Patent Description:
Super-cooled small water droplets tend to form ice only on leading edges of an aircraft's exterior surface. Super-cooled Large water Droplets (SLDs), however, can strike the leading edge of a wing and run back past the icing protection systems, or can traverse airflow vectors and strike surfaces aft of these leading edges. Ice that forms on unprotected surface regions can severely alter the aerodynamics of the aircraft. Such ice accretion may cause aircraft stall or result in unpredictable aircraft control variation that might lead to flight issues. When in a cloud, ice can form on control surfaces and/or lift surfaces.

Not every cloud, however, has a significant SLD population. Different clouds and different atmospheric conditions may be accompanied by various water droplet size distributions, different ice/liquid ratios, etc., some of which may be entirely safe to an aircraft, while others may not be safe. Such water droplet size distributions and ice/liquid ratios may be measured as cloud metrics using various types of instruments.

Some aircraft are equipped with Light Detection and Ranging (LIDAR) systems to measure cloud metrics. Such systems can characterize clouds that have water droplets that have a size distribution having a single mode. Either the mean droplet size or the mode droplet size can be calculated by inversion of a backscatter signal using such systems. These systems can also calculate the density of water droplets for such mono-modal distributions.

Multi-modal distributions of water droplet sizes, however, can be difficult to characterize. Such multi-modal distributions may occur, for example, when cumulus clouds drop drizzle or rain into a lower stratiform cloud deck, creating icing conditions. For droplet size distributions having a dominant mode and a secondary mode (e.g. large distribution of relatively small water droplets plus a small distribution of large water droplets), it can be difficult to detect the anomalous amounts of large water droplets in the secondary mode.

LIDAR systems often project pulses of a collimated laser beam into the cloud atmosphere and then sense the signal backscattered by the cloud atmosphere. The collimated laser beam samples a relatively small volume of the cloud, due to the collimated beam having a small field of view (e.g., <NUM> mrad of divergence is not atypical). Sampling such a small cloud volume can result in the beam encountering few, if any of the SLDs of a secondary distribution.

Depending on the size and density of the SLDs in the secondary distribution, the backscatter signal can appear as scintillation spikes superimposed on an otherwise smooth continuous range-resolved backscatter signal characteristic of the primary distribution. The size and frequency of occurrence of the scintillation spikes depends on the sizes of the SLDs and on the volume of space probed by the collimated laser beam.

Unlike the smooth range-resolved backscatter signal from the primary distribution, backscatter signals from distributions of large droplet have randomly occurring scintillation pulses. Averaging of such backscatter signals over multiple laser pulses, while boosting the signal-to-noise ratio of the small droplet contribution, can cause the sporadic spikes for the sparse large droplets to be attenuated, and perhaps even fall below a noise floor. Thus, the SLDs, which can be hazardous to aircraft, may not be sensed.

Mono-modal distributions of SLDs can also be problematic, if the density of SLDs is small. Again, the backscatter signal can be characterized by randomly located scintillation spikes. Averaging of such backscatter signals can result in a signal amplitude that is small. Such a small signal may even fall below an instrument noise floor. Measurement techniques and instruments, which can more accurately characterize water droplet distributions, are needed. Systems suitable for measuring cloud conditions are taught in <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

According to a first aspect, a system for measuring cloud conditions is provided according to claim <NUM>.

According to a second aspect, a method for measuring cloud parameters is provided according to claim <NUM>.

Apparatus and associated methods relate to sampling a large volume of a cloud atmosphere so as to obtain a large signal response from even a sparse distribution of water droplets in the cloud atmosphere. Such a large volume can be probed by projecting an uncollimated optical beam into the cloud atmosphere and sampling the signal backscattered from the water droplets located within the probed volume. The uncollimated optical beam is generated by projecting a pulse of light energy from an end of a first optical fiber. The pulse of light energy is projected from a polished surface of the first optical fiber without having a lens between the end of the optical fiber and the cloud atmosphere. The unlensed beam diverges as it projects from the end of the first optical fiber. Various metrics can be used to characterize the divergence of the projected optical beam. For example, angle of divergence (θ), numerical aperture (NA), focal ratio (F/#), and solid angle (Ω) can all be used as metrics characterizing the divergence of the projected optical beam.

