,**3 2,0,**3 +, +0. GPS Baseline Solutions with Tropospheric Correction by Using the JMA Numerical Weather Model for Monitoring Volcanoes

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1 // (,*+*) + + +, GPS,,**3 2,0,**3 +, +0 GPS Baseline Solutions with Tropospheric Correction by Using the JMA Numerical Weather Model for Monitoring Volcanoes, Akimichi T AKAGI, Keiichi FUKUIand Yoshinori SHOJI Japan Meteorological Agency (JMA) has installed and is operating GPS networks around major active volcanoes since,*** in order to monitor volcanic ground deformation. At present,,, volcanoes are under continuous observation using about +** GPS stations. At most observation points single-frequency receivers are adopted in consideration of power saving and mobility in rugged environments. GPS baseline solutions include errors due to tropospheric delays which are inhomogeneous in the actual atmosphere. Generally, computation of baseline solutions is done by using a simple atmospheric model assuming horizontal homogeneity. But if the adopted model is not consistent with the actual atmosphere, tropospheric delays cannot be accurately estimated, resulting in poor position estimates. Especially with regard to the volcano observation, the errors in the vertical component of baselines become large according to the large troposphere errors. In the case of baseline solutions between receivers with large vertical di# erence, the time variation of the vertical length is superposed by seasonal noise caused by spatial and temporal variations of refractive index of the atmosphere. For accurate monitoring of volcanic activities, more precise positioning in the vertical component is desirable, which should be realized by incorporating more accurate atmospheric model into the analysis procedure. For this purpose, an improved analysis process was developed, based on the JMA s operational meso-scale numerical weather analysis (MANAL). The MANAL is applied to daily meso-scale numerical weather prediction as initial field. Generally in the di# erential analysis process of positioning, zenith tropospheric delay (ZTD) is estimated by least-squares method together with the positioning. In this case, initial value of ZTD is given from a simple atmosphere model. In our approach, ZTD between both receiver sites is calculated from MANAL, and then the conventional analysis process is done fixing ZTD between sites. In calculation, analysis software package Bernese Ver. /*. was used, while a part of the program was personally modified. This correction strategy using MANAL was applied to the baseline solutions at Asamayama volcano, where ground deformation has been observed associated with the eruption activity from,**2 to,**3. Consequently we could approximately eliminate the vertical seasonal noise at a baseline whose vertical di# erence reaches to +./ km. This approach is quite convenient and e# ective for GPS observation at local and steep areas such as volcanoes. Key words : GPS baseline solution, tropospheric correction, JMA numerical weather model, Asamayama volcano -*/ **/, + + Technology - Japan. -*/ **/, + + Seismology and Volcanology Research Department, Meteorological Research Institute, ++ Nagamine, Forecast Research Department, Meteorological Re- Tsukuba, Ibaraki, -*/ **/, Japan. search Institute, + + Nagamine, Tsukuba, Ibaraki, : +** 23/3 -,, -*/ **/, Japan. Present address: Earthquake and Disaster-Reduction Corresponding author: Akimichi Takagi Research Division, Research and Development Bureau, atakagi@mext.go.jp Ministry of Education, Culture, Sports, Science and

2 2 +,**1 GPS - +/,*** GPS GPS EU Galileo, GLONASS,**/,, +** GPS GNSS GPS +,,+ GPS GPS GPS,/02 m - GPS - GPS,**0,.-- m GPS M. (Fig. + ) + -*, GPS MG,+** GPS MG,+/-,**0.,0,**2 / +/ 1/* ++3,**2 2 GPS, GPS conventional analysis Hobiger et al. (,**2) - GPS Fig. +. Distribution of the GPS receiver sites around Asamayama volcano. Solid circles and squares are GPS stations installed by MRI and JMA, - respectively. A temporary station M. near the summit was newly installed for this study.

