WO2015131384A1

WO2015131384A1 - Systems and methods for high reliability surveillance of aircraft

Info

Publication number: WO2015131384A1
Application number: PCT/CN2014/073024
Authority: WO
Inventors: Guoqing Wang; Yuanyuan Ding; Luning WANG; Dingli YAN
Original assignee: Honeywell International Inc
Current assignee: Honeywell International Inc
Priority date: 2014-03-07
Filing date: 2014-03-07
Publication date: 2015-09-11
Anticipated expiration: 2016-09-07
Also published as: CN106415299A; CN106415299B

Abstract

Systems and Methods for High Reliability Surveillance of Aircraft are provided. In one embodiment, an aircraft surveillance system 100 comprises: an aircraft 110 including at least one on-board GNSSreceiver112 processing a plurality of navigation signals 125 from a plurality of GNSS satellites 120, and further comprising at least one air-ground communication datalink 40, 132, 134, where the GNSS receiver 112 calculates current position reports that each includes a current position of the aircraft 110 as determined by the at least one on-board GNSS receiver 112 from the plurality of navigation signals 125; and wherein using the at least one air-ground communication datalink 140, 132,134 the at least one GNSS receiver 112 transmits the current position reports and raw GNSS measurement information including samples from the plurality of navigation signals 125 are transmitted together to a ground station 115 as a series of message units 310-1 to 310-6.

Description

Systems and Methods for High Reliability Surveillance of Aircraft

BACKGROUND

[0001] In addition to primary service radar (PSR) and secondary service radar (SSR) systems, aircraft autonomous position reporting is becoming increasingly important to air traffic service providers for traffic surveillance purpose. Automatic dependent surveillance-broadcast (ADS- B) is a widely used technology nowadays that enhances an air traffic controller's awareness of the aircraft activities, especially in remote areas where PSR and SSR radar coverage is not available.

[0002] The airborne autonomous position reporting systems designed for general aviation aircraft sometimes are integrated with low cost components, such as low end Global Navigation Satellite System (GNSS) chips, Satellite Communication (SATCOM) chips, and relatively limited central processing units. Using position reports generated by such aircraft, Aircraft Operations Center (AOC) and Air Traffic Control (ATC)end users are notified of the existence of such aircraft via aircraft symbols on their surveillance displays. However, integrity and accuracy information for these aircraft may not be always available or provide a sufficient level of confidence to serve the air traffic surveillance or flight tracking purposes.

[0003] For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for improved systems and methods for high reliability surveillance of aircraft.

SUMMARY

[0004] Embodiments of the present invention provide methods and systems for high reliability surveillance of aircraft and will be understood by reading and studying the following specification.

[0005] Systems and Methods for High Reliability Surveillance of Aircraft are provided. In one embodiment, an aircraft surveillance system comprises: an aircraft including at least one onboard GNSS receiver processing a plurality of navigation signals from a plurality of GNSS satellites, and further comprising at least one air-ground communication datalink where the GNSS receiver calculates current position reports that each includes a current position of the aircraft as determined by the at least one on-board GNSS receiver from the plurality of navigation signals; and wherein using the at least one air-ground communication datalink the at least one GNSS receiver transmits the current position reports and raw GNSS measurement information including samples from the plurality of navigation signals are transmitted together to a ground station as a series of message units.

DRAWINGS

[0006] Embodiments of the present invention can be more easily understood and further advantages and uses thereof more readily apparent, when considered in view of the description of the preferred embodiments and the following figures in which:

[0007] Figure 1 is a diagram illustrating a surveillance system of one embodiment of the present disclosure;

[0008] Figure 2 is a diagram illustrating a message unit of one embodiment of the present disclosure;

[0009] Figure 3 is a diagram illustrating communication of current position reports and a cycle of ram GNSS measurement information of one embodiment of the present disclosure; and

[0010] Figure 4 is a flow chart illustrating a method of one embodiment of the present disclosure.

[0011] In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize features relevant to the present invention. Reference characters denote like elements throughout figures and text.

DETAILED DESCRIPTION

[0012] 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 specific illustrative embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense.

