Detection and Estimation of Rainfall Through Data Analysis of Geostationary Ku-Band Satellite Signal

A Ku-band receiver system is configured in State College, Pennsylvania to evaluate the potential of a rainfall estimation technique using satellite-link wave attenuation measurements. The proposed method can provide continuous realtime rainfall intensity R and rainfall accumulation estimates throughout a day by monitoring commercial satellite signals at the receiver antenna. The method can be used for a precipitation measurement technique as an alternative or complementary to existing methods such as rain gauge and radar in complex environments, such as over hilly terrains and urban areas as well as parts of the oceans that lie within the footprint of the satellite. Power law relationships between specific attenuation A (dB/km) and rainfall intensity R (mm/h) are used to estimate R and the rainfall accumulation along the link path. Polarimetric radar measurements obtained from the National Weather Service WSR-88D system located 18:5km away from the receiver ground station are utilized to provide a comparison of rainfall accumulation estimates. Two tipping-bucket rain gauges, co-located with the satellite receiver, are also used for comparison. The effective rain height (ERH) used in converting total attenuation along the link path to attenuation rate is estimated from polarimetric radar observations. A method based on bit error ratio (BER) measurements for the commercial satellite link is used to identify periods of rain during which rainfall rate is estimated from signal attenuation measurements. Logistic regression analysis that is based on WSR-88D measurements and statistics of BER data during the years 2013 and 2014 is used to develop a rain detection algorithm. The rain detection algorithm is applied and rainfall estimates are presented for the selected days during the years 2015 and 2016. Satellite-based precipitation estimates show good comparisons with radar-based estimates (within 19%) for accumulations greater than 6mm and not so good (within 43%) for accumulations below 3mm as Ku-band link becomes less sensitive to light rain events, i.e. R < 1.5mm/h. Precipitation estimates through wave attenuation at Ka-band and difference of wave attenuation using dual-frequency links are also investigated and results are presented for several days. Problems associated with factors such as effective rain height (ERH), A--R models, classification of wet and dry periods, and attenuation reference level (ARL) are addressed and possible solutions are proposed as such factors have significant impact on rain estimates.