3 GPS 3 Table +. Description of GPS stations around Asamayama volcano. GPS + KWS +**0 m +.,1 m 1*3, m Table +, GPS KWS, + + L + ( +/1/.., MHz) + L+,, (GSM) GSM Fig.,. Horizontal distribution of MANAL s grid points (MSM) around Asamayama volcano. Open diamonds show +* km-grid MANAL. Solid squares show doublefrequency GPS stations which were used for the ionospheric correction. A square box over Mt. Asamayama indicates the area of GPS observation in Fig. +. MSM (MANAL) (GPV) GPS +* km,**,,**3.,**3 / km,**3 MANAL GPV MANAL +331 MANAL

4 4 Fig. -. Schematic figures showing zenith tropospheric delays (ZTD) of two GPS-receiver sites. (a) In the case of small vertical di# erence between two sites, atmosphere equally influences both ZTDs. (b) In the case of large vertical di# erence between two sites, the part of atmospheric between Receiver+ and Receiver, influences only ZTD of the lower sites (ZTD ). + Ver /.* (Dach et al.,,**1) Bernese Fortran KWS- + M. +./ km ++ Fig., MANAL -*,, KWS,- MANAL, m GPS GPS M. GPS Onset Computer Corporation (ZTD) (Fig. -a) HOBO Weather Station MR Receiver+ 0*** +, GPS Receiver,,**0 3,+,**2 Receiver+ Receiver, / +/ 0*,,*, + +, (Fig. -a) + (Fig. -b) - GPS Bernese

5 Receiver+ Receiver, GPS 5 Saastamoinen ( +31-) (m) Bauers íma ( +32-) SAAS +, p T e *.**,,11 +,//, p **/. ebtan z dr cos z T () + p, T, e (hpa) (K) (hpa) z (radian) B dr B Fig... Schematic figure showing how to estimate ZTD. dr calculated from MANAL. ZTD and position at p T e receiver sites are estimated fixing ZTD +, -. Berg ( +3.2) i i () + ZTD ZTD () - () / MANAL GPV +, N+ 0 + j + j hj.. j+ T+ j T+ j * * +, +, ZTD ZTD ZTD i i fix +, +, Fig.. Receiver+ Receiver, i i * Receiver, ZTD MANAL GPV p, T, e GPS () +, * ZTD ZTD p T e, SAAS,,, Receiver+ Receiver, GPS ZTD MANAL GPV +, GPS MG,+,* Hopfield ( +303 ) Essen and Froome ( +3/+ ), GPS MAP ( *) ( l) ( t) p e +* , 30, / e+ j * (-), T N Receiver+ Receiver, p T e Receiver+ 2. j * Receiver+ ZTD ZTD ZTD ZTD + j + j + j + j i i ZTD +, - (di# erence between ZTD+ and ZTD, ) is + GPS GPS h Receiver+ j-+ j j ZTD ZTD +,,,, +, () / (), (Hofmann-Wellenhof et al.,,**.) +..+ ZTD ().,

6 6 Fig. /. Temporal changes of ZTD between KWS and M., evaluated by the conventional analysis (a), by using MANAL (b), by using measured weather data (c), and those refer to temporal change by the conventional analysis., ZTD Fig. / Fig. 0a-b,**0,**2 KWS M. ZTD + Fig. 0d-e Fig. / a ZTD, Fig. / b MANAL GPV. cm ZTD Fig. / c, (Fig. 0d) ZTD (Fig. 0e) Fig. / d MANAL (Fig. 0a-b) GPV ZTD, cm.-,, ZTD +. cm, () - (/) (Fig. 0f) MANAL GPV,**1, - cm. cm., (Fig. 0d) +,. MANAL (Fig. 0e) GPS + ZTD, Saastamoinen ( +31-) (), ZTD () - ZTD + *, +, Fig. 0 KWS M.,**, MANAL

7 GPS 7 Fig. 0. Time series of baseline length (a-c) and height (d-f) of M. refer to KWS. (a) and (d) are calculated with the conventional analysis. (b) and (e) are calculated with this study method using MANAL. (c) and (f) are calculated using measured weather data. In the case of using MANAL, vertical seasonal noise could be approximately eliminated (e). GPS, +.., +, + GPS +, GPS, / GPS - cm, cm,, 30*0+. 3/- + m TAN,+3* m (Fig. 1c) 30*0+../ TAN,,. 202* m +,-1 m,**1. +,**3 -, MANAL -, Fig. 1 a,,. L+ + Fig. 1b +,