A second optical fiber is used to receive the optical signal backscattered from the cloud atmosphere. The second optical fiber is aligned parallel to the first optical fiber so as to be sensitive to optical signals backscattered from the probed volume. The second optical fiber also has substantially the same field of view as the first optical fiber, so as to receive signals from a volume of the cloud atmosphere that is substantially commensurate with the probed volume. By sampling the large volume of the cloud atmosphere, a continuous range-resolved backscatter signal can be detected, even for clouds having sparse distributions of water droplets.

The fields of view of the first and second optical fibers are substantially equal or substantially the same so that the volume of the cloud atmosphere probed by a signal projecting from the first optical fiber is substantially the same volume from which a backscattered signal is received by the second optical fiber. Two fields of view, and any of the measures of divergence that characterize such fields of view, are substantially equal to one another if they differ by less than ten percent. For example if <NUM>(θ<NUM>-θ<NUM>)/(θ<NUM>+θ<NUM>)<<NUM> then the two angles of divergence are substantially equal to each other.

<FIG> is a schematic view of an aircraft using an exemplary cloud conditions measurement system to measure various metrics of a cloud in the path of the aircraft. In <FIG>, aircraft <NUM> is traveling through cloud atmosphere <NUM>. Aircraft <NUM> is equipped with cloud conditions measurement system <NUM> that is probing cloud atmosphere <NUM> with collimated optical beam <NUM> and uncollimated optical beam <NUM>.

Collimated optical beam <NUM> has a relatively small divergence and probes first probe volume <NUM>. In some embodiments, the divergence of collimated optical beam <NUM> can be characterized by an angle of divergence of <NUM> mrad, for example. A cloud atmosphere sampled over a depth of ten meters by such a collimated optical beam results in a first probe volume <NUM> being equal to about <NUM>×<NUM>-<NUM> m<NUM>.

Uncollimated optical beam <NUM> has a relatively large divergence and probes second volume <NUM>. In some embodiments, the divergence of uncollimated optical beam <NUM> can be characterized by a numerical aperture of <NUM>, for example. A cloud atmosphere sampled over a depth of ten meters by such an uncollimated optical beam results in second probe volume <NUM> being equal to about <NUM><NUM>. Thus, second probe volume <NUM> is more than thirty-thousand times larger than first probe volume <NUM>.

<FIG> is a schematic diagram of an embodiment of a cloud conditions measurement system. In <FIG>, cloud conditions measurement system <NUM> is depicted probing cloud atmosphere <NUM>. Cloud conditions measurement system <NUM> includes collimated system <NUM> and uncollimated system <NUM>. Collimated system <NUM> generates collimated optical beam <NUM>. Uncollimated system <NUM> generates uncollimated optical beam <NUM>. Uncollimated optical beam <NUM> can be characterized by directional axis <NUM> and angle of divergence (θ), for example.

Uncollimated system <NUM> includes laser diode <NUM>, half-wave plate <NUM>, polarizing beam splitter <NUM>, condenser lens <NUM>, transmitter fiber <NUM>, window polarization scrambler <NUM>, receiver fiber <NUM>, and fiber-coupled detector <NUM>. Laser diode <NUM> generates a sequence of pulses of optical energy. In some embodiments the wavelength of the optical energy generated by laser diode <NUM> is about <NUM>, for example. In other embodiments, the wavelength of optical energy generated by laser diode <NUM> is about <NUM>, for example. The pulses of optical energy are transmitted through half-wave plate <NUM>, which is rotatable so as to provide a variable polarization of the transmitted optical beam. The polarized optical beam is then split by polarizing beam splitter <NUM>.

Polarizing beam splitter <NUM> in the beam path of the pulses of optical energy passes P-polarized light, which is used as a source for collimated system <NUM>. The S-polarization is reflected by polarizing beam splitter <NUM> and coupled into transmitter fiber <NUM> via condenser lens <NUM>. In this way, half-wave plate <NUM> permits adjustment of the polarization and hence the relative fraction of laser light entering collimated system <NUM> and uncollimated system <NUM>.

In some embodiments, transmitter fiber <NUM> is a multi-modal fiber, for example. Such a multi-modal fiber does not maintain the polarization state of the light entering therein. Thus, light projected from projecting end <NUM> of transmitter fiber <NUM> can have multiple polarization contributions. The light is projected through window/polarization scrambler <NUM>, which further suppresses any residual polarization remaining in the projected optical beam. In some embodiments, window-polarization scrambler <NUM> can be a Comu polarization scrambler, for example. The light is then projected in the direction of directional axis <NUM> with an angle of divergence (θ).

