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Figure 1: Completed WSR-88D installations within the U.S. and its territories.

 

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Slideshow 1: Current operational algorithm products.

Next-Generation Weather Radar (NEXRAD)

The Next Generation Weather Radar system (NEXRAD) is a network of Weather Surveillance Radar-1988 Doppler (WSR-88D) sites supported by three United States government departments. The responsible agencies within the departments are the Federal Aviation Administration (Transportation), the National Weather Service (Commerce), and the Air Force (Defense).

The NEXRAD Network

The network is composed of S-band (10-cm wavelength) Doppler radars used to remotely sense precipitation intensity, location, and motion. The network was deployed in the early 1990s and has a projected service life to around 2025.

The network is composed of about 158 radars total in the United States and its territories (Figure 1). The distribution is such that at 10,000 feet altitude there is nearly complete coverage from the radar network with the exception of some of the mountainous western United States. The radars are operated asynchronously providing new information at intervals of between about 4.5 and 10 minutes.

The NEXRAD network provides critical weather information (products) to a number of FAA weather systems including the Corridor Integrated Weather System (CIWS), the Integrated Terminal Weather System (ITWS), the Medium Intensity Airport Weather System (MIAWS), and the Weather and Radar Processor (WARP). Lincoln Laboratory is an active member of the NEXRAD community on behalf of FAA interests regarding signal processing and product development and their impacts on the aforementioned FAA weather systems.

NEXRAD Data Processing

The data processing system for the NEXRAD radar is composed of the Open Radar Data Acquisition (ORDA) unit and the Open Radar Product Generator (ORPG). The ORDA processes the radar pulse returns from the atmosphere into the three traditional Doppler-moment-based products—reflectivity, radial velocity, and spectrum width—while filtering out unwanted signals such as ground clutter, RF interference, and range-aliased echoes.

Lincoln Laboratory has implemented a number of FAA-sponsored algorithms into the NEXRAD ORPG. Current operational algorithm products, illustrated in Slideshow 1, are High Resolution Vertically Integrated Liquid (HRVIL), High Resolution Enhanced Echo Tops (HREET), Data Quality Assurance (DQA), and the Machine Intelligent Gust Front Algorithm (MIGFA). Lincoln Laboratory continues to support these products and improve their quality as the NEXRAD network adds new capabilities.

Lincoln Laboratory also is applying its expertise with radar signal processing within the TDWR RDA to the NEXRAD ORDA. Focus has been on studying the utility of applying some TDWR signal processing advances to NEXRAD and assessing the robustness of new proposed ORDA signal processing techniques.

The Future of NEXRAD

New capabilities continue to be added to NEXRAD. Improved range-velocity ambiguity mitigation is planned for 2007, super resolution data in 2008, and dual polarization data in 2009. These will help to improve data quality and better distinguish important features within the precipitation. The dual polarization capability will add the ability to estimate scatterer types to complement intensity/coverage and velocity/motion.

Details of the NEXRAD program can be found at http://www.roc.noaa.gov/nexrad.asp.

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