Studies on some characteristics of rain-induced depolarization of Ku-band signal over an earth-space path at a tropical location

• Differential phase shift is mostly responsible for Ku-band depolarization.
• The differential phase shift at Ku-band is significant for large rain drops.
• Presence of large rain drops significantly increases the depolarization effect.
• Rain DSD plays major role in determining the extent of depolarization at Ku-band.

The rain-induced depolarization of a Ku-band satellite signal has been studied at a tropical location, Kolkata (22°34′N, 88°29′E). The depolarization phenomenon is observed in terms of an enhancement of cross-polar component of a horizontally polarized Ku-band satellite signal at the present location. The differential phase shifts, dominantly responsible for causing depolarization caused by scattering of oblate spheroidal rain drops at Ku-band, are computed by employing the point matching technique and utilizing rain drop size distribution data, experimentally obtained at the present location. The differential phase shift is significant for large rain drops resulting in greater depolarization of signal. Consequently, rain drop size distribution plays an important role in determining the depolarization of the satellite signal. The relationship of cross-polar enhancement with rain rate shows a seasonal variation indicating higher extent of depolarization during the pre-monsoon period than during the monsoon period, the reason being the dominance of larger rain drops in the pre-monsoon period compared to the monsoon months for identical rain rates.