In the depicted embodiment, the function of uncollimated system <NUM> is to measure backscatter and extinction rather than cloud phase (e.g., ice vs. liquid). Collimated system <NUM> can be used to determine cloud phase, in the depicted embodiment. The signal projected by uncollimated system <NUM> is then backscattered by cloud atmosphere <NUM>. The signal backscattered by cloud atmosphere <NUM> then traverses back through, but in the reverse direction of, window/polarization scrambler <NUM>. The backscattered signal then is collected (e.g., received) by receiver fiber <NUM>, which has a large numerical aperture at reception end <NUM> of receiver fiber <NUM> so as to receive light backscattered from substantially the same volume as was probed by the projecting beam. Receiver fiber <NUM> is oriented substantially parallel to directional axis <NUM>. Receiver fibers are substantially parallel with transmitter fibers if their axes are aligned within ten degrees of one another. Light received by receiver fiber <NUM> has an angle of convergence substantially equal to the angle of divergence (θ) associated with transmitter fiber <NUM>.

Receiver fiber <NUM> then directs the received beam to fiber-coupled detector <NUM>. Fiber-coupled detector is capable of range-resolved measurements. Measurements can be deemed range-resolved if the frequency response of fiber-coupled detector is sufficient to distinguish signals backscattered from various ranges (e.g., various distances from uncollimated system <NUM>) within the probed volume. The backscattered signal detected by fiber-coupled detector <NUM> can then be modeled and then the backscatter and extinction coefficients can be derived by inversion methods. The backscatter and extinction coefficients can then be used to determine sizes of droplets in cloud atmosphere <NUM>.

Collimated system <NUM> includes quarter-wave plate <NUM>, laser diode <NUM> dichroic filter <NUM>, objective lens with turning mirror <NUM>, collimator lens <NUM>, dichroic filter <NUM>, bandpass filter <NUM>, condenser lenses <NUM>, <NUM>, <NUM> optical detectors <NUM>, <NUM>, <NUM> bandpass filter <NUM>, quarter-wave plate <NUM>, and polarizing beam splitter <NUM>. Collimated system <NUM> probes cloud atmosphere <NUM> using collimated beams of optical energy of two dissimilar wavelengths. Using two dissimilar wavelengths of optical energy can provide information used to determine liquid water content of cloud atmosphere <NUM>.

Laser diode <NUM> and laser diode <NUM> generate pulses of optical energy of dissimilar wavelengths. For example, laser diode <NUM> might generate pulses of optical energy having a first wavelength that corresponds to light having a relatively low water absorption coefficient. For example, various embodiments may have the first wavelength corresponding to light having a water absorption coefficient of less than <NUM>-<NUM>, less than <NUM>-<NUM>, or less than <NUM>-<NUM>. In an exemplary embodiment, the first wavelength may be about <NUM>. In such an embodiment, laser diode <NUM> might be selected so as to generate pulses of optical energy having a second wavelength that corresponds to light having a relatively high water absorption coefficient. For example, various embodiments may have the second wavelength may be about <NUM>.

The P-polarized portion of the pulses of optical energy generated by laser diode <NUM> that pass through polarizing beam splitter <NUM> are circularly polarized by quarter-wave plate <NUM>. Dichroic filter <NUM> passes light having first wavelength, as is generated by laser diode <NUM>, but reflects light of second wavelength, as is generated by laser diode <NUM>. Thus, the circularly polarized beam of the first wavelength passes through dichroic filter <NUM> and is then reflected by turning mirror <NUM>. Turning mirror <NUM> thus directs circularly polarized collimated beam, which has the first wavelength, in a direction parallel to directional axis <NUM> and into cloud atmosphere <NUM>.

A second collimated beam having the second wavelength is generated by laser diode <NUM>, reflected by both dichroic filter <NUM> and turning mirror <NUM>. The second collimated beam is also directed parallel to directional axis <NUM> and into cloud atmosphere <NUM>. Each of the first and second collimated beams is then backscattered by cloud atmosphere <NUM>. The first collimated beam can be used to determine an ice/liquid phase ratio of cloud atmosphere <NUM>.

An ice/liquid phase ratio of the water droplets in a cloud can be determined, as disclosed by <CIT>, titled "Apparatus and Method for In-Flight Detection of Airborne Water Droplets and Ice Crystals". The '<NUM> patent discloses:.

