Ice crystal detection and qualification by means of vertical weather cell structure

Description

BACKGROUND

[0001] The present invention is concerned with atmospheric ice crystals in and around clouds. Ice crystals are known to form in high altitude cloud structures as well as in and around developing and active convective activity. Areas with higher concentrations of atmospheric ice crystals pose significant risks to aircraft. Rather than accruing on aircraft surfaces, atmospheric ice crystals abrade and damage critical aircraft elements, such as engine components and pilot systems. This damage can be difficult to detect and can lead to costly repairs.

[0002] While pilots generally avoid convective activity, they do operate in high altitude cloud structures, as well as above, around, and below the strongest areas of convective activity. Currently, these convective areas can be detected by in-flight weather radar and lightning detection equipment on board the aircraft, and by dual polarimetric methods on the ground. Research and flight test data indicates that the radar measured echo strength for areas with higher Ice Water Content (IWC) tend to decrease at a slower rate with altitude / temperature than for areas that do not have higher probability IWC. However, there is currently no instruments capable of detecting ice crystals at longer ranges. Additionally, although current in-flight weather radar can infer the presence of ice crystals, they are prone to nuisance alerts and hence need to be qualified. Ice detection is disclosed in US 2019 / 113618 A1.SUMMARY

[0003] A system and method for ice crystal detection and qualification are provided as defined in claims 1 and 12. According to the invention, echo power is determined using a mechanically steered radar performing continuous or successive scans at different elevations with each scan spaced in time. In addition, an electronically steered antenna (ESA) may be utilized to perform two elevations scans that are not spaced in time. The echo power is analyzed to detect and then qualify the presence and location of IWC in two ways: (1) Detection 100 and (2) Qualification 200. Through detection 100, the radar signal processor (RSP) may directly use a vertical storm characteristic model to determine and annunciate the presence of ice crystals. Through qualification 200, in order to reduce nuisance alerts, the RSP may use other algorithms such as functions relating single pulse reflectivity (Z) and IWC to determine the probability of icing and use the vertical storm characteristics to qualify detection.

[0004] In other embodiments, the airborne radar may also consider vertical storm structure to infer the presence of ice crystals. For areas with high probability of ice crystals, the reflected power changes with altitude / temperature at a rate slower than the rate of areas with a lower probability of ice crystals. The radar computes a power residual based on scans at different elevations and compares a pair of scans against a threshold. Icing is confirmed if the power residual is less than the threshold. This method is also used to qualify ice crystals and hence reduces the probability of nuisance alerts.

[0005] In preferred embodiments of the present invention, first in-flight radar echo power is computed from at least two antenna elevations. Next, the logarithm of the powers is computed for the at least two elevations using an area parameter to reduce signal noise. A power residual which is computed as the ratio of the logarithm of the power is then computed and compared to a threshold. Aircraft crew may then be informed aurally or visually of water ice crystal presence when the determined ratio is lower than the selected or determined ratio.

[0006] This Summary is provided solely as an introduction to subject matter that is fully described in the Detailed Description and Drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The detailed description is described with reference to the accompanying figures. The use of the same reference numbers in different instances in the description and the figures may indicate similar or identical items. Various embodiments or examples ("examples") of the present disclosure are disclosed in the following detailed description and the accompanying drawings. The drawings are not necessarily to scale. In general, operations of disclosed processes may be performed in an arbitrary order, unless otherwise provided in the claims. In the drawings: FIG. 1is a flow diagram illustrating an embodiment of an IWC detection system of the present invention; and FIG. 2is a flow diagram depicting an embodiment of the IWC detection and qualification system of the present invention; and FIG. 3is an illustration of a first example of the power (dB) returns of first and second radar scans at a first and second elevation; and FIG.4is an illustration of a first example of a power residual and an estimate of the location of IWC in accordance with an embodiment of the present invention. DETAILED DESCRIPTION

[0008] Reference will now be made in detail to the subject matter disclosed, which is illustrated in the accompanying drawings.

[0009] Before explaining one or more embodiments of the disclosure in detail, it is to be understood that the embodiments are not limited in their application to the details of construction and the arrangement of the components or steps or methodologies set forth in the following description or illustrated in the drawings, and the scope of the invention is defined by the claims.

[0010] A system and method for ice crystal detection and qualification are disclosed.

[0011] Applicant's research and flight test data indicates that the radar measured echo strength for areas with higher IWC tend to decrease at a slower rate with altitude / temperature than for areas that do not have higher probability of IWC. Echo power is determined using a mechanically steered radar performing continuous or successive scans at different elevations with each scan spaced in time. In addition, an Electronically Steered Antenna (ESA) may be utilized to perform two elevations scans that are not spaced in time. The echo power is analyzed to detect and then qualify the presence and location of water ice crystals in two ways: (1) Detection 100 (FIG. 1): The Radar Signal Processor (RSP) may directly use a vertical storm characteristic model to determine and annunciate the presence of ice crystals; and (2) Qualification 200 (FIG. 2): In order to reduce nuisance alerts, the RSP may use other algorithms such as functions relating single pulse reflectivity (Z) and IWC to determine the probability of icing and use the vertical storm characteristics to qualify detection.

