Detection of Ice Hydrometeor Alignment Using an Airborne W-band Polarimetric Radar

Abstract

This paper presents airborne W-band polarimetric radar measurements at horizontal and vertical incidence on ice clouds using a 95-GHz radar on the University of Wyoming King Air research aircraft. Coincident, in situ measurements from probes on the King Air make it possible to interpret polarimetric results in terms of hydrometeor composition, phase, and orientation. One of the key polarimetric measurements recently added to those possible with the W-band radar data system is the copolar correlation coefficient HV. A discussion of the relation between cloud scattering properties and HV covers a test for isotropy of the distribution of observed hydrometeors in the plane of polarization and qualitative evaluation of the possible impact of Mie (resonant) scattering on HV measurements made at W band. Prior measurements of HV at S band and Ku band are compared with the W-band results. The technique used to measure HV , including the real-time and postprocessing steps required, is explained, with a discussion of the expected measurement error for the magnitude and phase of HV. Cloud data presented include melting-layer observations at vertical incidence, observation of a convective snow cell at vertical incidence, and observations of needle crystals at both horizontal and vertical incidence. The melting layer observations provide a consistency check for the measurements of HV and linear depolarization ratio (LDR) at W band through the test for isotropy. The vertical incidence measurements of a convective snow cell displayed significant mean orientation of the hydrometeors observed in the features evident in Z DR and the phase of HV. Data taken on needle crystals provided clear indication of particle alignment in the measurements of Z DR and LDR for the horizontal incidence case and equally clear indication of a lack of orientation for the vertical incidence case.

Evaluation of radar multiple scattering effects in Cloudsat configuration

“…In both panels, the bright band can be seen as an horizontal strip with LDR values around -12 to -15 dB located at about 2.5 and 1.5 km. These bright band features are in agreement with former melting layer observations at vertical incidence during the Winter Icing and Storms Project (see Galloway et al, 1997). However much higher values of LDR (up to about -3 dB) are observed in coincidence in strongly attenuating regions (as indicated by the low surface echo in the reflectivity panels).…”

“…The Wyoming Cloud Radar (see Galloway et al (1997) and references therein) has provided the first polarimetric airborne observations at 95 GHz. Observations during field experiments in 1992 and 1994 show typical LDR features from the melting layer and from preferentially aligned ice crystals.…”

Remote Sensing of Precipitation from Airborne and Spaceborne Radar

“…This chapter is intended to provide an overview of the theoretical basis and some practical implementations of precipitation retrieval algorithms for nadir (or near-nadir) looking airborne and spaceborne weather radars at attenuating frequencies, without consideration of polarimetric quantities or Doppler velocity. While dualpolarimetric radars are widely used from ground-based platforms to identify preferentiallyoriented, non-spherical hydrometeors, at near-nadir incidence angles these measurements are of limited utility although the linear depolarization ratio measurements can be useful for identifying melting layers and non-spherical ice particles (Pazmany et al, 1994;Galloway et al, 1997).…”

“…This chapter is intended to provide an overview of the theoretical basis and some practical implementations of precipitation retrieval algorithms for nadir (or near-nadir) looking airborne and spaceborne weather radars at attenuating frequencies, without consideration of polarimetric quantities or Doppler velocity. While dualpolarimetric radars are widely used from ground-based platforms to identify preferentiallyoriented, non-spherical hydrometeors, at near-nadir incidence angles these measurements are of limited utility although the linear depolarization ratio measurements can be useful for identifying melting layers and non-spherical ice particles (Pazmany et al, 1994;Galloway et al, 1997).Doppler velocities are useful for inferring hydrometeor fall speeds and at multiple frequencies can be highly effective in discerning cloud liquid from rain (e.g., Kollias et al, 2007) as well as identification of ice particle habits (Kneifel et al, 2016), but obtaining them from rapidlymoving satellite platforms is a difficult engineering challenge that will first be attempted in the EarthCARE mission (Illingworth et al, 2015). Table 1 -Characteristics of TRMM, GPM, and CloudSat Spaceborne Weather Radars…”

Cloud radar with hybrid mode towards estimation of shape and orientation of ice crystals

“…The plates were mounted into the waveguide system of a ground-based Ka-band radar, operated by the Wave Propagation Laboratory of the National Oceanic and Atmospheric Administration. A number of studies present polarimetric measurements of winter clouds taken by airborne (Galloway et al, 1997;Wolde and Vali, 2001) and groundbased cloud radars (Pazmany et al, 1994;Lohmeier et al, 1997;Reinking et al, 2002). Often such measurements were compared with the microphysical properties of the ice crystals observed in situ with aircraft or on ground.…”