Thus, a first optical signal that results from backscattering of the first collimated beam of circularly polarized light will include a component that is left-hand circularly polarized, and a component that is right-hand circularly polarized. Each of these components of the backscattered optical signal is focused by objective lens <NUM> and collimator lens <NUM>. This focused backscattered optical signal then passes through dichroic filter <NUM>, and bandpass filter <NUM>. Circularly polarized components of this backscattered optical signal are then converted to orthogonal planar polarized (e.g., S-polarized and P-polarized) components via quarter-wave plate <NUM>. Polarizing beam splitter <NUM> directs the planar polarized component corresponding to right-hand circularly polarized light to optical detector <NUM> via condenser lens <NUM>. Polarizing beam splitter <NUM> directs the planar component corresponding to left-hand circularly polarized light to optical detector <NUM> via condenser lens <NUM>.

Thus, a ratio of the magnitudes of left-hand circularly polarized light and right-hand circularly polarized light can be calculated based on amplitudes of the detected corresponding planar polarized components. This ratio can be used to calculate an ice/liquid phase ratio of cloud atmosphere <NUM>.

A second optical signal resulting from backscattering of the second collimated beam will similarly be focused by objective lens <NUM> and collimator lens <NUM>. The second backscatter signal will then be reflected by dichroic lens <NUM>. The reflected second backscattered signal will be filtered by bandpass filter <NUM>. The filtered backscattered second backscattered signal will be focused onto optical detector <NUM> by condenser lens <NUM>. The magnitudes of optical signals detected by detectors <NUM>, <NUM>, <NUM> can be used to calculate many cloud metrics, including, for example, droplet size, total water content, ice/liquid phase ratio, etc..

<FIG> is a schematic diagram of another embodiment of a cloud conditions measurement system. In <FIG>, cloud conditions measurement system <NUM> is shown probing cloud atmosphere <NUM>. Cloud conditions measurement system <NUM> includes only uncollimated systems <NUM>, <NUM>. First uncollimated system <NUM> includes first optical transmitter <NUM> and first optical receiver <NUM>. First optical transmitter <NUM> includes fiber-coupled laser <NUM>, transmitter fiber <NUM>, linear polarizer <NUM>, quarter-wave plate <NUM>, bandpass filter <NUM>, and window <NUM>.

Fiber-coupled laser <NUM> generates pulses of optical energy having first wavelength. Transmitter fiber <NUM> transmits these pulses of optical energy to a projecting end of transmitter fiber <NUM>. These pulses of optical energy diverge from the projecting end of the transmitter fiber so as to become an uncollimated beam. The uncollimated beam then projects from transmitter fiber <NUM> to probe cloud atmosphere <NUM> via transmission through linear polarizer <NUM>, quarter-wave plate <NUM>, bandpass filter <NUM>, and window <NUM>. These elements <NUM>, <NUM>, <NUM>, <NUM>, through which the uncollimated beam transmits, cause the uncollimated beam to be circularly polarized.

Cloud atmosphere <NUM> then backscatters the uncollimated beam that probes the cloud atmosphere. The backscattered signal then is transmitted back through window <NUM>, bandpass filter <NUM> and quarter-wave plate <NUM> in reverse order that the probing beam transmitted therethrough. These elements <NUM>, <NUM>, <NUM>, through which the backscattered signal transmits, cause the backscattered signal to have orthogonal planar polarized components.

First optical receiver <NUM> includes linear polarizers <NUM>, <NUM> receiver fibers <NUM>, <NUM>, and optical detectors <NUM>, <NUM>. Linear polarizers <NUM>, <NUM> are configured in orthogonal directions, one to another, so as to each permit transmission of components corresponding to backscattered signals that are circularly polarized in opposite directions (e.g., left-hand circularly polarized and right-hand circularly polarized). Receiver fibers <NUM>, <NUM> are oriented substantially parallel to and transmitter fiber <NUM>, and receiver fibers <NUM>, <NUM> have a field of view commensurate with (e.g., substantially equal to) the field of view corresponding to transmitter fiber <NUM>, so as to receive backscattered signals from the volume of cloud atmosphere <NUM> that is probed by the uncollimated beam projected from transmitter fiber <NUM>.

