Patent Publication Number: US-9846230-B1

Title: System and method for ice detection

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. application Ser. No. 13/841,893, now U.S. Pat. No. 9,244,166, filed on Mar. 15, 2013, which is related to U.S. application Ser. No. 13/717,052, now U.S. Pat. No. 9,395,438, filed on Dec. 17, 2012, which is a Continuation of U.S. application Ser. No. 12/075,103, now U.S. Pat. No. 8,902,100, filed on Mar. 7, 2008, entitled “SYSTEM AND METHOD FOR TURBULENCE DETECTION” by Woodell et al., and the present application is also a continuation in-part of U.S. patent application Ser. Nos. 14/206,239, 14/207,034, and 14/206,651 all of which are incorporated herein by reference in their entireties and assigned to the Assignee of the present application. U.S. patent application Ser. No. 11/370,085, now U.S. Pat. No. 7,515,087, U.S. patent application Ser. No. 11/402,434, now U.S. Pat. No. 7,486,219, U.S. patent application Ser. No. 11/256,845, now U.S. Pat. No. 7,598,902, and U.S. patent application Ser. No. 10/631,253 now U.S. Pat. No. 7,129,885 are herein incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     This disclosure relates generally to the detection of ice or ice crystals in the atmosphere. 
     Hazardous weather is generally associated with convective weather cells. Convective weather cells can produce turbulence, high winds, lightning, hail, and other weather hazards. In addition, convective cells can provide large updrafts that loft large amounts of moisture to higher altitudes (e.g., high portions troposphere). The moisture can be super cooled liquid at temperatures much colder than the freezing point of water because the water was lofted quickly by the updraft and has not encountered condensation nuclei upon which to crystallize as ice. 
     Non-convective rain clouds (e.g., stratiform rain) can also include ice crystals. Non-convective rain clouds are striated with temperature. At low altitudes where the temperature is above the freezing point, liquid water is present as rain. At high altitudes where the temperature is below the freezing point, ice crystals form. 
     Conventional aircraft hazard weather radar systems, such as the WXR 2100 MultiScan™ radar system manufactured by Rockwell Collins, Inc., have Doppler capabilities and are capable of detecting at least four parameters: weather range, weather reflectivity, weather velocity, and weather spectral width or velocity variation. The weather reflectivity is typically scaled to green, yellow, and red color levels that are related to rainfall rate. The radar-detected radial velocity variation can be scaled to a turbulence level and displayed as magenta. Such weather radar systems can conduct vertical sweeps and obtain reflectivity parameters at various altitudes and can detect the presence of ice using reflectivity parameters and temperature. However, such detection of ice cannot be performed at longer ranges. In some embodiments, the radar may be a single frequency radar (e.g., X-band radar) or a multi-frequency radar (e.g., a radar with both X-band and Ka-band frequencies). In some embodiments, the single or multi-frequency radar may include polarization diversity capabilities. 
     Ice or ice crystal formation at high altitudes can pose various threats to aircraft. Flying through ice or ice crystal formation at high altitudes can cause engine roll back, engine stall, engine flameout, and incorrect airspeed measurements. Detecting areas of ice and ice crystal formation at longer ranges is desirable so that pilots can avoid such areas. 
     Thus, there is a need for a system and method for more accurate, long range detection of ice and/or ice crystals high in the troposphere. There is also a need for inferring the existence of ice and/or ice crystals based on the detection and analysis of convective cells or hazards associated therewith. There is also a need to distinguish highly convective ice crystal formation areas form non-convective stratiform rain areas that do not produce high altitude ice crystals. Further still, there is a need to detect and locate convective cells by measuring the amount of moisture (e.g., liquid water, such as total water content) present at altitudes where the temperature is below the freezing point. Yet further, there is a need for an aircraft hazard warning system optimized to determine the location and presence of large areas of high altitude ice resulting from convective cell blow off. Further, there is a need for an aircraft hazard warning system that includes inferential ice detection and location. 
     It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs. 
