REGIONAL AND DIURNAL VARIATIONS OF RAIN ATTENUATION OBTAINED FROM MEASUREMENT OF RAINDROP SIZE DISTRIBUTION OVER INDONESIA AT KU, KA AND W BANDS

—The measured raindrop size distribution (DSD) and the International Telecommunication Union Radiocommunication Sector (ITU-R) model have been used to elucidate the regional and diurnal variations of rain attenuation in Indonesia, for Ku-band (13.6GHz), Ka-band (35.6GHz), and Wband (96GHz) frequencies. The DSDs were measured by the Parsivel disdrometer at Kototabang (KT; 100.32◦E, 0.20◦S), Padang (PD; 100.27◦E, 0.54◦S), Pontianak (PT; 109.37◦E, 0.00◦S), Manado (MN; 124.92◦E, 1.55◦N) and Biak (BK; 136.10◦E, 1.18◦S). In general, PD, KT and PT have lower rain attenuation than those at MN and BK, for the same rainfall rate, due to lower concentration of small-sized drops at these sites as reported by a previous study. Considerable differences between the attenuation obtained from the DSD and the ITU-R model are observed at all locations, in particular for very heavy rainfall (R > 50mm/h). For R < 50mm/h, the specific rain attenuation of measured DSD is in fairly good agreement with that obtained from the ITU-R model. The specific rain attenuation obtained from the DSD shows diurnal variation, in agreement with a previous study at KT. The diurnal variation of rain attenuation is dependent on the operating frequency and rainfall rate. At KT and PT, the lowest rain attenuation for Ku-band is observed during 06–12 LT, but during this period the largest attenuation is observed for Kaand W-bands. These phenomena may be due to the increasing role of small and medium-sized drops by increasing frequency.