Airborne turbulence location system and methods

• US 7,592,955 B2
• Filed: 10/31/2006
• Issued: 09/22/2009
• Est. Priority Date: 10/31/2006
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Tillotson, Brian J., Singleton, Marissa
• Primary Examiner(s): PHAN, DAO LINDA
• Application Number:
  US11/555,176
• Publication Number:
  US 20090009393A1
• Time in Patent Office: 1,057 Days
• Field of Search: 342/357.02, 342/357.06, 342/378, 342/352, 701/3, 701/10, 701/213
• US Class Current: 342/378
• CPC Class Codes: G01S 13/955 mounted on satellite
• CPC Class Codes: G01W 1/02 Instruments for indicating weather conditions by measuring two or more variables, e.g. humidity, pressure, temperature, cloud cover or wind speed G01W1/10 takes precedence
• CPC Class Codes: G01W 2001/003 Clear air turbulence detection or forecasting, e.g. for aircrafts
• CPC Class Codes: Y02A 90/10 Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

A system and methods for calculating a range to a turbulent air region from an antenna platform is disclosed. The methods determine a correlation lag value corresponding to a time shift in receiving propagation of an interference pattern traveling along a path that is subject to the turbulent air region at antennas responsive to incident electromagnetic energy. Based upon the correlation lag value, the methods calculate the range to the turbulent air region from the antenna platform and issue a warning that indicate the range.

Claims

1. A method for calculating a range from a turbulent air region to a platform to determine the location of the turbulent air region with respect to said platform, the method comprising:

propagating an electromagnetic signal from a satellite through the turbulent air region;

determining a correlation lag value in propagation of an interference pattern comprising said electromagnetic signal to a first antenna and to a second antenna on said platform, wherein the correlation lag value corresponds to a time shift in receiving propagation of said interference pattern with respect to said first and second antennas, said time shift caused by the turbulent air region, and wherein the turbulent air region is in a path of said electromagnetic signal sent from said satellite to the platform; and

calculating the range based upon the correlation lag value.

2. A method according to claim 1, wherein determining the correlation lag value further comprises:

sampling a first series of signal amplitudes, corresponding to the interference pattern, at the first antenna at a sampling interval;

sampling a second series of signal amplitudes, corresponding to the interference pattern, at the second antenna at the sampling interval;

calculating temporal correlation coefficients between the first and the second series of signal amplitudes;

calculating correlation lag values corresponding to the temporal correlation coefficients; and

selecting the correlation lag value corresponding to a highest value of the temporal correlation coefficients.

3. A method according to claim 1, further comprising issuing a warning indicating the range.

4. A method according to claim 1, wherein:

the turbulent air region is a stationary turbulent air region;

the platform is a stationary platform; and

calculating the range is based on the relationship

$R_t=-R_s<br><br>\left[\frac{L_0}{V_s<br><br>\mathrm{\Delta <br><br>}<br><br><br><br>t-L_0}\right],$

where R_t is the range from the stationary turbulent air region to the platform, R_s is the distance between the stationary platform and the satellite, L₀ is horizontal separation between the first antenna and the second antenna, V_s is horizontal velocity of the satellite, and Δ

t is the correlation lag.

5. A method according to claim 1, wherein:

the turbulent air region is a stationary turbulent air region;

the platform is a mobile platform; and

calculating the range is based on the relationship

$R_t=-R_s<br><br>\left\{\frac{\frac{L_0}{\mathrm{\Delta <br><br>}<br><br><br><br>t}+V_a}{V_s-\left(\frac{L_0}{\mathrm{\Delta <br><br>}<br><br><br><br>t}+V_a\right)}\right\},$

where R_t is the range from the stationary turbulent air region to the mobile platform, R_s is the distance between the mobile platform and the satellite, L₀ is horizontal separation between the first antenna and the second antenna, Δ

t is the correlation lag, V_a is horizontal velocity of the mobile platform, and V_s is horizontal velocity of the satellite.

6. A method according to claim 1, wherein:

the turbulent air region is a mobile turbulent air region;

the platform is a mobile platform; and

calculating the range is based on the relationship

$R_t=-R_s<br><br>\left\{\frac{V_t+\frac{L_0}{\mathrm{\Delta <br><br>}<br><br><br><br>t}+V_a}{V_s-\frac{L_0}{\mathrm{\Delta <br><br>}<br><br><br><br>t}-V_a}\right\},$

where R_t is the range from the mobile turbulent air region to the mobile platform, R_s is distance between the mobile platform to the satellite, V_t is horizontal velocity of the turbulence, L₀ is horizontal separation between the first antenna and the second antenna, at is the correlation lag, V_s is horizontal velocity of the satellite, and V_a is horizontal velocity of the mobile platform.

