US-12618766-B2 - Airborne-particle detector and detection method

US12618766B2US 12618766 B2US12618766 B2US 12618766B2US-12618766-B2

Abstract

An airborne-particle detector includes a first emitter unit, a second emitter unit, and a photodetector. The first emitter unit includes a first light emitter and a first imaging element, that outputs a first incident beam propagating in a first direction toward a scattering region. The second emitter unit includes a second light emitter and a second imaging element, that outputs a second incident beam propagating toward the scattering region in a second direction substantially antiparallel to the first direction. the first imaging element images the first light emitter to a first image plane. The second imaging element images the second light emitter to a second image plane. The scattering region is between the first image plane and the second image plane. The photodetector detects scattered illumination from the scattering region.

Inventors

RU-SHAN GAO
Joshua Peter Schwarz

Assignees

THE REGENTS OF THE UNIVERSITY OF COLORADO
UNITED STATES OF AMERICA, AS REPRESENTED BY THE SECRETARY OF COMMERCE

Dates

Publication Date: 20260505
Application Date: 20250709

Claims (20)

1 . An airborne-particle detector comprising: a first emitter unit, including a first light emitter and a first imaging element, that outputs a first incident beam propagating in a first direction toward a scattering region; a second emitter unit, including a second light emitter and a second imaging element, that outputs a second incident beam propagating toward the scattering region in a second direction substantially antiparallel to the first direction; and a photodetector that detects scattered illumination from the scattering region; wherein: the first imaging element images the first light emitter to a first image plane, the second imaging element images the second light emitter to a second image plane, the scattering region is between the first image plane and the second image plane, and either or both of, along the first direction: the first image plane is between (i) the second image plane and (ii) one or both of the second imaging element and the second emitter unit; and the second image plane is between (iii) the first image plane and (iv) one or both of the first imaging element and the first emitter unit.
2 . The airborne-particle detector of claim 1 , the first imaging element being between the first light emitter and the second imaging element along the first direction; and/or the second imaging element being between the second light emitter and the first imaging element along the first direction.
3 . The airborne-particle detector of claim 1 , a center emission wavelength of one or both of the first light emitter and the second light emitter being between 0.5 micrometers and 0.6 micrometers.
4 . The airborne-particle detector of claim 1 , an emission spectrum of one or both of the first light emitter and the second light emitter having a full-width half-maximum spectral width of at least 100 nanometers.
5 . The airborne-particle detector of claim 1 , the scattering region being intersected by at least one of a first optical axis of the first imaging element and a second optical axis of the second imaging element.
6 . The airborne-particle detector of claim 1 , further comprising a light-collector that collects the scattered illumination and directs the collected scattered illumination to the photodetector.
7 . The airborne-particle detector of claim 6 , further comprising a collimator between the light-collector and the scattering region.
8 . The airborne-particle detector of claim 1 , and further comprising: a reflector that reflects part of the scattered illumination toward the photodetector.
9 . The airborne-particle detector of claim 8 , the photodetector being on a first side of the scattering region, the reflector being on a second side of the scattering region opposite the first side and facing the photodetector.
10 . The airborne-particle detector of claim 8 , the reflector including a concave mirror.
11 . The airborne-particle detector of claim 1 , further comprising: a first tube extending between the first image plane and the second image plane, and having a first tube-axis that is substantially perpendicular to the first direction.
12 . The airborne-particle detector of claim 11 , the first tube being electrically conductive.
13 . The airborne-particle detector of claim 11 , an image of the first light emitter in the first image plane having a first image-height, an image of the second light emitter in the second image plane having a second image-height in a vertical direction substantially perpendicular to the first direction; and the first tube having at least one of (a) a first aperture-height in the vertical direction equals or exceeds each of the first image-height and the second image-height and (b) a first aperture-width in the first direction equals or exceeds a distance between the first image plane and the second image plane.
14 . The airborne-particle detector of claim 11 , a proximal end of the first tube, relative to a first optical axis of the first imaging element, being directly between the first imaging element and the second imaging element along the first direction; an image of the first light emitter in the first image plane having a first image-width in a horizontal direction substantially perpendicular to the first direction; an image of the second light emitter in the second image plane having a second image-width in the horizontal direction; and a distance between the proximal end and the first optical axis, exceeding each of the first image-width and the second image-width.
15 . The airborne-particle detector of claim 11 , a proximal end of the first tube, relative to a first optical axis of the first imaging element, being directly between the first imaging element and the second imaging element along the first direction; and further comprising: a second tube extending between the first image plane and the second image plane, and having a second tube-axis that is substantially parallel to the first tube-axis and extends through the first tube.
16 . The airborne-particle detector of claim 1 , a distance between the first imaging element and the second imaging element along the first direction exceeding a sum of a first focal length of the first imaging element and a second focal length of the second imaging element.
17 . A method for detecting scattered light, comprising: illuminating, with a first incident beam emitted by a first light emitter, a scattering region from a first side of the scattering region; illuminating, with a second incident beam emitted by a second light emitter, the scattering region from a second side of the scattering region that is opposite the first side; and directing light scattered from the scattering region to a photodetector; wherein: illuminating with the first incident beam includes imaging the first light emitter to a first image plane with a first imaging element; illuminating with the second incident beam includes imaging the second light emitter to a second image plane with a second imaging element; the scattering region is between the first image plane and the second image plane; and either or both of, along the first direction: the first image plane is between (i) the second image plane and (ii) one or both of the second imaging element and a second emitter unit, which includes the second light emitter and the second imaging element; and/or the second image plane is between (iii) the first image plane and (iv) one or both of the first imaging element and a first emitter unit, which includes the first light emitter and the first imaging element.
