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EP-3882655-B1 - MULTI-FIBER SINGLE LENS OPTICAL ICE DETECTOR

EP3882655B1EP 3882655 B1EP3882655 B1EP 3882655B1EP-3882655-B1

Inventors

  • RAY, MARK
  • ANDERSON, KAARE JOSEF

Dates

Publication Date
20260506
Application Date
20210108

Claims (12)

  1. A system (10) for determining parameters of a cloud atmosphere within a wind tunnel, the system comprising: a light projector configured to project a pulse of light energy into a projection field of view (20); multiple light detectors that each have a detection field of view (22,24) that forms a range-limited intersection with the projection field of view different from the detection field of view of any other of the multiple light detectors, each of the range-limited intersections having a maximum sampling range so as to exclude wall structures of the wind tunnel, wherein each of the multiple light detectors is configured to detect a backscattered portion of the projected pulse of light energy backscattered from within the range-limited intersection; a cloud parameter calculator configured to determine parameters of the cloud atmosphere based on the backscattered portions detected; and a lens (18) configured and arranged to collimate the projection field of view and the at least one detector field of view as to create collimated fields of view, wherein at least a portion of the collimated fields of view of the at least one detector intersect the collimated projection field of view.
  2. The system of claim 1, wherein the projection field of view does not have a limit to its range within the wind tunnel.
  3. The system of any preceding claim, comprising: a laser (12) configured to generate the pulse of light energy; and a transmitter fiber (72) configured to project the generated pulse of light energy from a transmitting face defining the projection field of view aligned about a projection axis into a cloud atmosphere within the wind tunnel.
  4. The system of any preceding claim, wherein each of the multiple detectors comprises a receiving fiber (16).
  5. The system of claim 4, wherein: the lens is a single lens, and the receiving fibers are arranged and spaced along the single lens.
  6. The system of any preceding claim, comprising. an additional light detector configured to detect a backscattered portion of the projected pulse of light energy backscattered from outside the range-limited intersection.
  7. The system of claim 6, further comprising: a plurality of linear polarizing elements (82, 84, 86, 88, 90) each configured to linearly polarize the projected pulse of light energy and at least one of the backscattered portions of the projected pulse of light energy received by at least one of the receiver fibers or further comprising: a circular polarizing element configured to polarize the projected pulse of light energy and arranged such that the projected pulse of light energy passes through the single collimation lens prior to being projected through the circular polarizing element and into the cloud atmosphere.
  8. A method (110) for determining parameters of a cloud atmosphere within a wind tunnel, the method comprising: projecting (112) a pulse of light energy into a projection field of view; detecting (114) a backscattered portion of the projected pulse of light energy backscattered from within a range-limited intersection of each of multiple detection fields of view formed by multiple light detectors and the projection field of view, each of the range-limited intersections having a maximum sampling range so as to exclude wall structures of the wind tunnel; determining (116) parameters of the cloud atmosphere based on the backscattered portions detected; collimating (118) the projection field of view and the multiple detection fields of view so as to create collimated fields of view projecting into the cloud atmosphere, wherein a single collimation lens is configured and arranged so as to span and collimate the projection field of view and the multiple detection fields of view.
  9. The method of claim 8, wherein each of the multiple light detectors includes a receiver fiber.
  10. The method of claim 9, wherein each receiver fiber has a reception face that is arranged along the single collimation lens (18).
  11. The method of claim 8, 9, or 10, further comprising: transmitting the pulse of light energy from a transmitting face of a transmitter fiber (12) defining the projection field of view aligned about a projection axis, such that the pulse of light energy is projected into the cloud atmosphere within the wind tunnel.
  12. The method of claim 8, 9, 10, or 11, further comprising: linearly polarizing the projected pulse of light energy and the backscattered portion or circularly polarizing the projected pulse of light energy and the backscattered portion.