Second uncollimated system <NUM> includes second optical transmitter <NUM> and second optical receiver <NUM>. Second uncollimated system <NUM> is similar to first uncollimated system <NUM>, except that polarization filters are not used. Another difference is that second uncollimated system <NUM> generates and detects signals of a second wavelength, different from the first wavelength used in first uncollimated system <NUM>. Cloud conditions measurement system <NUM> depicted in <FIG> differs from cloud conditions measurement system <NUM> depicted in <FIG>, in that only uncollimated beams are used for the probing cloud atmosphere <NUM> in the <FIG> embodiment.

Second optical transmitter <NUM> includes fiber-coupled laser <NUM>, transmitter fiber <NUM> and window <NUM>. Fiber-coupled laser <NUM> generates pulses of optical energy having the second wavelength. Transmitter fiber <NUM> transmits these pulses of optical energy to a projecting end of transmitter fiber <NUM>. These pulses of optical energy diverge from the projecting end of the transmitter fiber so as to become an uncollimated beam. The uncollimated beam then projects from transmitter fiber <NUM> to probe cloud atmosphere <NUM> via transmission through window <NUM>.

Cloud atmosphere <NUM> then backscatters the uncollimated beam that probes cloud atmosphere <NUM>. The backscattered signal then transmits through window <NUM>, bandpass filter <NUM>. Second optical receiver <NUM> includes receiver fiber <NUM>, and optical detector <NUM>. Receiver fiber <NUM> has a field of view commensurate with the field of view corresponding to transmitter fiber <NUM>, so as to receive backscattered signals from the volume of cloud atmosphere <NUM> that is probed by the uncollimated beam projected from transmitter fiber <NUM>.

<FIG> is a schematic diagram of an exemplary fiber bundle for use in a cloud conditions measurement system, such as that depicted in <FIG>. In <FIG>, fiber bundle <NUM> includes: optical fibers <NUM>, <NUM>, <NUM>, <NUM>, <NUM>; linear polarizers <NUM>, <NUM>, <NUM>; quarter wave plates <NUM>; bandpass filters <NUM>, <NUM>; and window <NUM>. Fiber bundle <NUM> depicts an exemplary embodiment of a portion of cloud conditions measurement system <NUM> depicted in <FIG>. The depicted configuration of optical elements shows transmitter fibers <NUM>, <NUM> bundled with receiver fibers <NUM>, <NUM>, <NUM>. Transmitter fibers <NUM>, <NUM> are adjacent to and aligned parallel to receiver fibers <NUM>, <NUM>, <NUM>. Such a configuration facilitates the alignment of receiver fibers <NUM>, <NUM> to corresponding transmitter fiber <NUM> and facilitates alignment of receiver fiber <NUM> to corresponding transmitter fiber <NUM>.

The depicted arrangement of optical elements in <FIG> also depicts transmitter fibers <NUM>, <NUM> that have substantially the same diameter as receiver fibers <NUM>, <NUM>, <NUM>. Such similarly sized fibers can provide similar fields of view for transmitter fibers <NUM>, <NUM> and receiver fibers <NUM>, <NUM>, <NUM>. Another advantage of the depicted configuration is that the resulting size of fiber bundle <NUM> is small, because of the compact arrangement of elements. One can direct transmitter fibers <NUM>, <NUM> and the receiver fibers <NUM>, <NUM>, <NUM> in a desired direction by bending the bundle of fibers <NUM>, <NUM>, <NUM>, <NUM>, <NUM> such that a projecting/receiving end <NUM> of fiber bundle <NUM> is oriented such that window <NUM> is has a normal vector directed in the desired direction for probing a cloud atmosphere.

<FIG> is a schematic diagram of a multiple-direction cloud conditions measurement system. In <FIG>, aircraft <NUM> is equipped with multiple-direction cloud conditions measurement system <NUM>. Multiple-direction cloud conditions measurement system <NUM> includes three fiber bundles 200a, 200b, 200c. Each of fiber bundles 200a, 200b, 200c can be directed in different directions relative to aircraft <NUM>. Each of fiber bundles 200a, 200b, 200c can transmit pulses of optical energy for probing cloud atmosphere <NUM> to and from optical transmitters and optical receivers, respectively. In some embodiments all three fiber bundles 200a, 200b, 200c can provide transmissions of optical signals simultaneously. In other embodiments, transmission of optical signals can be conducted sequentially in fiber bundles 200a, 200b, 200c.

