Real-time high-rate GNSS techniques for earthquake monitoring and early warning

Transcription

1 Real-time high-rate GNSS technique for earthquake monitoring and early warning vorgelegt von Dipl.-Ing. Xingxing Li au Hubei, China Von der Fakultät VI Planen Bauen Umwelt der Technichen Univerität Berlin zur Erlangung de akademichen Grade Doktor der Ingenieurwienchaften - Dr. Ing. - genehmigte Diertation Promotionauchu: Voritzender: Prof. Dr. Frank Flechtner Gutachterin: Prof. Dr. Harald Schuh Gutachterin: Prof. Dr. Ur Hugentobler Gutachterin: Dr. Maorong Ge Tag der wienchaftlichen Auprache: 14. July 2015 Berlin 2015

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3 Abtract In recent time increaing number of high-rate GNSS tation have been intalled around the world and et-up to provide data in real-time. Thee network provide a great opportunity to quickly capture urface diplacement, which make them important a potential contituent of earthquake/tunami monitoring and warning ytem. The appropriate GPS real-time data analyi with ufficient accuracy for thi purpoe i a main focu of the current GNSS reearch. The objective of thi thei i to develop high-preciion GNSS algorithm for better eimological application. The core reearch and the contribution of thi thei are ummarized a following: With the availability of real-time high-rate GNSS obervation and precie atellite orbit and clock product, the interet in the real-time Precie Point Poitioning (PPP) technique ha greatly increaed to contruct diplacement waveform and to invert for ource parameter of earthquake in real time. Furthermore, PPP ambiguity reolution approache, developed in the recent year, overcome the accuracy limitation of the tandard PPP float olution and achieve comparable accuracy with relative poitioning. In thi thei, we introduce the real-time PPP ervice ytem and the key technique for real-time PPP ambiguity reolution. We ae the performance of the ambiguity-fixed PPP in real-time cenario and confirm that poitioning accuracy in term of root mean quare (RMS) of 1.0~1.5 cm can be achieved in horizontal component. For the 2011 Tohoku-Oki (Japan) and the 2010 El Mayor-Cucapah (Mexico) earthquake, the diplacement waveform, etimated from ambiguity-fixed PPP and thoe provided by the accelerometer intrumentation are conitent in the dynamic component within few centimeter. The PPP fixed olution not only can improve the accuracy of coeimic diplacement, but alo provide a reliable recovery of earthquake magnitude and of the fault lip ditribution in real time. We propoe an augmented point poitioning method for GPS baed hazard monitoring, which can achieve fat or even intantaneou precie poitioning without relying on data of a pecific reference tation. The propoed method overcome the limitation of the currently motly ued GPS proceing approache of relative poitioning and global precie point poitioning. The advantage of the propoed approach are demontrated by uing GPS data, which wa recorded during the 2011 Tohoku-Oki earthquake in Japan. We propoe a new approach to quickly capture coeimic diplacement with a ingle GNSS receiver in real-time. The new approach can overcome the convergence problem of precie point poitioning (PPP), and alo avoid the integration proce of the variometric - iii -

4 approach. Uing the reult of the 2011 Tohoku-Oki earthquake, it i demontrated that the propoed method can provide accurate diplacement waveform and permanent coeimic offet at an accuracy of few centimeter, and can alo reliably recover the moment magnitude and fault lip ditribution. We invetigate three current exiting ingle-receiver approache for real-time GNSS eimology, comparing their obervation model for equivalence and aeing the impact of main error component. We propoe ome refinement to the variometric approach and epecially conider compenating the geometry error component by uing the accurate initial coordinate before the earthquake to eliminate the drift trend in the integrated coeimic diplacement. We propoe an approach for tightly integrating GPS and trong motion data on raw obervation level to increae the quality of the derived diplacement. The performance of the propoed approach i demontrated uing 5 Hz high-rate GPS and 200 Hz trong motion data collected during the El Mayor-Cucapah earthquake (Mw 7.2, 4 April, 2010) in Baja California, Mexico. The new approach not only take advantage of both GPS and trong motion enor, but alo improve the reliability of the diplacement by enhancing GPS integer-cycle phae ambiguity reolution, which i very critical for deriving diplacement with highet quality. We alo explore the ue of collocated GPS and eimic enor for earthquake monitoring and early warning. The GPS and eimic data collected during the 2011 Tohoku-Oki (Japan) and the 2010 El Mayor-Cucapah (Mexico) earthquake are analyzed by uing a tightly-coupled integration. The performance of the integrated reult are validated by both time and frequency domain analyi. We detect the P-wave arrival and oberve mall-cale feature of the movement from the integrated reult and locate the epicenter. Meanwhile, permanent offet are extracted from the integrated diplacement highly accurately and ued for reliable fault lip inverion and magnitude etimation. Keyword: High-rate GNSS; GNSS Seimology; Real-time GNSS; Precie Point Poitioning; PPP Ambiguity Reolution; Coeimic Diplacement; Fault Slip Inverion; Geohazard monitoring; Relative Poitioning; Dene Monitoring Network; Augmented PPP; Temporal Point Poitioning; Variometric approach; Seimic Senor; Tightly-integrated Filter; Integrated Diplacement; Earthquake Monitoring; Earthquake Early Warning. - iv -

5 Table of Content Abtract... iii Table of Content... v Lit of Abbreviation... vii Lit of Related Publication... ix 1 Introduction High-rate GNSS eimology uing real-time PPP with ambiguity reolution Introduction Real-time PPP ytem and algorithm Real-time PPP ervice ytem Obervation Model Real-time precie point poitioning Real-time etimation of the uncalibrated phae delay Ambiguity reolution for precie point poitioning Accuracy aement in real-time cenario Application to the 2011 Tohoku-Oki earthquake GPS data and analyi Comparing GPS and eimic waveform Fault lip inverion Application to the 2010 E1 Mayor-Cucapah earthquake GPS data and analyi Comparing GPS and eimic waveform Fault lip inverion Concluion Augmented PPP for eimological application uing dene GNSS network Introduction Augmented PPP approach Application of augmented PPP approach and reult Concluion Temporal point poitioning approach for GNSS eimology uing a ingle receiver Introduction Temporal point poitioning approach Application of TPP approach and reult Single-receiver approache for real-time GNSS eimology v -

