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During the mission duration of GRACE (about five years), a temporal geoid change of about 3 mm is expected in the centre of the Fennoscandian land uplift area (the Bothnian Bay), corresponding to a gravity change of about 100 nm/s2. The uplift effect reaches up to 11 mm/year at the Earth's surface. It can be observed geometrically by GPS, and gravitationally in space by GRACE as well as on the ground by absolute gravimetry. In this study, we determine gravity changes in Northern Europe from the monthly GRACE solutions as provided by CSR, University of Texas, and compare them with recent terrestrial gravity measurements carried out at some selected sites in the region. Each of the gravity data sets is affected by various geophysical processes such as atmospheric, oceanic and hydrological effects which conceal the uplift signal and therefore have to be removed. In this respect, also the processing and filtering of the various data sets is considered. [ABSTRACT FROM AUTHOR]

The primary objective of this paper is to present results of an experiment to determine the effects of moderate and severe ionospheric conditions on the GPS signal tracking by different L1/L2 receivers operating in the Southern Polar region. In this study, data collected by the Ohio State University (OSU) and the U.S. Geological Survey (USGS) joint team within the TAMDEF (Transantarctic Mountains Deformation) network were used together with the IGS and UNAVCO Antarctic stations. Seventeen Antarctic stations equipped with different dual-frequency GPS hardware were selected, and data were evaluated for two 24-hour periods of severe ionospheric storm (October 29th, 2003) and active ionospheric conditions (moderate storm of November 11th, 2003). The UNAVCO QC software was used to carry out the analyses. Depending on the data sampling rate and the elevation mask angle, the expected number of observations per receiver/satellite was compared to the actual number of measurements collected during the ionospheric storms, with a special emphasis on L2 data. Depending on the receiver model, the number of lost measurements during the severe ionospheric conditions ranged from 0.5% to 30.0%. In addition, the number of cycle slips (CS) per number of observations as a function of receiver model was computed; it shows great variation for different hardware. The possible variability of the ionospheric conditions at some of these sites (due to their separation) is considered in the conclusions. The results indicate that depending on the severity of ionospheric conditions, there is a significant difference in the impact on the operations of different hardware models. Thus, careful hardware selection is needed to assure data quality/continuity when observations may be affected by severe ionospheric disturbances. [ABSTRACT FROM AUTHOR]

Lunar Laser Ranging (LLR), which has been carried out for more than 35 years, is used to determine many parameters within the Earth-Moon system. This includes coordinates of terrestrial ranging stations and that of lunar retro-reflectors, as well as lunar orbit, gravity field, and its tidal acceleration. LLR data analysis also performs a number of gravitational physics experiments such as test of the equivalence principle, search for time variation of the gravitational constant, and determines value of several metric gravity parameters. These gravitational physics parameters cause both secular and periodic effects on the lunar orbit that are detectable with LLR. Furthermore, LLR contributes to the determination of Earth orientation parameters (EOP) such as nutation, precession (including relativistic precession), polar motion, and UT1. The corresponding LLR EOP series is three decades long. LLR can be used for the realization of both the terrestrial and selenocentric reference frames. The realization of a dynamically defined inertial reference frame, in contrast to the kinematically realized frame of VLBI, offers new possibilities for mutual cross-checking and confirmation. Finally, LLR also investigates the processes related to the Moon's interior dynamics. Here, we review the LLR technique focusing on its impact on Geodesy and Relativity. We discuss the modern observational accuracy and the level of existing LLR modeling. We present the near-term objectives and emphasize improvements needed to fully utilize the scientific potential of LLR. [ABSTRACT FROM AUTHOR]

Several modern solutions of the Mars gravity field have already been obtained from the Mars Gobal Surveyor (MGS) mission, by different NASA teams working at GSFC and at JPL, which also have shown that degree two and three lumped zonal coefficients exhibit time variations related to the seasonal cycle of carbon dioxide exchange between the planet surface and its atmosphere. A new solution of these time variations has been obtained by a third team working in Europe with a totally independent software. Five years of one and two way Doppler, and range tracking data collected by the Deep Space Network have been processed in three day arcs, taking into account all disturbing forces of gravitational and non gravitational origins; for each arc the state vector, drag and solar pressure model multiplying factors, and angular momentum dump parameters are adjusted. The zonal harmonics up to degree five and the k2 Love number are solved for. The zonals are estimated every ten days, or every thirty days in some variants, with a priori uncertainties either on their values or on their changes. The lumped C20 and C30 coefficients show similar patterns as in the anterior US solutions, also in accordance with the variations estimated from the output of a Global Circulation Model and from the HEND instrument on board Mars Odyssey. Annual and semiannual terms have been derived for comparisons and future evaluation in terms of global constraints put on such planetary mass transfer. Finally the values found for k2 (in the range 0.10 - 0.15 depending on the solution strategy) are discussed. [ABSTRACT FROM AUTHOR]

Information on planetary interiors can be obtained from planetary geodesy measurements of global parameters such as the gravity field and the rotation variations (including precession). These properties can be derived from radio science experiments in which Doppler shifts of radio signals between the Earth, planetary landers, and orbiters are measured. A radio link between the Earth and one lander on Mars has been successfully used to constrain the rotation and the precession, and consequently to obtain the moment of inertia of the planet, the global mass repartition, and its seasonal variations. A radio link between the Earth and one orbiter has also been used to determine the gravity field and its time variations. In particular, the tidal Love number k2 has been determined, from which the Martian core has been shown to be at least partially liquid. New missions that involve a space geodesy experiment addressing these topics are presented. A network of landers could probe the interior of the planet through seismic monitoring, magnetic sounding, and measurements of its rotational dynamics by radio science. This would allow the determination of the overall interior structure, including crust, mantle, and core divisions, and the state of the core (liquid/solid, density). Also composition, mineralogy, density, and temperature profiles could be inferred. Information on the interior of terrestrial planets (and large moons) other than Mars has also been determined by using radio tracking of an orbiter. For example, the tidal Love number k2 of Venus was deduced from Magellan's radio science experiment. Future missions such as Messenger and BepiColombo have dedicated onboard planetary geodesy instruments and will provide improved information on the interior of Mercury from Doppler measurements. [ABSTRACT FROM AUTHOR]

A GNSS-based platform for imaging ionosphere and atmosphere (GPFIIA) is being developed at the institute of geodesy and geophysics, Chinese Academy of Sciences, and School of Mathematical and Geospatial Sciences, RMIT University. The GPFIIA will be an important part of a scientific software platform for processing and analyzing a large amount of different types of data associated with ever increasing number of GNSS and low-orbit earth observation satellites. Currently, GPFIIA can combine a voxel-based ionosphere tomographic technique with ground-based and space-based GPS data to image the ionospheric electron density (IED) distribution over the area of coverage, to study the vertical structures and related properties of the ionosphere, as well as improving the accuracy of ionospheric delay correction. Dual frequency GPS data selected from the Crustal Movement Observation Network of China and some simulated GPS/MET data on 1 March 2003 are used to invert a time series of the IED profiles over China using to mographic algorithms. The reconstructed IED profiles were partially validated with those obtained using the IRI2001 model. The inverted results illustrate some active characteristics of the IED. The difficulties yet to be solved for using GPS data to invert the IED profiles in China are discussed and some suggestions are given for further investigation. [ABSTRACT FROM AUTHOR]

