EVALUATION OF IONOSPHERIC FARADAY ROTATION EFFECTS FOR THE CRYORAD EARTH EXPLORER CANDIDATE MISSION

K. Nagamine Urata¹, M. Martin-Neira¹, F. Ticconi¹, J. Angevain¹, M. Suess¹, F. Brauer¹, V. Dutto¹, M. Brogioni², G. Macelloni², J. Johnson³, J. Boutin⁴

¹European Space Agency, ²National Research Council of Italy, ³Ohio State University, ⁴Centre National de la Recherche Scientifique (CNRS), Sorbonne Université

CryoRad is one of Earth Explorer 12 candidate missions and is a wideband microwave radiometer operating in the 0.4-2 GHz spectrum to observe cryospheric processes at high latitudes (>40 degrees) by retrieving sea surface salinity, ice sheet temperature profile, and sea ice thickness. At such low microwave frequencies, CryoRad adopts circular polarization to minimize ionospheric effects. However, Faraday rotation (FR) combined with antenna impurities may still potentially introduce additional errors in the measured brightness temperatures (Tb).

This work focusses on quantifying these effects through a Stokes-Mueller formalism linking the true and measured Stokes parameters. A forward model was developed to account for both the ionospheric FR angle, derived from the International Geomagnetic Reference Field (IGRF) and total electron content (VTEC) maps, and for antenna non-idealities, represented by the axial ratio and in-quadrature phase delay.

Simulations were performed for the CyoRad configuration at 0.4 GHz, 8 degrees observation zenith angle, and 350 km ionospheric height.

Preliminary results suggest that although FR angle can vary significantly depending on the geomagnetic field orientation and TEC conditions, the resulting maximum Tb bias remains constant (~0.2 K for 0.4 GHz) suggesting that FR doesn’t amplify the Tb error magnitude but rather rotates the (Q,U) polarization vector. The largest contribution to the radiometric uncertainty comes from the antenna cross-polarization and non ideal circularity.

Ongoing work for mitigation strategies for CryoRad are discussed, which include minimizing antenna axial ratio and phase error, and L1b post processing corrections.