RadxDealias James and Houze 2001

Overview

RadxDealias implements a four-dimensional scheme to correct velocity data when wind speeds exceed the Nyquist velocity. Based on James and Houze 2001, RadxDealias uses a combination of corrected velocity data from a prior radar file and environmental soundings to unfold velocity data.

Background

Dealiasing (or folding) of Doppler velocity data occurs when moving hydrometeors produce a frequency shift too high for a radar's pulse repetition frequency (PRF) to resolve. The Doppler phase shift measured by the radar may differ from the true phase shift by a positive or negative integer multiplier of [math]\displaystyle{ 2*pi }[/math].

Dealiasing

Fundamentally, RadxDealias attempts to unfold velocity data by adjusting the velocity value at each gate by Nyquist intervals such that the velocity value at a gate is similar to values at nearby spatial and temporal gates. Working from higher to lower elevation angles, RadxDealias steps through several processes: quality control, deliasing using velocity data from a prior radar volume (or an environmental sounding, if no prior volume exists) as a reference, dealising using velocity data in the 8 neighboring gates from the same tilt as a reference, dealiasing using velocity data from nearby windows of 11x11 or 21x21 gates as a reference, and finally, comparing any remaining folded gates to the environmental sounding.

Sounding Quality

In the course of dealiasing radar data, it may become necessary to visualize to what degree the environmental sounding is influencing the final output. RadxDealias allows for the output sounding or Velocity Azimuth Display (VAD) velocities to be saved to the output files instead of the dealiased velocities by setting output_soundVol = TRUE. This option may be helpful in debugging.

References

James, C. N., & Houze , R. A., Jr. (2001). A Real-Time Four-Dimensional Doppler Dealiasing Scheme, Journal of Atmospheric and Oceanic Technology, 18(10), 1674-1683. Link