津波探知レーダの研究状況調査

平成23年8月26日
電波航法研究会渡辺康夫

講演内容
1. はじめに
2. 2004年12月26日のスマトラ沖津波と衛星搭載電波高度計
3. 2011年3月11日の東北太平洋沖地震の津波とHFレーダ
4. おわりに発表の背景と目的
2004年12月26日，スマトラ・アンダマン地震発生の約２時間後，海洋観測衛星Jason-1とTOPEX/Poseidonがインド洋を伝播中の津波の第一波の上空を偶然通過し，電波高度計によってdeep oceanにおける津波波高のプロファイル及びレーダ後方散乱強度を初めて明瞭に計測した．
2011年3月11日，東北太平洋沖地震の約22時間後，津波を待ち受けていたチリのHFレーダが沿岸に接近する津波のocean surface currentを初めて計測した．
本発表では注目すべきこの二件を中心に，関連研究を含めて文献をサーベイした結果を報告する．

Table 1a Instrument Characteristics ofJason-1 altimeter (Poseidon-2)
Pulse repetition freq.
Pulse duration
Pulse compression ratio
Integration time
Center frequency
Bandwidth
RF output power
Antenna gain
Tx pulse mode (nominal)

2060Hz±10%105.6μs
33600
50ms
Ku-bandC-band13.575GHz
5.3GHz320MHz320/100MHz
38.3dBm
43.0dBm
42.2dB
32.3dB
Interlace: 3Ku 1C 3Ku(G. Carayon et al., IGARSS-02, 2002)

Table 1b Example of measurement
performances
In flight
data

Groundtest

Mean SWH

2.18m

2.14m

SWH 1s noise

14.7cm13.1cmKu range 1s noise

1.7cm

2 cm

C range 1s noise

3.6cm5.3cm

Dual freq. range
1s noise

1.8cm

2 cm

Requirement
20cm

2.5cm

(G. Carayon et al., IGARSS-02, vol.2, 774-776, 2002)

Fig. 1. 2004 Indian Ocean tsunami
propagation

Measurement by Jason-1(NOAA News Online, 10 January
2005: 2004 tsunami propagation)

Fig. 2

Sea surface heightanomalies by Jason-1
Cycle 109
(26 Dec. 2004)
Ave. of cycles 108, 110

Cycle 109 withthe ave. subtracted(J. Gower, Int. J. Remote Sensing, vol.28, Nos.13-14, 2829-2913, July 2007)

Fig. 3 Sea surface height anomalies: themeasured and the theory for Jason-1
Corrected sea surface
height on cycle 109
Model sine wave ofwavelength 580km andamplitude 0.6m

Topex/Poseidon data
as for (a)(J. Gower, Int. J. Remote Sensing, vol.28, Nos.13-14, 2829-2913, July 2007)

Table 2 Six observations by thethree altimeters
Time UT

Epicenter 00:58:53

Lat.

Lon.

Time Distance Speed Av. Depth

(º)

(º)

(s)

3.2

94.2

(km)

(km/h)(m)
1530

Jason S

02:53:51 -4.56 84.12 6900

1415

7394300

Jason N

02:59:53 13.15 90.56 7260

1240

615

2975

Topex S 03:00:34 -4.06 82.88 7300

1495

738

4280

Topex N 03:06:26 13.15 89.13 7650

1180

554

2415

Envisat S 04:19:24 -17.01 82.57 12030

2590

7744715

Envisat N 04:09:18 18.93 90.65 11425

1795

565

2510

(J. Gower, Int. J. Remote Sensing, vol.28, Nos.13-14, 2829-2913), July 2007)

Fig. 4Multisatellite Time-Spatial
Interpolation

Proposed method

SLAref (φ,θ,t) = ∑(wi・SLAobs,i)/ ∑wi∑wi = exp[-(ri/R)2 –(ti/T)2]
htsunami (φ,θ,t) = SLAobs(φ,θ,t) - SLAref (φ,θ,t)(1)(2)(3)

Conventional method

htsunami (φ,θ,t) = SLAobs(φ,θ,t) - SLAobs(φ,θ,t-c)(4)

SLAref(φ,θ,t): the defined reference height at the latitude φ, longitude
θ, and date of a tsunami searching point.
SLAobs: an anomaly in an observed sea surface height.
htsunami: the tsunami height.
ri = the distance between the location of the ith datum and the tsunami
searching point.
ti = time difference of observations between a tsunami observation point(t) and the ith datum.
R, T = scale parameters, fixed at R = 45km and T = 10days.
(Y. Hayashi, J. Geophysical Research, vol. 113, C01001, 1/9-9/9, 2008)

Fig. 5 Profile of tsunami height extracted from
Jason-1 data by Multisatellite Time-Spatial
Interpolation method
SLA: sea level anomaly
RMSE: root mean square residualerrors(Y. Hayashi, J. GeophysicalResearch, vol. 113, C01001, 1/9-9/9,2008)

Table 3 Residual errors and number of valid
points in defined tsunami heightRMS residual error, cmSatellite

No. valid points

No.
sampl.
Hayashi Others pts.