     SUMMARY 
     One embodiment of the disclosure relates to an aircraft weather radar system. The aircraft weather radar system can include a radar antenna and a processor. The radar antenna receives radar returns and a processor. The processor can be configured for: 1. identifying on a display a region of potential ice associated with a blow off region in response to the radar returns, temperature data, and wind data; or 2. identifying on a display a region of potential ice associated with a stratiform region in response to radar returns, temperature data, and a history of convective cells in the stratiform region. 
     Another embodiment of the disclosure relates to a method of displaying an indication of a presence of ice on an aircraft display in an avionics system. The method includes receiving radar reflectivity data and temperature data and determining a presence of at least one stratiform rain area, determining whether at least one convective cell was present in the stratiform rain area, and providing the indication in response to a size of the stratiform rain area. 
     Another embodiment of the disclosure relates a method of displaying an indication of a presence of ice on an aircraft display in an avionics system. The method includes receiving radar reflectivity data and temperature data and determining a presence of at least one convective cell, and providing the indication at least in part in response to a wind parameter and a size of the convective cell. 
     Another embodiment relates to an aircraft hazard warning system. The aircraft hazard warning system includes a processing system for determining a presence of ice crystals. The processing system receives radar reflectivity data, and temperature data, and determines an ice crystal warning by: 1. determining a size of a convective cell using the radar reflectivity data, and temperature data and determining a blow off area associated with the convective cell in response to the size and a wind direction parameter, the blow off area being an area where ice crystals migrate due to wind; or 2. determining a size of a stratiform region and determining a presence of a convective cell previously in the stratiform region. 
     Another exemplary embodiment relates to an apparatus for determining a presence of a convective cell in an environment of an aircraft. The apparatus includes an input for radar reflectivity data and temperature data, and a processing system for determining the presence of the convective cell. The processing system receives the radar reflectivity data and the temperature data and determines the presence of the convective cell by determining an amount of liquid water present at altitudes above the freezing point. 
     Another exemplary embodiment relates to an aircraft warning system that provides a level of an icing condition on a display, the level can be one of two or more icing levels above no icing condition level. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will become more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like elements, in which: 
         FIG. 1  is a block diagram of a hazard warning system according to an exemplary embodiment; 
         FIG. 2  is a functional flow diagram of a process executed in the hazard warning system of  FIG. 1  according to an exemplary embodiment; 
         FIG. 3  is a functional flow diagram of a process executed in the hazard warning system of  FIG. 1  according to an exemplary embodiment; and 
         FIG. 4  is a functional flow diagram of a process executed in the hazard warning system of  FIG. 1  according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Before describing in detail the particular improved system and method, it should be observed that the invention includes, but is not limited to a novel structural combination of conventional data/signal processing components and communications circuits, and not in the particular detailed configurations thereof. Accordingly, the structure, methods, functions, control and arrangement of conventional components software, and circuits have, for the most part, been illustrated in the drawings by readily understandable block representations and schematic diagrams, in order not to obscure the disclosure with structural details which will be readily apparent to those skilled in the art, having the benefit of the description herein. Further, the invention is not limited to the particular embodiments depicted in the exemplary diagrams, but should be construed in accordance with the language in the claims. 
     An aircraft hazard warning system or other avionic system may infer or otherwise detect ice or ice crystals and provide a warning with respect to the geographical location and/or altitude of the ice crystals in one embodiment. The hazard warning system can detect blow off regions above convective regions as regions of inferred ice crystal detection in one embodiment. The hazard warning system can detect ice hazard regions associated with stratiform rain that follows convective cells in another embodiment. The system can combine direct detection of ice particles with inferred detection of ice particles to provide a unified indication of hazard. Alternatively, inferred detection of ice particles can use a different indication than direct detection. 
     The current regulatory environment as defined by governmental regulatory agencies supports display of basic radar sensor information as red, yellow, and green for radar reflectivity calibrated to rainfall rate and magenta as turbulence. The regulatory agencies do not currently provide guidance for changing the definition of the radar display based on inferred hazards. The radar display format may be selected to display radar colors consistent with turbulence and rainfall rate as currently defined by regulatory authorities or as defined in the future by such authorities. A hazard assessment indication can be provided in a manner that does not interfere with display of standard weather data. In one embodiment, a speckled yellow region is used for areas where ice is detected (directly or inferred) in a horizontal view and a vertical view on a weather radar display. 