[0013] Embodiments of the present disclosure provide systems and methods to provide air traffic surveillance and control personnel with accurate position information for aircraft such as general aviation aircraft that are not equipped with high performance position sensors or

Receiver autonomous integrity monitoring (RAIM) enabled on-board systems. With

embodiments of the present disclosure, an aircraft continues to broadcast position reports using its own low end onboard GNSS sensor for the ground terminal users but augments that data by also transmitting raw GNSS measurements. The ground system hosts sufficient computational power and comprises knowledge of GNSS satellite positioning error models which can be leverages to apply a variety of advanced methodologies on the raw GNSS measurements for a better positioning solution and/or estimate the position data integrity. As described herein, traditionally airborne RAIM functionality may be transferred and integrated with existing ground systems for better air traffic surveillance and flight tracking purpose compared to that which is available from low cost onboard components. In some embodiments, the ground station can apply one or more corrections typically performed by SBAS/GBAS stations to provide a better position solution. Finally this disclosure presents embodiments which leverage existing air-to-ground communications so as to minimize additional costs associated with transmitting the raw GNSS measurements from the aircraft to a ground station.

[0014] Figure 1 is a diagram illustrating an aircraft surveillance system 100 of one embodiment of the present disclosure. Surveillance system 100 comprises an aircraft 110 receiving navigation signals 125 from a plurality of GNSS satellites 120. Aircraft 110 is also in communication with at least one ground station 115 responsible for collecting and reporting surveillance data for airborne aircraft within a geographic region. For example, ground station 115 may comprise an airport or regional aircraft operations center or air traffic control center. Aircraft 110 comprises one or more GNSS receivers 112 which process the navigation signals 125 GNSS satellites 120 and computes a real time navigation solution that indicates the current position of aircraft 110 and transmits a position report of that current position to ground station 115.

[0015] As discussed above, for general aviation aircraft that are not equipped with high performance position sensors or receiver autonomous integrity monitoring (RAIM) enabled onboard systems, the current position data generated by on-board GNSS receiver 112 is not of sufficient integrity or accuracy for control personnel at ground station 115 to trust for air traffic surveillance or flight tracking purposes. In order to provide ground station 115 with the enhanced integrity and accuracy needed, with embodiments of the present disclosure aircraft 110 also transmits the GNSS raw satellite measurements as received by the on-board GNSS receivers 112 to ground station 115. The GNSS raw measurements sampled by GNSS receivers 112 may include, but are not limited to: the number and identification of satellites the on-board GNSS receiver observed, the numberand identification of satellites the receiver used for positioning, a timestamp associated with each sampling of the GNSS satellite signals, the pseudo range (or time shift) for each of the satellite observed, and optionally, the carrier phrase sampled for each of the GNSS satellites observed by the on-board GNSS receiver 112.

[0016] Also as shown in Figure 1, ground station 115 includes a processing system 150 which coupled to one or more surveillance workstations 160 each having a display unit 164 which provide a visual indication of aircraft position, air-speed, and other relevant data pertaining to aircraft within the airspace surveilled by ground station 115. Processing system 150 is coupled to either one or both of a SATCOM receiver 136 and a terrestrial radio receiver 142. In one implementation, aircraft 110 transmits the real time current position updates and the GNSS raw satellite measurements via an air-to-ground transmission 140 received by terrestrial radio receiver 142. In another implementation, aircraft 110 transmits the real time current position updates and the GNSS raw satellite measurements via a SATCOM transmission 132 to a communication satellite 130, which is then retransmitted to the ground station 115 via a satellite transmission 134 received by SATCOM receiver 136. In operation, aircraft 110 may select the use of an air-to-ground transmission 140 verses using communication satellite 130 based on cost, the operational capabilities of the ground station 115, or other factors. For example, aircraft 110 when travelling from one air traffic control region to another may switch between using air-to-ground transmissions and satellite transmissions.

[0017] In one embodiment, air-to-ground transmission 140 comprise 1090MHz or 978MHz ADS-B broadcasts. For example, the existing ADS-B position reporting message subtype codes represent HPL or HFOM/VFOM and some subtypes carry aircraft operational status

information which can be an indication of its integrity and accuracy when the onboard GNSS is RAIM capable. However, when the onboard GNSS system 112 provides no or limited RAIM due to cost restrictions, the position data will not be associated with quality indication or not qualified for ADS-B out specification. Potentially, new optional subtypes may be created for GNSS raw measurements to enable low cost aircraft to take the benefit of ADS-B.