6 4.4.1 Comparion of analyi method Error analyi and preciion validation Application to the 2011 Tohoku-Oki earthquake Concluion Tightly-integrated proceing of raw GNSS and accelerometer data Introduction Overview of combining GPS and accelerometer data The tightly-integrated algorithm Reult Comparion of GPS, eimic and integrated waveform Detection of P-wave arrival Extraction of permanent offet and fault lip inverion Concluion Concluion and outlook Reference vi -

7 Lit of Abbreviation AC ARP BDS BKG C/A CDDIS CODE CORS DCB DD DF DFG DOD ECMWF ESA EU EEW Galileo GEO GFZ GIM GLONASS GLOT GMF GNSS GPS GPST GSI IAR IGR IGS IGSO Analyi Center Antenna Reference Point the Chinee BeiDou navigation Satellite Sytem Federal Agency for Cartography and Geodey, Germany Coare/Acquiition code Crutal Dynamic Data Information Sytem Centre of Orbit Determination in Europe Continuouly Operating Reference Station Differential Code Biae Double Difference Dual-Frequency Deutche Forchunggemeinchaft (i.e. German Reearch Foundation) the U.S. Department of Defene European Centre for Medium-Range Weather Forecat European Space Agency European Union Earthquake Early Warning the European Union atellite navigation ytem Satellite in Geotationary Orbit Helmholtz-Centre Potdam-GFZ German Reearch Centre for Geocience Global Ionopheric Map the Ruian GLObal Navigation Satellite Sytem GLONASS time Global Mapping Function Global Navigation Satellite Sytem Global Poitioning Sytem GPS Time Geopatial Information Authority Integer Ambiguity Reolution IGS Rapid orbit International GNSS Service Inclined Geoynchronou Orbit - vii -

8 IGU IGS Ultra-rapid orbit IOV In-Orbit Validation IPP Ionopheric Pierce Point ITRF International Terretrial Reference Frame LC Ionophere-free Linear Combination LEO Low Earth Orbit MEO Medium altitude Earth Orbit MET Meteorology MW_WL MW Widelane Linear Combination NASA National Aeronautic and Space Adminitration NRTK Network-baed Real Time Kinematic poitioning OMC Obervation Minu Computation PCO Phae Centre Offet PCV Phae Centre Variation PNT Poitioning, Navigation and Timing PPP Precie Point Poitioning PPP-RA Precie Point Poitioning Regional Augmentation RMS Root Mean Square RTK Real-Time Kinematic SAPOS Satellite Poitioning Service of the German State Survey SD Single Difference SP3 IGS Standard Product 3 SPS Standard Poitioning Service STD Slant Total Delay UD Un-differenced UPD Un-calibrated Phae Delay UTC Coordinated Univeral Time WL Widelane Combination WGS-84 Word Geodetic Sytem 1984 ZHD Zenith Hydrotatic Delay ZTD Zenith Total Delay ZWD Zenith Wet Delay - viii -

9 Lit of Related Publication 1. Li, X., M. Ge, X. Zhang, Y. Zhang, B. Guo, R. Wang, J. Klotz, and J. Wickert (2013), Real-time high-rate co-eimic diplacement from ambiguity-fixed precie point poitioning: Application to earthquake early warning, Geophy. Re. Lett., 40(2), , doi: /grl Li, X., M. Ge, Y. Zhang, R. Wang, P. Xu, J. Wickert, and H. Schuh (2013), New approach for earthquake/tunami monitoring uing dene GPS network, Sci. Rep., 3, 2682, doi: /rep Li, X., M. Ge, B. Guo, J. Wickert, and H. Schuh (2013), Temporal point poitioning approach for real-time GNSS eimology uing a ingle receiver, Geophy. Re. Lett., 40(21), , doi: /2013gl Li, X., M. Ge, Y. Zhang, R. Wang, B. Guo, J. Klotz, J. Wickert, and H. Schuh (2013), High-rate coeimic diplacement from tightly integrated proceing of raw GPS and accelerometer data. Geophy J Int. 5. Li, X., X. Zhang, and B. Guo (2013), Application of collocated GPS and eimic enor to earthquake monitoring and early warning. Senor 13: Li, X., M. Ge, C. Lu, Y. Zhang, R. Wang, J. Wickert, and H. Schuh (2014), High-rate GPS eimology uing real-time precie point poitioning with ambiguity reolution. IEEE tranaction on Geocience and remote ening, pp Li, X., B. Guo, C. Lu, M. Ge, J. Wickert, and H. Schuh (2014), Real-time GNSS eimology uing a ingle receiver. Geophy. J. Int. doi: /gji/ggu113 In thi thei, the paper 1 and 6 contributed to the Chapter 2, the paper 2 contributed to the Chapter 3, the paper 3 and 7 contributed to the Chapter 4, and the paper 4 and 5 contributed to the Chapter 5. - ix -