<FIG> is a block diagram of an exemplary cloud conditions metric calculator. In <FIG>, optical cloud conditions metric calculator <NUM> includes: optical transmitter <NUM>, <NUM>; optical receivers <NUM>, <NUM>; processor <NUM>; memory <NUM> having data memory locations <NUM> and program memory locations <NUM>; cloud metrics calculation engine <NUM>; droplet size distribution calculator <NUM>; and input/output interface <NUM>. Each of the two optical transmitters <NUM>, <NUM> generates laser pulses of a specified wavelength and directs the generated pulses to a cloud atmosphere via optical bundle <NUM>. Each of the two optical receives <NUM>, <NUM> is then configured to receive light corresponding to one of the generated pulses and backscattered from the cloud atmosphere.

Processor <NUM> then receives backscattered signals from the optical receivers <NUM>, <NUM>. Processor <NUM> then calculates model parameters based on the received backscattered signals. Processor <NUM> communicates with data memory locations <NUM> and program memory locations <NUM> of memory <NUM>. Processor <NUM> communicates calculated model parameters to each of droplet size distribution calculator <NUM> and ice/liquid phase calculation engine <NUM>. Droplet size distribution calculator <NUM> calculates, based on the calculated model parameters, a size distribution of water particles in the cloud atmosphere. Droplet size distribution calculator <NUM> then communicates the calculated droplet size distribution to Processor <NUM>. In some embodiments, droplet size distribution calculation is performed by Processor <NUM>.

Ice/liquid phase calculation engine <NUM> calculates, based on the calculated model parameters, an ice/liquid ratio of water particles in the cloud formation. Ice/liquid phase calculation engine <NUM> then communicates the calculated ice/liquid ratio to Processor <NUM>. In some embodiments, calculation of an ice/liquid ratio is performed by Processor <NUM>. Processor 170in turn communicates both calculated droplet size distribution and ice/water ratio to a remote system via input/output interface <NUM>. An exemplary remote system can be a cloud parameter indicator located in a cockpit of an aircraft.

Processor <NUM>, in one example, is configured to implement functionality and/or process instructions for execution within cloud conditions metric calculator <NUM>. For instance, processor(s) <NUM> can be capable of processing instructions stored in storage device(s) <NUM>. Examples of processor(s) <NUM> can include any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other equivalent discrete or integrated logic circuitry.

Memory <NUM> can be configured to store information within cloud conditions metric calculator <NUM> during operation. Memory <NUM>, in some examples, is described as computer-readable storage media. In some examples, a computer-readable storage medium can include a non-transitory medium. The term "non-transitory" can indicate that the storage medium is not embodied in a carrier wave or a propagated signal. In certain examples, a non-transitory storage medium can store data that can, over time, change (e.g., in RAM or cache). In some examples, memory <NUM> is a temporary memory, meaning that a primary purpose of memory <NUM> is not long-term storage. Memory <NUM>, in some examples, is described as volatile memory, meaning that memory <NUM> do not maintain stored contents when power to cloud conditions metric calculator <NUM> is turned off. Examples of volatile memories can include random access memories (RAM), dynamic random access memories (DRAM), static random access memories (SRAM), and other forms of volatile memories. In some examples, memory 172is used to store program instructions for execution by processor <NUM>. Memory <NUM>, in one example, is used by software or applications running on cloud conditions metric calculator <NUM> (e.g., a software program implementing calculations of cloud conditions metrics) to temporarily store information during program execution.

In some examples, memory <NUM> can also include one or more computer-readable storage media. Memory <NUM> can be configured to store larger amounts of information than volatile memory. Memory <NUM> can further be configured for long-term storage of information. In some examples, memory <NUM> includes non-volatile storage elements. Examples of such non-volatile storage elements can include magnetic hard discs, optical discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories.

Input/output interface <NUM> can be used to communicate information between cloud conditions metric calculator <NUM> and an aircraft. In some embodiments, such information can include aircraft conditions, flying conditions, and/or atmospheric conditions. In some embodiments, such information can include data processed by cloud conditions metric calculator <NUM>, such as, for example, alert signals. Input/output interface <NUM> can also include a communications module. Input/output interface <NUM>, in one example, utilizes the communications module to communicate with external devices via one or more networks, such as one or more wireless or wired networks or both. The communications module can be a network interface card, such as an Ethernet card, an optical transceiver, a radio frequency transceiver, or any other type of device that can send and receive information. Other examples of such network interfaces can include Bluetooth, <NUM>, <NUM>, and Wi-Fi radio computing devices as well as Universal Serial Bus (USB). In some embodiments, communication with the aircraft can be performed via a communications bus, such as, for example, an Aeronautical Radio, Incorporated (ARINC) standard communications protocol. In an exemplary embodiment, aircraft communication with the aircraft can be performed via a communications bus, such as, for example, a Controller Area Network (CAN) bus.