[0018] In another embodiment, a communication satellite 130, comprises a satellite that operates as part of the Iridium or Inmarsat communication satellite network. A wide variety of products and services provide data link between aircraft and ground via satellites. For example, EMS Sky Connect offers an end-to-end system that is composed of onboard Iridium transceiver LRU, antenna, Iridium satellite network, ground Iridium gateway and terminal user application. The transceiver has built in GPS receiver and the position data is transmitted and relayed to Sky Connect server. The terminal user can therefore monitor and record the aircraft flight path for asset tracking. Those position messages are transmitted in manufacturer defined format with no or limited accuracy and integrity information, and thus might not meet the performance requirement for ATC surveillance purpose. In this case raw GNSS measurement samples can be appended to the position messages, the ground will take care of the position correction and RAIM to provide positioning quality indication. For a system implementing ACARS over Iridium, the raw GPS measurements can be optionally appended to user defined ADS-C slots.

[0019] In the embodiment shown in Figure 1, processing system 150 comprises a processor 161, memory 162, and one or more GNSS satellite positioning error models 163 which when executed by processor 161 implement GNSS data post processing algorithms. In one

embodiment, ground based post processing of the GNSS raw measurements may be completed at processing station 150. In other embodiments some or all of the post processing functions of processing system 150 may be hosted by either an off-site service provider or distributed among ground station 115 terminal user computers (such as surveillance workstations 160 for example) or in combination of thereof, wherever sufficient computational power and/or necessary satellite status and signal corrective information is available.

[0020] Processing system 150 is configured with one or more GNSS receiving capabilities (shown at 165) for ephemeris, almanac information or other necessary data, or/and maintaining correspondence to a GNSS operating agency 166(such, for example a GBAS station, a SBAS station, etc.)which may be implemented by executing the GNSS satellite positioning error models 163. There exists a number GNSS data post processing methods that can be applied to the current position and raw GNSS measurements transmitted by aircraft 110 to ground station 115 and processing system 150. For example, in one embodiment, GNSS satellite positioning error models 163 address errors such as atmospheric errors, satellite ephemeris errors, and satellite clock drift. In one embodiment, an available error model extractsthe most current error components from any available error model that can be acquired (for example, from a nearest GBAS airport, SBAS ground facility, or other agency where wide area GNSSargumentation data is available) and applies the model on each of the reported raw pseudo range measurement, to arrive at a correct position solution for aircraft 110 as well as positioning accuracy data.In other implementations, the GNSS satellite positioning error models 163 may correct for GNSS satellite signal multipath and/or signal erroneous lock errors using different combinations of raw and/or corrected pseudo range data for position solutions, compare each of the results and identify and isolate abad satellite signal and thus identify potential erroneous reported aircraft positions. With respect to GNSS satellite outages, authority publications (for example, GPS Notice to Airmen (NOTAM)), may be used in some embodiments to identify when known degraded GNSS satellitesare being used by aircraft 110 to produce current position reports.

That is, raw GNSS measurements transmitted by aircraft 1 10 to ground station 115 will include the number and identification of satellites the on-board GNSS receiver observed and the number and identification of satellites the receiver used for positioning. The satellite identification information obtained by the raw GNSS measurements may be correlated by processing system 150 against such a GNSS satellite outage report to tag a current position report as suspect and locally calculate a corrected position of aircraft 110 by omitting GNSS measurements from known degraded satellites. Further, this problem would not need to wait until the complete cycle of ran GNSS measurement packets have been received. As discussed below, theGNSS satellites used by onboard the GNSS receiver 112 are indicated in the header of the first report packet of the raw GNSS measurement transmission cycle so that inclusion of a degraded satellite will be identified immediately at the start of the cycle.

[0021] The major contributions to GNSS positioning accuracy error are in fact relatively stable in over a short period, and include phenomena such as, but not limited to, ephemeris error, ionosphere delay, troposphere delay, and satellite clock drift. Therefore positioning accuracy data does not necessarily need to be updated for each position report received from aircraft 110. For example, the raw GPS measurements associated with a specific position report can be transmitted evenly overa series of subsequent position report updates. The processing system 150 will determine a quality associated with that specific position report once a complete cycle of raw GNSS measurement packets is received and make it available to the terminal user surveillance workstations 160 until it is again updated after the cycle of raw GNSS

measurement packets is received.