18 . The method of claim 17 , said illuminating comprising illuminating the scattering region with illumination having a center wavelength between 0.5 micrometers and 0.6 micrometers.
19 . The method of claim 18 , an optical spectrum of the illumination having a full-width half-maximum spectral width of at least 100 nanometers.
20 . An airborne-particle detector comprising: a first emitter unit, including a first light emitter and a first imaging element, that outputs a first incident beam propagating in a first direction toward a scattering region; a second emitter unit, including a second light emitter and a second imaging element, that outputs a second incident beam propagating toward the scattering region in a second direction substantially antiparallel to the first direction; a photodetector that detects scattered illumination from the scattering region; and a first tube extending between a first image plane and a second image plane, and having a first tube-axis that is substantially perpendicular to the first direction; wherein: the first imaging element images the first light emitter to the first image plane, the second imaging element images the second light emitter to the second image plane, the scattering region is between the first image plane and the second image plane; a proximal end of the first tube, relative to a first optical axis of the first imaging element, is directly between the first imaging element and the second imaging element along the first direction; an image of the first light emitter in the first image plane has a first image-width in a horizontal direction substantially perpendicular to the first direction; an image of the second light emitter in the second image plane has a second image-width in the horizontal direction; and a distance between the proximal end and the first optical axis, exceeds each of the first image-width and the second image-width.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims the benefit of U.S. Provisional Application No. 63/669,107, filed on 9 Jul. 2024, the disclosure of which is incorporated herein by reference in its entirety. GOVERNMENT RIGHTS This invention was made with government support under grant number NA220AR4320151 awarded by NOAA. The government has certain rights in the invention. BACKGROUND Cirrus clouds in the upper troposphere play an important role in the climate system. The fundamental understanding of cirrus behavior still needs to be improved, which requires detailed measurements of cloud particle distributions. Currently there is no instrument available for routine in situ measurements to provide process-level relevant information about cirrus extent, thickness, and ice crystal size distribution. SUMMARY OF THE EMBODIMENTS In a first aspect, an airborne-particle detector includes a first emitter unit, a second emitter unit, and a photodetector. The first emitter unit includes a first light emitter and a first imaging element, that outputs a first incident beam propagating in a first direction toward a scattering region. The second emitter unit includes a second light emitter and a second imaging element, that outputs a second incident beam propagating toward the scattering region in a second direction substantially antiparallel to the first direction. The first imaging element images the first light emitter to a first image plane. The second imaging element images the second light emitter to a second image plane. The scattering region is between the first image plane and the second image plane. The photodetector detects scattered illumination from the scattering region. In a second aspect, a method for detecting scattered light includes illuminating a scattering region from opposite sides of the scattering region. The method also includes directing light scattered from the scattering region to a photodetector. BRIEF DESCRIPTION OF THE FIGURES FIGS. 1-3 are schematics of an airborne-particle detector, in an embodiment. FIGS. 4 and 5 are schematics of a shroud attached to an inlet tube of an embodiment of the airborne particle detector of FIGS. 1-3. FIG. 6A is a side view of an emitter unit, which is an example of an emitter of the airborne-particle detector of FIG. 1. FIG. 6B is a plan view of a light emitter of the emitter unit of FIG. 6A with a light-blocking element to restrict the area emitting light. FIG. 7 is a flowchart illustrating an embodiment of a method for detecting scattered light, which may be implemented with the airborne-particle detector of FIGS. 1-3. FIG. 8 is a plot of scattering amplitude as a function of particle diameter for single-wavelength illumination (λ=600 nm) and a broadband lime-green illumination. DETAILED DESCRIPTION OF THE EMBODIMENTS At present, the most reliable and low-cost method to obtain regular measurements in the upper troposphere is via weather balloons with disposable payloads. These require a lightweight and low-power draw instrument capable of measuring cirrus cloud properties. Airborne-particle detectors disclosed herein are an example of such an instrument. Embodiments disclosed herein include an in-situ balloon-borne airborne-particle detector. Embodiments of the particle detector measure cloud particle size spectra and cloud-crystal number densities. In a use scenario, embodiments of the detector are low cost (disposable), light weight (suitable for the weather balloon platform), and have a large sampling cross section (to sample reasonably large volume of air necessary for balloon applications directed at very low concentration particles). An airborne-particle detector may be designed for low sizing ambiguity and sensitivity even to smaller ice crystals. In embodiments, the detector can detect particles smaller than three micrometers in diameter. Embodiments of an in-situ balloon-borne airborne-particle detector include at least one the following features: 1. One or more LED light sources that emit broadband illumination, which contributes to low cost, robust performance, and reduction of Mie resonances that degrade accurate particle sizing.2. Illumination of the sensing area with two opposing light sources to provide a more uniform light field, which is important for accurate particle sizing.3. Large Fresnel lenses for more uniform and effective light-signal collection across the sensing area. This is important for accurate sizing, while being exceptionally light weight and low cost.4. An inlet shroud for directing sample flow into the flow tube in anticipation of the use in swinging balloon-borne payloads. Herein, a number in parentheses following a reference number is an instance of the referent of the reference number. For example, embodiments herein include light emitters 110(1) and 110(2). Statements describing features and/or properties of a referent using a reference number lacking parentheses, e.g., “light emitter 110” may apply to on