Rainfall Observation by X-Band Multi-Parameter Radar - MARCH 2005 NIED. National Research Institute for Earth Science and Disaster Prevention

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1 Rinfll Observtion by X-Bnd Multi-Prmeter Rdr - MARCH 2005 NIED Ntionl Reserch Institute for Erth Science nd Disster Prevention

2 Introduction Since 2000, the Ntionl Reserch Institute for Erth Science nd Disster Prevention (NIED) hs been conducting study on the prediction of lndslide dissters cused by torrentil rin. In 2003, the X-bnd multi-prmeter rdr (MP-X) ws instlled in Ebin, Kngw prefecture, nd continuous observtion of rinfll begn. The dt obtined from such observtions is used not only to predict lndslide dissters, but lso to reduce nturl dissters. Through its observtions, NIED ims to chieve the following: The estblishment of high-precision, high-resolution precipittion estimtion methodology The cretion of precipittion dt for shllow lndslide risk prediction nd flood prediction The development of short-term rinfll forecsting using three-dimensionl precipittion informtion An understnding of the microphysicl process of precipittion 5 The rel-time public disclosure of rinfll informtion using the Internet Using the content below, this brochure provides summry of our rinfll observtions nd describes the initil results obtined: Wht is multi-prmeter rdr? Types of rdr Principle of rinfll estimtion using multi-prmeter rdr Multi-prmeter rdr observtion prmeters Outline of rdr observtions Specilly prepred ringuge networks A new methodology: the R-K DP reltionship R-K DP method unffected by rin ttenution 500-meter mesh rinfll informtion Verifiction using ground-bsed ringuges Appendix History of NIED wether rdr reserch 1

3 Wht is multi-prmeter rdr? In order to study the cloud nd precipittion process, the multi-prmeter rdr system (MP rdr system) ws completed in 2000, following technology survey nd bsic nd detiled design processes which were conducted in The MP rdr system comprises dul wvelength high sensitivity rdr (MP-K/W rdr) for cloud observtion, nd 3 cm wvelength polriztion rdr (MP-X rdr) for rinfll observtion. Although the MP-X rdr ws originlly mounted on 4-ton truck to fcilitte mobile observtions, in 2003 it ws fixed top 4-story building locted in Ebin in Kngw prefecture so s to conduct continuous observtions of rinfll. This hs enbled the constnt monitoring of the genertion of hevy rinfll in the Tokyo metropolitn re. This brochure describes only the MP-X rdr. b 1 The multi-prmeter rdr system t NIED in 2000 (Tsukub). Left: MP-K/W, right: MP-X. 1b The MP-X fter reloction in 2003 (Ebin, Kngw prefecture). Tble 1 NIED MP-X Rdr Specifictions Frequency Antenn type Scnning rnge (speed): AZ EL Antenn gin Bem- width Trnsmission tube Pek power Pulse width Pulse repetition frequency Polriztion Doppler processing Noise figure Observtion rnge Observtion prmeters GHz 2. 1m dimeter prbolic ntenn 360 ( 36 deg/s) -2 ~ +92 ( 18 deg/s) db 1. 3 deg Mgnetron 50 kw 0.5 μs 1, 800 Hz H, V PPP, FFT 2. 3 db 80 km Z H, V D, W, Z DR, ρ hv, Φ DP, K DP 2

4 Types of Rdr Rdr is n cronym for rdio detection nd rnging. Rdrs, equipment used to detect nd mesure the distnce to trget vi rdio wves, cn be clssified by the type of rdio wves used nd the informtion tht cn be obtined. Conventionl rdrs, such s those used by the Jpn Meteorologicl Agency, mesure only the mplitude informtion of the rdio wves which hve bck-scttered from rindrops nd returned to the rdr (reflectivity fctor), nd with which rin rtes cn be estimted. Doppler rdrs, in opertion s irport rdrs, mesure frequency informtion (Doppler frequency) in ddition to the mplitude informtion, from which the rdil velocity (Doppler velocity) of rindrops to the rdr cn be mesured. Multi-prmeter rdrs enble the trnsmission of two types of rdio wves; verticl nd horizontl polriztion, while conventionl nd Doppler rdrs cn trnsmit only single type. Vrious prmeters cn be obtined from the signls tht re reflected from rindrops. The use of multi-prmeter rdr enbles ccurte rinfll estimtes, s polriztion prmeters re closely relted to rindrop shpe nd their drop-size distribution. Further, distinctions cn be mde such s tht between rin nd snow. Conventionl Rdr rinfll informtion rdio wves received rdio wves trnsmitted Z H : reflectivity fctor Doppler Rdr rdio wves received + rdil wind fd rdio wves trnsmitted Z H : reflectivity fctor, V D : Doppler velocity Multi-prmeter Rdr rinfll informtion + rdil wind + shpe nd number of rindrops horizontl polriztion verticl polriztion /b rdio wves received fd b φ DP Z H : reflectivity fctor, V D : Doppler velocity K DP, Z DR, ρ HV : polriztion prmeters 2 Rdr types nd the informtion tht cn be obtined. 3