[0012] Referring to FIG. 1, the system performs a pre-processing phase 102 followed by an IWC detection phase 104. During the pre-processing phase 102, the RSP commands the antenna to perform at least two scans 106 in at least two elevations. The elevation angles of the at least two scans 106 may depend, for example, on the aircraft altitude, static air temperature measured by the aircraft, total temperature, pressure, lapse rate, terrain, echo strength gradient, reflectivity gradient, and the like, as these variables may affect air density, light scattering, and radar functions. The echoes received from each elevation are sampled and stored in memory 108. During these scans 106, the radar can transmit a single pulse or a series of pulses. The pulse rate may be set at a rate that will not interfere with the transmission or receipt of sequential pulses. These pulses can be unmodulated pulses or can have some form of amplitude, frequency or phase modulation. For each pixel sampled for the at least two scans, the RSP computes the raw power, performs a log operation on the power to convert it into dB 110, and filters this power in dB to reduce noise and other unwanted echoes 112. For example, according to: Power dB = 10 ∗ log 10 raw power

[0013] Power is the radar echo strength for each range bin / pixel in front of the aircraft. It is a function of several radar parameters, such as transmitter power, antenna gain, frequency, and the like, as well as several environmental factors, such as the amount of rain, the ground, and the like. Power is calculated as I 2< + Q 2< , where I and Q are analog to digital voltage values.

[0014] Using the log power from the different elevations, the processing circuitry computes a power residual for all pixels 114. For a two-elevation scheme 300 with a first elevation with a certain power 302 and a second elevation with another power 304, the power residual 402 may be calculated as follows: Power Residual = Power dB at elevation 1 − Power dB at elevation 2

[0015] According to the invention, the power residual is computed as follows in equation 3: Power Residual = 10 ∗ log 10 Power dB at elevation 1 Power dB at elevation 2

[0016] This power residual is then compared with a threshold value 116. This exact threshold value is obtained based on data analyses and may vary for different IWC intensities (e.g., moderate vs high). An icing flag is set and IWC is annunciated if the power residual is less than the threshold 118. The logic for this comparison may be determined from: IF (power residual for a pixel or an area of pixels < threshold) THEN IWC for the pixel or area of pixels = TRUE ELSE IWC for the pixels or area of pixels = FALSE

[0017] In a power residual and IWC analysis 400, the RSP may assign a predetermined symbol (for example, yellow or red speckles) for each pixel or area of pixels where the IWC flag is TRUE and then send this information to be displayed 404.

[0018] In the case that the power residual is higher than the threshold, IWC is not annunciated and the system continues to other regions, if any exist 120.

[0019] Referring to FIG. 2, in this embodiment, the vertical storm structure is used for qualification 202 of detected IWC 200. For each pixel sampled, the RSP computes a reflectivity based on the measured power. Reflectivity (Z) is the sum of the diameter of each hydrometeor raised to the sixth power per cubic meter. It is a function of particle diameter and particle density, as well as a function of range. In relation to range, reflectivity decreases as a second power or fourth power. Reflectivity cannot be directly measured by a radar, but instead must be estimated based on radar parameters. The relationship between received power and reflectivity is calculated according to methods used by those skilled in the art. The industry standard term for this reflectivity is 'Z'. A log operation is performed on this Z which results in a parameter with units of dBZ. Z = f Power dBz = 10 ∗ log 10 Z

[0020] The RSP then computes an estimate to IWC based on the relationship between Z and IWC 204. One example of dBz-IWC relationship is given as: IWC = A B ∗ dBz C + D

[0021] Where the IWC is grams per cubic meter. The values of A, B, C and D will depend on several factors including altitude, static air temperature, total temperature, pressure, lapse rate, terrain, echo strength gradient, reflectivity gradient, and the like.

[0022] Preferably, the calculated IWC is then qualified to confirm real events and eliminate false or nuisance detection. In a preferred embodiment the qualification logic resembles the previously described detection logic. For the pixels having a valid IWC detection (for example, IWC > 0.8 grams per cubic meter), the power residual in that pixel or an area of pixels is compared to a threshold 208. The IWC in a pixel or an area of pixels is qualified and an icing flag is set to TRUE if the power residual is less than a predetermined threshold 210. All other IWC values are disqualified and a corresponding IWC flag for that pixel is set to false 212. The RSP can then assign a predetermined symbol (for example, yellow or red speckles) for each pixel or area of pixels whose IWC flag is TRUE and send this information to be displayed 210.

[0023] In further embodiments, the ice water crystal detection and qualification system may also utilize successive echo power versus reflectivity in determining the location and presence of ice water crystals in the flight path of an aircraft. For example, the system may calculate the presence and location (altitude and coordinates) via successive comparisons of a first comparison of the echo power of a pair of successive beams at different elevations against a second comparison of the reflectivity of a pair of successive beams at different elevations. Power and reflectivity below a set threshold calculated according to atmospheric characteristics (e.g., static temperature, total temperature, pressure, lapse rate, terrain, echo strength gradient, reflectivity gradient, and the like) are used to detect the presence and locations of ice crystals.