Ionospheric scintillation may present significant effects on GPS, mainly in equatorial and auroral regions, and during times of high solar flux. In the auroral regions scintillation occurrence mostly relates to geomagnetic activity and can affect GNSS users even at sub-auroral (and potentially mid-latitude) regions, with impact ranging from degradation of accuracy to loss of signal tracking. Recent work at Nottingham investigated the impact of ionospheric scintillation and Total Electron Content (TEC) gradients on GNSS users, through a network of four GPS Ionospheric Scintillation Monitors set up in the UK and Norway. Statistical analyses of the scintillation and TEC data, aiming to characterise ionospheric scintillation over Northern Europe, were also carried out. Critically to GNSS users these studies covered, in particular, aspects of availability and integrity, through the assessment of occurrence of loss of lock on GPS satellites due to high scintillation levels. However, accuracy aspects have also been investigated, through the analysis of standalone GPS, DGPS, EGNOS aided DGPS and carrier phase errors, which have been correlated with observed scintillation levels and geomagnetic indices. Horizontal errors in GPS C/A code point-positioning were seen to correlate to enhancement in the background TEC observed during times of occurrence of high scintillation. DGPS positioning accuracy was seen to be affected by TEC gradients occurring at auroral and sub-auroral latitudes, especially under enhanced geomagnetic activity. Missing corrections in the EGNOS ionospheric grid during periods of occurrence of high phase scintillation suggested an inability of the EGNOS reference stations to track one or both of the GPS signals of some satellites. In this paper the main focus is on carrier phase positioning experiments, which revealed an increase in the measurement noise and positioning accuracy degradation significantly correlated with the occurrence of high phase scintillation. [ABSTRACT FROM AUTHOR]

Total water vapor contents were monitored along lines of sight at such low elevation angles as 10 and 15 degrees with two water vapor radiometers, WVR1100™, WVR05 and 06. They were installed in two directions of N-S and E-W in Uji city, southwest Japan in the period from 1997 to 99. Results show that differences of wet delays between N and S directions, which correspond to the gradient of wet delays of microwaves, sometimes reach to 3 cm or more and continue to exist stably for a few days or longer. It is ascertained that the horizontal gradient of water vapor distribution in the N-S direction is caused by atmospheric conditions, especially by wind direction and velocity, and also probably by sunlight. Similar correlations are apparent between E-W gradients of wet delay and wind velocity. However, the data is not enough to draw definite conclusions on the E-W component. [ABSTRACT FROM AUTHOR]

Atmospheric refraction is an important accuracy-limiting factor in the use of satellite laser ranging (SLR) for high-accuracy science applications. In most of these applications, and particularly for the establishment and monitoring of the Terrestrial Reference Frame (TRF), of great interest is the stability of its scale and its implied height system. A new zenith delay (ZD) model developed by Mendes and Pavlis, [2004] called FCULzd, along with new mapping functions [Mendes et al., 2002] are now the adopted standard for refraction modeling. The model is valid for a wide spectrum of wavelengths and has showed sub-millimeter accuracies from 0.355 µm to 1.064 µm. Using 3-d ray tracing and globally distributed satellite data from the Atmospheric Infrared Sounder (AIRS) instrument on NASA's AQUA platform, as well as 3-d analysis fields from the European Center for Medium Weather Forecasting (ECMWF) and the National Center for Environmental Prediction (NCEP), we assess the new zenith delay model and mapping function both spatially and temporally. We also investigate the effects of horizontal refractivity gradients on the atmospheric delay, specifically with respect to seasonal changes and station location. [ABSTRACT FROM AUTHOR]

Indonesia has 129 active volcanoes. With a population of approximately 200 million, and the fact that the most populated island in Indonesia (i.e. Java) has the largest number of active volcanoes, then it is obvious that the Indonesian people live under the very real threat of volcanic eruptions. Monitoring volcanic activities can be done by using several methods, of which one of them is the deformation method. In Indonesia volcano deformation has been monitored using Tiltmeter observations, EDM measurements, Levelling Surveys, and Repeated or Continuous GPS Survey techniques. This paper will describe and discuss the implementation status of the GPS survey method for deformation monitoring of Indonesian volcanoes, along with their limitations and prospects. The obtained results and experiences will be presented to illustrate the discussions. [ABSTRACT FROM AUTHOR]

Since troposphere modelling is one of the major error sources in the geodetic applications of Global Positioning System (GPS) and Very Long Baseline Interferometry observations, mapping functions have been developed in the last years which are based on data from numerical weather models. This paper presents the first results with the Vienna Mapping Functions 1 (VMF1) implemented in a GPS software package (GAMIT/GLOBK). The analysis of a global GPS network from July 2004 until July 2005 with VMF1 and the Niell Mapping Functions (NMF) shows that station heights can change by more than 10 mm, in particular from December to January in the Antarctic, Japan, the northern part of Europe and the western part of Canada, and Alaska. The application of the VMF1 (instead of NMF) also improves the repeatability of the geodetic results and reduces seasonal signals in the station height time series. [ABSTRACT FROM AUTHOR]

The use of kinematic GPS for deformation monitoring and now deflection monitoring of structures is an ongoing topic of research. It is now possible to measure the 3D deflections of discrete points upon a structure at a rate of up to 100Hz with GPS alone. The precisions of these results are typically sub centimetre, and real time is possible. However, with the integration of GPS with other sensors such as accelerometers the data acquisition rate can be increased up to 2,000Hz or so. The GPS based deflection measurements have the distinct advantage over other sensors in that GPS doesn't drift, uses precise time and can be used in all weather. The following paper discusses some of the background to this work as well as showing three case studies whereby GPS has been used on bridges to measure the deflection and natural frequencies of the bridges. The bridges investigated are the Nottingham Wilford Suspension Bridge, The London Millennium Bridge and the Humber Bridge. The paper also uses this and previous knowledge to discuss the possible use of such a GNSS based deflection monitoring strategy and combining this with Finite Element Modelling of such a structure to allow a disaster monitoring tool to be developed. [ABSTRACT FROM AUTHOR]

Modern LiDAR systems offer ranging accuracy at 2-3 cm level at scanning rates of up to 100 kHz, assuring high point density that can support demanding mapping applications. However, the high complexity of the system may result in error sources that can degrade the accuracy of the points on the ground; thus, careful calibration and rigid connection among the system's components is crucial. Obviously, GPS/INS accuracy is required at the highest level to guarantee that the high ranging accuracy translates to a comparable accuracy of the collected ground points. One way to achieve the high accuracy required for engineering scale mapping is to use absolute control information in the data. The usual method is to use flat areas with known elevations or measure control profiles. This method, however, can refine only the vertical error, while the planimetric errors are usually more significant. A method proposed here rectifies both planimetric and vertical errors in LiDAR points by using well-identifiable LiDAR-specific ground control targets. This paper discusses the design of the optimal LiDAR targets, including the shape, size, and signal response, as well as the actual performance based on two data sets collected in Ohio, over local highways, using the Optech ALTM 30/70 LiDAR system operated by the Ohio Department of Transportation. A detailed performance analysis investigating the achievable LiDAR data accuracy improvement using LiDAR-specific ground control targets is presented. The point accuracies before and after the LiDAR strip transformation based on the target data points are compared. The preliminary results indicate that LiDAR-specific targets can improve the typical 20 cm or larger planimetric accuracy of the surface points to below the 10 cm level and the vertical accuracy can approach the 2-3 cm level (basically, the laser ranging error). [ABSTRACT FROM AUTHOR]