10 1 Introduction Recent detructive earthquake that truck Sumatra, Indoneia (Mw 9.2) in 2004, Wenchuan, China (Mw 7.9) in 2008, Maule, Chile (Mw 8.8) in 2010 and Tohoku, Japan (Mw 9.0) in 2011 have once again brought u to focu the urgent need for earthquake monitoring and early warning. Rapid ource and rupture inverion for large earthquake i critical for eimic and tunamigenic hazard mitigation (Allen and Ziv, 2011; Ohta et al., 2012), and earthquakeinduced ite diplacement i key information for uch ource and rupture inverion. For earthquake early warning (EEW) ytem, the etimation of accurate coeimic diplacement and waveform i needed in real-time. Traditionally, diplacement are obtained by double integration of oberved accelerometer ignal or ingle integration of velocitie oberved with broadband eimometer (Kanamori, 2007; Epinoa-Aranda et al., 1995; Allen and Kanamori, 2003). The broadband eimometer are likely to clip the ignal in cae of large earthquake. Although trong-motion accelerometer intrument do not clip, the diplacement converted from acceleration could be degraded ignificantly by drift caued by tilt and the non-linear behavior of the accelerometer (Trifunac and Todorovka, 2001; Boore, 2001). Since Remondi (1985) firt demontrated cm-level accuracy of kinematic GPS, Hirahara et al. (1994) labeled kinematic GPS a GPS eimology, which ha ince attracted more and more attention and application in eimology (ee, e.g., Ge et al. 2000; Laron et al., 2003). High-rate GNSS (e.g., 1 Hz or higher frequency) meaure diplacement directly and can provide reliable etimate of broadband diplacement, including tatic offet and dynamic motion of arbitrarily large magnitude (Laron et al., 2003; Bock et al., 2004). GPS-baed eimic ource characterization ha been demontrated in near- and far-field with remarkable reult (Nikolaidi et al., 2001; Laron et al., 2003; Bock et al., 2004; Ohta et al., 2008; Yokota et al., 2009; Avallone et al., 2011; Melgar et al., 2012; Crowell et al., 2012). GNSS-derived diplacement can be ued to quickly etimate earthquake magnitude, model finite fault lip, and alo play an important role in earthquake/tunami early warning (Blewitt et al., 2006; Wright et al., 2012; Hoechner et al., 2013). Conequently in the recent year, dene GPS monitoring network have been built in eimically active region, e.g., Japan GEONET (the GPS Earth Obervation Network Sytem, and UNAVCO Plate Boundary Obervatory (PBO, Thee network are complementary to eimic monitoring network and contribute ignificantly to earthquake/tunami early warning and hazard rik mitigation (Blewitt et al., 2006; Crowell et al., 2009)

11 Currently, two proceing trategie are mainly ued in mot of the tudie related to GPS eimology and tunami warning: relative baeline/network poitioning (e.g., Nikolaidi et al., 2001; Laron et al., 2003; Bock et al., 2004, Blewitt et al., 2006) and precie point poitioning (PPP) (Zumberge et al., 1997). For relative kinematic poitioning, at leat one nearby reference tation hould be ued for removing mot of biae and recovering integer feature of ambiguity parameter by forming double-differenced ambiguitie. Conequently, ambiguitie can alway be fixed to integer even intantaneouly for achieving high poitioning accuracy of few cm (Bock et al., 2011; Ohta et al., 2012). Therefore, it i already applied in real-time diplacement monitoring (e.g., Crowell et al., 2009). The technique of intantaneou poitioning (Bock et al., 2000) i one typical real-time relative poitioning method and i integrated into EEW ytem (Crowell et al., 2009) and i demontrated by applying the reult for centroid moment tenor (CMT) computation (Melgar et al., 2012), finite fault lip inverion (Crowell et al., 2012) and P wave detection by combining collocated accelerometer data and the GPS diplacement uing a Kalman filter (Bock et al., 2011; Tu et al., 2014). The real-time kinematic (RTK) technique i alo utilized by Ohta et al (2012) to analyze the diplacement of the 2011 Tohoku-Oki earthquake. All of the previouly mentioned tudie ued the relative poitioning technique, which i able to guarantee a high accuracy at 1 cm level. However, for the relative poitioning technique, GPS data from a network i analyzed imultaneouly to etimate tation poition. It i complicated by the need to aign baeline, overlapping Delaunay triangle, or overlapping ub-network. Thi i a ignificant limitation for the challenging imultaneou and precie real-time analyi of GPS data from hundred or thouand of ground tation. Furthermore, intermittent tation dropout complicate the network-baed relative poitioning. Relative poitioning alo require a local reference tation, which might itelf be diplaced during a large eimic event, reulting in mileading GPS analyi reult. In the cae of large earthquake, uch a the Mw 9.0 Tohoku-Oki event in Japan, the reference tation may alo be ignificantly diplaced, even when it i everal hundred kilometer away from the event. The reference tation hould be ufficiently far from the focal region, but mut alo be part of a ub-network that ha relatively hort baeline (uually within everal ten of kilometer). A the baeline length increae, the accuracy of relative poitioning would be ignificantly reduced becaue the atmopheric effect and atellite ephemeri error become le common and thu cannot be effectively cancelled out by double-difference technique. PPP provide a new concept of poitioning ervice by uing precie orbit and clock product generated from a global reference network (Kouba and Héroux, 2001). Kouba (2003) demontrated that PPP uing the orbit and clock product of the International GNSS Service (IGS) can be ued to detect eimic wave and atify the requirement of the GPS eimology

