Articles | Volume 35, issue 3
Regular paper
17 Mar 2017
Regular paper |  | 17 Mar 2017

Comparisons between high-resolution profiles of squared refractive index gradient M2 measured by the Middle and Upper Atmosphere Radar and unmanned aerial vehicles (UAVs) during the Shigaraki UAV-Radar Experiment 2015 campaign

Hubert Luce, Lakshmi Kantha, Hiroyuki Hashiguchi, Dale Lawrence, Masanori Yabuki, Toshitaka Tsuda, and Tyler Mixa

Abstract. New comparisons between the square of the generalized potential refractive index gradient M2, estimated from the very high-frequency (VHF) Middle and Upper Atmosphere (MU) Radar, located at Shigaraki, Japan, and unmanned aerial vehicle (UAV) measurements are presented. These comparisons were performed at unprecedented temporal and range resolutions (1–4 min and  ∼  20 m, respectively) in the altitude range  ∼  1.27–4.5 km from simultaneous and nearly collocated measurements made during the ShUREX (Shigaraki UAV-Radar Experiment) 2015 campaign. Seven consecutive UAV flights made during daytime on 7 June 2015 were used for this purpose. The MU Radar was operated in range imaging mode for improving the range resolution at vertical incidence (typically a few tens of meters). The proportionality of the radar echo power to M2 is reported for the first time at such high time and range resolutions for stratified conditions for which Fresnel scatter or a reflection mechanism is expected. In more complex features obtained for a range of turbulent layers generated by shear instabilities or associated with convective cloud cells, M2 estimated from UAV data does not reproduce observed radar echo power profiles. Proposed interpretations of this discrepancy are presented.

Short summary
Results of comparisons between data collected from a VHF Doppler radar and small unmanned aerial vehicles (UAVs) are presented. The UAVs, equipped with meteorological sensors, flew nearby the radar up to an altitude of ~ 4.0 km. Both instruments detected the same clear-air refractive index gradients at a vertical scale of ~ 20 m when the vertical stratification was strong. A VHF radar can thus provide a faithful image of the vertical stratification of the atmosphere down to decimeter scales.