Abstract:
A weather radar display system displays a beam indicator indicative of a radar beam. The beam indicator represents width of the radar beam as a function of range (distance from the radar beam source). The beam indicator allows a pilot to easily discern accuracy of detected weather conditions based on the beam width.

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/281,089, filed on Apr. 3, 2001. The entire teachings of the above application is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     A weather radar system measures rainfall intensity within a scanned area. Intense rainfall may include severe turbulence which can be hazardous to aircraft flight. The weather radar system includes an antenna receiver/transmitter unit. The unit emits a concentrated beam of microwave energy. The returned echo indicates the intensity of detected targets. The detected intensity is displayed as color coded targets depicting echos on a display. The intensity of the rainfall at a given location is indicated by the color displayed. For example, black represents very light or no precipitation, green represents light precipitation, yellow represents moderate precipitation, red represents heavy precipitation and magenta represents very heavy precipitation. 
     A radar beam increases in width with increased distance from the sensor. At a large distance the beam is very wide, sometimes on the order of tens of miles. The radar sensor detects a target at a particular distance based on the average intensity of the echo across the full beam width. FIG. 1 illustrates a radar beam  100  transmitted from an airborne weather radar  102 . As shown, the width (w) of the beam  100  increases with distance (d) from the airborne radar  102 . 
     A typical thunderstorm is only one mile in diameter. Thus, a storm detected within a beam that is 10 miles wide may only return an echo indicating one-tenth the intensity because of intensity averaging over the full beam width. Thus, the intensity is incorrectly represented as green instead of showing regions of red. The returned echo is misleading because it does not depict the real intensity of the weather ahead. 
     SUMMARY OF THE INVENTION 
     A weather radar display system displays a beam indicator indicative of a radar beam. A beam dimension routine in the weather radar display system computes dimensions of the beam indicator. A display in the weather radar display system shows a weather target found by a radar signal of the radar beam. The beam indicator sweeps over the displayed weather target. The width of the beam indicator is relative to the width of the weather target providing an indication of the reliability of the displayed weather target. 
     The displayed beam indicator is opaque and provides an indication that the radar signal is being transmitted and received. The beam dimension routine computes the dimensions of the beam indicator to be displayed dependent on the beam width of an airborne radar antenna which transmits and receives the radar signal. 
     The angle of the beam indicator to be displayed decreases as the diameter of the antenna is increased. The beam indicator follows the center of an airborne radar sweep. The width of the beam indicator is dependent on distance from the source of the radar signal. The dimensions of the beam indicator remain constant as the scale of the display is modified. The beam indicator is wedge-shaped. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
     FIG. 1 illustrates a radar beam transmitted from an airborne radar; 
     FIG. 2 is a graphical depiction of targets detected by an airborne weather radar including a beam width indicator indicative of a radar beam according to the principles of the present invention; and 
     FIG. 3 is a flowchart illustrating the steps implemented in a beam dimension routine for computing the dimensions of the beam indicator indicative of a radar beam shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A description of preferred embodiments of the invention follows. 
     FIG. 2 is a graphical depiction of targets  200 - 1 , . . .  200 - 4  detected by an airborne weather radar including a beam width indicator  202  indicative of a radar beam according to the principles of the present invention. A plurality of range rings  204  displayed on the display  220  indicate distance from the airborne weather radar mounted on the aircraft. In the embodiment shown, four range rings represent 20, 40, 60 and 80 Nautical Miles (NM) from the airborne weather radar. However, the invention is not limited to the range intervals shown. The number of range rings displayed is dependent on the installed airborne weather radar system and the maximum range selected to be displayed. For example, Bendix King&#39;s RT-1301 A/B can display range values 10, 20, 40, 80, 160 and 240 nautical miles and Collins&#39; WXT-250A can display range values 10, 25, 50, 100 and 250 nautical miles. The detected targets  200  are displayed on the display screen  220 . Each target can include a plurality of regions dependent on detected intensity within the target. For example, target  200 - 1  includes three intensity regions  208 - 1 ,  208 - 2  and  208 - 3 . The displayed color of each region is dependent on the detected intensity. 
     A graphical depiction of radar beam width is displayed as a wedge-shaped or pie-shaped beam width indicator  202  on the display  220 . The beam width indicator  202  sweeps over the displayed target  200  following the sweep of the radar antenna. The beam width indicator- 202  is opaque and is drawn in the normal sweep area, underneath the detected targets  200 - 1 , . . .  200 - 4 . The width of the beam indicator  202  increases with distance from the source of the radar signal. However, the size of the beam indicator remains constant as the scale of the display is modified. 
     The radar beam width is dependent on the diameter and type (parabolic or phased array (or flat-plate) of the installed antenna. The beam width indicator  202  represents the actual width of the radar beam at various distance ranges. The beam width provided in radar sensor and antenna documentation for the installed antenna is used to determine the width of the beam indicator. The width of the installed antenna is stored in memory in the weather radar display system and the representative beam indicator to be displayed is selected dependent on the stored width. The width of the radar beam decreases as the diameter of the installed antenna increases. Representative beam widths based on antenna diameter are shown in Table 1 below. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Antenna Diameter 
                 Generic Beam Width 
               
