Optical air data systems and methods
An optical air data system for an air vehicle includes a LIDAR module and a data processing module. The LIDAR module is configured to emit at least three laser beams, not all located in a common plane, and perform LIDAR measurements of a backscattered component of each of the laser beams. The data processing module includes a processor and machine-readable instructions that, when executed by the processor, processes the LIDAR measurements to determine at least one optically-based air data parameter. The overlap between the laser beams and one or more fields of view of the LIDAR module may be within two meters from the LIDAR module to determine the at least one optically-based air data parameter at short range from the air vehicle.
1. An optical air data system for an air vehicle, comprising:
a LIDAR module configured to emit at least three laser beams, not all located in a common plane, and perform LIDAR measurements of a backscattered component of each of the laser beams; and
a data processing module including a processor and machine-readable instructions that, when executed by the processor, processes the LIDAR measurements to determine at least one optically-based air data parameter;
wherein, for each of the laser beams, the LIDAR module includes a photodetector having a field of view that overlaps with the respective laser beam within two meters from the LIDAR module;
where the machine-readable instructions are configured to, when executed by the processor, perform steps of:
evaluating quality of the LIDAR measurements to select LIDAR measurements of acceptable quality; and
determining the at least one optically-based air data parameter based only upon the LIDAR measurements of acceptable quality;
the machine-readable instructions being configured to, when executed by the processor and in the step of determining, determine:
when LIDAR measurements of acceptable quality are available for each of more than three laser beams, not all located in a common plane, a full vector speed of the air vehicle; and
when LIDAR measurements of acceptable quality are available for only one or two of the laser beams, an estimate of waterline velocity of the air vehicle, the estimate of waterline velocity from velocity measured by the one or two remaining beams and known geometry of those beams.
2. The optical air data system of claim 1 , the machine-readable instructions being configured to, when executed by the processor and in the step of determining, determine an airspeed of the air vehicle, atmospheric temperature, and atmospheric pressure.
3. The optical air data system of claim 2 , the at least three laser beams including four laser beams.
4. The optical air data system of claim 3 , the machine-readable instructions being configured to, when executed by the processor, perform steps of:
evaluating quality of LIDAR measurements based upon the backscattered components to select LIDAR measurements of acceptable quality; and
when the LIDAR measurements are of acceptable quality for each of the four laser beams, calculating full vector speed of air vehicle based upon the LIDAR measurements of all of the four laser beams.
5. The optical air data system of claim 1 , the machine-readable instructions being configured to, when executed by the processor, fit at least one optically-based air data parameter to the LIDAR measurements to determine the at least one optically-based air data parameter.
6. The optical air data system of claim 1 , the LIDAR module being configured to obtain, for each of the laser beams, first LIDAR measurements based upon both aerosol scattering and second LIDAR measurements based upon molecular scattering.
7. The optical air data system of claim 6 , the machine-readable instructions being configured to, when executed by the processor, perform steps of:
determining two estimates of the at least one optically-based air data parameter respectively based upon the first LIDAR measurements and the second LIDAR measurements; and
evaluating the two estimates to refine the at least one optically-based air data parameter.
8. The optical air data system of claim 7 , the machine-readable instructions being configured to, when executed by the processor, perform steps of:
generating two estimates of the full vector speed respectively based upon the first LIDAR measurements and the second LIDAR measurements; and
determining a refined full vector speed based upon the two estimates.
9. The optical air data system of claim 6 , the machine-readable instructions being configured to, when executed by the processor, determine (a) full vector speed of the air vehicle, (b) atmospheric temperature at the air vehicle based upon the molecular scattering, and (c) atmospheric pressure at the air vehicle based upon the molecular scattering.
10. The optical air data system of claim 1 , the machine-readable instructions being configured to, when executed by the processor and based upon the LIDAR measurements, perform steps of:
determining full vector speed of the air vehicle, atmospheric temperature, and atmospheric pressure; and
evaluating accuracy of one of the full vector speed, the atmospheric temperature, and the atmospheric pressure based upon another one of the plurality of air data parameters.
11. The optical air data system of claim 1 , being implemented in an air vehicle that further includes:
a mechanical sensor system for generating at least one mechanical air data parameter; and
a flight control system for at least partly controlling operation of the air vehicle, the flight control system including a voting module for selecting at least one final air data parameter from the at least one optically-based air data parameter and the at least one mechanical air data parameter to perform said controlling.
12. A method for determining air data parameters for an air vehicle, comprising:
obtaining LIDAR measurements from at least three laser beams not located in a common plane; and
processing the LIDAR measurements to determine at least one optically-based air data parameter;
the step of processing comprising:
evaluating quality of the LIDAR measurements to select LIDAR measurements of acceptable quality; and
generating the at least one optically-based air data parameter based only upon the LIDAR measurements of acceptable quality; and
when LIDAR measurements of acceptable quality are available for each of at least three laser beams, not all located in a common plane, determining a full vector speed of the air vehicle; and
when LIDAR measurements of acceptable quality are available for only one or two of the laser beams, estimating waterline velocity of the air vehicle, the estimate of waterline velocity from velocity measured by the one or two remaining beams and known geometry of the one or two remaining beams.
13. The method of claim 12 , the step of obtaining comprising obtaining the LIDAR measurements from scattering events within two meters from the air vehicle to determine the at least one optically-based air data parameter within two meters from the air vehicle.
14. The method of claim 12 , the step of processing comprising determining (a) atmospheric pressure and temperature from LIDAR measurements based upon molecular scattering and (b) full vector speed from one or both of LIDAR measurements based upon aerosol scattering and LIDAR measurements based upon molecular scattering.
15. The method of claim 14 , the step of determining comprising determining the full vector speed from the LIDAR measurements based upon molecular scattering at least at altitudes with insufficient aerosol concentration for the LIDAR measurements based upon aerosol scattering to provide valid air data parameters.
16. The method of claim 12 , further comprising:
obtaining at least one mechanical air data parameter; and
evaluating the at least one optically-based air data parameter and the at least one mechanical air data parameter to determine at least one final air data parameter.
17. The method of claim 16 , the step of evaluating comprising:
identifying at least one atmospheric property based upon the at least one optically-based air data parameter; and
evaluating validity of the at least one optically-based air data parameter and the at least one mechanical air data parameter based upon the at least one atmospheric property.
18. The method of claim 17 , further comprising discarding at least one mechanical air data parameter based upon the at least one atmospheric property.
19. The method of claim 17 , the at least one atmospheric property including at least one of an aerosol mass density and an aerosol concentration.
20. The method of claim 12 , the step of estimating waterline velocity comprising assuming that the air vehicle is predominantly traveling in axial direction.
21. The method of claim 12 , the step of obtaining comprising obtaining LIDAR measurements from four laser beams not all located in a common plane, for improved redundancy.
22. The method of claim 21 , the step of determining comprising:
evaluating quality of the LIDAR measurements to select LIDAR measurements of acceptable quality; and
when the LIDAR measurements are of acceptable quality for each of the four laser beams, calculating full vector speed of air vehicle based upon the LIDAR measurements of all of the four laser beams.
23. The method of claim 12 , the step of processing comprising fitting at least one optically-based air data parameter to the LIDAR measurements to determine the at least one optically-based air data parameter.