The length (h) of a radar pulse in space is determined by the product of the pulse duration (~) and the speed of light (c):

For instance, a pulse of l-second duration would have a length of

Resolution describes the ability of the radar to show objects separately. There are two distinct resolution problems:

1. Range resolutionThe ability to distinguish between two targets in the same direction from the radar, but at different ranges.

2. Beam-width resolutionThe ability to distinguish between two targets at the same range, but in different directions.

Range Effect on Signal Strength and Echo Definition

The cross-sectional area of the radar beam is proportional to the range from the radar, becoming larger as the range increases. Accordingly, the energy incident on a unit area of the beam cross section decreases with range, being inversely proportional to the square of the range. This is often called range attenuation, although the term attenuation is more properly applied to the dissipation of energy by the medium through which it passes.

Now lets look at the history of doppler weather radar, as well as a discussion of principles, characteristics, and phenomena associated with doppler radar. Information on doppler radar maybe found in the Federal Meteorological Handbook No. 11 (FMH-11), Doppler Radar Meteorological Observations, parts B, C, and D. Additional information maybe found in The Doppler Radar Glossary, Thunderstorm Morphology and Dynamics, and Doppler Radar Principles, KWXN-5002, KWXN-1005, and KWXN-1002, which are practical training publications produced by the United States Air Force Training School at Keesler Air Force Base, Mississippi.

LEARNING OBJECTIVES: Discuss the history of doppler radar. Recognize velocity-aliased data, range-folded data, and ground clutter and assess their impact on radar interpretation. Evaluate doppler velocity and wind shear patterns. Interpret radar presentations of cloud layers and the bright band.

In the following we will be discussing a brief history of Doppler Radar from the first real-time Doppler display in 1967, to the present day Weather Surveillance Radar 1988 Doppler (WSR-88D).

In 1967, the first simultaneous observations of atmospheric flow patterns by two doppler radars were made. This was performed in central Oklahoma by the National Severe Storms Laboratory (NSSL) and Cornell Aeronautical Laboratory and concurrently in England by the Royal Radar Establishment. Data in these studies was stored in real time and analyzed later. At about the same time, the first real-time doppler radar display, The Plan Shear Indicator, was developed by the Air Force Cambridge Research Laboratories.

In the early 1970s, a unique new class of high-powered, sophisticated S-band doppler weather radar appeared, incorporating integrated circuitry and advanced computer processing. Two were built by the NSSL. Others were built by the National Center for Atmospheric Research and by the University of Chicago in cooperation with the Illinois State Water Survey in Champaign, Illinois. By the mid 1970s, technological advances allowed real-time processors to be linked to color displays.

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