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Tuesday, September 07, 2010

Today's Weather

General Weather: Normal summer weather , but dust haze at first.

Wind: Mainly n'ly 05 to 10kt reaching 10 to 15kt at times.

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Radar


	Education Centre

General Meteorology :	Air Masses - Cold Front - Fog - High Pressure - Humidity - Introduction to Weather - Large Thunderstorms - lightning - Low-Pressure - Meteorology - Occlusion Fronts - Rain - Sea Breaze & Land Breaze - Temperature - The Water Cycle - Tornadoes - Warm Front - Wind

Clouds :	Cirrus - Clouds - Cumulus - Cumulonimbus -

Radar :	General - Radar Technology - Attenuation in the atmosphere - Velocity measurements - Sources of error - Optimizing radar characteristics - Radar installation - Precipitation measurements

Velocity Measurements

The Doppler spectrum

Doppler radars measure velocity by estimating the frequency-shift produced by an ensemble of moving targets. Doppler radars also provide information about the total power returned and about the spectrum width of the precipitation particles within the pulse volume. The mean Doppler velocity is equal to the mean motion of scatterers weighted by their cross-sections and, for near horizontal antenna scans, is essentially the air motion toward or away from the radar. Likewise, the spectrum width is a measure of the velocity dispersion, that is, the shear or turbulence within the resolution volume.

A Doppler radar measures the phase of the returned signal by referencing the phase of the received signal to the transmitter. The phase is determined by shifting the return signal by 90' to produce the in-phase (1) and quadrature (Q) components of the signal. The I and Q are samples at a fixed range location. They are collected and processed to obtain the mean phase shift which is given by the ratio of the I and Q.

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