Polarimetric Radar Detection of Hail using X- and S-Band Frequencies

The focus of this research is to use the Colorado State University–University of Chicago–Illinois State Water Survey (CSU-CHILL) radar to identify areas of hail within a storm. This research was done as part of the CSU-CHILL REU program. The CSU-CHILL radar has the unique distinction of being able to make both dual-polarization and simultaneous dual-frequency (S- and X-band) measurements. Hydrometeors will enter a Mie backscattering regime from a Rayleigh one at smaller diameters for the X-band than for the S-band, due to the difference in wavelength size. Archived radar data from CSU-CHILL from two northern Colorado hail events (6/03/2015, 6/04/2015) is examined in this research. Both of these days featured 0.5-1” diameter hail stones, which is large enough to cause Mie scattering at X-band but not at S-band. Both storms show the expected Mie scattering effects at the X-band where hail was reported or detected by a hydrometeor identification algorithm (HID). A giant hail case (>4” in diameter) is also examined, where Mie scattering effects were present at the S-band as well. The results of this preliminary investigation into dual-pol/dual-frequency hail detection suggest that ϕ_dp and ρ_hv are feasible parameters to use to detect Mie scattering, and to subsequently locate areas of small-to-moderately sized hail that might otherwise go unnoticed using only the S-band.