Polarization of measurement for microwave temperature sounding of the mesosphere

This paper examines microwave measurement polarization for mesospheric temperature profile retrieval on a global basis, for which forthcoming satellite instruments are tasked. Retrieval performances at circular, horizontal, and vertical polarization are mapped across the range of geomagnetic conditions (field strength and view orientation) and are related to the impact of Zeeman line splitting on temperature channel weighting functions. Retrieval performance is hampered by conditions that cause clusters and gaps with respect to the heights at which the weighting functions peak, and this may be a greater detriment to sounding performance than the double-peaking of weighting functions that has been previously identified as a pitfall of sounding in linear polarization. Each of the measurement polarizations was better than the other two under some of the geomagnetic conditions. An orbit simulator was used to document the frequency of occurrence of each of the geomagnetic viewing conditions. With respect to overall global performance, circular polarization was found to be the best choice, regardless whether conical or cross-track scanning is used. Between the linear polarizations, vertical was preferable to horizontal for conical sounding at fine spectral resolution.