Description

The present invention relates to a system and method of for determining parameters of a cloud atmosphere within a wind tunnel. BACKGROUND Various cloud conditions can present risks to aircraft when traveling through them. If the temperature of a cloud atmosphere is below the freezing point for water, water droplets can become super-cooled liquid droplets. These super-cooled liquid droplets can then undergo a liquid-to-solid phase change upon impact with an aircraft surface. Ice accretes at different surface regions for different sizes of the super-cooled liquid droplets in the cloud atmosphere. Thus, characterizing the sizes of super-cooled water droplets in a cloud atmosphere can facilitate prediction of surface regions where ice will accrete as well as provide alerts of potentially dangerous conditions to a pilot. Some aircraft are equipped with Light Detection and Ranging (LIDAR) systems to measure cloud metrics, for example. An example of a compact, airborne LIDAR system is an optical ice detector (OID), which is intended to probe the airstream surrounding an aircraft to determine properties of the cloud atmosphere through which the aircraft is passing. The DID projects short pulses of laser light into the surrounding clouds and measures the backscatter as a function of the time-of-flight of a pulse to generate backscatter signals. Backscatter provides an estimate of a characteristic droplet or ice crystal size and the liquid and/or ice water content of the clouds Wind tunnel testing is an important means for research and development of various airborne systems, such as, for example, LIDAR systems. A wind tunnel can include a waterdrop spraying system, a refrigeration system, etc. Clouds and mist flow fields can be created to simulate aerial meteorological conditions, so that cloud parameters or conditions can be measured in the wind tunnel. Schnaiter M. et al.: "Influence of particle size and shape on the backscattering linear depolarization ratio of small ice crystals - cloud chamber measurements in the context of contrail and cirrus microphysics", Amospheric Chemistry and Physics, vol. 12, no. 21, 3 December 2012, pages 10465-10484, discloses a system for determining parameters of a cloud atmosphere. WO 2012/105973 A1 described optical atmospheric measurements by LIDAR devices, usable in wind farms as well as wind tunnels. US 2015/116692 A1 describes a LIDAR for determining atmospheric parameters. EP3351967A2 describes an optical system for determining parameters of a cloud atmosphere. The transmission and the receiving light are collimated by a common lens and the different field of views have limited overlap. SUMMARY According to a first aspect, there is provided a system for determining parameters of a cloud atmosphere within a wind tunnel according to claim 1. According to a second aspect, there is provided a method for determining parameters of a cloud atmosphere within a wind tunnel according to claim 11. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of an embodiment of a cloud conditions measurement system for use in a wind tunnel.FIG. 2 is another schematic diagram of the cloud conditions measurement system of FIG. 1.FIG. 3 is a schematic diagram of another embodiment of a cloud conditions measurement system for use in a wind tunnel.FIG. 3a is an exemplary graph of intensity of backscatter versus time for the cloud conditions measurement system of FIG. 3.FIG. 3b is an exemplary graph of intensity of transmitted laser beam intensity versus time for the cloud conditions measurement system of FIG. 3.FIG. 4 is a schematic diagram of a further embodiment of a cloud conditions measurement system.FIG. 5 is a flow chart of an exemplary method of measuring cloud conditions in a wind tunnel. DETAILED DESCRIPTION Systems and associated methods described herein relate to measuring cloud conditions, such as surrounding an aircraft, for example, so as to determine properties of clouds through which the aircraft is passing. During research and development, such systems may first be tested in a wind tunnel (i.e., a cloud chamber). There are challenges to testing a system, which will be used on an aircraft with a sampling range extending many meters, in a wind tunnel that may have relatively small volumes of calibrated cloud conditions. In such a wind tunnel, the maximum sampling range of a chamber in the wind tunnel is limited by a physical barrier, such as a far wall of the chamber. Systems and associated methods described herein include a system for determining parameters of a cloud atmosphere within a wind tunnel. The system includes: a light projector configured to project a pulse of light energy into a projection field of view; at least one light detector having a detection field of view that forms a range-limited intersection with the projection field of view, the range-limited intersection having a maximum sampling range so as to exclude wall structures of the wind tunnel, wherein th