Sky measurements with the imaging polarimeter SPIRA at 91 GHz

The Scanning Polarimetric Imaging RAdiometer SPIRA at 91 GHz with an angular resolution of 0.5° was used to investigate the dynamics of the atmosphere. We introduced a new imaging method by continuously scanning the sky over a range of elevation angles in a fixed azimuth direction. The measurements were realized during three different situations: clear sky, sky with water clouds and sky with cirrus clouds. Especially interesting structures were found in the images with water clouds. In contrast, cirrus clouds are highly transparent. Simulations of the applied imaging method helped to interpret the cloud images, especially concerning the cloud movement. Curves with an S shape are signatures of motions along the scan line. By extracting the observed shape from such curves we estimated the horizontal velocity of water clouds. It was also possible to estimate the Integrated Water Vapor (IWV) from the clear sky images. They allow a visualization of water vapor parcels. Some of these images contain S curves as well indicating advection of water vapor along the scan line. In future we plan to extend these measurements and to combine with multi-frequency observations.