[0022] In addition to simply not needing to provide ground station 115 with raw GPS

measurements at the same rate as position reports, some avionics communication datalinks can be expensive to utilize. For this reason, optimizing the utilization of the datalink can be prudent. For example, satellite data link applications may be sensitive to the size of data due to cost concern. The Sky Connect system for instance, charges users for each Message Unit (MU) transmitted via the Iridium Short Burst Data (SBD) service. As illustrated by the example Message Unit 200 in Figure 2, a current position report (shown at 210) can be transmitted using a predefined 256 bit (32 byte) segmentof data transferred through the Iridium network.The Multi Position Reporting features of the Iridium SBD service can pack at least 5 position report packages (shown at 205-1 to 205-5) into a single MU 200 for higher historic resolution.

However, only real time position data is beneficial for surveillance purposes. Thereforea portion (shown at 220) of the MU 200 equivalent in data size to at least 4 position reports are not being used. With embodiments of the present disclosure, those spare position (205-2 to 205-5) can be fully used for transmitting raw GNSS measurement data.

[0023] Referring next to Figure 3, the raw GNSS measurements can be packed in a bit- orientated approach within the same MUs transporting current position reports to ground station 115. For example, Figure 3 illustrates 6 sequential MUs 310-1 to 310-6 each comprising a regular current position report header comprising an MU identification number and a current position report. Accordingly, ground station 115 is refreshed with an updated current position report each time a new MU is received. The raw GNSS measurements are in turn

communicated to ground station 115 over a cycle of raw GNSS measurement packets transmitted in the otherwise unused portions of each of the MUs 310-1 to 310-6. The first raw GNSS measurement packet in the raw GNSS measurement packet cycle (i.e., shown in MU 310-1) comprises a raw GNSS measurement packet header which includes a pre-established code or "sign" that indicates that packet 310-1 is the first packet in the cycle. The raw GNSS measurement packet header also includes a high accuracy timestamp, the number of and identification of the GNSS satellites observed by GNSS receiver 112 (which in this example is 9 satellites with each satellite's respective identification illustrated by "a, b, c, d, e, f, g, h, i"), and similarly, the number of and identification of the GNSS satellites used by GNSS receiver 112 (which in this example is 5 satellites with each satellite's respective identification illustrated by "b, d, f, g, i") to derive the current position report located in the regular current position report header of MU 310-1. In this manner, the raw GNSS measurement packet header within MU 310-1 notifies processing system 115 that the raw GNSS measurement information provided in the following MUs 310-2 to 310-5 are correlated with the current position report transmitted in MU 310-1. Each of the subsequent MUs 310-2 to 310-5 carryraw pseudo range measurement samples for up to two of the GNSS satellites identified in the raw GNSS measurement packet header. Once acycle is complete, a new cycle commences. As should be appreciated, the total number of MUs comprising a packet cycle will vary depending on the number of satellites observed by the on-board GNSS receiver 112. In this way, raw GNSS measurement information is appended onto regular position reports resulting in no additional cost in service sine no additional MU are needed to provide the raw GNSS measurement information.

[0024] In one embodiment, each MU illustrated in Figure 3 is transmitted at 12 second intervals so that ground station 115 receives current position updates every 12 seconds. For a raw GNSS measurement packet cycle comprising 6 MUs, a complete set of raw GNSS pseudo range measurement samples for the set of observed GNSS satellites is received once every minute. Since the phenomena that result in GNSS measurement errors are relatively stable over periods of time much greater than one minute, processing system 115 can generate and apply position corrections as well as determine accuracy and integrity information for each of the current position reports provided by MUs 310-1 to 310-6 with sufficiently high confidence for use for air-borne surveillance purposes. Moreover, the timestamps and pseudo range information included in the raw GNSS measurement packets doesn't have to full length. That is, because we have preliminary knowledge of the location of the aircraft 110 from a reported baseline position, packets following the baseline packet may use an offset from a known time mark or range can significantly reduce the required bits, resulting in delay for the accuracy and integrity processing as short as possible.

[0025] For example, in one embodiment, aSATCOMcommunications server (which may be integrated within processing system 150 or other ground station 115 equipment) pulls SBD data from transmitted via satellite 130, decodes aircraft 110's position from the position reports following existing processes, and makes the current reported position for aircraft 110 as provided by each MU 310-1 to 310-6 immediately available to surveillance workstation 160upon reception. Additionally, processing system 150 refreshes a GNSS raw measurements buffer for this traffic starting from the first MU(i.e., 310-1) of the GNSS measurement packet cycle until the end of the GNSS measurement packet cycle ( i.e., MU 310-5 for the illustrated example in Figure 3). Upon receipt of final MU of the GNSS measurement packet

cyclegathering of the requisite data for processing system 150 to complete error calculations and quality determinations correlated with the position reported on the first MU 310-1 of the cycleis completed. Together with the GNSS satellite positioning error models 163 and any addition satellite error data that may be provided by a contracted agency, reported position 3D errors for each position report are figured out, and accuracy and integrity levels are determined. The position corrections can be applied to latitude, longitude and altitude data for aircraft 110 directly to the position report provided by the final MU of the raw GNSS measurement packet cycle, and the following cycle until new corrections are updated. The reported position, corrected position, along with associated quality data are sent to contracted ATC system interfaces, such as surveillance workstation 160, to enable surveillance of aircraft 110.