A moving inertial gravimetric system is now being developed, consisting of three high precision accelerometers measuring accelerations along three non-parallel axes. The system has been designed to make high resolution gravity measurements on motor vehicles, ships or aircraft at mGal level of precision. Position, velocity and attitude of the platform, needed for computing acceleration corrections, are provided by a 4-antenna GPS system rigidly mounted on the platform with a sampling rate of 1 or 2 Hz. Because acceleration and GPS measurements are not made at the same point, the signals derived from the accelerometers have to be corrected for lever arm effect. To this end, we derived the complete relationship connecting accelerometer and GPS measurements. The correction for the lever arm effect requires the computation of seven acceleration terms. The amplitude of the lever arm effect depends not only on the lever arm length, but also on the platform attitude. Our own findings based on both simulations and real measurements suggest that some of the seven lever arm terms have to be considered to reach a few mGals precision for gravity. We present a reliable method to assess the precision that can be achieved for lever arm effect determination given the precision of attitude and lever arm measurements. [ABSTRACT FROM AUTHOR]

This paper provides a review of a 3-year research program on the feasibility of using airborne LiDAR (Light Detection and Ranging) and imagery collected simultaneously over transportation corridors for estimation of traffic flow parameters such as: (1) vehicle counts, (2) vehicle classification, (3) velocity per vehicle category, and (4) intersection movement patterns. This work is conducted by The National Consortium for Remote Sensing in Transportation-Flows (NCRST-F), led by The Ohio State University, supported by the U.S. Department of Transportation and the National Aeronautics and Space Administration (NASA). The major focus is on improving the efficiency of transportation systems by integration of remotely sensed data with traditional ground data to monitor and manage traffic flows. The two primary research activities presented in our earlier publications were the accuracy and reliability of the sensor geolocation/georegistration and the image processing and object modelling. This paper is a summary overview of the NCRST-F research accomplishments over that past three years. The emphasis is on the demonstration of the operational/processing capabilities, while the algorithmic developments and implementation were published earlier in several papers cited here. Recent enhancements in spatial and temporal resolution of LiDAR data can now allow for effective detection and tracking of moving objects. Thus, in this paper, a special focus is on the LiDAR-based traffic flow extraction techniques. The methodology of extracting vehicle information together with the road surface modelling supported by precisely georeferenced LiDAR data augmented by LiDAR intensity information is discussed. We demonstrate that algorithms developed under the NCRST-F program are capable of fast and robust identification of the vehicles by their shape (especially the vertical profiles), proving LiDAR's ability to preserve the geometry of a moving object better as compared to conventional imaging, where the projection from 2D to 3D can significantly distort shape in the image domain. We demonstrate that if LiDAR data of sufficient spatial density are available, vehicle extraction and their classification can be effectively performed simultaneously with efficient and automated road surface extraction and modelling. It is shown, however, that for better accuracy and reliability, a fusion of LiDAR with frame image data is desirable. The examples of the vehicle extraction and the road surface modelling are based on two high-density (2-4 points/m2) LiDAR datasets collected on February 19, 2004 over the downtown Toronto area, and on December 2, 2004 over the U.S. Route 40 in the Madison County, OH calibration range, with the Optech ALTM 30/70 LiDAR system. High-accuracy georegistration of the LiDAR data was provided by the Applanix POS AV system (http://www.applanix.com/). [ABSTRACT FROM AUTHOR]

The standard description and modelling of the normal behaviour of structures under influence of factors like temperature or tides is done by means of correlation functions and power spectra that assume the condition of stationarity of the observed process. As a consequence of influencing parameters with highly irregular patterns, aging or damage to the structure the measured reaction of the structure may have non-stationary characteristics. Hence these functions give only a coarse description of the object's reaction and more detailed analysis techniques are needed. For these cases a method of data analysis based on the discrete wavelet decomposition and variance homogeneity testing of the wavelet coefficients is applied in this paper. After identifying the frequencies with high energy in a spectral analysis, the signal is decomposed on a scale base in order to analyse the different stationary and non-stationary components separately. The wavelet coefficients of each scale are separated into intervals with homogeneous variance by performing a test based on the cumulative sum of squares. The amplitude and phase shift of the detected frequencies are calculated for each interval in an adjustment step. Finally, using the modelled data the signal is reconstructed by wavelet synthesis. Because the wavelet transform is done without loss of information, an objective evaluation of the modelled data is possible. Continuously recorded tilt measurements at the tower of a wind energy plant were analysed both in the classical manner and with the proposed method, in order to test the latter's performance. It is shown that the new method performs well and lowers the standard deviation of the residuals by 30%, while the standard procedure does not remove the high energy components. [ABSTRACT FROM AUTHOR]

Several tasks in structural deformation monitoring require real-time or near real-time data acquisition methods. In one case, a lock gate is being deformed within a time period of 14 minutes due to the change of the water level inside the lock. In order to accomplish a comprehensive monitoring of the gate's deformations, the high speed laser scanner Z+F Imager 5003 has been used. The main advantage of this procedure is that object deformations and the corresponding variances can be derived without reflectors and with data acquisition rates of up to 500,000 points per second. The gate was scanned completely at different stages as well as in horizontal profiles at high speed. The analysis of the observed deformations was carried out by using methods from statistics such as Principle Component Analysis, which is well suited for the analysis of the interrelations of multiple data series. For this purpose, the object data was segmented into equally spaced blocks, which were treated as realizations of a time series. In combination with derived statistical measures, it was possible to determine the regions of the object which were mainly affected by deformations. [ABSTRACT FROM AUTHOR]

There has already been much research on how the kinematic and geodynamic behaviour of landslides can be predicted. However, until now, there has been no decisive breakthrough for a monitoring and evaluation system combined with an alert system. Therefore an interdisciplinary international project OASYS (Integrated Optimization of Landslide Alert Systems) was commenced to progress research in this area. The members of the project, supported by the European Union, believe a multidisciplinary integration of different methods has potential for substantial progress in natural hazards management. This project proposes a new method consisting of three different steps: 1.Detection of boundary lines of potential landslides based on large scale information.2.Detection of "taking-off-domains" and permanent local scale monitoring of these regions with high sensitivity geotechnical measurement methods.3.Knowledge-based derivation of real time information regarding actual risks to support alert systems. Following the methodology of the OASYS project, a mathematical method for the detection of taking-off-domains and the concept of a knowledge-based alert system is described in this paper. [ABSTRACT FROM AUTHOR]