Claims

1. An ice water content detection system comprising: a weather radar device, comprising a mechanically steered radar, the weather radar device being configured to transmit a first beam comprising radar signals at a first elevation; receive a reflection of the first beam at a first time, transmit a second beam comprising radar signals at a second elevation after transmitting said first beam, the second elevation being different from the first elevation; and receive a reflection of the second beam at a second time; and detect the presence of ice crystals by measuring a vertical gradient of return power of the radar signals reflected from weather targets processing circuitry configured to: determine a logarithm of the echo power based on the reflection of the first beam; determine a logarithm of the echo power based on the reflection of the second beam; determine a ratio of the logarithm of the echo power of said first and second beams respectively; compare said ratio of the logarithm to a threshold at least partially derived by air temperature; qualify the ice crystals according to the vertical gradient of return power from the weather targets; and announce the presence of ice water crystals if said ratio is lower than said threshold; and a display system configured to: display different colors corresponding to different calculated ratios of logarithms of echo powers to the threshold.

2. The ice water content detection system of claim 1, wherein the first and second elevation angles may depend at least partially on aircraft altitude, static air temperature, total air temperature, pressure, lapse rate, terrain, echo strength gradient, reflectivity and other factors known to the art.

3. The ice water content detection system of claim 1 or 2, wherein the first and second beams can be a single pulse or a series of pulses.

4. The ice water content detection of claim 3, wherein the single pulse or the series of pulses can be modulated or unmodulated.

5. The ice water content detection system of any preceding claim, wherein the echo power of the first and second beams is translated from a raw value into a decibel value via a log operation.

6. The ice water content detection system of claim 5, wherein the decibel value is further filtered to reduce noise and other unwanted echoes.

7. The ice water content detection system of any preceding claim, wherein the processing circuitry is further configured to generate an output displaying the presence of ice crystals in response to determining the presence of ice crystals relative to the position of an aircraft.

8. The ice water content detection system of claim 7, wherein the processing circuitry is further configured to determine and display a location of a storm cell based on the echo power of the first and second beams in a volume of space downwind from said storm cell.

9. The ice water content detection system of claim 8, wherein the processing circuitry is further configured to: classify and display a first portion of said volume of space as ice crystals by displaying a first color; classify and display a second portion of said volume of space as rain by displaying a second color; classify and display a third portion of said volume of space by displaying a third color; and classify and display a fourth portion of said volume of space as mixed phase by displaying a fourth color.

10. The ice water content detection system of any preceding claim, wherein the weather radar device is further configured to: transmit a first and a second beam not spaced in time via an electronically steered antenna; receive a first reflection of the first beam via the electronically steered antenna; and receive a second reflection of the second beam via the electronically steered antenna; and the processing circuitry is configured to: determine the logarithm of the echo power based on the reflection of the not spaced first beam; determine the logarithm of the echo power based on the reflection of the not spaced second beam; determine the ratio of the logarithms of the echo powers of said not spaced in time first and second beams; compare said ratio of the logarithms of the echo powers of said not spaced in time first and second beams to a threshold at least partially derived by air temperature; and announce the presence of ice water crystals if said ratio of the logarithms of the echo powers of said not spaced in time first and second beams is lower than said threshold.

11. The ice water content detection system of any of claims 1 to 9, wherein the weather radar device is further configured to: transmit a first beam comprising radar signals at a first elevation via an electronically steered antenna; receive a reflection of the first beam at a first time via the electronically steered antenna, transmit a second beam comprising radar signals at a second elevation after transmitting said first beam via the electronically steered antenna; and receive a reflection of the second beam at a second time via the electronically steered antenna; the processing circuitry is configured to estimate reflectivity values for the first beam and the second beam; compare echo power values for the first beam and the second beam; compare the reflectivity values for the first beam and the second beam; and calculate the presence and location of ice water crystals via a comparison of the echo power values and the reflectivity values for the first and second beams.

12. A method for detecting ice water content, the method comprising: transmitting, by means of a mechanically steered radar, a first beam comprising radar signals at a first elevation receiving, by means of the mechanically steered radar, a reflection of the first beam transmitting, by means of the mechanically steered radar, a second beam comprising radar signals at a second elevation after transmitting said first beam, the second elevation being different from the first elevation; and receiving, by means of the mechanically steered radar, a reflection of the second beam at a second time; detecting the presence of ice crystals by measuring a vertical gradient of return power of the radar signals reflected from weather targets determining the logarithm of the echo power based on the reflection of the first beam determining the logarithm of the echo power based on the reflection of the second beam determining the ratio of the logarithms of the echo powers of said first and second beams respectively; comparing said ratio of the logarithms to a threshold at least partially derived by air temperature; qualifying the ice crystals according to the vertical gradient of return power from the weather targets; and announcing the presence of ice water crystals if said ratio is lower than said threshold; and displaying different colors corresponding to different calculated ratios of logarithms of echo powers to the threshold