istricton2008-05-03.Thehorizontalaxesistime,theverticalistherainattenuationratio.Thesignalattenuationcorrespondingwiththetimeisshowninfigure.paredthetwographs,theseconclusioncanbedrawn:Theheavieristherainfall,thegreateristhecorrespondingrainattenuationratio.Whenthemaximumofrainfallhappenedatabout21:00houronMay3rd,thesignalattenuationhappenedjustatthattimethen.(2).Thesignalattenuationarenotonlyhappenduringtheraintime,butalsoaftertherain,becausethecloudinskyalsocausestheattenuationinsomerespects.Forinstance,during17:00-18:00onMay3rd,thoughthereisnotrain,butitisobviousthatthereisstillsignalattenuation.(3)Therainattenuationratioisrelativewiththeperiodwhichtherainfallislasting.Tothesamerainfall,thesignalattenuationwhichiscausedbytherainfallfor20minutesisclearlygreaterthanthatforoneortwominutes.
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