Definition: Doppler radar

A "Doppler" radar has the capability of measuring some information about winds (on top of the usual echo strength all radars measure) by using the Doppler effect. Although many radars are "Doppler", this additional information is almost never shown to the public because it can be difficult to interpret even for experienced meteorologists.

The most common wind information measured by a Doppler radar is the radial velocity, which is the component of the wind going in the direction of the radar (either towards or away). If we take the example of a constant wind from the north, strong approaching velocities will be observed when the radar looks north, strong receding velocities when the radar looks south, and no velocity when the radar looks east or west. This information can then be displayed, generally using progressively colder colors (for example blue) for increasingly strong approaching velocities and progressively warmer colors (for example red) for increasingly strong receding velocities.

Radial velocity images are usually more complicated than in this example because:

• The wind is rarely uniform;
• The area over which wind information can be obtained is limited to regions with targets (like rain, bugs, etc.) because the measurement of the radial velocity is possible only if there is a target to measure the speed of;
• The height at which radar observes the weather increases with distance because the radar generally points at some elevation over the horizon.