Abstract. Polar mesospheric summer echoes (PMSEs) are very strong radar echoes
caused by the presence of ice particles, turbulence, and free electrons in
the mesosphere over polar regions. For more than three decades, PMSEs have
been used as natural tracers of the complicated atmospheric dynamics of this
region. Neutral winds and turbulence parameters have been obtained assuming
PMSE horizontal homogeneity on scales of tens of kilometers. Recent radar
imaging studies have shown that PMSEs are not homogeneous on these scales and
instead they are composed of kilometer-scale structures. In this paper, we
present a technique that allows PMSE observations with unprecedented angular
resolution (∼0.6∘). The technique combines the concept of
coherent MIMO (Multiple Input Multiple Output) and two high-resolution imaging
techniques, i.e., Capon and maximum entropy (MaxEnt). The resulting
resolution is evaluated by imaging specular meteor echoes. The gain in
angular resolution compared to previous approaches using SIMO (Single Input
Multiple Output) and Capon is at least a factor of 2; i.e., at 85 km, we
obtain a horizontal resolution of ∼900 m. The advantage of the new
technique is evaluated with two events of 3-D PMSE structures
showing: (1) horizontal wavelengths of 8–10 km and periods of 4–7 min,
drifting with the background wind, and (2) horizontal wavelengths of
12–16 km and periods of 15–20 min, not drifting with the background wind.
Besides the advantages of the implemented technique, we discuss its current
challenges, like the use of reduced power aperture and processing time, as
well as the future opportunities for improving the understanding of the
complex small-scale atmospheric dynamics behind PMSEs.
Enhancing the spatiotemporal features of polar mesosphere summer echoes using coherent MIMO and radar imaging at MAARSY
