High altitude ice particle detection method and system

• US 9,116,243 B1
• Filed: 09/20/2013
• Issued: 08/25/2015
• Est. Priority Date: 09/20/2013
• Status: Active Grant

• Current Assignee: Rockwell Collins, Inc. (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: Rockwell Collins, Inc. (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Brown, Robert G.
• Primary Examiner(s): Pham, Hoa
• Application Number:
  US14/033,202
• Time in Patent Office: 704 Days
• Field of Search: 356335-343, 356/73, 356/28, 356/301, 250/373, 250/374, 250/376, 340/580, 340/581, 340/601, 340/962, 324/671
• US Class Current: 1/1
• CPC Class Codes: G01S 17/04 Systems determining the presence of a target
• CPC Class Codes: G01S 17/18 wherein range gates are used
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/58 Velocity or trajectory determination systems; Sense-of-movement determination systems
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 17/95 for meteorological use
• CPC Class Codes: G01S 7/4802 using analysis of echo signal for target characterisation; Target signature; Target cross-section
• CPC Class Codes: G01S 7/4812 transmitted and received beams following a coaxial path
• CPC Class Codes: G01S 7/4814 of transmitters alone
• CPC Class Codes: G01S 7/4816 of receivers alone
• CPC Class Codes: G01S 7/4861 Circuits for detection, sampling, integration or read-out
• CPC Class Codes: G01S 7/499 using polarisation effects
• 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

An optical system for detection of atmospheric ice particles is described. The optical system includes a laser light source configured to emit laser light, a photodetector, a first lens element and detection electronics. The first lens element is arranged to image light from the laser light source onto a measurement volume, and to direct scattered light received from the measurement volume to the photodetector. The detection electronics is connected to the photodetector, and is configured to receive a light detection signal from the photodetector and to indicate whether or not the atmospheric ice particles exist in the measurement volume based on the light detection signal.

Claims

1. An optical system for detection of atmospheric ice particles, comprising:

a laser light source configured to emit laser light;

a photodetector;

a first lens element arranged to image light from the laser light source onto a measurement volume, and to direct scattered light received from the measurement volume to the photodetector; and

detection electronics, connected to the photodetector, and configured to receive a light detection signal from the photodetector and to indicate whether or not the atmospheric ice particles exist in the measurement volume based on the light detection signal,

wherein the detection electronics is configured to detect the existence of ice particles based on the ratio of two Raman shifted wavelengths, and based on a depolarization coefficient of two orthogonal polarization components of backscattered light which is unshifted in wavelength.

2. The optical system of claim 1, wherein the first lens element is less than about 10 cm in diameter.

3. The optical system of claim 1, wherein the laser light source comprises a pulsed laser configured to be repetitively pulsed at a pulse repetition frequency.

4. The optical system of claim 3, wherein the pulsed laser is configured to be operated in q-switched or mode-locked mode.

5. The optical system of claim 3, wherein the pulsed laser is a YAG-based laser, or a CO₂ laser.

6. The optical system of claim 1, wherein first lens element comprises a single lens system.

7. The optical system of claim 6, wherein the first lens element comprises an annular, core-drilled lens.

8. The optical system of claim 1, wherein the laser light source is configured to emit laser light which is plane polarized or circularly polarized.

9. The optical system of claim 1, further comprising a spatial filter arranged to pass the scattered light directed by the first lens element and to reduce background noise light.

10. The optical system of claim 1, wherein the photodetector comprises a first photodetector and a second photodetector, and further comprising

a polarizing beamsplitter arranged to split the scattered light directed by the first lens element into the two orthogonal polarization components, and to direct the two orthogonal polarization components to the first photodetector and the second photodetector, respectively.

11. The optical system of claim 1, wherein the photodetector comprises an avalanche photodiode.

12. The optical system of claim 11, wherein the avalanche photodiode is used in Geiger mode.

13. The optical system of claim 1, wherein the detection electronics is configured to pulse the photodetector on/off in synchronism with laser pulses from the laser light source being off/on, such that the photodetector is turned off when the laser pulses are inside the optical system or in close vicinity to the optical system.

14. The optical system of claim 1, wherein the detection electronics is configured to scan the laser light angularly through space and to time gate the photodetector on and off, and to construct a three-dimensional plot including range and spatial location of the ice particles based on the scan and time gating.

15. A system comprising a land-based, air-borne or sea-born vehicle, where the optical system of claim 1 is mounted on the vehicle.

16. The system of claim 15, wherein the detection electronics is configured to operate the laser beam power of the laser light to be eye safe to passengers in another vehicle who are at risk of accidentally being irradiated by the laser light, at a range of approximately 9 km.

17. An optical system for detection of atmospheric ice particles, comprising:

a laser light source configured to emit laser light;

a photodetector;

a first lens element arranged to image light from the laser light source onto a measurement volume, and to direct scattered light received from the measurement volume to the photodetector;

detection electronics, connected to the photodetector, and configured to receive a light detection signal from the photodetector and to indicate whether or not the atmospheric ice particles exist in the measurement volume based on the light detection signal; and

a laser frequency shifting element arranged in a laser beam path of the laser light, wherein the detection electronics is configured to measure the relative frequency shift of the scattered laser light, and to determine the velocities of particles in the measurement volume based on the relative frequency shift, wherein the detection electronics is configured to detect and quantify Clear Air Turbulence (CAT) based on the measured relative frequency shift of the scattered laser light.

18. A method for detection of atmospheric ice particles, comprising:

imaging laser light onto a measurement volume;

directing scattered light received from the measurement volume to a photodetector; and

indicating whether or not the atmospheric ice particles exist in the measurement volume based on a light detection signal from the photodetector, which is based on the ratio of two Raman shifted wavelengths, and based on a depolarization coefficient of two orthogonal polarization components of backscattered light which is unshifted in wavelength.