The ROCSAT-1 IPEI Preliminary Results:Vertical Ion Drift Statistics

Abstract

A number of ground-based instruments,including 19.5GHz radiometer,optical raingauge,portable weather station,and high resolutiondisdrometer,were set up to conduct the Ka band propagation experimentof the Experimental Communication Payload(ECP)for ROCSAT-1.Inthis article,19.5GHz background sky noise temperatures measured atChung-Li and Tainan sites are presented and investigated.Long-term statisticsof the 19.5GHz background sky noise temperature observed by avertically pointed radiometer in precipitation-free condition over the Taiwanarea shows that the percentages of time that the sky noise temperatureexceeds 20K,30K,40K and 50K are,respectively,98%,85%,53%,and27%.However,in precipitating environments,statistics shows that the percentageof time that the sky noise temperature exceeds 55K,100K,150K,and 200K are,respectively,22%,13%,4.5%,and 2%.The statistics of skynoise temperatures observed at different zenith angles under environmentswithout precipitation is also made.The results show that 80% of the observedsky noise temperatures at zenith angles of 10°,30°,50°and 70°are,respectively,in the ranges of 92-180K,39-52K,26-33K,and 21-27K.In addition,a comparison between surface rainfall rate recorded by theoptical raingauge and sky noise temperature measured by 19.5GHz radiometershows that the former lags behind the latter by about 5 minutes,implying non-uniform and inhomogeneous distribution of precipitation inthe air.In order to measure the precipitation aloft,the Chung-Li VHF radarwas operated simultaneously.Champaign observation shows that thereis no latency between sky noise temperature and VHF backscatter fromprecipitation.This result implies that the VHF backscatter from precipitationcan be employed to validate the observed sky noise temperature.Inaddition,we also find that the sky noise temperature may be as high as 155K(corresponding to 3.6dB attenuation)under an environment withoutsurface precipitation.This feature is attributed to the dense water vaporand heavy cloud.