Although the description of Figures 2 and 3 primarily focused on Iridium Message Units, the term "message unit" and various other embodiments illustrated by these figures are so limited and may be applied to other message protocol structures where packets may be structured and utilized to communicate both position reports and raw GNSS measurements in the manner shown in Figure 3.

[0026] Figure 4 is a flow chart illustrating a method for aircraft surveillance of one embodiment of the present invention. The method begins at 410 with receiving a plurality of global navigation satellite system (GNSS) signals at and aircraft by an on-board GNSS receiver. The method proceeds to 420 with sending to a ground station a transmission comprising a position report that includes a current position of the aircraft as determined by the on-board GNSS receiver, and to 430 with sending to a ground station a transmission comprising raw GNSS measurements based on samples of the plurality of GNSS signals. As discussed above with respect to Figures 2 and 3, the transmission of position reports and raw GNSS measurements at 420 and 430 may be implemented concurrently by transmission of message units (such as but not limited to Iridium Message Units) structured to transport both. In one embodiment, complete current position reports are transmitted via each message unit while transmission of the raw GNSS measurements are distributed over a cycle comprising a plurality of message units. The GNSS raw measurement information may include, but is not limited to: the number and identification of satellites the on-board GNSS receiver observed, the number and identification of satellites the receiver used for positioning, a timestamp associated with each sampling of the GNSS satellite signals, the pseudo range (or time shift) for each of the satellite observed, and optionally, the carrier phrase sampled for each of the GNSS satellites observed by the on-board GNSS receiver. Also, in alternate embodiments the transmission of GNSS raw measurement information and current position reports may be implemented by either air-to- ground communication transmissions or satellite communication transmissions.

[0027] The process shown at 410, 420 and 430 illustrate a method embodiment which would be implemented on-board the aircraft. In one embodiment the method may continue at 440 ata ground station with receiving the current position reports and the GNSS raw measurement information. The ground station may then proceed to 450 with decoding the aircraft's position from the current position reports and providing the aircraft's position to a surveillance workstation. It should be appreciated that the method as shown at 450 and 460 may take place concurrently. The ground station also proceeds at 460 with applying one or more GNSS satellite positioning error models to the GNSS raw measurement information to compute error calculations and quality determinations, wherein the error calculations and quality

determinations are correlated with at least a first current position report of the current position reports. Accordingly, the method proceeds to 470 with determining a corrected aircraft position based on the error calculations and quality determination. Together with the GNSS satellite positioning error models and any addition satellite error data that may be provided, reported position 3D errors for each position report are calculated and applied to the aircraft position information displayed at the surveillance workstation. One or both of accuracy and integrity levels may also be displayed.

[0028] In one example of an embodiment in operation, an aircraft equipped with low cost integrated satellite data link position reporting equipment with voice call capability is traveling through a non-radar coverage area and is about to transition through a prohibited area via a 20km wide corridor assigned to civilian aviation operation. This aircraft, with a non-technical standard order (TSO) C129A compliant GNSS sensor, is normally not qualified for this transition. However, this traffic is signed with a terminal based argumentation functionality activated on the radar terminal, andcontrollers at anarea control center continue monitoring. Eventually, this traffic elicits an advisory on a controller's surveillance terminal due to a continuous airspace violation and/or integrity degradation of the aircraft's reported position. The controller pulls out the information of this traffic and selects a position correction option which utilizes raw GNSS measurements received from the aircraft such as described in any of the embodiments above. Based on post processing of the raw GNSS measurements at the ground station,a corrected position for the aircraft is plotted back to the transition route. The controller now pays more attention monitoring this traffic in addition to the regular air traffic workload and initiates a satellite voice call to the aircraft. The aircraft pilot is able to confirm his position via a landmark or visual flight rules (VFR) checkpoints after received the call, and resets the aircraft's on-board tracking component. The indication on the controller's surveillance terminal returns back to normal after re-acquisition of the aircraft's position.

