Passive polarimetric microwave radiometer for detecting aircraft icing conditions

• US 6,377,207 B1
• Filed: 09/27/2000
• Issued: 04/23/2002
• Est. Priority Date: 09/27/2000
• Status: Expired due to Fees

• Current Assignee: Albin J. Gasiewski, Fredrick S. Solheim
• Original Assignee: Albin J. Gasiewski, Fredrick S. Solheim
• Inventors: Solheim, Fredrick S., Gasiewski, Albin J.
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US09/671,665
• Time in Patent Office: 573 Days
• Field of Search: 342/26, 342/175, 342/192-197, 342/351, 731/701.6, 731/701.7, 731/701.8, 731/702.6, 731/702.7, 324/640, 324/637-639, 324/641-646
• US Class Current: 342/351
• 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

Abstract

The passive polarimetric microwave radiometer is a simple and low cost radiometric icing detection system that operates over a suitable set of frequency bands in the millimeter wave region of the spectrum to provide useful signatures for detecting aircraft icing conditions. This basic passive polarimetric microwave radiometer observes along a single line of sight and consists of a dual polarization dual frequency radiometer that is pointed in the direction of interest, such as the projected flight path, and operates at a frequency which is sensitive to the polarizing effects of hydrometeors. The passive polarimetric microwave radiometer could also observe in a horizontal plane around the aircraft or ground station and include both vertical and horizontal scanning capability. By utilizing polarimetric observations near two widely separated lines at frequencies with matching attenuations (and therefore matching range sensitivities) a stronger spectral signal providing information on hydrometeor habit (size and shape) can be obtained. Such additional information is especially important to characterize volumes containing mixed phases of liquid water and ice (wetted ice crystals, or interspersed ice and liquid hydrometeors) and for determining hydrometeor shapes and size distributions. The radiometric signals from the antenna can be downconverted with local oscillators centered at around 60 GHz, 118.75 GHz, and/or 183 GHz, and use filter banks to separate out baseband sidebands into a plurality of frequency intervals at various frequency separations from the local oscillator frequency, thus obtaining radiometric sensitivities with a variety of differing weighting functions, and therefore range sensitivities. Alternatively, direct detection of signals passing through high frequency filters at desired frequencies can be utilized.

Claims

1. A passive polarimetric microwave radiometer, located in an aircraft or at a suitably high location near an aircraft landing site, for detection of aircraft icing conditions, comprising:

means for monitoring a region of space located in the field of view of said radiometer to detect a presence of at least one predetermined radio frequency of brightness temperature signal;

means for calculating a spectral signature intensity among said at least one predetermined radio frequency, including at least one of;

signal magnitude, magnitude of signal in at least two orthogonal polarizations, signal attenuation; and

means for determining a presence of aircraft icing conditions based upon at least one of;

determined spectral and polarization signature differences.

2. The passive polarimetric microwave radiometer of claim 1 further comprising:

means for generating an alert indication from the class of indications including;

an icing probability-range indicator, cloud liquid water maps, audible warnings of imminent icing conditions.

3. The passive polarimetric microwave radiometer of claim 1 wherein said means for monitoring comprises:

means for scanning in at least one of;

a vertical direction through a predetermined angular range, a horizontal direction through a predetermined angular range, and in vertical and horizontal directions through a predetermined angular range for each of said vertical and horizontal directions.

4. The passive polarimetric microwave radiometer of claim 3 wherein said means for scanning comprises:

focal plane array means spanning at least one of;

the vertical and horizontal angles desired.

5. The passive polarimetric microwave radiometer of claim 3 wherein said means for scanning comprises:

a plurality of antenna means spanning the vertical and/or horizontal angles desired.

6. The passive polarimetric microwave radiometer of claim 1 wherein said means for monitoring comprises:

a plurality of polarimetric radiometers, each of which operates to monitor a signal of at least one of;

a predetermined elevation angle, a predetermined azimuth angle, a predetermined polarization, and a predetermined frequency.

7. The passive polarimetric microwave radiometer of claim 1 wherein said means for monitoring comprises:

a tunable polarimetric radiometer, which operates to monitor signals of a predetermined frequencies.

8. The passive polarimetric microwave radiometer of claim 1 wherein said means for calculating a spectral signature intensity comprises:

means for observing a spectral signature difference in at least two orthogonal polarizations among said at least one predetermined radio frequency.

9. The passive polarimetric microwave radiometer of claim 1 wherein said means for calculating a spectral signature intensity comprises:

means for observing a spectral signature difference in at least two orthogonal polarizations among each of a plurality of said at least one predetermined radio frequency.

10. The passive polarimetric microwave radiometer of claim 1 wherein said means for determining comprises:

means for calculating range by observing at least one of;

characteristic features utilizing the variation in attenuation, and therefore in distance, of the atmospheric spectrum, the change in intensity of signal from characteristic features with distance traveled, and therefore the distance to said features, and the rate of change of angular size of characteristic features in the radiometer observations as the airborne platform moves toward or away from these features.