The International Laser Ranging Service (ILRS) was established in September 1998 as a service within the IAG to support programs in geodetic, geophysical, and lunar research activities and to provide data products to the International Earth Rotation and Reference Systems Service (IERS) in support of its prime objectives. The ILRS develops the standards and specifications necessary for product consistency and the priorities and tracking strategies required to maximize network efficiency. This network consists of more than forty SLR stations, routinely tracking nearly thirty retroreflector-equipped satellites and the Moon in support of user needs. The Service collects, merges, analyzes, archives and distributes satellite and lunar laser ranging data to satisfy a variety of scientific, engineering, and operational needs and encourages the application of new technologies to enhance the quality, quantity, and cost effectiveness of its data products. The ILRS works with the global network to improve station performance, new satellite missions in the design and building of retroreflector targets to maximize data quality and quantity, and science programs to optimize scientific data yield. The ILRS Central Bureau maintains a comprehensive web site (http://ilrs.gsfc.nasa.gov) as the primary vehicle for the distribution of information within the ILRS community. During the last few years, the ILRS has addressed very important challenges: (1) Data from the network stations are now submitted hourly and made available immediately through the data centers, (2) Tracking on low orbit satellites has been significantly improved through the sub-daily issuance of predictions, drag functions, and the real-time exchange of time biases, (3) Analysis products are now submitted in SINEX format for compatibility with the other space geodesy techniques, (4) The Analysis Working Group is now generating an operational station position and Earth Orientation Parameter (EOP) product, and (5) SLR has significantly increased its participation in the International Terrestrial Reference Frame (ITRF) activity. [ABSTRACT FROM AUTHOR]

At the Fundamental Station Wettzell a wide range of geodetic measurement systems has been installed: an array of six different GNSS receivers, superconducting gravimeter, ring laser, 20 m radio telescope for VLBI and a Satellite Laser Ranging System. The precise ring laser "G", operated in an underground laboratory, is able to directly measure polar motion. Signals down to 10−8 of the Earth's rotation rate can be detected continuously. Due to the high relative resolution of 10−11 and the small drift of the instrument the superconducting gravimeter is able to detect e.g. the seismic induced eigenmodes of the Earth. Additionally, seismometers and tilt meters are also operated at the station. The Sumatra-Andaman earthquake on December 26, 2004, 0:58 UTC was one of the largest earthquakes ever and the first one of this magnitude (> 9.0) since continuous earthquake monitoring. It will be described how the different sensors at Fundamental Station Wettzell record the signals induced by the seismic waves. While deformation due to an earthquake in terms of elastic rebound could only be detected in local or regional distances to the centre of the earthquake by means of GPS, the horizontal deformation due to seismic surface waves was large enough to be analysed with highrate GPS data even 9000 km apart from the centre. The rotational component of the seismic waves is clearly recorded by the ring laser "G" which is the only type of instrument being able to measure this quantity. The results of the different sensors will be compared, the benefit of each sensor referred to seismic waves will be summarized. Conclusions for further investigations with respect to the Global Geodetic Observing System (GGOS) will be discussed. [ABSTRACT FROM AUTHOR]

The Nordic Geodetic Observing System (NGOS) integrates fundamental geodetic techniques for the long-term observation of Earth system parameters. The Nordic Geodetic Commission (NKG) established a Task Force with the mission to prepare a document providing the definition and draft for the implementation of the NGOS. The regional system aligns with international efforts such as the Global Earth Observation System of Systems (GEOSS) and Global Observing Systems and adheres to the Integrated Global Observing Strategy (IGOS). Recent developments in the structure and function of the International Association of Geodesy cumulated in the establishment of the Global Geodetic Observing System, GGOS. NGOS is planned as a regional implementation and densification of the GGOS. The NGOS is proposed as a system that will serve a wide range of scientific and practical applications. For the Nordic countries, a main focus will be on crustal motion, dynamics of glaciated areas and sea level. NGOS aims to provide geodetic observations for the Nordic area that are of sufficient quantity and quality to serve most of the needs of global Earth observation as well as practical and scientific applications in the region. In particular, NGOS will contribute to the GGOS and other IAG Services; European activities such as EUREF, ECGN, EUVN, and ESEAS; provide the reference frames for the Nordic countries, as well as contribute to the global ones; support scientific projects related to the geodynamics of the Nordic area and provide ground-truth for satellite missions. In this paper we describe the plans and current status of the NGOS. [ABSTRACT FROM AUTHOR]

When setting up GGOS as a project, the IAG Executive Committee asked the GGOS Steering Committee to establish a relationship with IGOS-P. IGOS-P addresses a number of problems and components of Earth observing systems in the frame of specific Themes. The IGOS-P Theme process will also be an important mechanism for the development of the components of the Global Earth Observation System of Systems (GEOSS). Many of the burning questions related to the water cycle, the climate, global change, and geohazards cannot be solved without sufficient knowledge of mass transports throughout the Earth system and the associated dynamics. All these processes affect the three fundamental geodetic quantities, namely the Earth's figure (geometry), its gravity field and its rotation. Thus, GGOS is an unique contribution to Earth observation in its capability to provide detailed information on the dynamics of the solid Earth and its fluid envelop on all relevant spatial and temporal scales. Focusing on the observing system for the mass transports within the Earth system the suggested ‘Earth System Dynamics' Theme has the goal to develop the science basis for and to facilitate the implementation of GGOS. The Theme will define the role of GGOS, the underlying strategy and its interface to the other components of GEOSS. The interaction of GGOS with the other IGOS-P Themes will facilitate the full exploitation of the geodetic contribution by all other global observing systems. The Theme will ensure that GGOS meets the user requirements both from the IGOS-P Themes and the nine societal benefit areas identified by the Earth Observation Summit II. [ABSTRACT FROM AUTHOR]

Properly designed and structured ground-based geodetic networks materialize the reference systems to support sub-mm global change measurements over space, time and evolving technologies. Over this past year, the Ground Networks and Communications Working Group (GN&C WG) has been organized under the Global Geodetic Observing System (GGOS) to work with the IAG measurement services (the IGS, ILRS, IVS, IDS and IGFS) to develop a strategy for building, integrating, and maintaining the fundamental network of instruments and supporting infrastructure in a sustainable way to satisfy the long-term (10-20 year) requirements identified by the GGOS Science Council. Activities of this Working Group include the investigation of the status quo and the development of a plan for full network integration to support improvements in terrestrial reference frame establishment and maintenance, Earth orientation and gravity field monitoring, precision orbit determination, and other geodetic and gravimetric applications required for the long-term observation of global change. This integration process includes the development of a network of fundamental stations with as many co-located techniques as possible, with precisely determined intersystem vectors. This network would exploit the strengths of each technique and minimize the weaknesses where possible. [ABSTRACT FROM AUTHOR]