8 8 Fig. 1. Comparison of seasonal noise s elimination from vertical positioning between doublefrequency analysis (a) and single-frequency analysis (b). (c) Distribution of GPS receivers around Mt. Ontakesan. Positioning of TAN refer to 30*0+. was calculated.,. +, MANAL GPS -* GPS MANAL - ZTD + + cm, cm MANAL / M. Fig. 2. Comparison of seasonal noise s elimination from - - GPS vertical positioning between,.-hours analysis (a) KWS and +, -hours analysis (b) by using MANAL. M ,1 m refer to KWS.,**0 /,**3 1 Fig. 3 0Fig. 2 M. G ++02 m M. +, 0 TAK 31+ m GPS,**2 2 +,,**3, (Fig. 2 b),. Fig. 2a, Fig. 0e KWS,**2 2,**3,

9 GPS 9 Fig. 3. Time series of height of all stations refer to KWS around Asamayama volcano from,**0 to,**3. (a) Conventional analysis. (b) By the method of this study using MANAL. Those of all stations could be approximately eliminated the vertical seasonal noise, especially G and TAK where are high.,**/ Fig. 3a G, TAK,**2 0,**3 + - (Fig. 3a) (Mogi, +3/2) (Fig. +* b) MaGCAP-V,**/,. 1 km 0 - +** m *. + +* m 1. - km - 0 km 0 - / +0..* +* m 0 -,3. km -*. +* m (Fig. +*,**2 0,**3 + a),**.

10 10 Fig. +*. Estimation of the inflation pressure source of Asamayama volcano by GPS observation from June,,**2 to January,,**3. (a) Result estimated by --D component of displacement with the method of this study using MANAL. (b) Result estimated by --D displacement with the conventional analysis. (c) Result estimated by only horizontal component of displacement with the conventional analysis. Fig. 3a TAK GPS G + GPS / Fig. +* c,3. km +,. km - *2. km *. +* m * m * +* m,

11 GPS ,.. +* m, / GPS GPS GPS -*,. +, MANAL - GPS GPS GPS MANAL - GPS - 0 MANAL (MSM),**0-B-*0 0 (,**/),**.,**/ MANAL /* /1/ /2.. Bauer síma, I. ( +32-) NAVSTAR/Global Positioning System (GPS), II., Mitteilungen der Satelliten-Beobachtungsstation Zimmerwald. +*, Astronomical Institute, Univer- sity of Berne., GPS + Berg, H. ( +3.2) Verlag, Bonn. Allgemeine Meteorologie, Dümmler s MANAL Dach R., U. Hugentobler, P. Fridez and M. Meindl ed. MANAL (,**1) Bernese GPS Software Version /*.. Astronomical Institute of University of Berne, 0+, p. GPS Essen, L. and K.D. Froome ( +3/+ ) The refractive indices and dielectric constants of air and its principal constituents,**2 at,.*** Mc/s. Proceedings of Physical Society, 0. (B), 20, 21/. 0-0km -km - +* m

12 12 (,**/) (,**,). (),.2-1 /3. V*// P- *--. ( +331) Hobiger, T., Ichikawa, R., Takasu, T., Koyama, Y. and.- +00pp. Kondo, T. (,**2) Ray-traced troposphere slant delays Mogi, K. ( +3/2) Relations between the eruptions of varifor precise point positioning. Earth Planets Space, 0*, e+ ous volcanoes and the deformations of the ground sure.. faces around them. Bull. Earthq. Res. Inst., -0, (,**1) Saastamoinen. J. ( +31-) Contribution to the theory of atmospheric refraction. Bulletin Géodésique, +*1, GEONET +*2 P- 2. (,**3) GPS : GPS Hofmann-Wellenhof, B., Lichtenegger, H. and Collins, J. (,**.) Global Positioning System : theory and practice, // +1-2 / th, rev. ed., Springer Wien New York, 33 +*/. (,**,) GPS (,**3).,03p.,+ (,**/) 0/ 1+. /* S1 S +2. Hopfield, H.S. ( +303) Two-quadratic tropospheric refractivity profile for correcting satellite data. J. Geophys. Res., 1.,