5 Principles of Multi-prmeter Rdr Estimtion Multi-prmeter rdr uses two polriztion wves, while conventionl meteorologicl rdrs use single-polriztion wve (Fig. 3). The principle of rinfll estimtion using multi-prmeter rdr is bsed on the fct tht rindrop shpes chnge from round to flt with increses in rinfll intensity. y Horizontl Polriztion y Verticl Polriztion x z x z 3 Structure of horizontlly nd verticlly polrized wves 3mm 4mm 5mm 6mm 7mm 8mm 3b Chnges in rindrop shpe Rdr prmeters used to estimte rinfll intensity: Reflectivity fctor Z H : The strength of the rdio wves reflected bck to the rdr fter it hits rindrops. Z H is prmeter tht is used in conventionl metrologicl rdr observtions. The rinfll intensity is computed using predetermined R- Z H reltionship. Differentil reflectivity Z DR : Defined s the rtio of the reflectivity fctor for horizontl polriztion Z H to tht for verticl polriztion Z V. Z DR is one of the importnt polriztion prmeters tht MP rdr cn mesure, nd from which prmeter informtion on rin drop size distribution cn be obtined. Specific differentil phse K DP : Defined s the difference in phse velocity per unit distnce of horizontlly- nd verticlly-polrized wves. K DP is one of the polriztion prmeters tht MP rdr cn mesure, nd from which ccurte rinfll intensity cn be determined. 4

6 Multi-prmeter Rdr Observtion Prmeters Reflectivity fctor Z H. b Doppler velocity V D. c Specific differentil phse K DP. d Differentil reflectivity fctor Z DR. e Correltion coefficient between two polriztions ρ HV. 4 Exmples of rinfll cused by typhoon T0310, which ws observed on August 9, A vriety of rin cloud informtion ws obtined through observtions with multi-prmeter rdr. 5

7 Outline of Rdr Observtions In June 2003, the MP-X ws moved to Ebin, Kwski in order to conduct continuous observtions of rinfll. Its observtion rnge of rdius 80 km covers mountinous res such s Mt. Fuji, Hkone nd Tnzw, nd flt res where big cities such s Tokyo nd Yokohm re locted. The MP-X enbles simultneous exmintion of rinfll distributions t two geologiclly different positions. There re two existing ringuge networks in the rdr observtion re, which networks re used for verifiction of rinfll estimte lgorithms. One, the Jpn Meteorologicl Agency AMeDAS ringuge network, provides 10-minute rinfll dt with spcing of bout 17 km. The other ringuge network is tht operted by municiplities such s Tokyo nd Kngw prefecture, from which is obtined 10-minute rinfll dt with spcing of bout 5 km. 5 NIED MP-X instlled in Ebin, Kngw prefecture (June 2003). observtion rnge (rdius 80 km) Sitm prefecture Ymnshi prefecture Tokyo Shizuok prefecture MP-X Kngw prefecture Chib prefecture observtion rnge (rdius 80 km) 6 MP-X loction nd observtion rnge. shows ground-bsed ringuge network in Tokyo nd Kngw prefecture. shows the Jpn Meteorologicl Agency s rinfll observtion points. 6

