US-12625278-B2 - Systems and methods for improving GNSS-based navigation

Abstract

A method for global navigation satellite system (GNSS)-based navigation may include retrieving terrain data for a geographical region and satellite orbit data for a GNSS comprising a plurality of satellites. Then, for of a plurality of time steps in a time period and for each of a plurality of lateral positions in the geographic region, a minimum height at which each satellite is visible from the lateral position at the time step may be determined. Unique combinations of satellites visible from the lateral position at the time step may be identified and error objects indicating GNSS performance quality corresponding to the unique combination of satellites may be generated. Performance quality information may be produced based on the one or more unique combinations of satellites and the respective one or more error objects. At least one aircraft may be operated based on this performance quality information.

Inventors

• Arthur K. SCHOLZ
• Emily V. Bates
• Kenneth William Schmitt
• Evan Tyler Dill
• Julian Gutierrez

Assignees

• THE MITRE CORPORATION
• NASA Langley Research Center

Dates

Publication Date

20260512

Application Date

20230915

Claims (20)

1. 1 . A method for global navigation satellite system (GNSS)-based navigation, the method comprising: retrieving, from one or more databases: terrain data for a geographical region comprising, for each of a plurality of lateral positions in the geographic region, elevation values associated with a height of the terrain at the lateral position, and satellite orbit data for a GNSS comprising a plurality of satellites, for each time step of a plurality of time steps in a time period and for each lateral position of the plurality of lateral positions in the geographic region: determining, for each satellite of the plurality of satellites in the GNSS, a minimum height at which the satellite is visible from the lateral position at the time step, determining one or more unique combinations of satellites visible from the lateral position at the time step based on the minimum heights at which each satellite is visible from the lateral position, and generating, for each of the one or more unique combinations of satellites, one or more error objects indicating GNSS performance quality corresponding to the unique combination of satellites; determining GNSS performance quality information based on the one or more unique combinations of satellites and the respective one or more error objects; and operating at least one aircraft based on the GNSS performance quality information.
2. 2 . The method of claim 1 , comprising receiving information indicating the geographical region and the time period.
3. 3 . The method of claim 1 , wherein the geographical region corresponds to a region in which the at least one aircraft will be operating and wherein the time period corresponds to a time frame in which the at least one aircraft will be operating.
4. 4 . The method of claim 1 , comprising, for each satellite of the plurality of satellites, propagating a trajectory of the satellite during the time period.
5. 5 . The method of claim 1 , wherein determining, for a satellite of the plurality of satellites in the GNSS, the minimum height at which the satellite is visible from a lateral position of the plurality of lateral positions at a time step of the plurality of time steps comprises: determining, at one or more locations along an azimuthal vector between the lateral position and the satellite, a minimum altitude required for line-of-sight to the satellite from the lateral position without obstruction by terrain at each azimuthal vector location.
6. 6 . The method of claim 1 , wherein determining, for a satellite of the plurality of satellites in the GNSS, the minimum height at which the satellite is visible from a lateral position of the plurality of lateral positions at a time step of the plurality of time steps comprises: iterating along a shadow line that starts at a height point corresponding to the lateral position and is directed away from the satellite; and at one or more lateral locations corresponding to one or more points along the shadow line, determining a minimum altitude required for the satellite to be visible based on a height of the shadow line at said point.
7. 7 . The method of claim 1 , wherein determining the one or more unique combinations of visible satellites at a time step of the plurality of time steps at a lateral position of the plurality of lateral locations comprises determining, based on the minimum heights at which each satellite is visible from the lateral position at the time step, for each of a plurality of height points located at the lateral position, a combination of satellites of the plurality of satellites that are visible at the height point.
8. 8 . The method of claim 1 , wherein the one or more error objects comprises a dilution of precision value.
9. 9 . The method of claim 1 , wherein the one or more error values comprises a covariance matrix.
10. 10 . The method of claim 1 , wherein the minimum heights at which each satellite is visible at each lateral position are determined simultaneously for each time step using a GPU.
11. 11 . The method of claim 1 , wherein the one or more unique combinations of visible satellites at each lateral position are determined simultaneously for each time step using a GPU.
12. 12 . The method of claim 1 , wherein outputting GNSS performance quality information comprises generating and displaying a graphical representation of GNSS performance quality in the geographical region at each time step.
13. 13 . The method of claim 1 , wherein operating the at least one aircraft comprises generating a flight plan for the one or more aircraft based on the GNSS performance quality information.
14. 14 . The method of claim 13 , comprising controlling the at least one aircraft based on the flight plan.
15. 15 . The method of claim 1 , wherein an aircraft of the at least one aircraft is an unmanned aerial vehicle (UAV).
16. 16 . The method of claim 1 , wherein the terrain data comprises one or more digital surface maps.
17. 17 . The method of claim 1 , wherein the orbit data comprises GNSS almanac data.
18. 18 . The method of claim 1 , wherein the geographical region comprises an urban environment.
19. 19 . The method of claim 1 , wherein the GNSS is the Global Positioning System (GPS).