12 Wright et al. (2012) ued PPP in real-time mode with broadcat clock and orbital correction to give tation poition every 1 ec and then carry out a imple tatic inverion to determine the portion of the fault that lipped and the earthquake magnitude. The PPP technique can provide abolute coeimic diplacement with repect to a global reference frame (defined by the atellite orbit and clock) with a tand-alone GPS receiver. A PPP proceing ytem ue information from a global reference network, which i applied to the monitoring tation, conequently the derived poition are referred to the global network, which itelf i hardly affected by the earthquake diplacement. Thank to the development of JPL Global Differential GPS Sytem (GDGPS) and the International GNSS Service (IGS) real-time pilot project (RTPP), real-time precie atellite orbit and clock product are now available online and PPP i widely recognized a a promiing poitioning technique (Caiy 2006; Dow et al., 2009; Bar-Sever et al., 2009). However, tandard PPP (float ambiguity) ha limited accuracy in real-time application becaue of unreolved integer-cycle phae ambiguitie. PPP ambiguity reolution developed in recent year provide an important promie to achieve comparable accuracy with relative/network poitioning (Ge et al., 2008; Li et al., 2013a). The German Reearch Center for Geocience (GFZ), a one of the IGS data analyi center, i operationally providing GPS orbit and clock, uncalibrated phae delay (UPD) and differential code biae (DCB) for real-time PPP ervice with ambiguity-fixing (Ge et al., 2011; Li 2012). The performance i further enhanced by new algorithm for peeding up the reconvergence through etimation of ionopheric delay (e.g., Geng et al., 2010; Zhang and Li, 2012; Li et al., 2013a). Although a convergence period of about 20 min i till required, PPP i able to achieve cm-level poitioning accuracy in real-time without the need for dedicated reference tation (Li et al., 2013b). Coloimo et al. (2011) propoed a variometric approach to determine the change of poition between two adjacent epoch (namely delta poition) baed upon the time ingle-difference of the carrier phae obervation, and then diplacement of the tation are obtained by a ingle integration of the delta poition. Thi approach doe not uffer from convergence proce, but the ingle integration from delta poition to diplacement i accompanied by a drift due to the potential uncompenated error. Uually, a limited duration of 3-4 minute may be enough for large diplacement retrieving. Under the aumption that the variometric-baed diplacement ha a linear trend within few minute, the etimated diplacement after linear trend removal are demontrated to be at a level of a few centimeter (Branzanti et al., 2013). Recent advance in the performance of real-time high-rate GPS, etimate of permanent diplacement directly, mean that it ue can potentially be complementary to the eimic-baed methodologie for earthquake early warning. The main weaknee of current GPS - 3 -

13 meaurement are the lower ampling rate (1~50Hz) and the larger high-frequency noie contribution, and o the GPS-derived dynamic motion are not accurate enough to identify the firt arrival wave (P-wave) with only millimeter-level amplitude. The noie of GPS diplacement i baically white acro the whole eimic frequency band. While trong motion enor are able to ample at very high rate (e.g. 200Hz) and perform very well in the high-frequency range a it i much more enitive to ground motion than GPS receiver, epecially in the vertical direction. However, the acceleration i accompanied by unphyical drift due to enor rotation and tilt (Trifunac and Todorovka, 2001; Lee and Trifunac, 2009), hyterei (Shakal and Peteren, 2001), and impreciion in the numerical integration proce (Boore et al., 2002; Smyth and Wu, 2006). It noie level, viewed in term of diplacement, will rie with decreaing frequency: at ome frequency thi noie level will exceed that of GPS. Therefore, GPS and eimic intrument can be mutually beneficial for eimological application becaue weaknee of one obervation technique are offet by trength in the other. The complementary nature of GPS and eimic enor for tation diplacement etimation and P-wave detection are well recognized and the integrated proceing of the two dataet i a hot topic in GPS eimology for obtaining more accurate and reliable diplacement and P- wave arrival time. Several looely-integrated approache have been propoed to fue accelerometer with collocated GPS diplacement data (Emore et al., 2007; Bock et al., 2011). A the GPS coordinate are already etimated prior to integration with the accelerometer, the precie dynamic information provided by accelerometer cannot be ued to enhance the GPSonly olution in thee integration algorithm. Currently, the available real-time high-rate GNSS data tream have the potential to contribute to EEW ytem. GFZ ha been working on the real-time precie poitioning for geohazard monitoring for year. The EPOS-RT oftware ha been developed for providing worldwide real-time PPP ervice. The accuracy and reliability of the global PPP hould be improved for better monitoring of geohazard, epecially for thoe cauing rather mall diplacement. It i a big challenge to achieve precie and reliable diplacement in real-time. Thu thi thei will focu on the development of high-preciion GNSS algorithm for better eimological application. We alo integrate the accelerometer data into the GNSS data proceing in order to combine all the advantage of GPS and eimic enor. Thi thei include the following chapter, Firtly, Chapter 1 preent the motivation, background and reearch objective of thi thei and pecifie the contribution of thi reearch

14 In the Chapter 2, the ambiguity-fixed PPP method i developed to etimate high-rate coeimic diplacement in real-time. Thi ambiguity-fixed PPP algorithm i decribed in detail. The PPP diplacement waveform are analyzed and compared with eimic waveform and the application of PPP waveform to EEW i decribed. Chapter 3 propoe a novel method for fat or even intantaneou poitioning, making full ue of the currently available global PPP ervice and regional GPS monitoring network. The derived atmopheric correction at the tation with fixed ambiguitie then can be provided to other monitoring tation for intantaneou ambiguity reolution, o that precie diplacement can alway be achieved within a few econd. The new method doe not depend on a pecific reference tation and therefore the analyi reult will not be affected by imultaneou haking of any particular tation. It alo ha better flexibility and efficiency compared to complicated network/ubnetwork analyi. Chapter 4 propoe a new approach for etimating coeimic diplacement with a ingle receiver in real-time. The approach overcome not only the diadvantage of the PPP and RP technique, but alo decreae the decribed drift in the diplacement derived from the variometric approach. The coeimic diplacement could be etimated with few centimeter accuracy uing GNSS data around the earthquake period. The efficiency of the new approach i validated uing 1 Hz GNSS data, collected during the Tohoku-Oki earthquake (Mw 9.0, 11 March, 2011) in Japan. Chapter 5 propoe an approach of integrating the accelerometer data into the GPS data proceing in order to take full ue of the complementary of GPS and eimic enor. Intead of combing the GPS-derived diplacement with the accelerometer data, a tightly-integrated filter i developed to etimate eimic diplacement from GPS phae and range and accelerometer obervation. The performance of the propoed tightly-integrated approach wa validated by the 2010, Mw 7.2 El Mayor-Cucapah earthquake (Mw 7.2, 4 April, 2010) in Baja California, Mexico and the Tohoku-Oki earthquake (Mw 9.0, 11 March, 2011) in Japan. Finally, Chapter 6 ummarize the main reult a obtained in the previou chapter, preent the final concluion and ugget recommendation for the future work

