机载监视系统：2-1机载气象雷达 - 气象雷达概述

1、Airborne Weather Radar(WXR) Con2: Introduction to WXROutlines For Con21 Aviation weather 2 Introduction purpose description display3 Operating Modes Weather Map Turbulence Predictive windshear4 Structure and Location 5 Latest Evolutions2Con2-1 Aviation weather An airborne radars pulse energy is opti

2、mized to detect water. The radiated radar energy reflects best when the bipolar (positive and negative) water molecules are able to align. When water freezes, the water molecules are locked into an ice crystal lattice and are unable to align to reflect radar energy efficiently. (example: microwave)W

3、ater (rain) is an excellent radar reflector.Dry snow and ice crystals are very poor reflectors of radar energy. Wet hail provides the strongest reflection of radar energy. Dry hail reflects some radar energy simply due to its size. Reflectivity characteristics 3Con2-1 Aviation weather A thunderstorm

4、 is composed of three parts：The bottom portion of the storm, below the freezing level, is composed entirely of liquid precipitation (i.e., rain) and is the most reflective portion of the storm.The middle portion of a thunderstorm occurs above the freezing level (0oC) and up to the altitude where the

5、 outside air temperature drops below 40oC. This section of the storm is composed of a combination of ice crystals and supercooled water.The top of a thunderstorm is composed entirely of ice crystals and reflects very little radar energy. At temperatures less than 40oC, liquid water no longer exists

6、and only ice crystals are present.Thunderstorm/rain4Con2-1 Aviation weather 湍流，也称为紊流，乱流，是指发生在一定空域中的急速且多变的运动气流。湍流区域中的不同位置，气流速度和方向的变化相当剧烈。湍流是根据区域中微粒的速度偏差来定义的，它与微粒的绝对速度无关。湍流报警门限为5m/s(18km/h)Turbulence5Con2-1 Aviation weather Black represents zero to minimal reflectivity. Green represents light reflecti

7、vity. Yellow represents moderate reflectivity. Red represents heavy to extreme reflectivity. Magenta indicates turbulence.A normal thunderstorm is circular or oval in shape. Variations from this normal shape are indicative of a shear condition within the thunderstorm and can serve as clues to hazard

8、ous weather.6Con2-1 Aviation weather WX (weather) mode: The four colors displayed represent different storm intensities. WX+T (Weather Plus Turbulence) Mode: It enables display of weather targets with turbulence information7Con2-1 Aviation weather Wind shear is the meteorologists way of describing a

9、 rapid change in either wind speed or wind direction over a short period of time or distance. Windshear occurs in all directions, but for convenience, it is measured along vertical and horizontal axis, thus becoming vertical and horizontal windshear.The rapid change in wind speed and/or direction po

10、ses a very real threat to airplanes during take-off and landing.Wind shear is caused by downburst. A downburst（下击暴流）is a strong downdraft which causes damaging winds on or near the ground.The term microburst and marcoburst describe the size of the downburst(4km). Microburst is more important than ma

11、rcoburst to aviation safety, it can cause damaging winds as high as 75m/s(168mph,270km/h). The key difference between downburst and tornado is in two words - IN and OUT8Con2-1 Aviation weather (a)低空风切变对飞机运行安全的影响示意图(b) 雷暴引发的风切变9Con2-1 Aviation weather Microbursts combine two distinct threats to aviat

12、ion safety: the downburst part, resulting in strong downdrafts; the outburst part, resulting in large horizontal windshear and wind component shift from headwind to tailwindHeadwind gust instantaneously increases the aircraft speed and thus tends to make the aircraft fly above intended path and/or a

13、ccelerate.A downdraft affects both the aircraft Angle-Of-Attack (AOA) and the aircraft path since it makes the aircraft sink.Tailwind gust instantaneously decreases the aircraft speed and thus tends to make the aircraft fly below intended path and/or decelerate.10Con2-1 Aviation weather (a) Headwind

14、 zone(b) Power reduction(c) Indicated airspeed transition(d) Recovery or loss of flight11Con2-2 General descriptionPurpose: the weather radar (WXR) system supplies these visual indications: weather conditions; windshear events; land contours.Description: WXR operates on the same principle as an echo

15、. The WXR system transmits radio frequency (RF) pulses in a 180 degree area forward of the airplane. Objects reflect the pulses back to the receiver. The receiver processes the return signal to show weather, terrain, and windshear events.Display: The WXR returns show in four different colors on the

16、navigation displays (ND). Colors of the indications give the crew information about the intensity of the returns.The predictive wind shear (PWS) cautions and warnings show in amber and red on the ND and PFD displays. Also, there are aural alerts for PWS cautions and warnings.12Con2-2 General descrip

17、tion1314Con2-2 General descriptionWXR provides the flight crew with a representation of weather (compensated for A/C attitudes): - Localisation (tilt and distance) and density of water particules - Turbulence information and windshear detection through particle horizontal speed detectionWXR-Airborne

18、 weather radar15Con2-2 General descriptionTwo Suppliers:Honeywell (RDR-4B/4000)2. Rockwell Collins (WXR-2100)16Con2-2 General description1NM=1852m1mile=1609m17Con2-2 General descriptionR 1 mm/h, Z1 20 dBz: black dBz: 10 log ZR 1 to 4 mm/h, Z2 30 dBz: green Z: reflectivity of the rainR 4 to 12 mm/h,

19、Z3 12 mm/h, Z4 40 dBz: red R expressed in mm/h4级编码方案，Z为反射系数，R为降雨量18反射率(mm/h)颜色显示无雨区50.8回波强度 降雨量大小大小Con2-3 Operating Modes(WX, WX+T)19Con2-2 General description20Accurate Weather that affects the aircraft flight path from the nose of the aircraft to 320 NM 40 NM40 NM100 NM100 NMGround Clutter Free300 NM300 NM1st Generation Hazard Analysis based on region and time of year Attenuation AlertCertified Turbulence to 40 NMAttenuation Alert40 NM TurbulenceOverFlightTM ProtectionOverFlight Protection200 NM200 N