die lonosphären-Durchstoßpunkte in der einen oder den mehreren gültigen lonosphärenregionen aufweisen, nicht in der Lage wäre, die VPL zu erzeugen, die in der Lage wäre, die für den gewünschten Präzisionsansatz erforderliche VAL zu erfüllen.
 
10. Verfahren (300) nach Anspruch 6, ferner umfassend das Markieren der GNSS-Satelliten (110), die einem lonosphären-Durchstoßpunkt in der einen oder den mehreren gültigen lonosphärenregionen aufweisen, als sicher für die Abschwächung unter Verwendung der zu weit begrenzten σVig; und
Markieren der GNSS-Satelliten (110), die einen lonosphären-Durchstoßpunkt außerhalb der einen oder den mehreren gültigen lonosphärenregionen aufweisen, als unsicher für die Abschwächung unter Verwendung der zu weit begrenzten σvig.
 


Revendications

1. Système de renforcement au sol, GBAS, (GBAS; Ground Based Augmentation System), (100) comprenant :
une pluralité de récepteurs de référence (104) de système mondial de navigation par satellite, GNSS (GNSS; Global Navigation Satellite System), configurés pour recevoir et traiter des signaux de satellite GNSS (110) ;
au moins un module de traitement (102) couplé en communication à la pluralité de récepteurs de référence GNSS (104), dans lequel le au moins un module de traitement (102) est configuré pour :

déterminer au moins une métrique de qualité d'ionosphère respective le long d'une ligne de visée entre au moins un récepteur de référence GNSS (104) et au moins un satellite GNSS (110) parmi une pluralité de satellites GNSS (110) observables au moyen de mesures de porteuse par code négatif provenant du au moins un satellite GNSS (110) ;

le système de renforcement au sol, caractérisé en ce que le au moins un module de traitement est en outre configuré pour :
établir au moins un écart-type de gradient d'ionosphère vertical σvig surdélimité pour le au moins un satellite GNSS (110) si la métrique de qualité d'ionosphère respective atteint un seuil de salubrité d'ionosphère ;
définir une ou plusieurs régions ionosphériques valides respectives, où le au moins un σvig surdélimité respectif peut s'appliquer en tant que région du ciel entourant le point de percée ionosphérique du au moins un satellite GNSS (110) lorsque la au moins une métrique de qualité d'ionosphère respective atteint le seuil ;
déterminer les satellites GNSS (110) supplémentaires parmi la pluralité de satellites GNSS (110) observables qui présentent un point de percée ionosphérique dans la ou les régions ionosphériques valides où le au moins un σvig surdélimité peut s'appliquer, dans lequel les satellites GNSS (110) supplémentaires n'ont pas été utilisés pour définir la ou les régions ionosphériques valides ; et
délivrer en sortie le au moins un σvig surdélimité et une indication précisant les satellites GNSS (110) qui présentent un point de percée ionosphérique dans la ou les régions ionosphériques valides.


 
2. GBAS (100) selon la revendication 1, dans lequel la sortie du au moins un σvig surdélimité et de l'indication précisant les satellites GNSS (110) qui présentent un point de percée ionosphérique à l'intérieur de la ou des régions ionosphériques valides comprend la diffusion du au moins un σvig surdélimité et l'indication précisant les satellites GNSS (110) qui présentent un point de percée ionosphérique dans la ou les régions ionosphériques valides avec un module de diffusion.
 
3. GBAS (100) selon la revendication 1, dans lequel le module de traitement (102) est en outre configuré pour calculer et diffuser des corrections différentielles pour des mesures provenant des satellites GNSS (110) présentant un point de percée ionosphérique dans la ou les régions ionosphériques valides.
 
4. GBAS (102) selon la revendication 3, dans lequel la pluralité de satellites GNSS (110) observables comprend des satellites provenant de multiples constellations GNSS ; et
dans lequel les corrections différentielles sont diffusées pour des satellites GNSS (110) depuis une seule constellation GNSS.
 
