Abstract: A system includes an optical ice detection (OID) sub-system optically coupled to light collection optics. A water vapor differential absorption LIDAR (WV-DIAL) sub-system is optically coupled to the OID laser source or light collection optics. The OID sub-system and the WV-DIAL sub-system share at least a portion of an optical path of the light source or through the light collection optics. The OID sub-system, the WV-DIAL sub-system, and the illumination and light collection optics can all be aboard an aircraft. A method includes using a set of illumination and light collection optics aboard an aircraft to obtain data indicative of optical ice detection (OID) and water vapor differential absorption LIDAR (WV-DIAL), e.g. to detect contrail forming conditions for the aircraft and/or predict persistence of contrails from the aircraft.

Abstract: A method includes checking an optical detector with a field of view for degradation by: directing the optical detector to a surface of an object in the field of view, wherein the surface is positioned at a given distance from the optical detector, and wherein the surface has a known reflectance; detecting an optical return from the surface with the optical detector to generate a return signal; and determining whether the return signal is representative of a degraded signal. The method includes outputting an alert for maintenance action if the return signal is indicative of a degraded signal.

Abstract: A cloud phase detection system can include a light receiver system configured to receive reflected light from a cloud, and a cloud phase module operatively connected to the light receiver system and configured to calculate a fourth Stokes parameter and a multiple scattering ratio (MSR) parameter based on the reflected light. The cloud phase module can be configured to determine a phase of a cloud based on a relationship between the fourth Stokes parameter and the MSR parameter.

Abstract: A gas detection system includes a first optical fiber bundle connected to a first multi-pass cell for connecting the first multi-pass cell to a Raman spectrum analyzer. A second optical fiber bundle is connected to the first multi-pass cell for connecting the first multi-pass cell to a second multi-pass cell. The second optical fiber bundle can include a delay coil configured to provide temporal spacing between spectral returns from the first multi-pass cell and from the second multi-pass cell. The first and second multi-pass cells can be biconic multipass cells with a the first optical fiber bundle directed toward a first D-mirror, which is directed toward a T-mirror, which is directed toward a second D-mirror, which is directed toward the second optical fiber bundle. The D-mirrors can be on an opposite end of the first multi-pass cell from the T-mirror and the first and second optical fiber bundles.

Abstract: A system includes a first sensor positioned to sense presence of a contrail in a first volume, wherein the first volume at least partially overlaps an expected volume of a contrail proximate an aircraft. A second sensor is positioned to sense a background reference in a second volume, where the second volume does not overlap the expected volume of a contrail proximate an aircraft. A controller is operatively connected to the first and second sensors. The controller includes machine readable instructions configured to cause the controller to utilize data input from both the first and second volumes to determine if a contrail is present from the aircraft. A system includes machine readable instructions configured to cause the controller to predict persistence of contrails on an intended route through the volume of airspace and to determine an improved route and/or propulsion operation to reduce contrail formation and persistence relative to the intended route.

Abstract: In accordance with at least one aspect of this disclosure, a method of detecting a fault in a plurality of optical detectors includes receiving a first return beam from a first optical detector interrogation beam to generate a first optical signal indicative of an atmospheric condition from a first location on board the aircraft and receiving a second return beam from a second optical detector interrogation beam to generate a second optical signal indicative of the atmospheric condition from a second location on board the aircraft. The method includes, comparing each of the first and second optical signals with a baseline value to determine whether there is a fault in at least one optical detector of the plurality of optical detectors.

Abstract: A method of optically detecting the presence of a bimodal droplet size distribution in the atmosphere. The method comprising monitoring statistical fluctuations in a backscattered signal received from a series of pulsed laser light beams directed into a cloud and analyzing the statistics of the fluctuations of the backscattered signals to identify the presence of larger diameter droplets.

Abstract: A method of detecting optical subsystem failures includes emitting a pulsed light beam from a laser through a window. A reflection signal indicative of a portion of the beam reflected by the window is compared to an expected signal to monitor for degradation of an optical component.

Abstract: A method of detecting optical subsystem failures includes emitting a pulsed light beam from a laser through a window. A reflection signal indicative of a portion of the beam reflected by the window is compared to an expected signal to monitor for degradation of an optical component.

Abstract: A method of optically determining the presence of volcanic ash within a cloud comprises emitting a circularly polarized illuminating beam within a cloud and analyzing backscatter light to identify the presence of volcanic ash within the cloud. The method further includes determining the degree to which the cloud has altered the polarization state of the emitted beam. The index of refraction of the backscatter light and the opacity of the backscatter light are also analyzed.

Abstract: A method of optically determining the presence of volcanic ash within a cloud comprises emitting a circularly polarized illuminating beam within a cloud and analyzing backscatter light to identify the presence of volcanic ash within the cloud. The method further includes determining the degree to which the cloud has altered the polarization state of the emitted beam. The index of refraction of the backscatter light and the opacity of the backscatter light are also analyzed.

Abstract: A method of optically detecting the presence of a bimodal droplet size distribution in the atmosphere. The method comprising monitoring statistical fluctuations in a backscattered signal received from a series of pulsed laser light beams directed into a cloud and analyzing the statistics of the fluctuations of the backscattered signals to identify the presence of larger diameter droplets.

