Monitoring cross-channel correlation solar scan measurements using the Iowa X-band polarimetric radars

The sun is a convenient and frequently employed external radiation source for calibrating weather radar antenna and receiver characteristics. However, changes in solar activity can be a major source of error in interpreting the results of solar calibration for lower frequency bands. The cross-correlation of horizontal and vertical polarization signals, which is zero for perfectly unpolarized electromagnetic radiation, could give non-zero estimates if a quiet sun is not observed by the radar. In this paper, solar scan measurements are made at X-band to detect the effect of solar activity on this cross-correlation coefficient. To facilitate mitigation of instrument-wide errors, we employ multiple XPOL radars to simultaneously observe the sun. Though our experiments during a limited period show that the cross-channel correlation estimates obtained by X-band weather radars remain relatively unaffected by the variations in solar flux, the paper makes suggestions on improving the results.