Accuracy and integrity index and position corrections are then available after completion of a raw GNSS measurement packet cycle (about one minute) indicating that the aircraft is actually clear of the prohibited area, avoiding the need for further investigation and possible interception of the aircraft.

Example Embodiments

[0029] Example 1 includes a method for aircraft surveillance, the method comprising: receiving a plurality of global navigation satellite system (GNSS) signals at an aircraft by an on-board GNSS receiver; sending to a ground station a transmission comprising current position reports that each includes a current position of the aircraft as determined by the on-board GNSS receiver; and sending to a ground station a transmission comprising raw GNSS measurement information based on samples of the plurality of GNSS signals as received at the aircraft.

[0030] Example 2 includes the method of example 1, wherein at the ground station the method further comprising: receiving the current position reports and the stream of GNSS raw measurement information; decoding the aircraft's position from the current position reports and providing the aircraft's position to a surveillance workstation; applying one or more GNSS satellite positioning error models to the GNSS raw measurement information to compute error calculations and quality determinations, wherein the error calculations and quality

determinations are correlated with at least a first current position report of the current position reports; and determining a corrected aircraft position based on the error calculations and quality determination.

[0031] Example 3 includes the method of example 2, further comprising: displaying on a surveillance workstation a symbol representing the aircraft based on the corrected aircraft position.

[0032] Example 4 includes the method of any of examples 1-3, wherein the current position reports and the raw GNSS measurement information are transmitted together over a plurality of packets within a datalink communication stream structured to transport both the current position reports and the raw GNSS measurement information.

[0033] Example 5 includes the method of example 4, further comprising transmitting the plurality of packets to the ground station over a satellite communication datalink.

[0034] Example 6 includes the method of any of examples 4-5, further comprising transmitting the plurality of packets to the ground station over an Automatic dependent surveillance- Broadcast (ADS-B) communication link.

[0035] Example 7 includes the method of any of examples 4-6, wherein the plurality of packets comprises a series of message units, where a first message unit comprises a first header that includes a first current position report, and wherein a first cycle of GNSS raw measurement information associated with the first current position report is distributed over a plurality of the series of message units.

[0036] Example 8 includes the method of example 7, wherein the series of message units comprise Iridium Message Units. [0037] Example 9 includes the method of any of examples 7-9, wherein the first message unit further comprises a second header associated with the GNSS raw measurement information, the second header including a timestamp associated with the first position report, a number and identification of GNSS satellites observed by the on-board GNSS receiver, and a number and identification of GNSS satellites used by the on-board GNSS receiver to derive the first current position report.

[0038] Example 10 includes the method of example 9, wherein the first cycle of GNSS raw measurement information includes raw pseudo range measurement samples captured by the onboard GNSS receiver from each of the plurality of GNSS signals observed by the on-board GNSS receiver.

[0039] Example 11 includes an aircraft surveillance system, the system comprising: an aircraft including at least one on-board global navigation satellite system (GNSS) receivers processing a plurality of navigation signals from a plurality of GNSS satellites, and further comprising at least one air-ground communication datalink, where the at least one GNSS receiver calculates current position reports that each includes a current position of the aircraft as determined by the at least one on-board GNSS receiver from the plurality of navigation signals; and wherein using the at least one air-ground communication datalink the at least one GNSS receiver transmits the current position reports and raw GNSS measurement information including samples from the plurality of navigation signals are transmitted together to a ground station as a series of message units.

[0040] Example 12 includes the system of any of examples 10, wherein a first message unit comprises a first header that includes a first current position report, and wherein a first cycle of raw GNSS measurement information associated with the first current position report is distributed over a plurality of the series of message units.

[0041] Example 13 includes an aircraft surveillance system, the system comprising: a processing system located in an air traffic surveillance ground station; one or more surveillance workstations coupled to the processing system, wherein at least one surveillance workstation includes a display unit providing a visual indication of aircraft position information; and at least one air-ground communication receiver coupled to the processing system and further communicatively coupled to a global navigation satellite system (GNSS) receiver on-board an aircraft; wherein the processing system receives current position reports from the GNSS receiver on-board the aircraft and causes the at least one surveillance workstation to generate the visual indication of aircraft position information based on the current position reports;

wherein the processing system further receives raw GNSS measurement information from the GNSS receiver on-board the aircraft, the raw GNSS measurement information including samples of raw pseudo range measurements captured by the GNSS receiver from navigation signals transmitted by a plurality of GNSS satellites observed by the GNSS receiver; wherein the processing system applies one or more GNSS satellite positioning error models to the raw GNSS measurement information to calculate correction data and the visual indication of aircraft position information at the first surveillance workstation is corrected based on the correction data.