Abstract: In one aspect, methods of determining a size distribution of water droplets in a cloud are described herein. In some embodiments, a method of determining a size distribution of water droplets in a cloud comprises sampling a depth of the cloud with a beam of electromagnetic radiation, measuring a scattering signal of the electromagnetic radiation returned from the cloud over a range of field of view angles to provide a measured scattering curve [ptotal(?)], removing a portion of the measured scattering curve, replacing the removed portion with an extrapolation of the remaining measured scattering curve to provide an estimated scattering curve, and determining a first estimate droplet size distribution [n(1)(D)] from the estimated scattering curve.

Abstract: In one aspect, methods of determining a size distribution of water droplets in a cloud are described herein. In some embodiments, a method of determining a size distribution of water droplets in a cloud comprises sampling a depth of a cloud with a beam of electromagnetic radiation, measuring echo intensities of the electromagnetic radiation returned from the cloud with a detector, determining a measured optical extinction coefficient from the measured echo intensities, determining a measured backscatter coefficient from the measured echo intensities, determining a lidar ratio from the measured optical extinction coefficient and the measured backscatter coefficient, determining from the lidar ratio a value pair comprising a shape parameter (?) and median volume diameter (DMVD) of the water droplets, and determining a size distribution of the water droplets using the value pair (?, DMVD).

Abstract: In one aspect, methods of determining a size distribution of water droplets in a cloud are described herein. In some embodiments, a method of determining a size distribution of water droplets in a cloud comprises sampling a depth of the cloud with a beam of electromagnetic radiation, measuring a scattering signal of the electromagnetic radiation returned from the cloud over a range of field of view angles to provide a measured scattering curve [ptotal(?)], removing a portion of the measured scattering curve, replacing the removed portion with an extrapolation of the remaining measured scattering curve to provide an estimated scattering curve, and determining a first estimate droplet size distribution [n(1)(D)] from the estimated scattering curve.

Abstract: An apparatus for detecting icing conditions on an aircraft includes a laser system configured to direct a light signal into a cloud, a lens component configured to collect echo signals from a cloud caused by the light signal directed into the cloud, a beam splitter component configured to redirect signals received and passing through the lens component into at least first and second paths and a supercooled large droplet (SLD) detector to receive the redirected signals. The SLD includes a first signal detector component configured to perform a first color measurement on the first redirected signal, and a second signal detector component configured to perform a second color measurement on the second redirected signal. The SLD detector is configured to use the first and second color measurements to determine liquid water content and droplet diameter distribution for the cloud.

Abstract: An apparatus for detecting icing conditions on an aircraft includes a laser system configured to direct a light signal into a cloud, a lens component configured to collect echo signals from a cloud caused by the light signal directed into the cloud, a beam splitter component configured to redirect signals received and passing through the lens component into at least first and second paths and a supercooled large droplet (SLD) detector to receive the redirected signals. The SLD includes a first signal detector component configured to perform a first color measurement on the first redirected signal, and a second signal detector component configured to perform a second color measurement on the second redirected signal. The SLD detector is configured to use the first and second color measurements to determine liquid water content and droplet diameter distribution for the cloud.

Abstract: An airborne multiple field-of-view water droplet sensor includes an illumination portion and a detection portion. The illumination portion includes a first optical beam emitter configured to output a light beam. The detection portion includes a kaleidoscope configured to channel a first portion of the backscattered light towards an inner reflective surface of a circle-to-line converter, a multiple field of view subsystem having at least a first detector configured to receive light reflected by the circle-to-line converter, and a single field-of-view subsystem configured to receive a second portion of the backscattered light, the second portion not having been reflected by the circle-to-line converter. The single field-of-view subsystem may include a dual channel circular polarization detector for distinguishing between liquid water droplets and ice crystals based on information in the single field-of-view.

Abstract: A device for optically detecting and distinguishing airborne liquid water droplets and ice crystals includes an illumination portion and a detection portion. The illumination portion outputs a circularly polarized illuminating beam. The detection portion receives circularly polarized backscattered light from moisture in the cloud, in response to the illuminating beam. The circularly polarized backscattered light is passed through a circular polarizer to convert it into linearly polarized backscattered light, which is split into two components. Each of the two components is optionally subject to further linear polarization to filter out any leakage-type orthogonal polarization. The two components are then optically detected and the resulting detection signals are used to calculate one or more parameters reflective of the presence or absence of airborne ice crystals and/or water droplets.

Abstract: An airborne multiple field-of-view water droplet sensor includes an illumination portion and a detection portion. The illumination portion includes a first optical beam emitter configured to output a light beam. The detection portion includes a kaleidoscope configured to channel a first portion of the backscattered light towards an inner reflective surface of a circle-to-line converter, a multiple field of view subsystem having at least a first detector configured to receive light reflected by the circle-to-line converter, and a single field-of-view subsystem configured to receive a second portion of the backscattered light, the second portion not having been reflected by the circle-to-line converter. The single field-of-view subsystem may include a dual channel circular polarization detector for distinguishing between liquid water droplets and ice crystals based on information in the single field-of-view.