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In conventional radar systems, there is a one-to-one real-time correspondence between the approximately 4 second side-to-side movements of the antenna, and the radar image update on the displays.  In such systems, the display update is synchronized to the antenna tilt angle and sweep.  Only the data needed for immediate display is collected and processed.  In contrast, the RDR-4000 system has eliminated this limitation.  The mechanical scanning pattern of the antenna is de-coupled from the weather images shown on the displays.  The radar system continuously scans the entire 3D space in front of the aircraft, and stores all reflectivity data in 3D memory.  This memory is continuously updated with reflectivity data from new scans, and the data is compensated for aircraft movement.  This reflectivity data is extracted from memory to generate the selected views without having to make (and wait for) view-specific antenna scans. 

 
3D SCANNING AND PROCESSING
 
Views are no longer limited to the single diagonal slice that is inherent to conventional radars.  The standard horizontal view of the radar represents a weather envelope based on flight path slope, and corrected for the curvature of the earth.  Horizontal views are generated independently for each side of the cockpit. 
GROUND CLUTTER EXTRACTION 
The radar processor contains an internal terrain database with elevation data.  The radar compares the collected reflectivity data with the terrain database.  Reflectivity data that correlates to terrain data is considered ground-clutter, and is suppressed from the weather images.  However, the data that is suppressed from the weather images is retained for display when the radar’s MAP Mode is selected. 

 
 
 
The following pictures demonstrate some of the improved features of the RDR-4000 Weather Radar System. 
 CONVENTIONAL RADAR RDR-4000

 
IMPROVED CLUTTER REJECTION / ENHANCED WEATHER PRESENTATION
 
 

 
IMPROVED CLUTTER REJECTION/ENHANCED WEATHER PRESENTATION
(ALBUQUERQUE ~70 NM, RIGHT OF TRACK)
FLIGHT PATH WEATHER VS. SECONDARY WEATHER 
AUTO mode is used for the strategic detection of weather.  This fully automatic weather detection is enabled by the 3D volumetric memory.  In this mode, “Flight Path Weather”, or weather near the altitude of the intended flight path, is displayed as distinct from “Secondary Weather”, which is further removed in altitude from the flight path.  The result is a presentation of weather information that is intuitive, improves awareness of the entire weather situation, and reduces the potential for misinterpretations, thus reducing crew workload. 
The separation of “flight path” from “secondary” weather is based on several parameters: 
. aircraft altitude 

. flight phase (climb, level flight or descent) 

. flight path 

The separation is done by applying an envelope around the intended flight path: weather within the envelope is considered flight path weather; weather outside the envelope is secondary weather.  On the display, secondary weather is distinguished from flight path weather by black stripes (see illustration on page 13).  The flight path angle is computed based on the ratio of calculated vertical speed to ground speed.  The expected flight path altitude is extrapolated to 60 nm.  Beyond 60 nm, level flight at the calculated altitude is assumed.
ENVELOPE BOUNDARY DEFINITION 
The upper and lower boundaries of the separation envelope are based on the parameters listed above.  The envelope is not bounded in the horizontal plane.  During level flight the envelope extends from 4000 ft above to 4000 ft below the aircraft’s altitude.  However, the lower boundary cannot go higher than 25,000 ft.  Conversely, the upper boundary cannot go lower than 10,000 ft.  Additionally, absolute envelope boundaries of 60,000 ft and ground level apply.  The resulting rules are shown in the following table. 
　
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本文鏈接地址：WX RADAR RDR4000-PILOT GUIDE 氣象雷達 RDR4000飛行員指南(15)