Radar: How it Works

Radar

Eddie sez:

Radar was invented by the militaries of the world leading up to World War II as a method of detecting and determining direction and range to an enemy. The term RADAR was coined by the United States Navy: Radio Detection And Ranging. A scientist at M.I.T., working for the United States Air Force, came up with a way to use radar to detect weather. Interesting? Maybe not, but it is a good introduction to understanding how weather radar works.

Everything here is from the references shown below, with a few comments in an alternate color.

Last revision:

20131128

Radar: How it Works

How a Radar Works

The purpose of the radar is:

  • Find the distance to a target
  • Find the direction to a target
  • Determine the target's reflective characteristics (size, movement, and depth)

(1) Distance: Radar Signal Flow

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Figure: Radar signal flow diagram, from Honeywell Radar Training Course, Part 1, Slide 12.

A radar signal travels at the speed of light: 186,280 statute miles per second. The radar tracks the time from transmission, reflection, and reception to determine the distance of the target.

(2) Direction: Radar Sweep Angle

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Figure: Finding the target's direction, from Honeywell Radar Training Course, Part 1, Slide 15.

The radar continuously sweeps from side-to-side, and only receives reflections from targets in the beam width during that instantaneous moment, enabling it to determine direction relative to the aircraft.

(3) Reflective Characteristics: Signal Amplitude

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Figure: Determining reflection characteristics, from Honeywell Radar Training Course, Part 1, Slide 16.

The radar measures the amplitude of the reflected signal to determine the size of the return, displaying increasing amplitudes in green, yellow, and red (or more variations, depending on radar.)

How the Radar’s Information is Presented to the Pilot

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Figure: Providing radar information to the display, from Honeywell Radar Training Course, Part 1, Slide 17.

A "radial" of information isn't a "degree" of information, rather it is a series of colors for a snapshot in time for that particular direction. A wider beam width will paint all the weather in a particular distance to be the same. The narrower the beam width, the greater the fidelity of the information you are seeing.

More about that: Radar - Beam Width.

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Figure: How targets are displayed, from Honeywell Radar Training Course, Part 2, Slide 5.

The radial range bins appear side-by-side to make up a composite picture of the lateral view, a slice of the weather.


Honeywell Airborne Weather Radar Training, Rev E, 12/09/02, Honeywell Inc. Commercial Flight Systems Group, Phoenix, AZ.

Honeywell Primus 880 Pilot's Guide, Pub. No. A28-1146-102-03, Revised January 2006, Honeywell International Inc. Commercial Electronic Systems, Glendale, AZ.