20. 20 . A system for global navigation satellite system (GNSS)-based navigation, the system comprising: at least one aircraft; and a computer system comprising one or more processors, wherein the one or processors are configured to: retrieve, from one or more databases: terrain data for a geographical region comprising, for each of a plurality of lateral positions in the geographic region, elevation values associated with a height of the terrain at the lateral position, and satellite orbit data for a GNSS comprising a plurality of satellites, for each time step of a plurality of time steps in a time period and for each lateral position of the plurality of lateral positions in the geographic region: determine, for each satellite of the plurality of satellites in the GNSS, a minimum height at which the satellite is visible from the lateral position at the time step, determine one or more unique combinations of satellites visible from the lateral position at the time step based on the minimum heights at which each satellite is visible from the lateral position, and generate, for each of the one or more unique combinations of satellites, one or more error objects indicating GNSS performance quality corresponding to the unique combination of satellites; determine GNSS performance quality information based on the one or more unique combinations of satellites and the respective one or more error objects; and operate the at least one aircraft based on the GNSS performance quality information.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 63/407,273, filed Sep. 16, 2022, the entire contents of which is incorporated herein by reference. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT This invention was made with Government support under contract number 80NSSC21P2774 awarded by NASA. The Government has certain rights in the invention. FIELD The present disclosure relates generally to computational techniques for improving GNSS-based navigation, particularly in obstacle-dense environments such as cities. BACKGROUND Advanced Air Mobility (AAM) is an emerging air transport system that aims to use aircraft to transport people and property in various environments. AAM applications currently in development include the use of unmanned aerial vehicles (UAVs) for package delivery as well as the use of (potentially autonomous) vertical-takeoff-and-landing (VTOL) vehicles as on-demand, airborne taxis. Urban Air Mobility (UAM), a subset of AAM, focuses specifically on the utilization of highly automated aircraft at low altitudes in urban areas and has been the subject of increasing volumes of investment and research. A major predicted advantage of UAM solutions is a considerable reduction in travel time, both for those traveling by car—since increased use of aircraft for intra-city transportation will reduce roadway congestion—as well as for individuals and cargo traveling by aircraft, since aircraft can take more direct routes between locations than motor vehicles. Additionally, the electric infrastructure in urban environments may allow for the use of electric and hybrid-electric aircraft; UAM may, as a result, urban pollution may be significantly mitigated. AAM technologies rely on global navigation satellite systems (GNSS) for positioning, navigation, and timing information. However, communication between an aircraft and a satellite system such as the Global Positioning System (GPS) frequently becomes problematic when the aircraft is in a complex environment such as a city. Obstacles such as buildings and trees may attenuate satellite signals and prevent the aircraft from receiving critical navigation data, increasing the risk of crashes, particularly if the aircraft is unmanned or highly automated. SUMMARY Provided are systems and methods for predicting GNSS performance in order to improve GNSS-based navigation. A combination of satellite orbit data and elevation data may be used to predict satellite visibility at varying locations within a given geographic region over a given period of time. These predictions may be used to supplement flight planning processes by assisting in the identification of safe, GNSS-visible routes between locations. Thus, the provided systems and methods may be employed in conjunction with AAM/UAM navigation systems to protect (particularly unmanned) aircraft from hazards and increase the likelihood that satellites in a GNSS remain visible to aircraft throughout flight. A method for global navigation satellite system (GNSS)-based navigation may include retrieving, from one or more databases, terrain data for a geographical region and satellite orbit data for a GNSS comprising a plurality of satellites. The terrain data may comprise, for each of a plurality of lateral positions in the geographic region, elevation values associated with a height of the terrain at the lateral position. Then, for each time step of a plurality of time steps in a time period and for each lateral position of the plurality of lateral positions in the geographic region, the method may involve determining, for each satellite of the plurality of satellites in the GNSS, a minimum height at which the satellite is visible from the lateral position at the time step, determining one or more unique combinations of satellites visible from the lateral position at the time step based on the minimum heights at which each satellite is visible from the lateral position, and generating, for each of the one or more unique combinations of satellites, one or more error objects indicating GNSS performance quality corresponding to the unique combination of satellites. GNSS performance quality information may then be generated based on the one or more unique combinations of satellites and the respective one or more error objects. At least one aircraft may be operated based on the GNSS performance quality information. Information indicating the geographical region and the time period may be received, e.g., from a user. The geographical region may correspond to a region in which the at least one aircraft will be operating. Similarly, the time period may correspond to a time frame in which the at least one aircraft will be operating. The terrain data comprises one or more digital surface maps and the orbit data may comprise GNSS almanac data. The GNSS may be the Global Positioning System (GPS). An aircraft of the at least one aircraft may be an un