<FIG> is a flow chart of an exemplary method for measuring cloud conditions. In <FIG>, method <NUM> is depicted from the perspective of processor <NUM> (shown in <FIG>). Method <NUM> begins at step <NUM> where processor <NUM> initializes index I. Then, at step <NUM>, processor <NUM> sends a command signal to optical transmitters <NUM>, <NUM> to generate a pulse of light energy. In response to the command signal, first optical transmitter <NUM> generates a first pulse of optical energy having a first wavelength, and second optical transmitter <NUM> generates a second pulse of optical energy having a second wavelength different from the first wavelength. Each of the first and second pulses of optical energy is then transmitted to fiber bundle <NUM>. A first transmitter fiber transmits the first pulse of optical energy from first optical transmitter <NUM> and projects the pulse of optical energy into a cloud atmosphere external to the aircraft. A second transmitter fiber transmits the second pulse of optical energy from second optical transmitter <NUM> and projects the pulse of optical energy into the cloud atmosphere external to the aircraft. Each of the first and second pulses of optical energy are projected into the cloud atmosphere in an uncollimated fashion, such that these projected pulsed of optical energy diverge.

At step <NUM>, processor <NUM> waits to receive backscatter signals from optical receivers <NUM>, <NUM>. When processor <NUM> receives backscatter signals corresponding to right-hand circularly polarized light and left-hand circularly polarized light from optical receiver <NUM> as well as a backscatter signal from optical receiver <NUM>, method <NUM> proceeds to step <NUM>. The received backscatter signals are received by receiver fibers that have a field of view commensurate with the field of view of the transmitter fibers. The backscatter signals are then transmitted from a receiving end of the receiver fibers to optical receivers <NUM>, <NUM>. When backscatter signals are received by optical receivers <NUM>, <NUM>, optical detectors detect the received signals and provide the detected received signals to processor <NUM>. At step <NUM>, processor <NUM> sends the received backscatter signals to droplet size distribution calculator <NUM> and to ice/liquid phase calculation engine <NUM>.

Then, at step <NUM>, processor receives calculated cloud metrics from droplet size distribution calculator <NUM> and ice/liquid phase calculation engine <NUM>. At step <NUM>, processor <NUM> generates a communication signal, based on the received calculated cloud metrics, and sends the communication signal to a pilot via input/output interface <NUM>. Then, at step <NUM>, processor <NUM> increments index I, and method <NUM> returns to step <NUM>, where processor <NUM> sends another command signal to optical transmitters <NUM>, <NUM> to generate new pulses of light energy.

A system for measuring cloud conditions includes a laser diode configured to generate a pulse of light energy. The system includes a transmitter fiber configured to receive the generated pulse of light energy and to project the received pulse of light energy into a cloud atmosphere. The projected pulse of light energy is projected over a field of view determined by a numerical aperture of a transmission end of the transmitter fiber. The system includes a receiver fiber having a reception end aligned proximate and substantially parallel to the transmission end of the transmitter fiber. The receiver fiber is configured to receive a portion of the transmitted pulse of light energy backscattered by the cloud atmosphere. The system also includes a detector configured to detect the portion of the transmitted pulse of light energy received by the receiver fiber. A numerical aperture of the reception end of the receiver fiber is substantially equal to the numerical aperture of the transmission end of the transmitter fiber.

The system of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: a processor; a second laser diode; a second detector; a second transmitter fiber; a second receiver; a third receiver fiber; a third detector; and/or a circular polarizing element.

The processor can be configured to calculate a super-cooled large droplet size based on the detected portion of the transmitted light energy received by the receiver fiber.

In some embodiments, the laser diode is a first laser diode, the pulse of light energy is a first pulse of light energy of a first wavelength, the transmitter fiber is a first transmitter fiber, the receiver fiber is a first receiver fiber, and the detector is a first detector. The second laser diode can be configured to generate a second pulse of light energy of a second wavelength different from the first wavelength. The second detector can be configured to detect the portion of the second pulse of light energy backscattered by the cloud atmosphere.