     Referring to  FIG. 1 , a weather radar system or hazard warning system  10  includes sensor inputs  12 , a processor  14 , a display  16 , a user input  18 , and a memory  20 . Hazard warning system  10  may acquire horizontal and/or vertical reflectivity profiles and direct turbulence detection information via sensor inputs  12 . Sensor inputs  12  generally include a radar antenna  22 , a wind detector  23 , a lightning detector  24 , and a temperature sensor  26 . According to other exemplary embodiments, sensor inputs  12  may include any type of sensor or detector that may provide data related to direct or inferred measurement or detection of weather conditions and/or hazards. 
     Wind detector  23  can be part of processor  14  or separate from processor  14 . Detector  23  provides a wind parameter. The wind parameter can be high altitude wind speed and direction data. The data can be calculated from track angle and heading of the aircraft, or be provided by the flight management system (FMS) or other navigation equipment. The wind parameter data can also be provided by a source remote from the aircraft. 
     In one embodiment, the hybrid approach of hazard warning system  10  correlates radar reflectivity and lightning data to overcome the shortcomings of the lightning strike inaccuracy. The hybrid approach determines lightning strike position relative to radar reflectivity measurements, with sufficient accuracy, to make a convective assessment on a weather event. 
     Processor  14  is generally configured to process data received from sensor inputs  12  to determine a hazard threat level, receive input from user input  18 , and provide hazard indication on display  16 . Processor  14  includes ice detector  28 , convective cell detector  29 , and cell tracker  30 . Processor  14  can generate a velocity parameter  32  or other Doppler data, a spectral width parameter  34 , a reflectivity parameter  36 , and a range parameter  38  based on return data from sensor inputs  12 , data or commands from user input  18 , or data or instructions from memory  20 . According to various exemplary embodiments, processor  14  can be any hardware and/or software processor or processing architecture capable of executing instructions and operating on data related to hazard detection. According to various exemplary embodiments, memory  20  can be any volatile or non-volatile memory capable of storing data and/or instructions related to hazard warning system  10 . 
     Ice detector  28  is configured to provide inferred detection of regions of based upon the strength of a convective cell ice in one embodiment. In one embodiment, convective cell detector  29  uses vertical sweeps on weather cells to assess the vertical extent of moisture with respect to altitude. Air temperature data from sensor  26  (e.g., temperature measurements) can be used to assess air temperature with respect to altitude. Detector  29  can use the combination of reflectivity and temperature to determine the convective strength of the cell. 
     Temperature data can include a local atmospheric temperature, local temperature variations with time, local temperature variations with altitude, a remotely determined temperature, and/or remotely determined temperature gradients in either range or altitude. Detector  29  can receive data inputs derived from one or more of spectral width parameter  34 , reflectivity parameter  36 , and/or range parameter  38  to assess and locate convective cells. 
     Detector  28  can use the assessed convective strength of the cell to determine the updraft potential of the cell and hence, the potential of the cell to loft moisture high into the atmosphere where ice crystals form. Higher indications of reflectivity at higher altitudes and lower temperatures indicates a stronger cell and greater potential for ice formation. A specific reflectivity at an altitude where the temperature is at or below the freezing level may indicate the presence of a convective cell. Accordingly, areas above such cells are indicated as warning areas associated with ice. Weaker or smaller cells have less probability of up drafting moisture that forms ice. 
     In addition, processor  14  can use a direct measurement of spectral width, for example spectral width parameter  34 , from radar antenna  22  to assess the strength of the convective cell. In one embodiment, processor  14  can use a hybrid approach of that correlates radar reflectivity and lightning data from detector  24  to make a convective assessment on a weather event. 
     The detection of lightning generally indicates the presence of a convective cell and of turbulence within the cell. Detection of a single lightning bolt can infer the presence of a convective cell. The use of lightning history data may provide a more accurate inferred convective cell assessment. If lighting history indicates a high lighting strike rate in a given cell the probability of convection with high magnitude within that cell is high. 