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16 2 High-rate GNSS eimology uing real-time PPP with ambiguity reolution 2.1 Introduction Earthquake-induced ite diplacement i key information for locating the epicentre and etimating the magnitude of earthquake. For earthquake early warning (EEW) ytem, the etimation of accurate coeimic diplacement and waveform i needed in real-time. Traditionally, diplacement are obtained by double integration of oberved accelerometer ignal or ingle integration of velocitie oberved with broadband eimometer (Kanamori, 2007; Epinoa-Aranda et al., 1995; Allen and Kanamori, 2003). Compared to eimic intrument that are ubject to drift (accelerometer) or that clip the ignal in cae of large earthquake (broadband eimometer), GPS receiver oberve diplacement directly, making it particularly valuable in cae of large earthquake (Laron et al., 2003; Blewitt et al., 2006). Until now, pot-proceing or imulated real-time relative kinematic poitioning i utilized in mot of the tudie related to GPS eimology (e.g., Nikolaidi et al., 2001; Laron et al., 2003; Bock et al., 2004) and tunami warning (e.g., Blewitt et al., 2006). For relative kinematic poitioning, at leat one nearby reference tation hould be ued for removing mot of biae and recovering integer feature of ambiguity parameter by forming doubledifferenced ambiguitie. Conequently, ambiguitie can alway be fixed to integer even intantaneouly for achieving high poitioning accuracy of few cm (Bock et al., 2011; Ohta et al., 2012). However, the relative poitioning technique relie on reference tation located cloely. To monitor large region, conequently a large number of reference tation i required which increae cot and ytem complexity. More critical i the fact that the derived diplacement alo depend on the earthquake-induced movement of the reference tation. Thank to the development of JPL Global Differential GPS Sytem (GDGPS) and the International GNSS Service (IGS) real-time pilot project (RTPP), real-time precie atellite orbit and clock product are now available online and PPP i widely recognized a a promiing poitioning technique (Caiy 2006; Dow et al., 2009; Bar-Sever et al., 2009). However, tandard PPP (float ambiguity) ha limited accuracy in real-time application becaue of unreolved integer-cycle phae ambiguitie. In recent year, integer ambiguity fixing approach for PPP ha been developed to improve it performance (Ge et al., 2008; Li et al., 2013)

17 In thi chapter, we introduce the ytem tructure of the real-time PPP ervice by taking the operational real-time PPP ervice, developed at the German Reearch Center for Geocience (GFZ) for both precie poitioning and geophyical application a an example. The GPS data proceing trategie including the obervation model, real-time PPP, and PPP ambiguity reolution are decribed in detail. The poitioning preciion i carefully aeed in real-time cenario. We etimate high-rate coeimic diplacement in imulated real-time PPP mode for 1 Hz GPS data, collected during the Tohoku-Oki earthquake (Mw 9.0, March 11, 2011) in Japan and 5 Hz GPS data, collected during El Mayor-Cucapah earthquake (Mw 7.2, April 4, 2010) in Mexico. The derived diplacement waveform are analyzed, compared with eimic waveform, and finally applied for fault lip inverion to further validate the real-time PPP ervice with ambiguity reolution. 2.2 Real-time PPP ytem and algorithm Real-time PPP ervice ytem In a global real-time PPP ervice ytem, real-time data from a global reference network with a certain number of evenly ditributed tation i eential for generating precie orbit and clock for precie poitioning at the deired location. The real-time orbit i uually predicted baed on orbit determined in a batch-proceing mode uing the latet available obervation (generally 5 min ampling interval) due to the dynamic tability of the atellite movement. More challenging i the etimation of the atellite clock correction, which mut be updated much more frequently due to their hort-term fluctuation (Zhang et al., 2011). Under the framework of the IGS RTPP, data from a global real-time network of more than 100 tation i available and the related data communication for the obervation, retrieving and product cating wa etablihed (Caiy 2006). Furthermore, everal real-time analyi center (RTAC) were etablihed and have been running operationally to contribute their real-time product for comparion and combination. Mot of the RTAC ue a proceing procedure imilar to that for generating the IGS ultra-rapid orbit, but the update time of 6 hour could be hortened for a better orbit accuracy. The atellite clock product are etimated every 5 econd together with receiver clock, ambiguity and zenith tropopheric delay (ZTD) parameter with fixed or tightly contrained atellite orbit and tation coordinate. A in both the orbit determination and clock etimation, tation coordinate are fixed, obervation affected by earthquake-induced diplacement will have large reidual and be rejected a outlier. A the diplacement will not occur at the ame time for mot of the tation, precie atellite orbit and clock are till available during the earthquake time

18 With the real-time orbit and clock, tandard PPP can be carried out at the uer-end where ionopheric delay are uually eliminated uing the ionophere-free combination and ZTD mut be etimated a unknown parameter. Uually, it need an initialization time of about 30 min to obtain poition of cm-level accuracy. Initialization mut be repeated if mot of the atellite loe lock which i referred a to re-convergence and might occur during earthquake. Moreover, a in relative poitioning, the float olution could be further improved by integer ambiguity reolution. For recovering the integer feature of the ambiguitie at the uer-end, uncalibrated phae delay (UPD) at the atellite or imilar product hould be etimated and tranmitted to uer. The approach for thi UPD etimation and integer ambiguity reolution at the uer-end will be preented in detail in the following ection. Taking the operational real-time PPP ervice, developed at GFZ, a example (Ge et al., 2011; Li et al., 2013), the data tream of about 80 globally ditributed IGS tation are proceed in real-time by uing the EPOS-RT oftware for generating and broadcating orbit and clock for tandard PPP ervice. Furthermore, for reolving the integer ambiguity at uer-end, UPD correction are generated and updated in real-time with the ame data et which are ued to etimate orbit and clock product. The data flow at the erver-end, including precie GPS orbit determination, clock etimation and UPD retrieval i hown in Fig Figure 2.1: Data flow at the erver-end of a global real-time PPP ervice. The GPS clock and orbit are baic product and UPD i for PPP ambiguity reolution at the uer-end. At the uer-end, the real-time product tream of orbit and clock are received and applied to the obervation for tandard PPP. If UPD i alo available, PPP with integer ambiguity reolution then can be performed. Due to the product tranmiion delay and higher ampling - 9 -

