航空电子设备：WXR(English)机载气象雷达系统

1、Civil Aviation Flight University of China,Airborne Weather Radar System,机载气象雷达系统,Airborne Weather Radar System,Civil Aviation Flight University of China,The weather radar (WXR) system is designed to provide the flight crew with a topographic map type of display of moisture laden weather formations i

2、n order to avoid heavy precipitation or turbulence. As a secondary function, the weather radar antenna can be tilted downward to provide a display of major terrain features such as rivers, coastlines, major mountain peaks, and cities,Airborne Weather Radar System,Civil Aviation Flight University of

3、China,Airborne Weather Radar System,Weather radar systems operate in the X-band. Maximum range of modern radars is about 300nm. Detected weather conditions and ground mapping information can be displayed in the cockpit. The antenna is normally stabilized using attitude signals from one of the vertic

4、al gyros, or inertial references, to avoid clutter from ground,returns during turns,Civil Aviation Flight University of China,A weather radar system consists of a receiver/transmitter (R/T), an antenna, a control panel, and indicators. The control panel allows the crew to control power application a

5、nd to select various modes of weather radar operation. Using the control panel selections, the receiver/transmitter generates and transmits high energy radio frequency (RF) pulses. These RF pulses are sent to the antenna, and radiated,Airborne Weather Radar System,Basic Principles,Civil Aviation Fli

6、ght University of China,The antenna oscillates to sweep the pencil shaped radar beam about 90 either side of the nose, and can be tilted up and down to about +/-15. Moisture Laden clouds or the terrain will reflect some of these RF pulses back to the antenna. This reflected energy is received by the

7、 antenna, processed by the R/T unit and displayed on the indicators,Airborne Weather Radar System,Basic Principles,Civil Aviation Flight University of China,What target will reflect the radars pulses and thus be displayed on the indicator? Only precipitation (or objects more dense than water such as

8、 earth or solid structures) will be detected by X-band weather radar. Therefore weather radar does not detect clouds, thunderstorms or turbulence directly. Instead, it detects precipitation which may be associated with dangerous thunderstorms and turbulence. The best radar reflectors are raindrops a

9、nd wet hail. Generally, ice, dry snow, and dry hail have low reflective levels and often will not be displayed by the radar,Airborne Weather Radar System,Basic Principles,Civil Aviation Flight University of China,Airborne Weather Radar System,Basic Principles,Civil Aviation Flight University of Chin

10、a,Airborne Weather Radar System,Basic Principles,Figure 5.1,Civil Aviation Flight University of China,Airborne Weather Radar System,Basic Principles,Turbulence may be divided into two basic types: clear-air turbulence; and turbulence associated with thunderstorms and precipitation. The weather radar

11、 is not possible to detect clear air turbulence. The radar returns are processed by the receiver-transmitter and shown on the EHSI in color as weather or map information. Areas of heaviest rainfall appear in red, moderate rainfall in yellow and light rainfall in green. Turbulence information is show

12、n using magenta,Civil Aviation Flight University of China,Airborne Weather Radar System,Basic Principles,Figure 5.2,Heaviest Rainfall,Moderate Rainfall,Light Rainfall,No Rainfall,Turbulence Area,Turbulence Area,Civil Aviation Flight University of China,Figure 5.3,Airborne Weather Radar System,Contro

13、l Panel,Weather Radar Control Panel,Civil Aviation Flight University of China,Figure 5.3,Airborne Weather Radar System,GAIN The system gain may be adjusted in the WX, WX+T, or MAP modes by the GAIN control. The control has ten detented positions including the CAL position, where the system gain is a

14、utomatically calibrated,Civil Aviation Flight University of China,Figure 5.3,Airborne Weather Radar System,TILT The antenna tilt position is controlled by the TILT control. The tilt range is from 15down to 15up,Civil Aviation Flight University of China,Figure 5.3,Airborne Weather Radar System,WX Pre

