Monochromatic waves drifting against the wind

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Monochromatic waves drifting against the wind
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MAARSY Radar - Andoya, Norway

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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 in scales of tens of kilometers. Recent radar imaging studies have shown that PMSEs are not homogeneous in 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 (Multi-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 and multiple-output) and Capon is at least a factor of 2, i.e., at 85 km, we obtain a horizontal resolution of ∼ 900 meters. The advantage of the new technique is evaluated with two events of three-dimensional PMSE structures showing: (1) horizontal wavelengths of 8-10 km and periods of 4-7 minutes, drifting with the background wind, and (2) horizontal wavelengths of 12-16 km and periods of 15-20 minutes 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.
Keywords MIMO Radar Imaging Polar Mesospheric Summer Echoes High resolution images MAARSY


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