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1. Introduction
The WSR-88D network is undergoing a life extension program to improve its capability and performance until at least 2030. Parallel to this effort, the National Oceanic and Atmospheric Administration is looking ahead for candidate replacements. One potent nascent technology is the agile-beam phased array radar (PAR), which could augment the weather-observing mission (Zrnić at al. 2007) and serve other purposes, such as air traffic control and monitoring, protection of terminals, and homeland security (Weber et al. 2007).
To be a viable replacement, the PAR should meet all WSR-88D performance standards. One of these is the superresolution mode. The term means that spectral moments are produced at an azimuthal spacing of half a beamwidth while the antenna is rotating at a rate at which statistical errors produced a beamwidth apart are acceptable. In the superresolution mode, the effective beamwidth of the antenna pattern is about 25% narrower than in the standard mode (Torres and Curtis 2007). This increase in azimuthal resolution comes at a price of larger estimate errors.
Simulations indicate (Brown et al. 2002) the superresolution (at 0.5° on the WSR-88D) extends by at least 50% the detection range of mesocyclones and tornadoes. Moreover, the estimates of the Doppler velocity difference between the extreme positive and negative values also increase, better quantifying the strengths of the circulation. Thus, the superresolution data enable forecasters to more easily recognize small hazardous features and to forewarn the public of eminent dangers. Because of increased statistical errors in estimates, the superresolution data are only directly processed by the mesocyclone detection algorithm. For other algorithms, the superresolution data are recombined to form radials of spectral moments spaced 1° apart.
In principle, the PAR could scan as a conventional radar. However, that would degrade the inherent advantages of no beam smearing, such as better filtering of ground clutter (its spectrum width is not broadened) and smaller statistical errors in Doppler variables. This paper introduces a way to obtain superresolution data on the PAR at the same volume coverage speeds as on the WSR-88D with the same azimuthal resolution but lower statistical errors.
The next section discusses the proposed superresolution method, including step scans, window functions, and effective beamwidth. Predicted errors in spectral moment estimates from the PAR in the...