RDR-4000 SEATTLE AREA MAP DISPLAY

 
SEATTLE AREA SATELLITE IMAGE
(Picture from earth.google.com)
GAIN CONTROL (GAIN) 
GAIN control is active in all modes except TEST.  The calibrated (CAL) position is the same as AUTO gain mode and is the only position where the colors represent the FAA defined reflectivity and rainfall rates as shown in the table below. The CAL gain setting provides a standard reference which all radar manufacturers must follow. Immediately after turning the GAIN control in either direction out of the detent position (CAL), the “VAR” annunciation appears on the display indicating that the system is no longer in the calibrated mode.  Rotating the GAIN control counterclockwise decreases gain and rotating the GAIN control clockwise increases gain.  The gain setting has no effect on turbulence detection or display.  After using gain to assess weather it should be returned to the CAL position. 
 
Reflectivity Color Codes (Gain at CAL)
Color
 Returns
 Reflectivity
 Rainfall Rate
 
Black
 Very light or none
 Less than 
20 dBz
 Less than 0.7 mm/hr 
(0.028 in/hr)
 
Green
 Light
 20 – 30 dBz
 0.7 – 4 mm/hr
(0.028 – 0.16 in/hr)
 
Yellow
 Medium
 30 – 40 dBz
 4 – 12 mm/hr 
(0.16 – 0.47 in/hr)
 
Red
 Strong
 40 dBz or greater
 Greater than 12 mm/hr (0.47 in/hr)
 
Magenta
 Turbulence
 N/A
 N/A
 

 
In all modes except TEST, rotating the GAIN Knob to the minimum (MIN) position reduces gain by approximately 16 dBz.  Rotating the GAIN Knob to the maximum (MAX) position increases gain by approximately 10 dBz. 
Proper use of the gain control can aid in the detection and assessment of storm cells.  Gain reduction can be useful in several ways.  Reducing the gain to MIN provides a quick assessment of the relative intensity between displayed cells.  Since gain does not affect turbulence detection, reducing gain in the AUTO mode to MIN will show turbulence information along with the strongest cells.  This is important since the probability of turbulence increases with higher levels of reflectivity.  Often when flying in areas of heavy stratus rain the display can show large areas of strong returns. 

Reducing the gain can also help identify embedded storm cells within the stratus rain.  It can help identify areas of significant attenuation by making radar shadows more prominent.  Areas of missing terrain returns in MAP mode that correspond with strong weather echoes may indicate a larger area of precipitation than is apparent on the weather display.  (See SHADOWED AREAS on page 36.)
MAX gain should only be used at cruise altitudes.  In MAN mode it should be used when looking at altitude slices above the freezing level where particles are less reflective.  High levels of moisture above the freezing level are key ingredients in hail formation.
Momentarily increasing the gain may also be useful at any altitude to discover the relative reflectivity of a weather formation that may be seen out the window but which is not initially displayed by the radar due to reflectivity below the standard threshold for green weather.  

SECTION 4: EQUIPMENT DESCRIPTION 
UNIT DESCRIPTIONS 
RP-1 RADAR PROCESSOR 
The Radar Processor contains the electronics necessary to process the radar data received from the transmitter/receiver, control the modes of the radar and to format the radar data for display.  The RP-1 is normally located in the Forward EE-Bay. 
　
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