     Reflectivity parameter  36  can include data related to area reflectivity, gradient reflectivity, magnitude reflectivity, reflectivity shape, and/or a sharp change in reflectivity. Very high gradients (e.g., rapid changes from red to black to yellow) can indicate the presence of a convective cell and thus turbulence. According to one exemplary embodiment, the very high gradient may be a change in cell reflectivity within a few range bins (e.g., one nautical mile). According to another exemplary embodiment, the very high gradient may be a change in cell reflectivity within three nautical miles. In some embodiments, reflectivity information can be used to compute an area and/or volume of reflectivity, and the area and/or volume of reflectivity can be used to determine the convective level associated with the cell. In some embodiments, the volume of reflectivity may be translated into a Vertical Integrated Reflectivity measure. Further information regarding computation of areas and/or volumes of reflectivity can be found in the parent U.S. Patent Application titled “Weather Hazard Threat Level Computation and Display,” U.S. application Ser. No. 13/837,538 filed concurrently with the U.S. application Ser. No. 13/841,893, filed on Mar. 15, 2013, which is incorporated herein by reference in its entirety. 
     If a cell is detected to be growing at a very high rate, it may be a convective cell containing turbulence. If a cell is detected that has grown at a very high rate in the past, the cell may be convective and contain turbulence. For example, the growth may be detected by a vertical structure analysis. The vertical structure analysis data may include vertical height, vertical growth rate, a vertical history assessment, an assessment of whether the aircraft path will intersect a portion of a weather cell, and/or cell maturity data. 
     In one embodiment, detector  29  can determine the amount of liquid water at altitudes at temperatures below the freezing point as an indication of a strong convective cell. Amount of liquid can be detected using the reflectivity parameter. In this way, detector  29  can distinguish between non-convective and convective cells because convective cells cause larger amounts of super cooled water to be up drafted above the freezing point altitude. 
     Convective cell detector  29  can process at least one of parameters  34 ,  36 ,  38  and/or data from detector  24  to provide a convective hazard indication on display  16 . In addition, detector  29  can cause system  10  to perform further analysis in response to information from lightning detector  24  and/or a parameter  34 ,  36 ,  38 . The further analysis can even include causing system  10  to perform weather radar queuing and control in elevation and azimuth as well as examining new data or historical data. 
     After acquiring data from sensor inputs  12 , processor  14  may use a variety of processing techniques to assess the ice hazard levels and regions. Processor  14  may identify and track relevant weather cells via cell tracker  30 . The cells may be prioritized in terms of their threat to the aircraft and detailed vertical scans can be conducted on high priority targets. Tracker  30  can store a history of cell locations and cell characteristics including but not limited to cell strength, size, vertical height, vertical growth rate, and/or cell maturity data. 
     Ice detector  28  uses data associated with areas around convective cells and former convective cells to provide warnings related to the potential presence of ice or actual presence of ice. In one embodiment, ice detector  28  can advantageously detect large areas of high altitude ice resulting from convective blow off or from areas of old convection which are difficult to detect using conventional techniques. Ice in these areas is difficult to detect because convective cells are not necessarily located in the regions (e.g., areas of zero convectivity). Generally, it is more difficult to detect ice crystals with conventional techniques when the ice crystals are not being actively formed such as in blow off regions or stratiform rain regions. 
     Blow off regions are areas of ice presence due to ice crystals being blown from the top of a convective cell by high altitude winds. High altitude ice can also remain above old convective cells (no longer existing cells). A convective cell is an old convective cell if it existed over the region within a predetermined amount of time (e.g., past 5 minutes, past 10 minutes, etc.). Applicants believe that such high altitude ice is generally present over the area associated with old strong convective cells or multiple old convective cells that is occupied by stratiform rain clouds. The larger the stratiform rain area that follows the old convective cell and the more embedded cells of convectivity in the stratiform rain region, the higher the likelihood of presence of ice. Stored history of cell locations and characteristics can be used to identify whether an old convective cell existed in the region and its characteristics while in the region. 
