Geometric considerations of polar mesospheric summer echoes in tilted beams using coherent radar imaging

[摘要] We present observations of polar mesospheric summer echoes (PMSE) using theMiddle Atmosphere Alomar Radar System in Northern Norway(69.30° N, 16.04° E). The radar is able to resolve PMSEat high spatial and temporal resolution and to perform pulse-to-pulse beamsteering. In this experiment, 81 oblique beam directions were used withoff-zenith angles up to 25°. For each beam pointing direction andrange gate, coherent radar imaging was applied to determine the meanbackscatter location. The location of the mean scatterer in the beam volumewas calculated by the deviation from the nominal off-zenith angle of thebrightest pixel. It shows that in tilted beams with an off-zenith anglegreater than 5°, structures appear at the altitudinal edges of thePMSE layer. Our results indicate that the mean influence of the location ofthe maximum depends on the tilt of the beam and on the observed area of thePMSE layer. At the upper/lower edge of the PMSE layer, the mean backscatterhas a greater/smaller off-zenith angle than the nominal off-zenith angle.This effect intensifies with greater off-zenith beam pointing direction, sothe beam filling factor plays an important role in the observation of PMSElayers for oblique beams.

[学科分类] 电子、光学、磁材料