Characterization of bright-band in a tropical station for satellite communications

Abstract

Tropical regions experience signal degradations due to hydrometeors in addition to paucity of database for slant path rain propagation estimations. The melting layer is the region where rain starts to occur; lying just below the 0oC isotherm height. Frozen hydrometeors exhibit peculiar characteristics in the form of increased radar reflectivity as they fall from the sky, morphing from solid to liquid; and manifesting itself as the popular bright-band signature. Knowledge of the formation and recognition of the bright-band is necessary to characterize the melting layer. Adequate information on diurnal, seasonal and annual variation effects on rain height can give valuable information for satellite equipment design and planning. Rain height is highly correlated with signal attenuation and co-channel interference resulting from scattering. This work involves the characterization of bright-band data for UTM Johor Bahru campus, Malaysia. Thirteen months (1 November, 2006 to 30 November, 2007) 3D RAPIC ground radar data at 500 m range bins resolution were sourced from MMS. Additionally, twenty-two months (January 2011 to May 2013) TMPA-RT radar data at 50 x 50 latitude-longitude horizontal resolution were obtained to complement the ground radar data. The reflectivity from these data was analysed to characterize the melting layer. Malaysia experiences two monsoon events yearly: The North-East monsoon and the South-West monsoon. Results from this work suggest that freezing and rain heights are highest in the months of November 2006, March and September 2007; which coincides with the end of the two monsoons. Equally, these parameters are observed to be lowest in February, April, July and October; thus suggesting seasonal and annual variability. The bright-band is thicker in the day, while freezing and rain heights are higher at night than in the day time, suggesting diurnal dependence. However, data for a longer period of time is needed to consolidate these findings. The results show good degree of agreement when compared with similar previous findings from Malaysia. But, ITU-R.P. 618 model largely underestimated the total measured attenuation. Thus, there is a need to include the melting layer effect in satellite communication attenuation prediction in the tropics for improved Quality of Service.