[0042] Example 14 includes the system of example 13, wherein current position reports and the raw GNSS measurement information are received by the at least one air-ground communication receiver as a series of message units; wherein a first message unit comprises a first header that includes a first current position report, and wherein a first cycle of raw GNSS measurement information associated with the first current position report is distributed over a plurality of the series of message units.

[0043] Example 15 includes the system of any of examples 14, wherein the first message unit further comprises a second header associated with the GNSS raw measurement information, the second header including a timestamp associated with the first position report, a number and identification of the GNSS satellites observed by the on-board GNSS receiver, and a number and identification of GNSS satellites used by the on-board GNSS receiver to derive the first current position report.

[0044] Example 16 includes the system of any of examples 14-15, wherein the first cycle of raw GNSS measurement information includes raw pseudo range measurement samples captured by the GNSS receiver from each of a plurality of GNSS satellites observed by the GNSS receiver.

[0045] Example 17 includes the system of any of examples 13-16, where the at least one air- ground communication receiver communicatively is coupled to the GNSS receiver on-board the aircraft over a satellite communication datalink.

[0046] Example 18 includes the system of any of examples 13-17, where the at least one air- ground communication receiver communicatively is coupled to the GNSS receiver on-board the aircraft over an Automatic dependent surveillance-Broadcast (ADS-B) communication link. [0047] Example 19 includes the system of any of examples 13-18, wherein the one or more GNSS satellite positioning error models correct the current position reports for at least one of atmospheric errors, satellite ephemeris errors, and satellite clock drift.

[0048] Example 20 includes the system of any of examples 13-19, where the processing system applies one or more GNSS satellite positioning error models to the raw GNSS measurement information through an function hosted by a service provider off-site from the ground station.

[0049] In various alternative embodiments, any of the systems or methods described throughout this disclosure may be implemented on one or more on-board avionics or ground based computer systems comprising a processor executing code to realize the processes, models, modules, functions, managers, software layers and interfaces and other elements described with respect to Figures 1-4, said code stored on an on-board non-transient data storage device.

Therefore other embodiments of the present disclosure include program instructions resident on computer readable media which when implemented by such on-board avionics computer systems, enable them to implement the embodiments described herein. As used herein, the term "computer readable media" refers to tangible memory storage devices having non-transient physical forms. Such non-transient physical forms may include computer memory devices, such as but not limited to punch cards, magnetic disk or tape, any optical data storage system, flash read only memory (ROM), non-volatile ROM, programmable ROM (PROM), erasable- programmable ROM (E-PROM), random access memory (RAM), or any other form of permanent, semi-permanent, or temporary memory storage system or device having a physical, tangible form. Program instructions include, but are not limited to computer-executable instructions executed by computer system processors and hardware description languages such as Very High Speed Integrated Circuit (VHSIC) Hardware Description Language (VHDL).

[0050] Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.

Claims

CLAIMS claimed is:

A method for aircraft surveillance, the method comprising:

receiving a plurality of global navigation satellite system (GNSS) signals at an aircraft by an on-board GNSS receiver;

sending to a ground station a transmission comprising current position reports that each includes a current position of the aircraft as determined by the on-board GNSS receiver; and

sending to the ground station a transmission comprising raw GNSS measurement information based on samples of the plurality of GNSS signals as received at the aircraft.

The method of claim 1 , wherein at the ground station the method further comprising:

receiving the current position reports and the stream of GNSS raw measurement information;

decoding the aircraft's position from the current position reports and providing the aircraft's position to a surveillance workstation;

applying one or more GNSS satellite positioning error models to the GNSS raw measurement information to compute error calculations and quality determinations, wherein the error calculations and quality determinations are correlated with at least a first current position report of the current position reports; and

determining a corrected aircraft position based on the error calculations and quality determination.

The method of claim 2, further comprising:

displaying on a surveillance workstation a symbol representing the aircraft based on the corrected aircraft position.

The method of claim 1, wherein the current position reports and the raw GNSS measurement information are transmitted together over a plurality of packets within a datalink communication stream structured to transport both the current position reports and the raw GNSS measurement information.

