This paper deals with Terminal Doppler Weather Radar (TDWR) installed in airports to provide wind shear detection services and precipitation reflectivity data to controllers and supervisors. The TDWR’s narrow beam and aggressive ground clutter suppression algorithms provide excellent data on boundary layer reflectivity and winds – in particular the locations of thunderstorm outflow boundaries. These data are known to be essential for providing high resolution convective weather forecasts out to two hours. Similarly, its narrow beam could be useful for detection of severe weather signatures (e.g., tornado vortices) with small azimuth extent. Relative to the Weather Service Radar 88-D (NEXRAD) it scans rapidly (e.g., surface updates once per minute), facilitating monitoring of rapidly evolving low altitude wind shear hazards. It is typically located near to population centers and congested airspace, so that it is well situated for supporting weather services for operationally important areas.
As the name suggests, the Terminal Doppler Weather Radar (TDWR) was purposely built to serve the terminal area of
The airport. Its mission is to detect wind shear and microburst associated with convective storms, so as to enhance the safety of aircraft landing and taking off. It is located near the airport at a distance of 12km so that it has a clear view of the runways, airport approach and departure zones.
The TDWR is specially designed to operate in a high clutter environment normally present in the vicinity of airports. It makes use of a variety of methods to minimize clutter and to eliminate the influence of such moving targets as birds, aircraft and automobiles. In this way the TDWR can accurately measure the radial wind speed and its fluctuation from which low level wind shear can be computed. Equipped with sophisticated computer programs, the TDWR is able to automatically detect thunderstorm-induced wind shear phenomena.

The TDWR system was designed and built in the late 1980’s, and is encountering issues related to parts obsolescence. To ensure that the system continues to be maintainable, the FAA has commenced a Service. Life Extension Program (SLEP) to improve supportability and, where appropriate, introduce improved capability.
A simplified block diagram of the TDWR is shown in Figure. The RPG subsystem, shown in green on the upper left, has recently been re-hosted from a Harris Nighthawk UNIX system to one based on a pair of redundant SGI Origin computers. The next major digital subsystem to be addressed,

and the focus of this paper, is the RDA, which includes the receiver and DSP subsystems. The existing TDWR DSP subsystem hardware consists of a mixture of COTS and custom cards, installed in a single 19” Multibus system chassis. The COTS boards include a 68020-based single-board computer (SBC), and a SCSI and serial controller. The custom components include five boards to handle the A/D interface and timing needs, eight boards to perform clutter filtering, and six boards to handle the generation of moment’s data.
Air Traffic Control, management of aircraft proceeding along civil airways, including airport arrivals and departures.

The minimum instruments required under VFR include an airspeed indicator, altimeter, and magnetic direction indicator. Minimum flying conditions in radar-controlled airspace in transition areas specify a cloud ceiling about 215 m (700 ft) above ground level and 1.6 km (1 mi) visibility. Other VFR requirements for visibility and distance from clouds depend on altitude and whether operation is in controlled or uncontrolled airspace. VFR flight is not permitted in all airspaces, and terminal control areas sometimes require positive (radar) air traffic control. Airport traffic areas typically encompass a radius of 8 km (5 mi) and are extended laterally for the control of instrument-dependent departures and landings. Control zones around airports extend upwards with no limit.
The National Weather Service turned off the last of its 1957-model weather radars on Dec. 2, 1996. The radar, at the Charleston, S.C., Airport went into service in 1959, the 16th of 66 WSR-57 radars the NWS eventually installed around the USA.
WSR-57 stood for Weather Surveillance Radar-57 for 1957, the year it was designed. The old radars were replaced by 88-D radars, which stand for a 1988-design Doppler radar. The new radars are more sensitive, which means they can detect more weather details than the old ones could. The Doppler capability also means they can detect wind speeds and directions, giving a much better picture of bad weather.
The new radars make extensive use of computers, which means they can be programmed to sound an alarm when weather patterns are beginning to appear dangerous. With the old radars, someone had to watch the screen constantly when storms were possible to make sure nothing important was missed.
“It took considerable skill to determine storm intensities from green blotches on the radar scope,” said Steve Rich, meteorologist-in-charge of the Charleston office. “It took even greater skill to tell if a storm had tornado characteristics.” 

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