MSC Introductory Weather Radar Course

An logarithmic expression for ratio of two quantities. dBm is a decibel with respect to 1 milliwatt.

Mathematically:

Ratio between the reflectivity received at vertical polarization, but transmitted with horizontal polarization, and the reflectivity at horizontal polarization. Depolarization of the horizontal polarized pulse is caused by asymmetric particles which are not aligned horizontally. Depolarization of rain is normally very small (app. -40 dB). It is high (-20 to -10 dB) for melting snow and water coated hail or graupel.

Description

Differential phase shift φDP is the phase shift between the horizontally polarized wave and the vertically polarized wave.

Notes

• Since φDP is not affected by attenuation, it can be used to develop and check attenuation correction schemes.
• Attenuation correction based on using the total Differential Phase Shift as a constraint is selectable for reflectivity products. Reflectivity products can be viewed with or without attenuation correction. Correction of Differential Reflectivity due to differential attenuation is also available.

Ratio between the reflectivity of a horizontal polarized pulse and the reflectivity of a vertical polarized pulse. ZDR depends on the asymmetry of the shape, the orientation and the falling behaviour of the particles. ZDR is positive for oblate raindrops, zero or slightly negative for hail and graupel. Note that ZDR is strongly biased by differential attenuation during the passage of the radar pulse through heavy rainfall.

The area or two-dimensional product of the X and Y coordinates represented by one picture element (pixel) of a raster scan display.

Undesired change in a signal resulting in unfaithful reproduction of video or audio.

The interdependence of maximum unambiguous range and maximum unambiguous velocity on the pulse repetition frequency, PRF. As PRF is increased (decreased), the range of unambiguous velocities increases (decreases), but the unambiguous range decreases (increases).

Change in observed frequency of wave energy due to relative motion of the observer and wave source.

A radar which utilizes the Doppler effect to determine the radial velocity of a target.

Reflectivity-weighted average velocity of targets in the pulse volume. Determined by phase measurements from a large number of successive pulses. Also called radial velocity. Gives only the radial component of the velocity vector. It is generally assumed that raindrops and other particles are advected with the wind and have no own motion except their falling velocity. Motion towards the radar are negative (blue colours), motions away from the radar are positive (red colours).