GPS-TEC : a new versatile sensor of the Earth

Transcription

1 2006 Jun. VI Hotine-Marussi Symp. Theor. Computational Geodesy GPS-TEC : a new versatile sensor of the Earth Kosuke Heki (Hokkaido Univ., Sapporo, Japan)

2 Ionospheric disturbances can be measured with GPS TEC (total electron content) Unit: # electron/m 2 ionosphere To remove ionosphere L3=f 12 /(f 12 -f 22 ) L1 - f 22 /(f 12 -f 22 ) L2 To isolate ionosphere L4=L1-L2 L2 Line-of-sight Differential delay L4=L1-L2

3 Short-term term variation of TEC is useful for Ionospheric sciences Traveling Ionospheric Disturbance (TID) (Saito et al., 2002) Sudden Increase of TEC (SITEC) by Solar flares (Zhang & Xiao, 2005) TEC decrease by Solar eclipses (Afraimovich et al., 2002) Urumqi Medium-scale TID on Nov.14, 2005

4 Short-term term variation of TEC provides unique occurs information also by Various phenomena of the Solid Earth Coseismic uplift of earthquakes (Heki et al., JGR, accepted) Passage of Rayleigh waves (Ducic et al., 2003) Tsunami (Artru et al., 2005) Volcanic explosion (Heki, GRL, in revision) and human activities Surface explosion (Calais et al., 1998) Rocket ascent (Calais & Minster, 1997) Sat.13 Heki & Ping, EPSL, 2005

5 Coseismic uplift Acoustic They Waves disturb Associated the ionosphere with Earthquakes Compressive atmospheric pulse Positive initial TEC change Acoustic wave (direct) Acoustic wave (Surface wave origin)

6 Best recorded Coseismic Ionospheric Disturbance (CID): 2003 Tokachi-Oki Eq. A B C D E Negative initial TEC change for normal faulting Heki and Ping (2005)

7 ~ 1.0 km/sec Sound velocity within ionosphere Sat.24

8 Observed vs Synthesized TEC change curves Sat. 13 Sat. 24 Sat.13 Low incidence angle Large TEC disturbance Source function Sat.24 High incidence angle Small TEC disturbance

9 2004 Sumatra (Mw=9.2) 2004 Sumatra 2003 Tokachi (Mw=8.0) Sat Tokachi PHKT Sat.20 Fault parameters after Tanioka et al. (2004) Mw=9.2 Mw=8.0

10 Atmospheric filtering/resonance of acoustic waves Tokachi Eq. ~4.5 min. resonance (Tahira, 1995) Attenuated Sumatra Eq. Gravity wave window Georges (1968)

11 CHMI/CMU SIS2 ~1.0 km/sec BNKK/KMI CPN PHKT ~1.0 km/sec SAMP Estimate slip slip distribution from waveforms PDNG

12 Rupture propagation and sequential excitation of sound waves #5 ~0.9 km/sec TEC Sat. 1 #4 #3 time ~2.5 km/sec #2 #1 TEC Sat. 2 Contribution from each point source ~1.0 km/sec time

13 Relative amplitudes of point sources Contribution from point sources of unit strength Contribution from point sources of real strength #1 #2 #3 #4 #5 #6 #7 #8 #2 #1 x Strength = #3 #4 #5 #6 #7 #8 Scaling the Total CID synth. obs. Proportional to average uplift

14 Obs. Synth. 2.5 km/sec Sat.23 (discrete arrival) 13 SIP 23 Sat.13 (simultaneous arrival) SAMP

15 Synth. Obs. Sat.13 (contribution from northern sources only) km/sec PHKT 13 PHKT Sat.20 (contribution from southern sources only) 20

16 relative amplitudes arrival times waveforms 2.5 km/sec

17 GPS-TEC for seismology Sensitive to medium-slow rupture (~4.5 min., bridges the gap between seismomter and tsunami) Useful for early warning of tsunami (TEC disturbance appears ~12 min. after the quake, as early as the tsunami attack at Banda Aceh) L4 is geometry-free!

18 Ionospheric Disturbances Associated with Eruptions

19 time Vulcanian ~11:02 UT Sep N-shaped source function (~0.16 TECU peak-to-peak, period ~1.25 min.)

20 Past data enable calibration 1.5 Kt blast ~0.03 TECU perturbation Calais, E. et al., Ionospheric signature of surface mine blasts from Global Positioning System measurements, Geophys. J. Int., 132, , 1998.

21 Comparison between the two cases Total energy Amplitude Period Velocity Asama eruption 43? Kt 0.16 TECU 1.25 minutes 1.1 km/sec Black thunder coal mine blast 1.5 Kt 0.03 TECU 4~5 minutes 1.2 km/sec Latitude ~35N ~43N Azimuth Background Incidence ang. South ~10 TECU shallow South ~20 TECU deep

22 Disturbance Apparent Empirical 2004/Sep/01 velocity estimation ~0.16 TECU Asama of the of in disturbance the total energy amplitude eruption disturbed and was ~1.25 ~1.1 was ionosphere min. km/sec ~43 Kt in period (comparison with the 1.5 Kt mine blast)

23 All you need to start GPS-TEC Read GPS data file and create TEC time series No need to calculate receiver position, satellite position, ERP, atmospheric delays Calculate apparent position of GPS satellites from ephemerides Broadcast orbits will do Software: Easy (suitable for undergraduates)

24 GPS-TEC with dense array opens a new era Ionospheric disturbances provides unique information on Not only solar-terrestrial study But also seismology and volcanology Future new targets:? Earthquake precursor (?) - abnormal VHF propagation Bolides (??) complement infrasound observations Thank you for your attention