QUASI-OPTICAL DESIGN OF TEMPERA-C POLARIMETER AND CHARACTERISING POLARISATION DEPENDENT BIASES

R. Albers¹, W. Krochin^1,2, G. Stober^1,2, A. Murk^1,2

¹Institute of Applied Physics, University of Bern, ²Oeschger Centre for Climate Change Research, University of Bern

The Institute of Applied Physics at University of Bern has designed and manufactured a fully polarimetric radiometer for ground-based temperature sounding called TEMPERA-C. The polarimeter operates in the 60 GHz oxygen band and compensates the Zeeman broadening effect to extend the upper altitude limit of the retrieval. TEMPERA-C is designed for campaign measurements, such as at the High Altitude Research Station on the Jungfraujoch.

The instrument uses an orthomode transducer and two coherent receiver chains connected to a digital FFT spectrometer. A corrugated feedhorn illuminates a static parabolic mirror, which collimates the beam. A secondary flat flip mirror is used to switch between an ambient load inside the instrument and the scanning mirror. The flat scanning mirror is located inside a rotatable periscope, which allows for full 360° scanning in the vertical plane. The ambient load is wedge shaped and uses another parabolic mirror for coupling from the flip mirror to reduce the required aperture size of the load.

This paper covers the quasi-optical design of the TEMPERA-C instrument and an investigation of the polarimetric biases induced by the quasi-optics using TICRA Tools. Aside from the wedge shaped load, other polarisation dependent effects arise from the offset parabolic mirrors and the rotating scanning mirror. It will also cover the particularities of correctly modelling such effects in TICRA tools. Lastly, measurement results from the Jungfraujoch station through a snow covered window will be presented, which demonstrate polarimetric biases.