The second transmitter fiber can be configured to receive the generated second pulse of light energy and to project the received second pulse of light energy into a cloud atmosphere. The projected second pulse of light energy can be projected over a field of view determined by a numerical aperture of a second transmission end of the second transmitter fiber.

The second receiver fiber can have a reception end aligned proximate and substantially parallel to the transmission end of the second transmitter fiber. The second receiver fiber can be configured to receive a portion of the transmitted second pulse of light energy backscattered by the cloud atmosphere. A numerical aperture of the reception end of the second receiver fiber can be substantially equal to the numerical aperture of the transmission end of the second transmitter fiber.

The third receiver fiber can have a reception end aligned proximate and substantially parallel to the transmission end of the second transmitter fiber. The third receiver fiber can be configured to receive a portion of the transmitted second pulse of light energy backscattered by the cloud atmosphere.

The third detector can be configured to detect the portion of the transmitted second pulse of light energy received by the receiver fiber. A numerical aperture of the reception end of the third receiver fiber can be substantially equal to the numerical aperture of the transmission end of the second transmitter fiber.

The circular polarizing element can be configured to circularly polarize the second pulse of light energy. The second and third detectors can be configured to detect circularly polarized light energy of opposite polarization directions.

A further embodiment of any of the foregoing systems, wherein the numerical apertures of the transmission end of the transmitter fiber and the reception end of the receiving fiber can be greater than a predetermined threshold. In some embodiments, the predetermined threshold can be <NUM>, <NUM>, or <NUM>, for example. A further embodiment of any of the foregoing systems, wherein the second pulse of light energy is a collimated beam.

A method for measuring cloud parameters includes generating a pulse of light energy. The method includes diverging the generated pulse of light energy over a first solid angle greater than a predetermined threshold. The method includes projecting the diverged pulse of light energy into a cloud atmosphere. The projected pulse is projected in a projection direction aligned with a directional axis. The method includes receiving a portion of the projected pulse of light energy backscattered by the cloud atmosphere. The received portion is received over a second solid angle substantially equal to the first solid angle of the diverged pulse. The received portion is received from a reception direction substantially parallel to the directional axis. The method also includes detecting the received portion of the projected pulse of light energy.

The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: calculating a super-cooled large droplet size; generating a second pulse of light energy; projecting the generated second pulse of light energy into the cloud atmosphere; receiving a portion of the projected second pulse of light energy backscattered by the cloud atmosphere; detecting the received portion of the second pulse of light energy; diverging the generated second pulse of light energy over a third solid angle, wherein the third solid angle is substantially equal to the first solid angle; circularly polarizing the second pulse of light energy; and detecting a right-hand circularly polarized portion of the second pulse of light energy.

A further embodiment of any of the foregoing methods, wherein the numerical apertures of the transmission end of the transmitter fiber and the reception end of the receiving fiber can be greater than a predetermined threshold. In some embodiments, the predetermined threshold can be <NUM>, <NUM>, or <NUM>, for example. A further embodiment of any of the foregoing methods, wherein the second pulse of light energy is a collimated beam.

Claim 1:
A system for measuring cloud conditions comprising:
a laser diode (<NUM>) configured to generate a pulse of light energy;
a transmitter fiber (<NUM>) configured to receive the generated pulse of light energy and to project the received pulse of light energy into a cloud atmosphere, the projected pulse of light energy projected, without a lens, into a cloud atmosphere over a diverging field of view determined by a numerical aperture of a transmission end of the transmitter fiber;
a receiver fiber (<NUM>) having a reception end aligned proximate and substantially parallel to the transmission end of the transmitter fiber, the receiver fiber configured to receive, without a lens, a portion of the transmitted pulse of light energy backscattered by the cloud atmosphere, wherein a field of view of the receiver is substantially commensurate with the diverging field of view of the transmitter fiber; and
a detector (<NUM>) configured to detect the portion of the transmitted pulse of light energy received by the receiver fiber; and
a cloud conditions metric calculator (<NUM>) comprising a processor (<NUM>) configured to calculate model parameters based on the received backscattered signals,
wherein a numerical aperture of the reception end of the receiver fiber is substantially equal to the numerical aperture of the transmission end of the transmitter fiber.