P15r.1 the Detectability of Tornadic Signatures with Doppler Radar: a Radar Emulator Study

The design of a weather radar system, as well as its scanning strategies, involves various tradeoffs based upon the goal of observing certain features of interest. The tradeoffs made in this design are based on certain assumptions about the performance of the radar system and on characteristics of the feature of interest. Often, the development of algorithms and optimal scanning strategies requires large datasets to test the range of operating parameters and find those that yield the best results. By simulating the operation of a radar, using a software radar emulator, one can artificially generate large data sets that span the range of radar operating characteristics. These generated datasets are attained much more quickly and with less effort than would otherwise be expended in collecting actual data spanning such characteristics. Many approaches have been taken previously in simulating radar data, varying in sophistication from reflectivity calculation to full simulation of radar returns from each pulse. Krajewski et al. (1993) calculated values of reflectivity factor and differential reflectivity from rainfall rates from a numerical model, using an assumed drop size distribution. Similarly, Chandrasekar and Bringi (1987) looked at the variation of simulated reflectivity values as a function of raindrop size distribution parameters. Neither of these studies was concerned with the Doppler velocity information. Wood and Brown (1997) evaluated the effects of WSR-88D (Weather Surveillance Radar-1988 Doppler) scanning strategies on the sampling of mesocyclones and tornadoes. The effects of the scanning strategy were accounted for by using an effective beamwidth for the radar that was used to scan an analytic vortex. Capsoni and D'Amico (1998) simulated the pulse to pulse time series of radar data by combining the simulated returns from individual hydrometeors within a radar volume. Due to the computational requirements of this approach, the radar data were generated for only a single range gate, and thus the aspects of scanning the radar were not simulated. This work describes a radar emulator designed to simulate the returns from a scanning Doppler radar on a pulse to pulse basis. Starting with output from a high resolution numerical simulation of a supercell thunderstorm (Xue 2004), the emulator generates radar reflectivity, Doppler velocity, and Doppler spectrum width, based on the configured radar and scanning strategy. This emulator is capable of simulating many of the impacts of radar and scanning strategy design on the resolution and quality of collected data. The application of this emulator to studying the detectability of tornadoes by broad-beam, low power radars is shown as an example of the utility of this tool.