     With reference to  FIG. 2 , a method  200  can be performed by system  10  to provide a warning of a presence of ice in the vicinity of an aircraft. At a step  202 , convective cell detector  29  can detect one more convective cell by any technique. In one embodiment, convective cells can be identified and located using weather radar data. For example, processor  14  can detect the presence of reflectivity at a certain range (e.g.,  100 ,  80 ,  40  nautical miles) and perform a vertical sweep to determine a level of conductivity in accordance with the algorithms discussed in the patents and applications incorporated herein by reference. In one embodiment, detector  29  can use vertical structure analysis. In one embodiment, the size and location of the convective cell is obtained. 
     At a step  204 , the convective cell is assessed to determine if the cell has a potential for providing high altitude ice by detector  28 . Generally, the larger and stronger the cell, the higher the probability of providing high altitude ice. High altitude ice can be directly sensed using radar returns in one embodiment. If there is a potential for high altitude ice formation, detector  28  determines a size and location of the blow off region at a step  206 . If there is no or less potential for high altitude ice formation, processor  14  can return to step  202 . 
     In some embodiments, the radar or avionics equipment may receive uplink or off-aircraft information regarding detected and/or forecast regions with icing or icing potential. The radar may be used to qualify or confirm the assessment by adjusting radar parameters when scanning the detected regions (e.g., gain, etc.), increasing the dwell time in those regions, performing additional scans in those regions, etc. The off-aircraft assessment may be used to increase the confidence in the icing assessment and be used to display an icing hazard warning in that region. In some embodiments, the uplink or remote information (e.g., from ground, other aircraft, satellite, etc.) may include an observation or forecast of one or more of weather information of interest, including icing potential, convective level, size, maturity, reflectivity, winds, temperature, etc. The information can be utilized in performing the icing threat assessment. The icing threat assessment and information originating on the aircraft for the icing assessment may also be down linked or sent to a ground station or off-aircraft system, so that the off-aircraft system can aggregate multiple aircraft observations for the development of a global icing map or global icing forecast that can then be uplinked to other aircraft in the vicinity or using the airspace in the future. 
     At step  206 , detector  28  uses a high altitude wind parameter and the strength of the convective to determine the size and location of the blow off region. The size and location of the blow off region is determined from the wind speed and direction. The size is generally greater if the strength of the convective cell is greater and the wind speed is greater. At a step  210 , the blow off region is displayed as a hazard or warning area. The blow off region can be displayed as a speckled yellow or red area, other color region, or with other symbols. After step  210 , processor  14  can return to step  202 . In some embodiments, an overshooting top may indicate a cell spreading out regardless of wind speed. For example, a cell could spread in all directions even if there is no significant wind or a downwind condition is present. 
     In some embodiments, the radar response may be received from a multi-frequency radar system, and the radar response from at least two frequencies may be compared to determine the likelihood of ice formation. The difference or ratio between the signals can be used to separate ice detection from traditional rain detection. For example, the larger the response differences from the two frequencies, the greater the likelihood is that the response is from icing. 
     In some embodiments, the radar response may be received from a polarization diversity radar system, and the radar response from at least two polarization diverse radar signals are compared. The difference or ratio between the signal may be used to separate ice detection from traditional rain detection. For example, the larger the ratio between the horizontal and vertical polarization radar signals, the greater the likelihood that the response is from icing. 
     In some embodiments, the icing assessment may not be binary (i.e., may not be merely “ice threat” or “no ice threat”). The icing assessment may include a scaled assessment, such that the icing threat potential is identified as one of several levels (e.g., low/medium/high, number on a numerical scale, etc.). In some embodiments, colors, shading, patterns, symbols, icons, etc. used to display the icing threat may be mapped to the different graduated icing levels. 
     In some embodiments, the icing assessment may be predictive. Weather information associated with a region may indicate an increasing likelihood of icing or may indicate a weather trend that, if it continues, may result in the region experiencing some icing at a future time. In some embodiments, prediction based on regional weather information and/or weather trends may be utilized, alone or in combination with other factors described herein, to provide a predictive icing assessment. In some embodiments, colors, shading, patterns, symbols, icons, etc. may be used to indicate that a displayed threat is related to a predictive icing assessment. 
