Terminal Doppler Weather Radar (TDWR)

A microburst is an intense localized downdraft that is sometimes generated by a thunderstorm.  If an aircraft inadvertently encounters a microburst while flying at low altitude, it may lose altitude rapidly and not be able to recover in time to avoid a crash.  In fact, a series of commercial aviation accidents in the 1970s and 80s led the FAA to commission a sensor capable of remotely detecting low-altitude wind shear phenomena such as the microburst.  The resulting product was the Terminal Doppler Weather Radar (TDWR), which is now deployed at 45 major airports around the country (Figure 1).

TDWR - radar image and photo of a microburstExample of a classic microburst-producing thunderstorm. A vertical cross-section of the storm's core as seen by radar (left) is compared with a visual photograph of a similar storm that produced a microburst (right).









Developed by Lincoln Laboratory and manufactured by Raytheon, the TDWR (technical specifications) has been a great success as no commercial airline accidents caused by wind shear have occurred at airports protected by it. Besides its primary use for detecting wind shear, TDWR data are also ingested by weather integration systems such as ITWS, CIWS, and the National Weather Service’s Advanced Weather Information Processing System (AWIPS). The general public can easily view TDWR data via the Weather Underground’s interactive display site. The TDWR’s narrow beam and excellent ground clutter suppression capability provide high quality data on boundary layer dynamics, a key to improving convective initiation forecasting, as well as small-scale phenomena such as tornadoes. Relative to the NEXRAD it scans rapidly (e.g., surface updates once per minute), facilitating monitoring of rapidly evolving convective weather phenomena. TDWRs are typically located near population centers and congested airspace, which make them well-situated for supporting weather services for operationally important areas.

TDWR in Cklahoma City, OKTDWR in Las Vegas, Nevada. (Photo: Jeff Simpson)

After more than a decade of highly successful operational use, the FAA initiated activities to extend the operational service life of TDWR beyond 2020 and to enhance its wind-shear detection capabilities.; Lincoln Laboratory was subsequently tasked to retrofit the Radar Data Acquisition (RDA) system. The enhanced RDA system is largely based on commercial off-the-shelf (COTS) technology for extended supportability, and has an open, scalable architecture for ease in introducing future upgrades. Its increased computing capacity has also enabled the use of more advanced signal processing techniques to combat difficult data quality issues such as range-velocity ambiguity (Figure 2) and unwanted clutter signals due to moving targets such as birds and cars (Figure 3). Innovative approaches such as adaptive waveform transmission and processing and 2D range-spectral analysis are being implemented to make the TDWR data quality even better. The new RDA system has been retrofitted at two operational sites (Las Vegas, Nevada and Salt Lake City, Utah) and the FAA has programmed funding to begin national deployment in 2010.

TDWR Technical Specifications

Operating Frequency 5.6 to 5.65 GHz
Instrumented Range Reflectivity 460 km
Doppler 89 km
Antenna Beamwidth 0.55°
Peak Power 250 kW
Pulse Length 1.1 μs
Clutter Suppression 60 dB

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