VLBI provides highly accurate and unique products for the realization and maintenance of the celestial and terrestrial reference frames, ICRF and ITRF, as well as for the Earth Orientation Parameters. In 2001 the products were reviewed with respect to obtaining highest accuracy and to improving the observing sessions in order to make best use of the resources which are made available by the IVS member institutions. Since 2002 improved observing sessions were coordinated by the IVS aiming at fast turn-around products for EOP and better products for TRF and CRF. The number of observations increased by more than 30% from 2002 to 2004. New products, e. g. the troposphere zenith path delay, are now being generated. Concerns about the aging technology, which has been used for the past three decades, and about radio interference problems that decrease the number of useable observations, led to the establishment of IVS Working Group 3. The working group was asked to examine current and future requirements for geodetic VLBI, including all components from antennas to analysis, and to create recommendations for a new generation of VLBI systems. The results are summarized in a vision paper, VLB12010 (Niell et al., 2005), which is recommended for coordination of new developments in VLBI and for plans to invest in new components by member institutions. This paper reviews IVS activities of recent years and gives a perspective about new developments for meeting future requirements, which are set up by GGOS. [ABSTRACT FROM AUTHOR]

The Geodesy Subcommitee of the National Committee of IUGG created the working group "Geopotential Origin" in December 2000 in order to coordinate the national activities, establish and set down a new Vertical Reference System and to interact with Group III of SIRGAS (Geocentric Reference System for the Americas) Project. For that, all the activities were organised in four items. This contribution describes the main results obtained in each of them as well as future tasks for the near future: Tide Gauges: The origin of the Argentine Vertical Reference System, defined by means of tide gauge records, is affected by the sea surface topography at the gauge locations. A project to observe and model the sea level variations using both, tide gauges and satellite altimetry, is being carried out since 1998. Four permanently observing GPS stations have already been installed close to gauges along the Argentine Atlantic coast and integrated in the International GPS Tide Gauge (TIGA) Monitoring Project.Geopotential Numbers: All first order levelling network unadjusted height differences were migrated to digital media and merged with the benchmark positions and gravity values. The resulting database consists of 16,000 level differences distributed along about 3,170 lines. Gravity values are missing for 20 percent of the benchmarks. The data set is currently being checked for consistency.Linking of Altimetric Networks from Neighbour Countries: During 2002 the first link between the altimetric networks of Chile and Argentina was done. The result was a difference of 22 cm, the higher value corresponding to Argentine levelling lines. The border point, where the levelling lines of both countries are connected, is Puesto Monte Aymond, near Estrecho de Magallanes in the south extreme of South America. The corresponding activities in order to make two or three new comparisons along the 5,000 km long borderline between these countries are being coordinated.Recently, the determination of a natural water surface (Fagnano Lake) was used like an equipotential surface to connect the altimetric networks of Chile and Argentina where the classical spirit levelling is not accessible due to the lack of roads.Compensation of Height and Gravity Networks: Adjustment of the national gravity and altimetric networks and their linking with the nets of neighbouring countries are in progress, including both new absolute and relative gravity determinations, which are necessary for the adjustment and optimisation processes. [ABSTRACT FROM AUTHOR]

The Global Geodetic Observing System (GGOS) is going to be the interface between the IAG services and a wide range of external users ranging from the Global Earth Observation System of Systems(GEOSS) over the European Global Monitoring for Environment and Security (GMES) Programme and the Themes of the Integrated Global Observing Strategy Partnership (IGOS-P) to practical application in monitoring of infrastructure and the control of processes. Taking the user requirements (UR) compiled by the different IGOS-P Themes and GEOSS as a starting point, a detailed set of URs for the GGOS products is derived. The URs are specified in terms of spatial and temporal resolution, accuracy, and latency. The analysis of the URs reveals that GGOS is facing a rather demanding set of URs ranging from high accuracy observations of the Earth's surface displacements in near-real time to long-term observations of Earth system parameters such as gravity, Earth's rotation and sea level over several decades. In order to integrate GGOS into on-going programs such as GEOSS and IGOS-P and to enable users to fully exploit the products and services offered by GGOS, outreach activities are a central issue for GGOS, including educational measures. A suggested IGOS-P Theme centered around mass transports in the Earth system and the associated dynamics has considerable potential to achieve the integration of GGOS into the main global Earth observation programs and to enable the full implementation of GGOS. [ABSTRACT FROM AUTHOR]

Geodesy is the science of measuring and mapping the Earth including the associated variations with time. The Global Geodetic Observing System (GGOS) as the "flagship" of the International Association of Geodesy (IAG) aims at the coordination and integration of the corresponding observations in order to generate a uniform set of geodetic parameters for monitoring the phenomena and processes in the System Earth. Coordination means to bring the different geodetic observing techniques and analysis methods together for a consistent performance. The same standards, conventions, models and parameters have to be used in the reduction of observations and in the data analysis for producing compatible results in identical reference systems. Integration implies the inclusion of all relevant information for parameter estimation. The elements of the System Earth are transmitting a variety of signals observable by geodetic techniques. They all have to be considered in a combined analysis. This comprises in particular the integration of geometric and gravimetric data, and the common estimation of all the necessary parameters representing the solid Earth, the hydrosphere (including oceans, ice-caps, continental water), and the atmosphere. Geometric parameters describe primarily the shape of the Earth and its deformation; the gravimetric parameters are functions of the Earth's mass distribution. Considering these facts, the scientific rationale of GGOS is focussing on the central theme "Global deformation and mass exchange in the System Earth". [ABSTRACT FROM AUTHOR]

Analysing time series of space-geodetic station coordinates, we show that VLBI, SLR and DORIS station motions have a white noise error spectrum, while the majority of GPS station motion have a flicker noise error spectrum. In the latter case, discontinuities in the series do not account for this spectrum. Atmospheric loading has a white noise spectrum, at a much lower level than geodetic measurement errors in the long term. The series of transformation parameters derived for the GPS colocation sub-networks with VLBI, SLR and DORIS have very close spectral characteristics, reaching the 1 mm stability level at one-year interval in a white noise context. [ABSTRACT FROM AUTHOR]

Unlike the previous versions of the International Terrestrial Reference Frame (ITRF), the ITRF2005 will be constructed with input data under the form of time series of station positions and Earth Orientation Parameters (EOP's). This paper presents some preliminary results of the analysis of the time series submitted to the ITRF2005, focusing on the frame parameters and in particular the origin and the scale, as well as the EOP alignment to the combined frame. Quality assessment of the preliminary combinations is addressed in view of the ITRF2005 official solution. [ABSTRACT FROM AUTHOR]

In this paper we analyze the errors introduced by the use of transformation grids. A transformation grid is an intermediate step during the transformation of coordinates of points attached to distinct geodetic reference frames. The use of transformation grids simplifies the transformation when compared to the reference transformation that the grid represents. Transformation grids have become a standard way of making transformation distortion models available for end-users. They are widely accepted by the GIS industry, being already supported by a host of commercial and free programs. They are adopted in countries like Canada and Australia, and are currently being considered for adoption in Brazil. The work described in this paper was conducted by addressing a number of questions in the following sequence: (i) "Is there an upper bound in the error introduced by a transformation grid?"; (ii) "What is the coarsest spacing between nodes for a transformation grid to introduce only negligible errors?"; and, (iii) "How does the error introduced by a transformation grid vary spatially?" To answer these questions we transformed a set of random test points twice, once using a transformation grid and once using the reference transformation that the grid represents. Then, we analyzed the difference between the two results. We show that: (i) yes, there is an upper bound in the error introduced by the grid; (ii) the coarsest spacing can be found by plotting error versus distance to nearest grid node; and, (iii) the error varies spatially partially in proportion to the norm of the second derivative of the reference transformation. [ABSTRACT FROM AUTHOR]

