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
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Topographic Change of the Summit Crater of the Asama Volcano during ,**. Eruption
Derived from Repeated Airborne Synthetic Aperture Radar (SAR) Measurements
Shoichi OKI῍, Makoto MURAKAMI῍῍, Nobuyuki WATANABE῍῍῍,Bokuro URABE῍῍῍ and Masanori MIYAWAKI῍῍῍῍
The Asama volcano (elevation ,/02 m), central Japan, erupted on September +, ,**.. Since then thickvolcanic fumes prevented monitoring of the topography on the summit crater ﬂoor by standard optical methods.
To detect geomorphic changes of the volcano, Airborne Synthetic Aperture Radar (AirSAR) measurements
including interferometry were repeatedly carried out on September +0, October ,,, December +/, ,**. and March+*, ,**/. The comparison of AirSAR result in September with a digital elevation model (DEM) by laser
proﬁling measurements in October ,**- revealed that a pancake shape lava mound (volume*.3+*0 m-) was
formed on the ﬂoor. The subsequent AirSAR measurement on October ,, indicated that the pancake shapemound had disappeared and a small pit hole was formed. The volume of ejecta amounted to ,.++*0 m-. The
AirSAR results in December ,**. and March ,**/ suggested that the shape of the crater ﬂoor stayed generally
unchanged during that time window. From these, we infer that lava extrusion during the ,**. Asama eruption
occurred within a short period around September and October.
Key words : Asama volcano, SAR, DEM, topography, volume of lava
+ῌ ῐ ῎ ῑ ῏ (,,/02 m) .abcdc3e";K8D5F f;"O ,* gh>!"#$%&'!(i.)j k8abcdcl(emBC5)nG)*+,-./01 2(3456789

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Ministry of Land, Infrastructure and Transport, ,ῌ+ῌ- Kasumigaseki, Chiyoda, Tokyo +**ῌ23+2, Japan.
 -*/ῌ*2++¡¢£¤¥ ¦ + &3 §3 3¨9©ª«,dc
Geography and Geodynamics Research Center, The
Geographical Survey Institute, +ῌKitasato, Tsukuba,
Ibaraki -*/ῌ*2++, Japan.
 -*/ῌ*2++¡¢£¤¥ ¦ + &3 §¬­

Topographic Department, The Geographical Survey
Institute, +-Kitasato, Tsukuba, Ibaraki -*/ῌ*2++,
Japan.
 +2-ῌ2/*+
'R¥ ®¯ +ῌ+*°X±²³´µ¶·¸¹º±²µ¶·¸»¼
NEC Aerospace Systems, Ltd., Defense and Aeronautic Systems Division, +st Engineering Department,+ῌ+* Nisshin-cho, Fuchu, Tokyo +2-ῌ2/*+, Japan.
Corresponding author : Makoto Murakami
e-mail : mccopy@gsi.go.jp

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Fig. +. A : Assembled airborne SAR equipments used for the repeated observation over the Asama volcano on
September +0, October ,, and December +/, ,**.. This radar is capable of interferometric measurements to
produce a precise Digital Elevation Model (DEM). B : The aircraft (Cessna ,*2) with onboard SAR
instruments mounted.

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l +.2 cmµ <¼01g<(D& ' CC' 8- @Fig. ,. Schematic illustration of airborne SAR measurements over a volcano. SAR is advantageous inmeasurements during night or through cloud, mist and volcanic plume. In addition, airborne SAR is more
ﬂexible about the observing conditions, such as ﬂight direction, o#-nadir angle and time of measurements
comparing with satellites.

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Table +.

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Speciﬁcations of repeated airborne SAR measurements over the Asama volcano during ,**. eruption.

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405

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T

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T)+,

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-.(R/0.ῌ,

1+2+,! B> S3T45U.

67V

89:W;<=>0- ,**- ?XNYNZBy

Fig. / # $ 1+2£ DEM j¤,**. ῒ +* ῏῍ῐῌ῎ῑ

1+¦o(

B`zT§¨__# A 3 NFte  +*  ,,  +,  +/ [P\]^(B @A B *./ m $,**/ ? -  +*  ? (Table +) © DEM C

5-  !'# y_ 5 DEM (` K% B-</0> 1+a2>#RD?5-e  -? fg

bcd Bh SAR (?iE
G?HA  

5

B> Fj1+

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NOKnP-EQ _  5RS>
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Fig. / #+*  ,, !

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a£x +.,¥+*0 m- 1-

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DEM B&hA

2 DEM j? +* akj Table , # , v DEM Walm
R ,ῌ. m nC `o> W p B`zC Btu Fig. . #T( 1+2>b

!

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-y'z

 +* 

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h>¤ _?

,**- ?cq DEM  3  +0  DEM r)-.ῌs.