8 Observtion of Rinfll by X-Bnd Multi-Prmeter Rdr Specilly Prepred Ringuge Networks I n ddition to the existing ringuge networks, for the 2003 observtions specil instruments were instlled jointly by universities t home nd brod. Pukyong Ntionl University in Kore provided two networks. One of them, Network 1 (Fig. 7), comprises four tipping bucket ringuges plced bout 10 km wy from the rdr with spcing of bout 300 meters. The rinfll intensity in spce, which the rdr mesures, cn thereby be obtined. The other, Network 2, comprises four ringuges plced in mountinous re, on stright line from the rdr. Network 2 ws put in plce so s to confirm the ccurcy of rinfll estimtes for mountinous res. Such ringuges hve resolution of 0.1mm, nd smpling intervl of one minute. In ddition to these networks, three impct type disdrometers were deployed, with which devices rindrop size distributions cn be mesured. Furthermore, 2D-video disdrometer, which enbles the mesurement of rindrop size, ws deployed by Colordo Stte University. Verifiction using ringuges nd disdrometers Network 2 1-minute intervl dt recording tipping bucket ringuges 1min. rin guge (Pukyong Univ.) (Pukyong Ntionl University) MP-X 2D-video disdrometer (Colordo Stte University) 2D-video disdrometer (CSU) Network 1 Impct disdrometers (NIED, Ngoy University) JW disdrometer (NIED, Ngoy Univ.) 7 Network comprised of specilly prepred ringuges nd disdrometers (2003). b 2D-Video Disdrometer 2D-video disdrometer (CSU) sensor unit Sensor Unit 1-minute, 1 min. Rintipping Guge bucket ringuge (Pukyong Univ.) signl Processor processor Signl JW Disdrometer impct (NIED,disdrometer Ngoy Univ.) 8 () 2D-video disdrometer plced on the rooftop of the NIED Hirtsuk Testing Yrd (Hirtsuk, Kngw). (b) One-minute intervl dt recording tipping bucket ringuge nd impct disdrometer plced t the sme loction. 7

9 New Methodology: The R-K DP Reltionship The method generlly used to perform rinfll intensity estimtes with conventionl wether rdrs is tht of estimting rinfll intensity from reflectivity fctor Z H (the so-clled R-Z H method). Since this method is sensitive to fluctutions in rindrop size distribution, it is known tht there re substntil errors in rinfll intensity estimtes. On the other hnd, one feture of the R-K DP method, which uses specific differentil phse, is tht it is not so sensitive to fluctutions in rindrop size distribution. Simultions show tht the R-K DP method hs n estimtion error of below 30 percent, while the Z-R method hs n estimtion error of 100 percent or more. 9 The R-Z H reltionship obtined by mesured rindrop size distribution through simultion. 9b The R-K DP reltionship obtined by mesured rindrop size distribution through simultion. 10 Comprison between ctul rinfll intensity (trnsverse xis) nd rinfll intensity obtined using the R-Z H reltion (longitudinl xis). The dispersion of points shows tht this method is sensitive to fluctution in rindrop size distribution. 10b Comprison between ctul rinfll intensity nd rinfll intensity obtined using the R-K DP reltion. The dispersion is smller thn tht obtined when the trditionl method ws used. 8

10 Observtion of Rinfll by X-Bnd Multi-Prmeter Rdr R-KDP Method Unffected by Rin Attenution A fter World Wr II, when the use of rdrs for rinfll observtion ws in its infncy, high expecttions were plced on compct, low-cost X-bnd rdrs for their use in hydrology. However, fter it becme known tht X-bnd rdrs were gretly ffected by rin ttenution due to their short wvelength, nd tht they were unsuitble for quntittive mesurement, such expecttions drsticlly fded. Multi-prmeter rdrs re unffected by rin ttenution, s they use K DP informtion insted of reflectivity fctor. The R-K DP method hs thus enbled quntittive rinfll estimtes, which were conventionlly difficult to obtin. Clssic method (R-Z reltionship) b 11 () Rdr reflectivity fctor of rin induced by Typhoon T0111. (b) Distribution of rinfll intensity estimted from rdr reflectivity fctor. Hevy rinfll within the re shown in the dotted-line circle is not being detected due to ttenution cused by the strong rin bnd ner the rdr. New method (R-KDP reltionship) b 12 () Specific differentil phse K DP of rin induced by Typhoon T0111. (b) Distribution of rinfll intensity estimted from the K DP. The hevy rinfll re, which ws not detected in Fig. 11, is being detected. 9

11 Observtion of Rinfll by X-Bnd Multi-Prmeter Rdr 500-meter Mesh Rinfll Informtion T he sptil resolution of the rdr-amedas precipittion chrts, which is opertionlly provided by the Jpn Meteorologicl Agency s fields of hourly precipittion mounts, is 2.5 km. On the other hnd, observtions mde with the MP-rdr re t resolution of 500 meters. Fig. 13 nd Fig. 14 show the difference between these sptil resolutions. The 500m sptil resolution enbles the provision of more detiled rinfll distribution compred with the 2.5 km sptil resolution. In order to predict dissters such s urbn f loods nd shllow lndslides, it is necessry for rinfll informtion to be s detiled s possible. 0 03/08/09 03:48:16 1 km Y(km) R(mm/h) Hkone region topogrphicl mp, with mesh size of 2.5 km X(km) b Rinfll distribution t 2.5-km mesh size. 0 03/08/09 03:48:16 1 km Y(km) R(mm/h) Hkone region topogrphicl mp, with mesh size of 500m X(km) b Rinfll distribution t 500m mesh size

