Operational calibration of a ground-based fully polarimetric radiometer for stratospheric temperature retrievals

<p>The oxygen emission band at 60 GHz is a commonly used frequency band for atmospheric temperature sounding. The fine structure emission lines used to retrieve temperature in the stratosphere and mesosphere are affected by the Zeeman effect, which has a characteristic influence on the spectral shape of different polarization states. As a consequence of this effect, a <span class="inline-formula"><i>V</i></span>-Stokes component is generated, indicating symmetry breaking between right and left circular polarized radiation. In this study, we present the full-rank Stokes vector of the fine structure emission lines at 53.067 and 53.596 GHz, measured with a fully polarimetric radiometer. We discuss the advantages of the fully polarimetric approach compared to single-polarization observations for temperature sounding by comparing both simulations and observations. Our findings show that using circular polarization in the retrieval algorithm improves both the upper altitude limit and vertical resolution by several kilometers. Additionally, we introduce an operational calibration method and present calibrated spectra for the four components of the Stokes polarization vector. We also provide a continuous series of retrieved temperature profiles, demonstrating that the calibration is valid for continuous observations.</p>