5. GBAS (100) selon la revendication 1, dans lequel le au moins un module de traitement est en outre configuré pour délivrer une indication précisant les satellites GNSS (110) qui ne présentent pas de point de percée ionosphérique dans la ou les régions ionosphériques valides, dans lequel l'indication comprend un avis indiquant que des signaux provenant de satellites GNSS (110) qui ne présentent pas de point de percée ionosphérique dans la ou les régions ionosphériques valides ne sont pas sans danger pour une atténuation au moyen du σvig surdélimité.
 
6. Procédé d'atténuation d'erreurs de décorrélation spatiale dans un système de renforcement au sol, GBAS, (GBAS; Ground Based Augmentation System), provoquées par des gradients ionosphériques (300), le procédé comprenant :

la détermination d'au moins une métrique de qualité respective de l'ionosphère le long d'une ligne de visée entre au moins un récepteur de référence (104) de système mondial de navigation par satellite, GNSS, (GNSS; Global Navigation Satellite System), parmi une pluralité de récepteurs de référence (104) GNSS et au moins un satellite GNSS (110) parmi une pluralité de satellites GNSS (110) au moyen de mesures de porteuse par code négatif provenant du au moins un satellite GNSS (110) (302) ;

le procédé étant caractérisé en ce qu'il comprend en outre :
l'établissement d'au moins un écart-type de gradient d'ionosphère vertical (σvig) surdélimité pour des mesures à partir du au moins un satellite GNSS (110) lorsque la métrique de qualité de l'ionosphère le long de la ligne de visée du au moins un satellite GNSS (110) atteint un seuil de salubrité d'ionosphère (304) ;
la définition d'une ou plusieurs régions ionosphériques valides respectives à une période donnée dans le temps où le au moins un σvig surdélimité respectif peut s'appliquer alors que la région dans le ciel entourant le point de percée ionosphérique du au moins un satellite GNSS (110) respectif le long de la ligne de visée où la au moins une métrique de qualité respective de l'ionosphère (306) atteint le seuil ;
la détermination pour définir les satellites GNSS (110) supplémentaires parmi la pluralité de satellites GNSS (110) qui présentent un point de percée ionosphérique dans la ou les régions ionosphériques valides où le au moins un σvig surdélimité est applicable (308), dans lequel les satellites GNSS (110) supplémentaires n'ont pas été utilisés pour définir la ou les régions ionosphériques valides ;
la délivrance en sortie du au moins un σvig surdélimité et d'une liste de satellites GNSS (110) présentant un point de percée ionosphérique dans la ou les régions ionosphériques valides (310).


 
7. Procédé (300) selon la revendication 6, dans lequel la définition de la ou des régions ionosphériques valides à une période donnée dans le temps où le σvig surdélimité est applicable comprend la comparaison des métriques de qualité de l'ionosphère le long de plusieurs lignes de visée pour une pluralité de satellites GNSS (110) qui se trouvent à une distance seuil les unes des autres et la détermination pour définir si la différence entre les métriques de qualité est inférieure à un seuil.
 
8. Procédé (300) selon la revendication 6, comprenant en outre la détermination pour préciser si le nombre de satellites GNSS (110) présentant des points de percée ionosphérique dans la ou les régions ionosphériques valides permettra de produire une limite de protection verticale, VPL, (VPL; Vertical Protection Limit), qui atteindrait une limite d'alerte verticale, VAL, (VAL; Vertical Alert Limit), requise pour une approche de précision souhaitée.
 
9. Procédé (300) selon la revendication 8, comprenant en outre l'attente d'une période de temporisation avant de reprendre le fonctionnement lorsque le nombre de satellites GNSS (110) présentant des points de percée ionosphériques dans la ou les régions ionosphériques valides ne permettrait pas de produire la VPL qui permettrait de répondre à la VAL requise pour l'approche de précision souhaitée.
 
10. Procédé (300) selon la revendication 6, comprenant en outre le marquage des satellites GNSS (110) présentant un point de percée ionosphérique dans la ou les régions ionosphériques valides comme étant sûrs pour une atténuation au moyen du σvig surdélimité ; et
le marquage des satellites GNSS (110) qui présentent un point de percée ionosphérique hors de la ou des régions ionosphériques valides comme étant dangereux pour une atténuation au moyen du σvig surdélimité.
 




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Cited references

REFERENCES CITED IN THE DESCRIPTION



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Non-patent literature cited in the description