               
                   
                   
               
             
             
               
                   
                 10″ 
                  10° 
               
               
                   
                 12″ 
                   8° 
               
               
                   
                 18″ 
                   5° 
               
               
                   
                 24″ 
                   4° 
               
               
                   
                 28″ 
                 3.5° 
               
               
                   
                 30″ 
                   3° 
               
               
                   
                   
               
             
          
         
       
     
     The beam indicator  202  on the display  220  represents the actual radar beam width at various distances from the radar sensor. The displayed relationship between the width of the beam indicator  202  and the target reinforces to a pilot that echoes depicted by targets  200 - 1 , . . .  200 - 4  at large distances are highly inaccurate and should not be relied on for safe navigation. 
     The beam indicator  202  is displayed only when the airborne radar is operating. As a side benefit, the beam indicator  202  reminds the pilot that the radar sensor is operating. This information is useful during the busy after-landing segment of the flight where it is important to safely turn the radar OFF before approaching the line personnel or fuel facilities. 
     The beam indicator  202  is displayed within the sweep pattern of the radar depiction, centered on the depicted location of the aircraft  206  increasing in width to the outer edge of the depicted distance range. The display of the beam indicator  202  can be turned on or off through the use of a selectable menu item on a user interface displayed on the display. 
     FIG. 3 is a flowchart illustrating the steps implemented in a beam dimension routine stored in memory of the weather radar display system for computing the dimensions of a beam indicator indicative of a radar beam shown in FIGS. 1 and 2. 
     At step  300 , the beam dimension routine checks if the radar is on. The beam display indicator is displayed, only if radar is operating. Thus, if radar is off no further processing is required by the beam dimension routine. 
     At step  302 , the beam dimension routine reads the stored beam width for the installed antenna. The beam width is a fixed value based on the diameter of the antenna and is stored in memory in the display system. Processing continues with step  304 . 
     At step  304 , the beam dimension routine reads display enable status stored in memory to determine if the display of the beam indicator is enabled. The state of the display enable status parameter can be selected through a selectable menu item on a user interface by the user of the display. If the display is enabled, processing continues with step  306 . If not, the beam indicator is not displayed and processing continues with step  300 . 
     At step  306 , the beam dimension routine determines the location of the center of the antenna sweep. The beam indicator is displayed moving across the display with the center of the antenna sweep. Processing continues with step  308 . 
     At step  308 , the beam dimension routine displays the beam indicator  202 , based on the stored beam width for the installed antenna, moving across the display with the antenna sweep. In one embodiment, the dimensions of the beam indicator are computed once based on the stored diameter of the installed antenna for each distance range displayed. 
     Beam width at a particular distance from the antenna is computed using the following algorithm: 
     
       
         Width=sin( deg )*distance/sin((180 −deg )/2)*6076 
       
     
     where: deg=Beam width in degrees 
     distance=distance (in nm) from aircraft at which the measurement occurs 6076 is a constant (feet per nm) 
     Beam width for representative antenna diameters at different distances from the radar source are shown in Table 2 below: 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Generic 
                 Width (feet) 
                 Width (feet) 
                 Width (feet) 
                 Width (feet) 
               
               
                 Beam Width 
                 at 20 nm 
                 at 40 nm 
                 at 60 nm 
                 at 80 nm 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10° 
                 21,182 
                 42,364 
                 63,547 
                 84,729 
               
               
                 8° 
                 16,954 
                 33,907 
                 50,860 
                 67,814 
               
               
                 5° 
                 10,601 
                 21,203 
                 31,804 
                 42,405 
               
               
                 4° 
                 8,482 
                 16,964 
                 25,492 
                 33,928 
               
               
                 3° 
                 6,362 
                 12,724 
                 19,086 
                 25,448 
               
               
                   
               
             
          
         
       
     
     For purposes of display  220 , the dimensions of the beam indicator  202  are determined from the calculated beam width. The end points of the polygon to be drawn on the display are determined based on the beam width. Once the end points are determined, the polygon is filled in using a standard polygon fill technique. The beam indicator is displayed on the display within the sweep of the radar beam as long as the display of the indicator beam is enabled and the radar is operating. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.