The concept of dynamic datum, in which the coordinates of sites change as a function of time, was relied on to estimate the regional land movement functions for any geodetic or mapping applications. The test area was selected for a deformation active island, Taiwan, and categorized into several regions depending on the similar pattern of the horizontal land movement. The velocity field computed for the Taiwan area was based on the coordinates of first-order control stations measured in 1997 and 2000, both using high precision GPS. The regional movement functions derived from the velocity information can then be estimated with several mathematical models, e.g. averaging, weighted mean and surface fitting. Furthermore, those regional functions were practically applied to estimate and examine the horizontal coordinate movement in the test regions. It is further expected to utilize those regional functions to assess the coordinate qualities of the control stations over a period of time, in order to determine an applicable duration for the geodetic maintenance. It is realized from the internal errors that the horizontal movement velocity obtained using the regional functions based on a second-degree surface fitting model are tested to be better than 0.4 cm/yr. When these regional functions were tested with another independent set of GPS-based coordinates measured in 2002, the external estimation errors of those regional functions were assessed to be approximately 1.7 cm/yr in all test regions. It is, hence, suggested that the coordinate accuracy of the first-order GPS control stations in the Taiwan area can only be maintained for no more than 4 years. In addition, the revision of 1/1,000 digital maps is estimated to be probably required for every 10 years when regional land movement, instead of the topographic changes, is taken into account. [ABSTRACT FROM AUTHOR]

With the adoption of the Geocentric Reference System for the Americas (SIRGAS), the determination of temporal variations and deformations in its frame are a necessary task. These tasks are fundamental in order to maintain the consistency of the frame with respect to the definition of SIRGAS, especially in the Chilean deformation area, where the variations are larger compared with the rest of the plate due to the convergence between the South American and Nazca plates. 21 permanent GPS stations was used. 14 of them are regional stations of the International GNSS Service (IGS), and 7 permanent GPS stations are from different regional networks. 10 of these 21 stations are located in the Chilean Andes were used to study the kinematic effects in this area. Some of them are also SIRGAS stations. Five years of GPS observations from 2000 to 2004 were selected in order to have a sufficient time period with enough coverage for the considered stations. Daily solutions were generated with the Bernese GPS Software 5.0 using IGS precise ephemeris, clocks and ERP. The normal equations were then accumulated and solved in a final combination where the coordinates and velocities of selected stations are weighted for the datum definition compatible with ITRF2000. The estimated velocities of the north Chilean Andes regions are ∼26-30 ± 2mm/yr, decreasing up to ∼16-25 ± 2mm/yr and for the south Chilean Andes the estimated velocities are ∼9-12 ± 2mm/yr. For the stable part of the continent the estimated velocities are ∼8-12 ± 2mm/yr. The final results are discussed and compared with the NUVEL-1A and SIRGAS velocity models (SIRGAS-VM). [ABSTRACT FROM AUTHOR]

Since the beginning of its establishment, in December of 1996, the Brazilian Network for Continuous Monitoring of GPS - RBMC has been playing the role as the fundamental geodetic frame in the country, providing users with a direct connection to the Brazilian Geodetic System - SGB. This role has become more relevant with the adoption of the new geodetic system, SIRGAS2000, as of February 25, 2005. In this paper, the current RBMC status is presented, as well as the expansion and modernization plans for its structure, functionality and services to be provided to users. RBMC currently works in post-mission mode, where users are able to freely download from the Internet data collected by each of its 19 stations 24 hours after the observations are collected. The modernization plans specify, in a first step, the network expansion with six additional stations in the Amazon region, including the reactivation of Manaus station, and the connection of all stations to the Internet, to support real time transfer of 1 Hz data to the control center, in Rio de Janeiro. When available at the control center, the data will support WADGPS (Wide Area Differential GPS) corrections to be transmitted, in real time, to users in Brazil and surrounding areas. This new service is under development based on a cooperation signed at the end of 2004 with the University of New Brunswick, supported by the Canadian International Development Agency and the Brazilian Cooperation Agency. It is estimated that users will be able to achieve a horizontal accuracy around 0.5 m (1-σ) in static and kinematic positioning. The expected accuracy for dual frequency receiver users is even better. The availability of the WADGPS service — at no cost -will allow users to tie to the new SIRGAS2000 system in a more rapid and transparent way in positioning and navigation applications. It should be emphasized that support to post-mission static positioning will continue to be provided to users interested in higher accuracy levels. [ABSTRACT FROM AUTHOR]

In its function as an ITRS Combination Center, DGFI has developed refined methods for the terrestrial reference frame computation. The advanced approach is based on the combination of epoch normal equations (weekly/daily data sets) containing Station positions and Earth orientation parameters (EOP) obtained from different geodetic space techniques such as VLBI, SLR, GPS and DORIS. This refined approach allows to account for nonlinear effects (e.g., periodic signals and discontinuities) in Station positions and to ensure consistency between TRF and EOP. The ITRF2004 submissions were used as input for a refined realization of the terrestrial reference frame. This paper presents the combination methodology and the current Status of the ITRF2004 computations at DGFI. [ABSTRACT FROM AUTHOR]

The integration of gravity data within the Brazilian leveling network is very difficult due to the historical dissociation between leveling and gravity surveys. This research was started, in the context of SIRGAS Project, to resolve this problem by evaluating different strategies and procedures with the aim of establishing some kind of gravity coverage over vertical reference stations. Data employed in this article comes from one of the few areas where the points of the Brazilian fundamental leveling network are entirely covered with gravity surveys and, in addition, connect three permanent GPS stations, two of which belong to the SIRGAS 2000 Reference Network. This will allow for several analyses regarding the Brazilian realization of SIRGAS Vertical System, including: an evaluation of the effects of adopting different types of heights; and the investigation of strategies and procedures to solve the absence of gravity values over benchmarks. Values of geopotential differences were computed and adjusted, for a 2300 km network consisting of six loops with perimeters ranging from 136 km to 690 km. Dynamic, Helmert, Normal and Normal-Orthometric reductions were generated and compared. The status of the development of a GIS designed for the tasks involved in geopotential numbers computation to be applied in the studies related to the SIRGAS Vertical Reference System is also presented. [ABSTRACT FROM AUTHOR]

The new SIRGAS vertical reference system is based on the determination of an equipotential reference surface W0 within a global definition, i.e. optimally fitting the worldwide mean sea surface. The corresponding W0 value (mean geopotential value over the total ocean surface) is empirically estimated using different combinations of global gravity models (EGM96, TEG4, GGM02S, EIGEN-CG03C) and mean sea surface models (CLS01, KMS04, GFSC00.1 and a series of annual models from 1993 to 2001 derived at DGFI from T/P). The results show the W0 dependence on the GGM's degree n, on the latitudinal extension, and on time. The recommended W0 value (62 636 853,4 m2s−2) is derived from EIGEN-CG03C (n = 120) and referred to the epoch 2000.0. It differs from previous computations by 3 m2s−2 (e.g. Bursa et al. 2002, Bursa et al. 2004). A preliminary realisation of this new reference level is accomplished by transforming the existing South American classical height datums (defined individually at different tide gauges) through the combination of GNSS positioning, high resolution (quasi)geoid models and physical heights derived from spirit levelling and terrestrial gravity data. [ABSTRACT FROM AUTHOR]