15、ssing the WX pushbutton switches the R/T unit to the weather mode, and weather data will be displayed on the EHSI,Civil Aviation Flight University of China,Figure 5.3,Airborne Weather Radar System,WX+T Pressing the WX+T pushbutton switches the R/T unit to the weather plus turbulence mode, and turbul

16、ence as well as weather data will be displayed on the EHSI. Turbulence with 40 nm or less is displayed,Civil Aviation Flight University of China,Figure 5.3,Airborne Weather Radar System,MAP Pressing the MAP pushbutton switches the R/T unit to the ground mapping mode, and terrain features will be dis

17、played on the EHSI,Civil Aviation Flight University of China,Figure 5.4,Airborne Weather Radar System,TEST The test mode is selected by pressing the TEST pushbutton. In the TEST mode, a test pattern and the system status messages will be displayed on the EHSI,Civil Aviation Flight University of Chin

18、a,Figure 5.3,Airborne Weather Radar System,IDNT This pushbutton activates ground clutter suppression to reduce ground clutter in WX and WX+T modes,Civil Aviation Flight University of China,Figure 5.3,Airborne Weather Radar System,STAB Stabilization is engaged by pressing the STAB pushbutton. With st

19、abilization selected, the antenna stabilization is provided by the IRS through the R/T unit,Civil Aviation Flight University of China,Airborne Weather Radar System,Display-EHSI Presentation,On modern commercial airplanes, the weather radar data is usually shown on the EHSI. The EHSIs show the weathe

20、r radar data in Expanded NAV, Expanded VOR/ILS, MAP and Center MAP modes. The WXR switch on the EFIS control panel is used to turn on the weather radar system and to turn on weather radar display,Civil Aviation Flight University of China,Airborne Weather Radar System,Figure 5.5,Turbulence Area,Civil

21、 Aviation Flight University of China,Airborne Weather Radar System,The weather or map display is color coded. Targets providing the most intense returns are shown using the color red. Targets with less intensity are shown using the colors yellow, green and black. Turbulence information is shown usin

22、g magenta,Civil Aviation Flight University of China,Airborne Weather Radar System,Operation In-Flight,Early Detection of En-route Weather To set the antenna tilt to optimize the radars ability to quickly identify significant weather, follow these steps: Select the WX mode of operation. Adjust Bright

23、ness control as desired. Select the 40 or 80 nm range. Adjust the antenna tilt control down until the entire display is filled with ground returns. Slowly work the antenna tilt up so that ground returns are painted on or about the outer one third of the indicator area,Civil Aviation Flight Universit

24、y of China,Airborne Weather Radar System,Operation In-Flight,Early Detection of En-route Weather Watch the strongest returns seen on the display. If, as they are approached, they become weaker and fade out after back inside the near limit of the general ground return pattern, they are probably groun

25、d returns or insignificant weather. If they continue strong after working down into the lower half of the indicator, you are approaching a hazardous storm or storms and should deviate immediately. Examine the area behind strong targets. If radar shadows are detected you are approaching a hazardous s

26、torm or storms and should deviate immediately, regardless of the aircrafts altitude. If weather is being detected, move the antenna tilt control up and down in small increments until the return object is optimized,Civil Aviation Flight University of China,Airborne Weather Radar System,Operation In-F

27、light,Blind Alley A “Blind Alley” or “Box Canyon” situation can be very dangerous when viewing the short ranges. Periodically switch to longer-range displays to observe distant conditions. As shown in Figure 5.6, the short-range returns show an obvious corridor between two areas of heavy rainfall bu

28、t the long-range setting shows a larger area of heavy rainfall,Figure 5.6,Civil Aviation Flight University of China,Airborne Weather Radar System,Operation In-Flight,Path Planning Considerations Avoid cell containing magenta and red areas by at least 20 nautical miles. Do not deviate downwind unless

29、 absolute necessary. Your chances of encountering severe turbulence and damaging hail are greatly reduced by selecting the upwind side of the storm. If looking for a corridor, remember corridors between two cells containing magenta and /or red areas should be at least 40 nautical miles wide from the outer fringes of the radar