When analyzing radar data, it is often helpful to know the height of the radar volume. Numerous charts exist that show this information on a gross scale. We thought a simple interactive SWF to compute this information for a specific range gate would be more applicable. The application provides the user the beam center height, beam top height, beam bottom height, and the beam width. Most charts that provide beam heights don't contain information on these other parameters.

The application derives this information using some simple approximations and equations. Assuming a standard atmosphere, the height of a radar beam can be computed using the following equation:

h = (R*sin(PHI)) + (R² /2*IR*R_e),

where:

h   =   height of the beam centerline above radar-level (ARL) in km,
R  =   slant range observed on radar in kilometers (km),
PHI =   radar elevation angle (in degrees),
IR = refractive index (1.21), and
R_e = radius of the earth (6371 km) .

The beamwidth of the radar beam is calculated using

,

where:
 
=   the angular beamwidth
s   =   the beamwidth (or arc length)
r   =   the distance of the range gate from the antenna.

To determine the beam top and beam bottom heights, the component of the beamwidth perpendicular to the ground is first calculated using

.

This distance is then divided in half and added (subtracted) from the beam center height to get the beam top (beam bottom) height.
 
To compute these values, just use the SWF interface (accessed through the link below) with a radar type (WSR-88D or TDWR), an elevation angle, range and unit of measurement system, and then press the "Calculate Beam Properties" button. The applet will compute several beam characteristics for you. Each time you change one of the four primary input variables, reclick the "Change Beam Properties" button to update your beam characteristics. Enjoy!

Open the Beamwidth Calculator!