- ¡? +,  +/  ¢H!

 c+,,=-£_`?¤¥>) F +* cq(R +*­+/ m $§?5B`z) ix) 5 DEM XNYNZ[P\]^( 1+

W> ,ῌ. m? 52N{K%

B

U ,**/ ? -  +*  cqx)  ²)h³-´®

?A µ¶·) +0.1 GHz Kuµ2: h¯xl7  ¸¹ (Table+) +, !j£_ B`z>&?- +,¶O-+,,@±³-·N{|am> 1+2j# 0/ m } #-?) 55 +,,-V'd77§¸,,-2* m ?)

)T   - ! > #RD

406  

Fig. -. Images around the summit of the Asama volcano derived from Airborne SAR measurements on September+0, ,**/. Monochrome images are mapped backscatter amplitude, whereas colored ones are interferograms
derived from single pass airborne SAR interferometry. The topographical map of the area is given in thecenter of the ﬁgure. Each image corresponds to data acquired from one of the ﬂight paths from . directions.
The distance between the ﬂight path and summit is , km. The other observation parameters are given in
Table +. One cycle of the color change in the interferogram corresponds to height di#erence of the topography by about +.1 m.

LM{¹º» PAST¼T (SAR) O %8y@¡ ,**. !"@|+@A E
Table ,. Di#erence between DEMs by single pathairborne SAR interferometry and laser proﬁler
measurement.

407

"V +* ' /m G 'D[lA @A#<3*+%& 5^  Bp] G

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(

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 "@1 ,**-

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

v BV gn}&W]

( ["@ =B  @A#<*+3P@A Q'& \w 9@=A

@5^X"V/! Bp>?@"@W +,    |/ 3 Vc/_`aTb5^XB Cm/   ! "  #$

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%&

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 

()* 

%+(, -. //   012345

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n}&WY o+- +*  ,, ) @A#/or$%+K. +* q"  3 04 / ;<" =%> DEM ?3 @A_`aTb5^%+ %*X(,  EZ  +* RT

=%>BCD 

3=F DEM GHI ( /[./ B0x@A# \$X

 DEM #J/&/IKu \$ j "V/0(4 \ 5^ /]"V/
/ῌ ῍

῎

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%& ,**. ! 3 "@PQRSTUT#

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cXIK // G}"@. YZ ,**. ! 3  +, ) +*  ,, ) +,  +/%${RSTUTWA =AKd E "V$%&'WX() - [O




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KxYqy Zz[O*{\7 |O}]#ῐ ῕ ῔ ῑCurlander, J. C. and McDonough, R. N. (+33+) Synthetic
Aperture Radar - systems and signal processing. John
Wiley & Sons, New York, +ῌ00.
Fujiwara, S., Nishimura, T., Murakami, M., Nakagawa,N., Tobita, M. and Rosen, P. A (,***) ,./-D surface
deformation of M0.+ earthquake near Mt Iwate detected by SAR interferometry. Geophys. Res. Lett., ,1, +.,,*.3ῌ,*/,.
^I_`a bc ~defg (,***) &qhij %k& 9Z&/l +, 5$m/(!n O? +0+ῌ+0,.
^I_`a defgbc ~o (,**+) hijpk%& bB% q No. 3/ +,+ῌ+,2.
Hasegawa, H., Sato, P. H., Iwasaki, J. and Yoshida, S.

(,**/) Continuous caldera changes in Miyakejima volcano after ,**+. Earth Planets Space (submitted).
rstuvtwxsI yzh@{ |  }~    EP  g l ~| (,**.) $ ,**. 5 3 W:<:. 9Z/ ,**. 5$mz? +21.
u{` (,**/) ,**. 5 3 W\ $G) %r/d/ ,**/ 5z? V*//pῌ**+.
F (,**/a) 9ZG  -  ,1*ῌ,22.
F (,**/b) G) l +0 5 0 W $ p 0.
F (,**/c) G) l +0 5 1 W $ p 0.
Kobayashi, T., Umehara, T., Satake, M., Nadai, A.,
Uratsuka, U., Manabe, M., Masuko, H., Shimada, M.,
Shinohara, H., Tozuka, H. and Miyawaki, M. (,***)
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+3/..
Massonnet, M., Briole, P. and Arnaud, A. (+33/) Deﬂationof Mount Etna monitored by spaceborne radar interferometry, Nature, -1/, /01ῌ/1*/.
Sa~   o J{t7v`~ ~~¡ (,**,) 9: ; SAR  q  h i j  %  DEM   SARWorkshop ,**, q¢ -,ῌ-/.
£ K (,**-) $G)|¤x E¥/%`aLq 12 . ,2-ῌ.0-.
Mouginis-Mark, P. J. and Garbeil, H. (+33-) Digital topography of volcanoes from radar interferometry : anexample from Mt. Vesuvius, Italy. Bull. Volcanol., //,/00ῌ/1*.
a  (,**/) GPS 0&UV ¦# $§¨§©ªg  /* -.1ῌ-0+.
Pritchard, M. E. and Simons, M. (,**,) A satellite geodetic
survey of large-scale deformation of volcanic centres in
the central Andes. Nature, .+2, +01ῌ+1+.
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