The New Zealand Geodetic Datum 2000 (NZGD2000) has an associated deformation model that allows horizontal coordinates to be reduced to a reference epoch of 2000.0 and is therefore a semi-dynamic datum. Currently, the deformation model does not account for either discrete or continuous horizontal deformation that can be associated with localised events such as earthquakes and landslides. Such events will distort the geodetic network by as little as a few millimetres a year, or as much as several metres in a matter of seconds. Using the August 2003 M 7.2 Fiordland earthquake as a case study, we demonstrate the implementation of a Localised Deformation Model (LDM) into the NZ National deformation model. LDMs employ triangulated interpolation techniques that predict surface displacement. In the Fiordland earthquake, eleven existing monitoring sites were resurveyed immediately following the earthquake and movements of up to 17 cm were observed. To model the associated co-seismic deformation, a LDM was generated from surface displacements predicted by a dislocation model of the earthquake. The LDM covered an area of approximately 56,000 km2. The implementation of a LDM into the NZGD2000 deformation model was successfully demonstrated. [ABSTRACT FROM AUTHOR]

The New Zealand Geodetic Datum 2000 (NZGD2000) is a semi-dynamic datum, in that coordinates are fixed to their values at 1 January 2000 and velocities from a horizontal deformation model are used to transform the coordinates of data collected before or after that date. The deformation model was calculated from GPS campaign data collected between 1991 and 1998, and was aligned with ITRF96. We examine the performance of this model in 2005 from two points of view: (1) how different are the ITRF2000 velocities from 1TRF96, and (2) for new stations, and older stations where additional data have been collected, how well do the newly estimated velocities match those in the deformation model (after the ITRF96-ITRF2000 transformation)? We have calculated ITRF2000 velocities at points throughout New Zealand. The ITRF96 and ITRF2000 velocities differ by 4.8 mm/yr at azimuth −101° in the southwest of the country, and by 5.4 mm/yr at azimuth −111° in the northeast. The differences between newly-calculated ITRF2000 site velocities and velocities from the deformation model transformed to ITRF2000 range between zero and about 4 mm/yr. Velocities of some continuous GPS stations installed in the past few years differ by more than this (in two cases by >7 mm/yr), in part because the new velocities cannot be estimated reliably from relatively short spans of data, and in part because the velocities at some sites are not linear. Significant vertical velocities up to a few mm/yr are estimated for continuous GPS stations that have been established for at least four years. These comparisons suggest that an upgrade to the deformation model should be considered. Alignment of the deformation model with ITRF2000 (or its successors) will have benefits in combining newly collected data with existing data, as the ITRF96 to ITRF2000 transformation step will no longer be needed. [ABSTRACT FROM AUTHOR]

The U.S. Naval Observatory (USNO) and the Australia Telescope National Facility (ATNF) are collaborating in a continuing VLBI research program in Southern Hemisphere ICRF source imaging and astrometry using USNO, ATNF and ATNF-accessible facilities. These observations are aimed specifically toward improvement of the International Celestial Reference Frame (ICRF) in the Southern Hemisphere. We present the contributions of this program to the densification of the ICRF in the Southern Hemisphere and the imaging of all southern hemisphere ICRF sources for calculation of a "structure index". The impact of both these contributions to the improvement of the ICRF in the Southern Hemisphere will be discussed. [ABSTRACT FROM AUTHOR]

Extragalactic radio sources, such as those that define the International Celestial Reference Frame (ICRF), display a variety of structure down to milliarcsecond scales. Further they are all variable on scales of years to weeks. This departure from the point source approximation introduces error in the observable variables (dc-lay and rate). The effect of source structure on Position can be as large as tens of milliarcseconds (e.g. [4]). Also, as the structure of these sources varies with time, it is important to image them at several epochs in order to define a time dependent source model. Multi-epoch observations, using the Very Long Baseline Array (VLBA) to image northern hemisphere sources and the Australian Long Baseline Array (LBA) to image southern hemisphere sources have been progressing successfully for a few years. However, the need for such extensive monitoring programs could be dramatically reduced if a population of extragalactic radio sources that have little or no milliarcsecond scale structure was available. Very Long Baseline Interferometry (VLBI) observations of extragalactic radio sources which exhibit interstellar scintillation suggest that such sources are among the most compact in the sky. In particular, the most variable weak sources, might be the most point-like and, thus, some of the best candidates for densification of the ICRF and consequent improvement in its accuracy. Further, the advent of the MarkV VLBI recording System, with its enhanced sensitivity, will make use of weaker sources easier. We present the evidence for and discuss the viability of this idea which has the potential to revolutionize future Upgrades of the ICRF. [ABSTRACT FROM AUTHOR]

A new theory is presented for calculating co-seismic strain caused by four independent types of seismic source in a spherically symmetric, non-rotating, perfectly elastic, and isotropic (SNREI) Earth model. Expressions are derived by introducing strain Green's functions. A proper combination of these expressions is useful to calculate co-seismic strain components resulting from an arbitrary seismic source at any position in the Earth. Numerical computations are performed for four independent sources at a depth of 32 km inside the 1066A Earth model. Results in the near field agree well with that calculated for a half-space Earth model. A case study is performed and Earth model effects are investigated. Furthermore, the effects of spherical curvature and the stratified structure of the Earth in computing co-seismic strain changes are also investigated using the present dislocation theory and Okada's (1985) formulation. Curvature effects are small for shallow seismic events, but they are larger for greater source depths. Stratified effects are very large for any depth and epicentral distance, reaching a discrepancy greater than 30% almost everywhere. [ABSTRACT FROM AUTHOR]

At the XXIII General Assembly of the International Astronomical Union (IAU) held on 20 August 1997 in Kyoto, Japan, the International Celestial Reference Frame (ICRF) was adopted as the fundamental celestial reference frame. The ICRF is currently defined by the radio positions of 212 extragalactic objects. Since its inception there have been two extensions to the ICRF. Current efforts toward ICRF maintenance include both analysis and observational improvements and an effort is now underway to define a second realization of the ICRF by the year 2009. [ABSTRACT FROM AUTHOR]

For the purpose of modernization of the vertical datum in Canada, rates of change of geoid and orthometric height are computed independently of postglacial rebound simulations. The designed procedure is based on the general least-squares collocation approach and uses as input rates of change of absolute gravity and absolute vertical motion velocities. The procedure is applied in a stepwise manner in order to account for new available data. The predicted geoid rate has a peak value of 1.3-1.4 mm/yr over Hudson Bay and agrees within the computational accuracy, i.e. ±0.1 mm/yr, with the postglacial rebound simulated rate. The predicted rate of change of orthometric height has the general pattern of the vertical motion of the rebounding crust, but also shows some local effects mainly inherited from the rates of gravity data, e.g., the uplift predicted over Southern Alberta as a result of the strong negative gravity rate signal and the subsidence in the Mackenzie River delta. It is found that the achieved prediction accuracy of ±2.4 mm/yr can be increased by using more accurate GPS velocities and extending their coverage to the north as well as incorporating precise relevelled data. Also, improvement is expected from using vertical velocities from a combination of tide gauge records and satellite altimetry sea surface heights. [ABSTRACT FROM AUTHOR]