19 rate (e.g., 1Hz) at uer-end, a linear extrapolation of a few econd will be applied. The data flow at the uer-end i hown in Fig Figure 2.2: Data flow at the uer-end for tandard PPP and PPP with integer ambiguity reolution Obervation Model The obervation equation for undifferenced (UD) carrier phae L and peudorange P repectively, can be expreed a following: L t t ( b b ) N I T (2.1) r, j r g r j r, j j j r, j r, j r r, j P t t c( d d ) I T e (2.2) r, j r g r r, j j r, j r r, j where indice, r, and j refer to the atellite, receiver, and carrier frequency, repectively; t and t r are the clock biae of atellite and receiver; N, r j i the integer ambiguity; br, j dr, jand and bj are the receiver- and atellite-dependent UPD; j i the wavelength; d j are the code biae of the receiver and the atellite; Ir, j i the ionopheric delay of the ignal path at frequency j ; Tr i the correponding and frequency independent tropopheric delay; er, jand r, jare meaurement noie of the peudorange and carrier phae obervation. Furthermore, denote the geometric ditance between the phae center of the g atellite and receiver antenna at the ignal tranmitting and receiving epoch, repectively. Thi mean, that the phae center offet and variation and tation diplacement by tidal loading mut be conidered. Phae wind-up and relativitic delay mut alo be corrected according to

20 the exiting model (Kouba and Héroux, 2001), although they are not included in the equation. A idereal filter can be ued to effectively reduce the impact of multipath error (Choi et al., 2004). The lant tropopheric delay conit of the dry and wet component and both can be expreed by their individual zenith delay and mapping function. The tropopheric delay i uually corrected for it dry component with an a priori model, while the reidual part of the tropopheric delay (conidered a zenith wet delay Z ) at the tation r i etimated from the obervation. r, j r g r j r, j j j r, j r, j r r r, j r L t t ( b b ) N I m Z (2.3) P t t c( d d ) I m Z e (2.4) r, j r g r r, j j r, j r r r, j where m i the wet mapping function. r For multi-frequency obervation, the ionopheric delay at different frequencie can be expreed a, I I ; / (2.5) 2 2 r, j j r,1 j j 1 At the uer-end, the real-time product tream of orbit and clock are received and applied to the obervation for tandard PPP. If UPD i alo available, PPP with integer ambiguity reolution then can be performed. Due to the product tranmiion delay and higher ampling rate (e.g., 1Hz) at uer-end, a linear extrapolation of a few econd will be applied. The data flow at the uer-end i hown in Fig The ionopheric delay can be eliminated by forming the linear combination of obervation at different frequencie. Uually, the ionophere-free obervation i employed in PPP (Kouba and Héroux, 2001). Alternatively, the dual-frequency data can be proceed by etimating the lant ionopheric delay in raw obervation a unknown parameter (Schaffrin and Bock 1988). The line-of-ight ionopheric delay on the L1 frequency I r,1 are taken a parameter to be etimated for each atellite and at each epoch. In order to trengthen the olution, a priori knowledge about thee delay can be utilized a contraint on the ionopheric parameter. The temporal change of the lant ionopheric delay of a atellite-tation pair can be repreented by a tochatic proce according to their temporal correlation. Ionopheric gradient parameter could be ued to take into account the patial ditribution of the ionopheric delay. The temporal correlation, patial characteritic and ionopheric model contraint are comprehenively conidered to peed up the convergence in PPP ambiguity

21 reolution (Li et al., 2013c). Thee contraint, to be impoed on obervation of a ingle tation can be ummarized a: I I w w N 2 rt, rt, 1 t, t ~ (0, wt) vi I / f a a dl a dl a db a db, I r r vi I, 2 r r I ripp, (2.6) where t i the current epoch; t 1 i the previou epoch; w t i a zero mean white noie with variance of 2 wt (generally a few millimeter for 1Hz ampling and an elevation-dependent weighting trategy i applied); vi r i the vertical ionopheric delay with a variance of f 2 vi ; ripp, i the mapping function (Schaer et al., 1999) at the ionopheric pierce point (IPP); the coefficient 0,1, 2,3, 4 a i decribe the planar trend, the average value of the ionopheric i delay over the tation; a 1, a 2, a 3, and a 4 are the coefficient of the two econd-order polynomial that ued to fit the eat-wet and outh-north horizontal gradient; dl and db are the longitude and latitude difference between the IPP and the tation location; I r i the 2 ionopheric delay obtained from external ionopheric model with a variance of I Real-time precie point poitioning Intead of the ionophere-free linear combination, we ue the raw carrier phae and peudorange obervation of Eq (2.3), (2.4), and (2.5) and etimate the lant ionopheric delay a unknown parameter with ionopheric contraint of (2.6). The linearized equation for (2.3) and (2.4) can be repectively expreed a following, l u r t t ( b b ) N I m Z (2.7) r, j r r j r, j j j r, j j r,1 r r r, j p u r t t c( d d ) I m Z e (2.8) r, j r r r, j j j r,1 r r r, j where l r, jand pr, jdenote oberved minu computed phae and peudorange obervable from atellite to receiver r at the frequency j ; u r i the unit vector of the direction from receiver to atellite; r denote the vector of the receiver poition increment. With the received real-time correction of GPS atellite orbit, clock and differential code biae (DCB), the correponding term in the obervation equation can be removed. The raw obervation equation then can be implified a, l u r t B I m Z (2.9) r, j r r j r, j j r,1 r r r, j p u r t c d I m Z e (2.10) r, j r r j r,1 j r,1 r r r, j