HayashiOthers

Jason-1

4.3

6.6

412

356

482

Topex/
Poseidon

4.9

6.5

285

88490

Envisat

4.4

9.3

659

642

702

GFO

4.2

8.0

938

923

938

4.9

10.0

971

928

996

(Track 208)

GFO
(Track 210)

(Excerpt: Y. Hayashi, J. Geophysical Research, vol. 113, C01001, 2008)

Fig. 6 Tsunami shadows
A conceptual representation of“tsunami shadows” and their
theoretically predicted relation to thetsunami-induced wind velocity
perturbations. “Tsunami shadows”(hatched) are parallel to the tsunami
wave front and occur in between thetsunami troughs and crests where
the wind perturbation is maximal.
Perturbed (solid lines) andunperturbed (dotted lines) windvelocity is shown as a function ofheight above the ocean surface.

(O. A. Godin, J. Geophysical Research, vol. 109, C05002, 2004)

Fig. 7 Jason-1 data for pass 129
from 6º to 2ºS
Sea surface height(1) Obtained days before(2) coincident with cycle 109(3) 10days after.

Ku-band radar backscattering strength

C-band radar backscattering strength(O. A. Godin et al., NaturalHazards and Earth SystemSciences, vol. 9, 1135-1147,2009)

Fig. 8 A stylized shore line (bold) at the top
and offshore bathymetry contours
landland(a) refract swell energy and wind waves(entering the diagram along ray paths
from bottom) onto the headlands andaway from the bays

sealandlandsea(b) direct the momentum in a tsunami
along the bathymetry contours to givethe most intense effects in the bays
(M. L. Heron et al., International Journal of
Remote Sensing, vol. 29, No. 21, 6347-6359,
10 Nov. 2008)

Fig. 9 Model calculation for the impact of the 26
Dec. 2004 tsunami on the Seychelles(a) the bathymetry around the Seychelles shows a platform in otherwise deep
water,(b) the large scale amplification of sea surface height (contours) and surface
current (vectors) when the first tsunami wave encounters the edge of thecontinental shelf, and(c) a section of the shelf-edge (corresponding to the box in (a) and (b)), whichshows the area that could be monitored by a HF ocean radar.
(M. L. Heron et al., Int. J. Remote Sensing, vol. 29, No. 21, 6347-6359, 10 Nov. 2008)

Fig. 10 German Indonesian Tsunami
Early Warning System (GITEWS)

http://www.gitews.de/Fig. 11 The HF radar WERA (WellenRadar) system installation(a) the transmitting array(b) the receiving array(A. Dzvonkovskaya et al., European Journal of Navigation, vol. 7, No. 2, 17-23, 1 Aug. 2009)

Fig. 12 Example of measured rangeDoppler power spectrum(A. Dzvonkovskaya et al.,European Journal of Navigation, vol. 7, No. 2, 17-23, 1 Aug. 2009)

Fig. 13 Simulated tsunami-induced current
velocity by HAMSOMHAMSOM:
Hamburg
Shelf OceanModel(A. Dzvonkovskayaet al.,EuropeanJournal ofNavigation, vol. 7,No. 2, 17-23, 1 Aug.
2009)

Fig. 14 Measured spectrum

without tsunami.

superimposed with tsunami currents(19min after the earthquake)(A. Dzvonkovskaya et al.,European Journal of Navigation, vol. 7, No. 2, 17-23, 1 Aug. 2009)

Fig. 15 Map of radial ocean surface current
velocity of Fig. 13(A. Dzvonkovskaya et al.,European Journal of Navigation, vol. 7, No. 2, 17-23, 1 Aug. 2009)

Fig. 16

Japan (East Coast of Honshu)
tsunami, March 11, 2011

(NOAA Center for Tsunami Research)

http://nctr.pmel.noaa.gov/

http://www.helzel.com/

Fig. 17 WERA ocean radar system atRumena, Chile
The system operates
at 22MHz andconsists of a shortarray of 8 antennas
that receives thebackscattered signal.

http://www.helzel.com/

Fig. 18
Current
velocities asfunction of timeand range

Tide gaugemeasurement at50km.

Barrick, Lipa等の東北太平洋沖津波探知の研究発表
1 Remote Sensing, 2011, 3, 1663-1679
Belinda Lipa, Donald Barrick, Sei-Ichi Satoh, YoichiIshikawa, Toshiyuki Awaji, John Largier, and NewellGarfield,“Japan tsunami current flows observed by HF radars ontwo continents.”
2 IEEE Ocean-2011, September Hawaii.
Donald Barrick and Belinda Lipa,“Japan tsunami detected by HF radars on two continents.”

おわりに2004年 マイクロ波帯電波高度計がdeep oceanの津波を明瞭に探知 波高のプロファイルとtsunami shadows2011年 HFレーダがcoastの津波を明瞭に探知
surface currentのDoppler signature
レーダは津波の研究及び早期探知警戒のための有力なツール
地球物理学や海洋工学等の科学技術知識とのシナジー
今後の期待
中小の津波, 様々な気象海象下で有効なレーダ
未開拓のsignature