11. The passive polarimetric microwave radiometer of claim 1 wherein said means for determining comprises:

means for calculating range by using tomographic methods on intersecting vectors of observations obtained by scanning the field of view of the radiometer in at least one of;

the horizontal plane, the vertical plane, and a combination of both said horizontal plane and said vertical plane.

12. The passive polarimetric microwave radiometer of claim 1 wherein said means for determining comprises:

means for identifying abrupt changes in the time series of the spatial distribution of said determined spectral signature difference to identify regions of electrification and potential icing and high turbulence conditions.

13. A method of operating a passive polarimetric microwave radiometer, located in an aircraft or at a suitably high location near an aircraft landing site, for detection of aircraft icing conditions, comprising the steps of:

monitoring a region of space located in the field of view of said radiometer to detect a presence of at least one predetermined radio frequency of brightness temperature signal;

calculating a spectral signature intensity among said at least one predetermined radio frequency, including at least one of;

signal magnitude, magnitude of signal in at least two orthogonal polarizations, signal attenuation; and

determining a presence of aircraft icing conditions based upon at least one of;

determined spectral and polarization signature differences.

14. The method of operating a passive polarimetric microwave radiometer of claim 13 further comprising the step of:

generating an alert indication from the class of indications including;

an icing probability-range indicator, cloud liquid water maps, audible warnings of imminent icing conditions.

15. The method of operating a passive polarimetric microwave radiometer of claim 13 wherein said step of monitoring comprises:

scanning in at least one of;

a vertical direction through a predetermined angular range, a horizontal direction through a predetermined angular range, and in vertical and horizontal directions through a predetermined angular range for each of said vertical and horizontal directions.

16. The method of operating a passive polarimetric microwave radiometer of claim 15 wherein said step of scanning comprises:

operating a focal plane array spanning at least one of;

the vertical and horizontal angles desired.

17. The method of operating a passive polarimetric microwave radiometer of claim 15 wherein said step of scanning comprises:

operating a plurality of antenna means spanning the vertical and/or horizontal angles desired.

18. The method of operating a passive polarimetric microwave radiometer of claim 13 wherein said step of monitoring comprises:

operating a plurality of polarimetric radiometers, each of which operates to monitor a signal of at least one of;

a predetermined elevation angle, a predetermined azimuth angle, a predetermined polarization, and a predetermined frequency.

19. The method of operating a passive polarimetric microwave radiometer of claim 13 wherein said step of monitoring comprises:

operating a tunable polarimetric radiometer, which operates to monitor signals of a predetermined frequencies.

20. The method of operating a passive polarimetric microwave radiometer of claim 13 wherein said step of calculating a spectral signature intensity comprises:

observing a spectral signature difference in at least two orthogonal polarizations among said at least one predetermined radio frequency.

21. The method of operating a passive polarimetric microwave radiometer of claim 13 wherein said step of calculating a spectral signature intensity comprises:

observing a spectral signature difference in at least two orthogonal polarizations among each of a plurality of said at least one predetermined radio frequency.

22. The method of operating a passive polarimetric microwave radiometer of claim 13 wherein said step of determining comprises:

calculating range by observing at least one of;

characteristic features utilizing the variation in attenuation, and therefore in distance, of the atmospheric spectrum, the change in intensity of signal from characteristic features with distance traveled, and therefore the distance to said features, and the rate of change of angular size of characteristic features in the radiometer observations as the airborne platform moves toward or away from these features.

23. The method of operating a passive polarimetric microwave radiometer of claim 13 wherein said step of determining comprises:

calculating range by using tomographic methods on intersecting vectors of observations obtained by scanning the field of view of the radiometer in at least one of;

the horizontal plane, the vertical plane, and a combination of both said horizontal plane and said vertical plane.

24. The method of operating a passive polarimetric microwave radiometer of claim 13 wherein said step of determining comprises:

identifying abrupt changes in the time series of the spatial distribution of said determined spectral signature difference to identify regions of electrification and potential icing and high turbulence conditions.

25. A passive polarimetric microwave radiometer, located in an aircraft, for detection of aircraft icing conditions, comprising:

a plurality of polarimetric radiometers, each of which operates to monitor a signal of a predetermined frequency, for monitoring a region of space located in front of said aircraft to detect a presence of a plurality of predetermined radio frequencies of clear-air brightness temperature signals;

signal processor means for calculating a spectral signature difference among said plurality of predetermined radio frequencies, including at least one of;

signal magnitude, signal polarization, signal attenuation; and

spectral signature processor means for determining a presence of aircraft icing conditions based upon said determined spectral signature difference.

26. The passive polarimetric microwave radiometer of claim 25 further comprising:

means for generating an alert indication from the class of indications including;

an icing probability-range indicator, cloud liquid water maps, audible warnings of imminent icing conditions.