12 Verifiction Using Ground-bsed Ringuges Ringuge TMH SKD SBS MP-X Time Ringuge Ringuge Time Time 15 Verifiction of results of rinfll intensity estimtion formul R(K DP ). Comprison with ringuges plced on stright line in westerly direction from the rdr. They mtch extremely well. b c d 16 Verifiction for 1-hour ccumulted rinfll obtined by four rinfll estimtion methods. () R(Z H ) method before rin ttenution correction. (b) R(Z H ) method fter rin ttenution correction. (c) R(K DP ) nd R(Z H ) method before rin ttenution correction. (d) R(K DP ) nd R(Z H ) method fter rin ttenution correction. 11

13 Appendix History of NIED Wether Rdr Reserch Mny of the tmospheric phenomen tht trigger dissters re mesoscle in nture, with sptil scles of from few hundred meters to severl hundred kilometers nd with life cycle of severl tens of minutes to bout two dys. Torrentil rins, hevy snowfll, lightening nd torndoes, which occur in Jpn every yer, nd which cuse dmge to life nd vluble ssets, re typicl exmples of mesoscle phenomen. Mesoscle phenomen, which hve gret diversity of forms nd geogrphicl chrcteristics, re on smll scle nd sometimes occur unexpectedly. Wether rdrs re effective mens to monitor such mesoscle phenomen. The use of rdrs with Doppler function enbles informtion on wind distribution to be obtined, in ddition to the reflectivity informtion tht is conventionlly obtined. The use of multi-prmeter rdrs with Doppler polriztion function enbles non-z-r reltion-bsed rinfll estimtes to be performed, nd informtion on precipittion prticle types to be obtined. From globl point of view, it ws 50 yers or so go tht wether rdrs mde their full-scle debut. The trnsfer of World Wr II er militry rdrs to civilin use led to the dvent of wether rdrs. The first wether rdr ws introduced to NIED in Considering the fct tht NIED ws estblished in 1963, it cn be sid tht with the introduction of wether rdr, NIED hs undertken reserch since the erly stges of its estblishment. Looking t the history of NIED reserch using wether rdr, it is divided brodly into three phses; non-doppler rdr, Doppler rdr, nd multi-prmeter rdr. A brief introduction to the min observtions conducted by NIED is given here, with photogrphs Snow storm observtion (Tsugru Plin, 1989 ~ 1992) 2. Snow cloud observtion (Skt, 1989 ~ 1992) 3. Snowstorm observtion (Ishikri Plin, 1994 ~ 1996) 4. Typhoon observtion (Miyko Islnd, 1993) 5. Rinfll observtion/duetto (Ishikri Plin, 1994) Tsukub Region Rinfll Observtion (Knto Plin, 1993 ~ 1996) Nrit Interntionl Airport rdr verifiction experiment (Knto Plin, 1995) JATMEX (Drwin, Austrli, 1999 ~ 2000) 8. Snowfll observtion (Ngok, 2000) 9. Miyke Islnd volcnic sh observtion (Shikine Islnd, 2000) 10. Snow cloud observtion (Niigt 2001) 11. DDX01/Dul Doppler (Knto Plin, 2001) 12. SZW01/Artificil snowfll experiment (Niigt, 2001) 13. MMX03 Rinfll observtion (Kngw, 2003 ~) 4 (blck: XDOP nd/or XPOL, red: MPX rdr) A1 Loctions nd themes of rdr observtion conducted from

14 Observtion of Rinfll by X-Bnd Multi-Prmeter Rdr Appendix Observtion sites A2 First rdr (1969). A3 Snowstorm reserch (X-DOP; 1988, Tsugru Plin in Aomori prefecture). A4 Snowstorm reserch - X-POI (1944, Otru, Hokkido). A5 Observtion of volcnic sh from Mt. Oym, Miyke Islnd - MP-X (October November 2000, Shikine Islnd, Tokyo). A6 Tropicl squll line observtion (X-DOP [left] nd X-POL [right]; , Drwin, Austrli). A7 Cloud nd precipittion process nd wind observtion (August - October 2001, Ksumigur Lkeside, Ibrki prefecture). A8 Artificil snowfll experiment - MP-X nd MP-K/W (December 2001, Shiozw, Niigt prefecture). 13

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16 Tropicl squll line observed in Drwin, Austrli Ntionl Reserch Institute for Erth Science nd Disster Prevention Tennodi, Tsukub, Ibrki Jpn Telephone / Fcsimile: MARCH 2005 design by grficom info@fncygrphics.com