     With reference to  FIG. 3 , a method  300  can be performed by system  10  to provide a warning of a presence of ice in the vicinity of an aircraft. At a step  302 , convective cell detector  29  can detect stratiform rain by any technique. In one embodiment, stratiform rain can be located using weather radar data. In one embodiment, detector  29  can determine stratiform rain in response to a reflectivity parameter and a spectral width parameter which indicate the presence of rain without convection. Other techniques for identifying stratiform rain can be utilized. 
     At a step  304 , the area associated with the stratiform rain is analyzed to determine whether a convective cell or front of convective cells existed within a predetermined time. Detector  29  can use cell tracker to determine whether an old convective cell existed in the region of interest. For example, a Midwestern United States squall line can produce convective cells behind the squall line in areas of stratiform rain. A high density of these conductive cell indicates a higher probability of ice regions. 
     If an old convective cell existed, processor  14  advances to a step  306  and detector  28  determines an ice region based upon the size of the stratiform rain and the number of old convective cells associated with the region. If an old convective cell did not exist, processor  14  returns to step  302 . The size of a cell is generally directly proportional to the age/longevity or maturity of the cell. 
     Generally, the larger the stratiform rain region and the more embedded cells, the larger region of potential ice crystals. Detector  28  can determines a size and location of the ice region using wind data. 
     At a step  310 , the ice region is displayed as a hazard or warning area. The ice region can be displayed as a speckled yellow area, other color region, or with other symbols or icons. After step  310 , processor  14  can return to step  302 . 
     With reference to  FIG. 4 , a method  400  can be performed by system  10  to determine a presence of a convective in the vicinity of an aircraft by detector  29 . At a step  402 , convective cell detector  29  detects presence of liquid water using weather radar data (e.g., reflectivity parameters). Vertical radar scans can be performed by system  10  to obtain the weather radar data for step  402 . At a step  404 , detector  29  can determine the amount of water at altitudes above the freezing point using the weather radar data and temperature data. If liquid water is present above the altitude associated with the freezing point, processor  14  advances to a step  406  and detector  289  makes a convective cell assessment. The convective cell assessment can include a vertical structure assessment in one embodiment. Water has a higher reflectivity in liquid form than in ice form. If liquid water is not present above the altitude associated with the freezing point, processor  14  returns to step  402 . 
     According to various exemplary embodiments, methods  200 ,  300  and  400  of  FIGS. 2-4  may be embodied as hardware and/or software. In exemplary embodiments where the processes are embodied as software, the processes may be executed as computer code on any processing or hardware architecture or in any weather radar system such as the WXR-2100 available from Rockwell Collins. Methods  200 ,  300 , and  400  can be performed separately, simultaneously, sequentially or independently with respect to each other. 
     While the detailed drawings, specific examples, detailed algorithms and particular configurations given describe preferred and exemplary embodiments, they serve the purpose of illustration only. The inventions disclosed are not limited to the specific forms shown. For example, the methods may be performed in any of a variety of sequence of steps or according to any of a variety of mathematical formulas. The hardware and software configurations shown and described may differ depending on the chosen performance characteristics and physical characteristics of the weather radar and processing devices. For example, the type of system components and their interconnections may differ. The systems and methods depicted and described are not limited to the precise details and conditions disclosed. The flow charts show preferred exemplary operations only. The specific data types and operations are shown in a non-limiting fashion. Furthermore, other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the exemplary embodiments without departing from the scope of the invention as expressed in the appended claims. 
     Some embodiments within the scope of the present disclosure may include program products comprising machine-readable storage media for carrying or having machine-executable instructions or data structures stored thereon. Such machine-readable storage media can be any available media which can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable storage media can include RAM, ROM, EPROM, EEPROM, CD ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer or other machine with a processor. Combinations of the above are also included within the scope of machine-readable storage media. Machine-executable instructions include, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing machine to perform a certain function or group of functions. Machine or computer-readable storage media, as referenced herein, do not include transitory media (i.e., signals in space).