5. The method of claim 4, further comprising transmitting the plurality of packets to the ground station over a satellite communication datalink.

6. The method of claim 4, further comprising transmitting the plurality of packets to the ground station over an Automatic dependent surveillance-Broadcast (ADS-B) communication link.

7. The method of claim 4, wherein the plurality of packets comprises a series of message units, where a first message unit comprises a first header that includes a first current position report, and wherein a first cycle of GNSS raw measurement information associated with the first current position report is distributed over a plurality of the series of message units.

8. The method of claim 7, wherein the series of message units comprise Iridium Message Units.

9. The method of claim 7,wherein the first message unit further comprises a second header associated with the GNSS raw measurement information, the second header including a timestamp associated with the first position report, a number and identification of GNSS satellites observed by the on-board GNSS receiver, and a number and identification of GNSS satellites used by the on-board GNSS receiver to derive the first current position report.

10. The method of claim 9, wherein the first cycle of GNSS raw measurement

information includes raw pseudo range measurement samples captured by the on-board GNSS receiver from each of the plurality of GNSS signals observed by the on-board GNSS receiver.

11. An aircraft surveillance system, the system comprising:

an aircraft including at least one on-board global navigation satellite system (GNSS) receiver processinga plurality of navigation signals from a plurality of GNSS satellites, and further comprising at least one air-ground communication datalink, where the at least one GNSS receiver calculates current position reports that each includes a current position of the aircraft as determined by the at least oneon-board GNSS receiver from the plurality of navigation signals; and

wherein using the at least one air-ground communication datalink the at least one GNSS receiver transmits the current position reports and raw GNSS measurement information including samples from the plurality of navigation signalsare transmitted together to a ground station as a series of message units.

12. The system of claim 10, wherein a first message unit comprises a first header that includes a first current position report, and wherein a first cycle of raw GNSS measurement information associated with the first current position report is distributed over a plurality of the series of message units.

13. An aircraft surveillance system, the system comprising:

a processing system located in an air traffic surveillance ground station; one or more surveillance workstations coupled to the processing system, wherein at least one surveillance workstation includes a display unit providing a visual indication of aircraft position information; and

at least one air-ground communication receiver coupled to the processing system and further communicatively coupled to a global navigation satellite system (GNSS) receiver on-board an aircraft;

wherein the processing system receives current position reports from the GNSS receiver on-board the aircraft and causes the at least one surveillance workstation to generate the visual indication of aircraft position information based on the current position reports;

wherein the processing system further receives raw GNSS measurement information from the GNSS receiver on-board the aircraft, the raw GNSS measurement information including samples of raw pseudo range measurements captured by the GNSS receiver from navigation signals transmitted by a plurality of GNSS satellites observed by the GNSS receiver; and

wherein the processing system applies one or more GNSS satellite positioning error models to the raw GNSS measurement information to calculate correction data and the visual indication of aircraft position information at the first surveillance workstationis corrected based on the correction data.

14. The system of claim 13, wherein current position reports and the raw GNSS measurement information are received by the at least one air-ground

communication receiver as a series of message units;

wherein a first message unit comprises a first header that includes a first current position report, and wherein a first cycle of raw GNSS measurement information associated with the first current position report is distributed over a plurality of the series of message units.

15. The system of claim 14, wherein the first message unit further comprises a second header associated with the GNSS raw measurement information, the second header including a timestamp associated with the first position report, a number and identification of the GNSS satellites observed by the on-board GNSS receiver, and a number and identification of GNSS satellites used by the on-board GNSS receiver to derive the first current position report.

16. The system of claim 14, wherein the first cycle of raw GNSS measurement information includes raw pseudo range measurement samples captured by the GNSS receiver from each of a plurality of GNSS satellites observed by the GNSS receiver.

17. The system of claim 13, where theat least one air-ground communication

receiver communicatively is coupled to the GNSS receiver on-board the aircraftover a satellite communication datalink.

18. The system of claim 13, where the at least one air-ground communication

receiver communicatively is coupled to the GNSS receiver on-board the aircraft over an Automatic dependent surveillance-Broadcast (ADS-B) communication link.

19. The system of claim 13, wherein the one or more GNSS satellite positioning error models correct the current position reports for at least one of atmospheric errors, satellite ephemeris errors, and satellite clock drift. The system of claim 13, where the processing system applies one or more GNSS satellite positioning error models to the raw GNSS measurement information through an function hosted by a service provider off-site from the ground station.