We present the recent dynamic crustal movements in the Tokai Region, Central Japan, observed by Global Positioning System (GPS) measurements. Since October 2000 the abnormal crustal movements began to move southeastward in the area inland Tokai Region, the reverse motion to the secular crustal movements, suggesting the slow slip between the subducting Philippine Sea slab and the subducted southwest Japan (SWJ). The abnormal crustal movements were fast and wide during October 2000 and December 2001, and slow and narrow during January and December 2002, and again fast and wide during January 2003 and April 2004. Since around June 2004, the abnormal crustal movements became again slow and narrow, and then in September 2004 a M7.4 earthquake occurred at around 200 km southern southwest of the Tokai Region near the Nankai Trough. Co-seismic motions are southward 10-30 mm displacement in the Tokai Region. Since the occurrence of the earthquake the southward motion began in the southeast end of SWJ including the Tokai Region. On the other hand the abnormal crustal movements are still ongoing to be slow and narrow. [ABSTRACT FROM AUTHOR]

The recent Mw = 9.3 Sumatra-Andaman earthquake on December 26th 2004 has strongly excited the low-frequency seismic modes of the Earth. In particular the large amplitude of the fundamental radial mode 0S0, which consists of a roughly uniform compression and dilatation of the whole Earth, and of the seismic core modes, like 3S2, means that much energy was radiated toward the core. Also the degree one mode 2S1, which corresponds to a translation of the core in the mantle, was clearly observed for the first time without any stacking process on seismometers and on gravimeters. 2S1 is the first harmonic of the degree one mode 1S1, the so-called Slichter triplet. In fact, the Slichter mode is not an elastic spheroidal mode like 2S1 since its main feedback force is the Archimedean force. The Slichter mode corresponds to a translation of the solid inner core inside the fluid outer core. The theory concerning this mode is still poorly constrained and no convincing detection has been suggested yet. This paper presents theoretical predictions of the amplitude of the Slichter mode after the 2004 Sumatra-Andaman earthquake as well as after some largest events in the past decades. The computation is based on the usual normal mode theory for a spherically symmetric non-rotating Earth model. The source parameters are finally investigated to find the optimal seismic mechanism to excite the translational motion of the inner core. [ABSTRACT FROM AUTHOR]

Although hydrological effects on gravity are known nearly as long as the influence of barometric pressure, they are not as well understood as the latter. The improvement of gravity data quality during the last years adds weight to the importance of understanding the hydrological influence. Moxa observatory is one station at which studies regarding hydrological effects are carried out. From soil moisture, water level and meteorological observations the effects of different hydrological contributors including snow can be modelled and compared to the gravity residuals of the superconducting gravimeter (SG). The total peak-to-peak amplitude amounts to 35 nm/s2. Contributions from the various areas around the observatory partly compensate due to the hilly morphology. The comparison between residuals and computed total hydrological effect yields a good agreement, but also shows that not all hydrological influences have been taken into account. A significant additional hydrological influence is due to the hill flank near the SG. Besides the possibility of giving an additional constraint to water balance computations, gravity observations might become of interest to hydrologists studying interflow processes. A local gravity network was established around Moxa observatory in order to find out whether slow, e.g. season-related hydrological changes or large-scale fluctuations as caused by snow melt can be detected by repeated gravity measurements. From the six campaigns carried out so far a trend becomes visible: Wet conditions lead to a decrease in the gravity differences between observation points at the foot of the hill and on the upper part of the hill flank. Dry conditions result in increased gravity differences. The changes in the differences which are in the range of several ten nm/s2 can be explained by variations in the amount of water stored in the hill flank. [ABSTRACT FROM AUTHOR]

Ground gravity measurements based on a test mass (relative and absolute gravimeters) are influenced by mass redistribution within the atmosphere which induces gravity variations (atmospheric pressure effect) in µgal range (about 15 µgal for the Sutherland superconducting gravimeter (SG) station). These variations are disturbing signals in gravity data and they must be reduced very carefully for detecting weak gravity signals. The atmospheric pressure effect consists of a deformation and a Newtonian attraction term. The deformation term can be modelled well with two-dimensional (2D) surface atmospheric pressure data e.g. with the Green's function method. For precise modelling of the Newtonian attraction term three-dimensional (3D) data are required. From European Centre For Middle Weather Forecasts (ECMWF) 3D atmospheric pressure, humidity and temperature data are available. These data are used for modelling of the Newtonian attraction term. Two 3D models for the attraction term have been tested based on mass point attraction and gravity potential of the air masses. The results show a surface pressure independent (SPI) part of gravity variations induced by mass redistributions within the atmosphere in the order of some µgal. In the past, different methods have been developed for modelling of the atmospheric pressure effect. These methods use 2D atmospheric pressure data measured at the Earth's surface and a standard model for the height dependency of the atmospheric pressure. With these models the SPI part couldn't be detected. For different SG sites and one absolute gravimeter location the 3D attraction models have been applied and the SPI part was calculated. Its influence is shown on tidal parameter computation for long periodic tidal waves, SG measured polar motion, comparison of SG with GRACE and hydrology model derived gravity variations. Furthermore it is shown how absolute gravity measurements are attected by trie SPI part, The omission of the SPI part correction in the gravity data leads to a misinterpretation of about 2 µgal. It can be shown that the application of the SPI part increases the precision of the atmospheric pressure reduction on gravity data. [ABSTRACT FROM AUTHOR]

The effect of air pressure variations, soil moisture variations and groundwater level variations on time-series of gravity measurements acquired with the tidal gravimeter ET-15 at the Astromctric-Gcodctic Observatorium Westerbork (WAGO), The Netherlands, has been investigated. The gravity measurements have been corrected for gravimeter drift, Earth body tide, and ocean loading effects. The residual signal has been smoothed using a variational smoothing algorithm. An agro-hydrological model provided the change in soil moisture in the vicinity of the gravity bunker over the measurement period. A precise finite element model of the gravity bunker and the surrounding layers was developed to compute the impact of changes in soil moisture content and ground water level variations on gravity. The combined effect of soil moisture variations and groundwater level variations varies between −7 μGal and −3 μGal. It is dominated by soil moisture variations in the layers above the gravimeter between −7 μGal and −5.5 μGal. Soil moisture variations below the gravimeter and groundwater level variations contribute between 0 μGal and 2.5 μGal. The analysis of two years of gravity and local air pressure variations show high correlation factors above 80% for periods of one day and shorter, whereas periods between one day and half a week are correlated between 50% and 80%. Over periods shorter than half a week, an admittance factor of −0.37 μGal/mbar has been obtained. The correlation for periods longer than half a week is very low, i.e. these periods should not be used to determine an admittance factor from local air pressure data. Rainfall events have a significant influence on gravity measurements at the WAGO site. A proper modeling requires measurements of precipitation, evaporation and run-off. This is the subject of future studies. [ABSTRACT FROM AUTHOR]