MSC Introductory Weather Radar Course

The VAD (Velocity Azimuth Display) technique is used to retrieve the vertical wind profile at the radar site with a Doppler radar. PPI scans at an elevation of about 20° cover various heights with one scan.

Ambiguous detection of radial velocities outside the Nyquist Interval by Doppler Radar.

Description

Radar product giving the vertical profile of the reflectivity taken over a specified surface area. For each height level this product delivers a set of parameters that describes the reflectivity field inside the considered volume. The Vertical profile of reflectivity is the main factor in the accurancy of precipitation measurements at distances of 50-250 km. The origins of large bias of 2-20 dB are based on the difference between the actual reflectivity of ground level and in the contribution volume aloft.

Notes

• The profile is taken in a vertical cylinder based above a ground area of specified form and position. Typically it is taken within a circular area centred around the radar station. If this is not the case (e.g. for an arbitrary form) the surface is described by its gravity centre and equivalent radius.
• The data quantification method describes the algorithm used to associate a reflectivity value to an height level. "When the vertical stratification is not regular the sequence of the used heights is to be specified.
• The base area and the quantification method can optionally be omitted.

Example Image

Description

Radar product with the vertical profile of the wind estimated from Doppler measurements above the weather radar station. For each height level this product gives a set of parameters describing the wind field.

Parameters

Vertical spacing: height difference between successive samples in m
Vertical range: range of considered altitudes (lowest, upper) in 0.1 km a.s.l.
Volume shape: Cylindrical, Conical, ...
Quality information: (OK or suspect or not-applicable or missing)
Product data quantity for each height level: horizontal and vertical velocity in 0.1 m/s and direction in degrees

Notes

• Detailed information is present in documents OPERA 22-1/99 and 22-2/99. "
• When the vertical stratification is not regular the sequence of the used heights is to be specified. "
• The volume shape can optionally be omitted.

Example Image

Description

2D map containing the integrated liquid water content between set upper and lower limits in altitude in the vertical column over each surface point.

Parameters

Product data quantity: W (intergrated liquid water content)
Unit: mm
Upper limit altitude: km
Lower limit altitude: km
Z/W relationship used
Optional: height of melting layer
Image size: number of pixels per row (# of columns) and per column (# of rows)
Pixel size: horizontal and vertical extension of the pixel in km
Level slicing method: list of values or formula parameters (see section 7)
Level slicing unit: mm

Notes

• Z/W relationships are different for snow and water
• The bright band biases VIL results, so the top and bottom should be either above or below melting layer altitude.

Problems caused to radar products

Volcanic ash has different dielectric characteristics from liquid water and ice but ash and soot from forest fires and/or volcanic eruptions can still be detected by weather radars.

Example Image

The process of completing a series of antenna rotations at specified elevation angles.