22 B N b b (2.11) r, j r, j r, j j where B r, ji the real-valued undifferenced ambiguity. At the epoch k, obervational equation for all the atellite can be expreed a, where the etimated parameter are, Y A X N (2.12) 2 k k k Y, ~ (0, ) k Y Y X r Z t d I ) B ) B ) (2.13) T T T r r r,1 r,1 r,1 r,2 A equential leat quare filter i employed to etimate the unknown parameter for realtime proceing. Pk denote the weight matrix at epoch k, X ˆ P A PY P X ˆ (2.14) 1 T k Xˆ k k k ˆ k 1 k X k1 Q P ( A P A P ) (2.15) 1 T 1 Xˆ Xˆ k k k Xˆ k k k1 The increment of the receiver poition r are etimated epoch by epoch without any contraint between epoch for retrieving rapid tation movement. The tropopheric zenith wet delay Z i decribed a a random walk proce with noie of about 2-5 mm / r T hour. The receiver clock i etimated epoch-wie a white noie and the carrier-phae ambiguitie B r, j are etimated a contant over time Real-time etimation of the uncalibrated phae delay From the carrier phae obervational equation of (2.9), one can ee that undifferenced phae ambiguitie cannot be fixed to integer becaue of the exitence of UPD. The real-valued ambiguitie can be expreed by integer number plu the UPD at receiver and atellite a Eq. (2.11). Recent tudie how, that the UPD can be etimated with high accuracy (Ge et al., 2008; Li and Zhang, 2012) or aimilated into clock parameter (Collin et al., 2008; Lauricheee et al., 2008). In our procedure of real-time UPD etimation, the PPP float olution i firtly carried out for all tation of the reference network. In thi PPP proceing, the coordinate of the reference tation are fixed to well-known value, for example, determined from weekly olution in advance, o that the undifferenced (UD) float ambiguitie could be obtained with higher quality. Aume that we have a network with n tation (generally more than 15 tation for regional network or more than 80 tation for a global network) tracking m atellite, the UD float

23 ambiguitie at each tation are etimated a B, we have the obervation equation in the form of Eq. (2.16) for thee ambiguitie (Li and Zhang, 2012), i N1 B1 I R1 S1 N2 B2 I 0 R2 S2, Q (2.16) 0 I Nn B n I Rn Sn br b where B i the UD float ambiguity vector for tation i ; i vector for tation i ; b r and N i i the UD integer ambiguity b are the UPD for receiver and atellite; R i and Si are the coefficient matrice for receiver and atellite UPD repectively; Q i the co-variance matrix of the UD float ambiguitie; In matrix R i one column with all element i 1 and the other are zero. For matrix S i each line i one element of -1, the other are zero. Under the condition that all the integer ambiguitie are exactly known and one UPD i fixed to zero, other UPD can be etimated by mean of the leat quare adjutment. Furthermore, for integer ambiguity reolution, the fractional part of UPD i ufficient intead of UPD itelf a the integer part can be aborbed by the ambiguity parameter anyway. Therefore, we will not ditinguih UPD and UPD fractional part hereafter. Aume the receiver UPD at the firt arbitrarily elected tation i zero, then the nearet integer of the UD ambiguitie at thi tation are their integer ambiguitie and the fractional part are etimate of the related atellite UPD. Applying thi atellite UPD to the common atellite of the next tation, the corrected UD ambiguitie hould have very imilar fractional part. The mean value of the fractional part of all the common atellite i taken a UPD of the receiver. With thi UPD, the UPD of the upcoming atellite, oberved at the tation, can be etimated. Repeating thi procedure for all tation, we can have the approximate UPD for all receiver and atellite. After correcting the UD float ambiguitie with the UPD, they hould be very cloe to integer, thu ambiguity reolution can be attempted. Replacing integer ambiguity parameter with their fixed value in equation (2.16), the remaining parameter can be etimated and the UPD etimate are urely improved and will help to reolve more integer ambiguitie. The above decribed procedure can be done iteratively until no more integer ambiguitie can be fixed. The UPD of the lat iteration are the information needed for the uer ide for PPP ambiguity reolution. Finally, we broadcat the atellite UPD to PPP uer together with orbit,

24 clock and DCB product tream, o that PPP with integer ambiguity reolution can be performed at a ingle tation Ambiguity reolution for precie point poitioning Integer ambiguity reolution for PPP require not only precie atellite orbit and high-rate atellite clock correction but alo the above mentioned UPD. With the received UPD correction, atellite UPD are removed at the uer-end and the obervational equation of (2.9) can be implified a, l u r t N b I m Z (2.17) r, j r r j r, j j r, j j r,1 r r r, j The receiver UPD can be eaily eparated by adapting one UD ambiguity to it nearet integer. Afterward, the UD ambiguitie have integer feature and the L1 and L2 ambiguitie can be fixed imultaneouly uing integer etimation method (ee, e.g., Teunien 1995; Xu et al., 2012). The ratio of the econd minimum to the minimum quadratic form of reidual i applied to decide the correctne and confidence level of integer ambiguity candidate (the threhold for the ratio tet i et to 3 a uual). 2.3 Accuracy aement in real-time cenario For aeing the preciion of our real-time product tream, fifteen real-time GPS tation (1Hz ampling), which are not ued for erver-ide product generation, are elected a uer tation. The PPP float olution and PPP with ambiguity reolution are carried out in parallel for thee tation from day 325 to (November 20 to 29, 2012). The ame orbit and clock correction are ued to feed the float PPP and the ambiguity-fixed PPP. Compared with GFZ final product (be regarded a truth), the 3D RMS (root mean quare) of orbit error i about 4.0 cm, the RMS of clock error i about 5.1cm, and the RMS of uer range error (URE) i about 3.5cm. The tation coordinate are etimated epoch-by-epoch without any contraint between epoch for teting the real-time kinematic performance. The etimated coordinate are compared with the coordinate derived from pot-proceed daily olution to ae the poitioning accuracy. A a typical example, the difference of the etimated poition with repect to their daily olution for tation A17D (Potdam) on day 326 are exemplarily hown in Figure 2.3. Figure 2.3a how the poition difference (with repect to pot-proceed daily olution) of the PPP float olution in the north, eat and up component. The difference are within 10 and 15 cm for the horizontal and vertical component, repectively. The vertical i, a expected, the noiiet component, due to the atellite contellation geometry and the high correlation between zenith tropopheric delay and the height component. There are long-term variation

