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Figure 1: Locations of TDWR installations.
Figure 2: Example of data quality improvements.
Terminal Doppler Weather Radar (TDWR)
The Terminal Doppler Weather Radar (TDWR) was designed at Lincoln Laboratory in the late 1980s and early 1990s, and is now deployed at 45 major U.S. airports (Figure 1). The radar’s mission is to provide wind shear detection and precipitation reflectivity data to air traffic controllers, and its data now feed larger data fusion systems such as CIWS and ITWS. Lincoln Laboratory continues to support refinement of the wind shear detection algorithms used in the TDWR, and has provided a major upgrade to its signal processing capability.
Example of a classic microburst-producing thunderstorm. On the left is the plan view of surface reflectivity (top) and Doppler velocity (bottom) with strong surface outflow toward and away from the radar. On the right, a vertical cross-section through the storm's reflectivity core is compared with a visual photograph of a similar storm.The characteristics of the TDWR make it well-suited for additional applications. Its narrow beam (0.55º) and aggressive ground clutter suppression algorithms (55+ dB) provide excellent data on boundary layer reflectivity and winds—in particular the locations of thunderstorm outflow boundaries. 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 convective weather phenomena. It is typically located near population centers and congested airspace, which makes it well-situated for supporting weather services for operationally important areas.
TDWR in Oklahoma City, OK.Radar Data Acquisition (RDA) Retrofit Project
In 2001, under FAA funding, Lincoln Laboratory began a new effort to develop and demonstrate an enhanced Radar Data Acquisition (RDA) system for TDWR. The RDA consists of the intermediate frequency (IF) receiver and digital signal processor (DSP).
The objectives of this effort were to:
- Improve supportability of TDWR by replacing obsolete DSP hardware with an open commercial off-the-shelf (COTS) architecture.
- Enhance the sensor's ability to provide wind shear detection services by implementing modern signal processing algorithms to improve the quality of the reflectivity and Doppler velocity imagery generated by the system.
In FY 2007, the Lincoln-designed, enhanced RDA was deployed to the operational TDWR in Salt Lake City, UT (SLC) and Las Vegas, NV (LAS). This was the culmination of several years and several phases of engineering prototypes that were demonstrated and refined using non-operational TDWR sites in Oklahoma City, OK, in close cooperation with the FAA. The FAA is validating the hardware and software design and will begin deploying the new RDAs nationwide in FY 2008.
The new signal processing algorithms will provide significant mitigation from the data quality problems caused by range-ambiguous echoes, velocity aliasing, and clutter residue. These data quality improvements will benefit not only the users of the wind sheer detection algorithms, but also the larger weather sensing systems such as CIWS and ITWS (see Figure 2).
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