7. A method according to claim 1, wherein:

the turbulent air region is a stationary turbulent air region;

the platform is a stationary platform; and

calculating the range is based on the relationship

$R_t=-R_s<br><br>\frac{H_0}{V_{\mathrm{sz}}<br><br>\mathrm{\Delta <br><br>}<br><br><br><br>t-H_0},$

where R_t is the range from the stationary turbulent air region to the stationary platform, R_s is the distance between the stationary platform and the satellite, H₀ is vertical separation between the first antenna and the second antenna, V_sz is vertical velocity of the satellite, and Δ

t is the correlation lag.

8. A method according to claim 1, wherein:

the turbulent air region is a stationary turbulent air region;

the platform is a mobile platform; and

calculating the range is based on the relationship

$R_t=-R_s<br><br>\left\{\frac{\frac{H_0}{\mathrm{\Delta <br><br>}<br><br><br><br>t}+V_{\mathrm{az}}}{V_{\mathrm{sz}}-\left(\frac{H_0}{\mathrm{\Delta <br><br>}<br><br><br><br>t}-V_{\mathrm{az}}\right)}\right\},$

where R_t is the range from the stationary turbulent air region to the mobile platform, R_s is the distance between the mobile platform and the satellite, H₀ is vertical separation between the first antenna and the second antenna, Δ

t is the correlation lag, V_az is vertical velocity of the mobile platform, and V_sz is vertical velocity of the satellite.

9. A method according to claim 1, wherein:

the turbulent air region is a mobile turbulent air region;

the platform is a mobile platform; and

calculating the range is based on the relationship

$R_t=-R_s<br><br>\left\{\frac{V_{\mathrm{tz}}+\frac{H_0}{\mathrm{\Delta <br><br>}<br><br><br><br>t}+V_{\mathrm{az}}}{V_{\mathrm{sz}}-\frac{H_0}{\mathrm{\Delta <br><br>}<br><br><br><br>t}-V_{\mathrm{az}}}\right\},$

where R_t is the range from the mobile turbulent air region to the mobile platform, R_s is the distance between the mobile platform and the satellite, V_tz is vertical velocity of the mobile turbulent air region, H₀ is vertical separation between the first antenna and the second antenna, Δ

t is the correlation lag, V_tz is vertical velocity of the mobile turbulent air region, V_az is vertical velocity of the mobile platform, and V_sz is vertical velocity of the satellite.

10. A method according to claim 1, wherein:

the turbulent air region is a mobile turbulent air region;

the platform is a mobile platform; and

the calculating step is based on the relationship

$R_t=-R_s<br><br>\left\{\frac{V_{\mathrm{t\_el}}+\frac{H_{0<br><br>\mathrm{\_el}}}{\mathrm{\Delta <br><br>}<br><br><br><br>t}+V_{\mathrm{a\_el}}}{V_{\mathrm{s\_el}}-\frac{H_{0<br><br>\mathrm{\_el}}}{\mathrm{\Delta <br><br>}<br><br><br><br>t}-V_{\mathrm{a\_el}}}\right\},$

where R_t is the range from the mobile turbulent air region to the platform, R_t being corrected for platform-to-satellite line of sight, R_s is the distance between the mobile platform and the satellite, V<sub>t—

el</sub> is vertical velocity of the mobile turbulent air region projected onto an elevation unit vector, H<sub>0—

el</sub> is vertical separation between the first antenna and the second antenna projected onto the elevation unit vector, Δ

t is the correlation lag, V<sub>a—

el</sub> is vertical velocity of the mobile platform projected onto the elevation unit vector, and V<sub>s—

el</sub> is vertical velocity of the satellite projected onto the elevation unit vector.

11. A method according to claim 1, further comprising obtaining data for calculating the range based upon the correlation lag value, the data including:

a horizontal velocity of the platform;

a horizontal velocity of a satellite;

a horizontal velocity of the turbulent air region;

a horizontal separation between the first antenna and the second antenna;

a distance of the platform from the satellite;

a vertical velocity of the platform;

a vertical velocity of the satellite;

a vertical velocity of the turbulent air region; and

a vertical separation between the first antenna and the second antenna.