25 and hort-term fluctuation in the poition erie even after a long convergence period of 24 hour (day 325). The poition difference of the fixed olution are hown in Figure 2.3b. The improvement i ignificant, when compared with the related float olution. In the ambiguityfixed olution, the fluctuation are much maller than thoe in the float olution and there are not obviou biae. A poition accuracy of better than 5 and 10 cm in horizontal and vertical component i repectively achieved once the ambiguitie are uccefully fixed. Comparion of the PPP float and fixed olution for tation BELL on day 326 are hown in Figure 2.4 and imilar improvement are achieved in the ambiguity-fixed olution. Figure 2.3: Real-time kinematic PPP olution for tation A17D (Potdam) on day (a), PPP without ambiguity-reolution; (b), PPP with fixed ambiguitie. The north, eat and up component are indicated by the green, red and black line, repectively

26 Figure 2.4: Real-time kinematic PPP olution for tation BELL on day (a), PPP without ambiguity-reolution; (b), PPP with fixed ambiguitie. The north, eat and up component are indicated by the green, red and black line, repectively. The RMS, tandard deviation (STD) and mean bia of the poition difference erie are calculated a tatitical indicator for the accuracy aement. The tatitical reult of the poition difference erie of day 326 to (November 21 to 29, 2012) for tation A17D and BELL are ummarized in Table 1. The RMS of the elected fifteen uer tation for both PPP float and fixed olution are alo hown in Figure 2.5. From Fig. 2.5, the poition RMS in north, eat and vertical direction of the float olution are improved from about 3, 5 and 6 cm to 1, 1 and 3 cm, repectively, by integer ambiguity reolution. Among thee ignificant improvement the larget i in the eat component. The STD of float olution are reduced from about 2 and 5 cm for the horizontal and vertical component to 1 and 2.5 cm, repectively. It i worth to mention that the biae are alo

27 decreaed evidently by ambiguity reolution, epecially in the eat component from about 3-4 cm to everal mm. Table 2.1: Statitical reult including RMS, STD and mean biae. Station RMS (cm) STD (cm) Mean bia (cm) &Accuracy Float Fixed Float Fixed Float Fixed North(A17D) Eat(A17D) Up(A17D) North(BELL) Eat(BELL) Up(BELL)

28 Figure 2.5: RMS of the poition difference of day 326 to (November 21 to 29, 2012) for the elected fifteen uer tation (Global). The RMS of north, eat and up component are hown in the top, middle and bottom ub-figure. The float olution are in blue and the fixed one in red. 2.4 Application to the 2011 Tohoku-Oki earthquake GPS data and analyi The Mw 9.0 Tohoku-Oki earthquake occurred on March 11, 2011 at 05:46:24 UTC in the north-wetern Pacific Ocean at a relatively hallow depth of 30 km, with it epicenter approximately 72 km eat of the Ohika Peninula of Tohoku, Japan. The Tohoku-Oki event i one of the bet recorded large earthquake in hitory a Japan ha one of the denet GPS network in the world. The Geopatial Information Authority of Japan (GSI) operate more than 1,200 continuouly recording GPS tation (collectively called the GPS Earth Obervation Network Sytem, GEONET) all over Japan ( The GEONET data provide an ideal opportunity to evaluate the performance of real-time PPP derived coeimic diplacement. We proce 1 Hz data of about 80 globally ditributed real-time IGS tation uing the EPOS-RT oftware of GFZ in imulated real-time mode (data i edited in real-time proce without pre-clean) for providing GPS orbit, clock and UPD correction at 5 ampling interval. Compared with GFZ final product, the 3D RMS of orbit error i about 4.1 cm, the RMS of clock error i about 5.3 cm, and the RMS of URE i about 3.6 cm. Baed on thee correction, we replayed the 1 Hz GPS data collected at the GEONET tation during the 2011 Tohoku-Oki earthquake. In the near future, it i difficult for mot countrie at threat from large earthquake and tunami to afford uch a dene GPS network a Japan GEONET. To tet the utility of a pare GPS network for earthquake/tunami early warning (Wright et al., 2012), ixty high-rate GPS tation are elected from the GEONET for fault lip inverion in thi tudy. The ditribution of the elected GPS tation i hown in Figure

29 Figure 2.6: Location of the 2011 Tohoku-Oki earthquake epicenter and the ditribution of the elected high-rate GPS tation and trong motion tation. The epicenter i marked by the red tar. The blue circle repreent tation with GPS only, wherea the gray triangle are for tation with collocated GPS and trong motion eimometer. We calculated the RMS of the poition difference of the ixty elected GPS tation over the 2 hour before the earthquake event for the PPP float and fixed olution, repectively. It reveal that RMS in eat, north and vertical of the float olution of about 2.8, 4.4 and 9.7 cm are improved to 1.9, 1.9 and 4.0 cm, correpondingly by integer ambiguity reolution. Similarly, we alo calculated the RMS of the diplacement-derived velocitie over thee two hour for the ixty GPS tation which are 2.7, 1.8 and 4.6 mm/ repectively in the north, eat and up component. The diplacement waveform from PPP fixed olution and the velocitie of five tation are hown a example in Figure 2.7a and 2.7b, repectively