12. A method for calculating a range from a turbulent air region to a platform to determine the location of said turbulent air region with respect to said platform, the method comprising:

propagating an electromagnetic signal from a satellite through said turbulent air region;

sampling a first series of said electromagnetic signal amplitudes, corresponding to an interference pattern, at a first antenna and at a sampling interval;

sampling a second series of said electromagnetic signal amplitudes corresponding to the interference pattern, at a second antenna and at the sampling interval;

calculating temporal correlation coefficients between the first series and the second series of signal amplitudes;

calculating correlation lag values corresponding to the calculated temporal correlation coefficients;

selecting the correlation lag value corresponding to the highest value of the calculated temporal correlation coefficients, wherein the correlation lag value corresponds to a time shift, caused by the turbulent air region, in receiving the interference pattern at the first antenna and the second antenna; and

calculating the range based upon the correlation lag value.

13. A method according to claim 12, further comprising storing:

the first series of signal amplitudes and the second series of signal amplitudes;

the calculated temporal correlation coefficients;

the correlation lag values; and

the sampling interval.

14. A method according to claim 12, wherein the highest value of the calculated temporal correlation coefficients is at a peak of a temporal correlation curve.

15. A method according to claim 14, further comprising determining thickness of the turbulent air region based upon the peak of the temporal correlation curve.

16. A method according to claim 15, further comprising:

indicating a thick turbulent air region if the peak of the temporal correlation curve is relatively wide; and

indicating a thin turbulent air region if the peak of the temporal correlation curve is relatively narrow.

17. A system for calculating a range from a turbulent air region to a platform to determine the location of said turbulent air region with respect to said platform, the system comprising:

a plurality of antennas, each responsive to incident electromagnetic energy propagated through the turbulent air region to produce a received interference pattern, wherein the electromagnetic energy travels along a path that is subject to the turbulent air region;

a receiver coupled to the antennas and configured to measure properties of the received interference pattern; and

a processing logic element coupled to the receiver and configured to;

determine a correlation lag value, wherein the correlation lag value corresponds to a time shift in, receiving propagation, caused by the turbulent air region, of said interference pattern with respect to a first antenna and a second antenna on the platform;

calculate the range based upon the correlation lag value.

18. A system according to claim 17, wherein the processing logic element is further configured to:

sample a first series of signal amplitudes, corresponding to the received interference pattern, at the first antenna and at a sampling interval; and

sample a second series of signal amplitudes, corresponding to the received interference pattern, at the second antenna and at the sampling interval.

19. A system according to claim 18, further comprising a correlator module coupled to the processing logic element and configured to:

calculate temporal correlation coefficients between the first and the second series of signal amplitudes;

calculate correlation lag values corresponding to the calculated temporal correlation coefficients; and

select the correlation lag value corresponding to a highest value of the calculated temporal correlation coefficient.

20. A system according to claim 19, further comprising a memory module coupled to the processing logic element and configured to store:

the first and the second series of signal amplitudes;

the calculated temporal correlation coefficients;

the correlation lag values; and

the sampling interval.

21. A system according to claim 17, wherein the antennas are separated vertically along the height of the platform.

22. A system according to claim 17, wherein the antennas are separated horizontally along the length of the platform.

23. A system according to claim 17, wherein the receiver comprises a satellite receiver.

24. A system according to claim 17, further comprising a communication network coupled to the processing logic element and configured to issue a warning that indicates the range.

25. A system according to claim 17, wherein the processing logic element is further configured to:

sample a first series of signal phases, corresponding to the received interference pattern, at the first antenna and at a sampling interval; and

sample a second series of signal phases, corresponding to the received interference pattern, at the second antenna and at the sampling interval.

26. A system according to claim 19, wherein the correlator module is further configured to:

calculate temporal correlation coefficients between a first and a second series of signal phases;

calculate correlation lag values corresponding to the calculated temporal correlation coefficients; and

select the correlation lag value corresponding to a highest value of the calculated temporal correlation coefficient.

27. A method for calculating a range from a turbulent air region to a platform to determine the location of said turbulent air region with respect to said platform, the method comprising:

propagating an electromagnetic signal from a satellite through said turbulent air region;

sampling a first series of said electromagnetic signal phases, corresponding to an interference pattern, at a first antenna and at a sampling interval;

sampling a second series of said electromagnetic signal phases, corresponding to the interference pattern, at a second antenna and at the sampling interval;

calculating temporal correlation coefficients between the first series and the second series of signal phases;

calculating correlation lag values corresponding to the calculated temporal correlation coefficients;

selecting the correlation lag value corresponding to the highest value of the calculated temporal correlation coefficients, wherein the correlation lag value corresponds to a time shift, caused by the turbulent air region, in receiving the interference pattern at the first antenna and the second antenna; and

calculating the range based upon the correlation lag value.