Paul Tregoning: Publications

Click on the number of the publication to view the PDF file. Conference abstracts can be found here

Books, Book Chapters and Reports


Tregoning, P., SC McClusky, AIJM van Dijk, R. Crosbie and J. Pena-Arancibi, Assessment of GRACE satellites for groundwater estimation in Australia, Waterlines Report, 71, National Water Commission, ISBN: 978-1-921853-54-8, 82pp, 2012.


M. Leblanc, S. Tweed, G. Ramillien, P. Tregoning, F. Frappart, A. Fakes and I. Cartwright,
Groundwater change in the Murray basin from long-term in-situ monitoring and GRACE estimates,
In Climate change effects on groundwater resources: A global synthesis of findings and recommendations, Eds. H. Treidel and J.J. Gurdak, CRC Press, November 22, pp 169-187, 2011.

G. Blewitt, Z. Altamimi, J. Davis, R. Gross, C. Kuo, F. Lemoine, A. Moore, R. Nielan, H.P. Plag, M. Rothacher, C. Shum, M.G. Sideris, T. Schone, P. Tregoning and S. Zerbini,
Geodetic Observations and Global Reference Frame Contributions to Understanding Sea-Level Rise and Variability
In Understanding Sea-level Rise and Variability, Eds. John A. Church, Philip L. Woodworth, Thorkild Aarup and W. Stanley Wilson. Blackwells Publishing, London., Wiley Blackwell, 2009.

Tregoning, P. and C. Rizos (2007) Dynamic Planet: Monitoring and Understanding a Dynamic Planet with Geodetic and Oceanographic Tools, IAG Symposia, 130, 909pp, 2007.

Itikarai, I., and Tregoning, P., The 16 November 2000 southern New Ireland earthquake and its aftershocks. Papua New Guinea Geological Survey Report 2003/1, 2003.

Refereed Journal Articles


van Dijk, AIJM, Renzullo, LJ, Wada, Y and P. Tregoning, 2013, A global water cycle reanalysis (2003-2012) reconciling satellite gravimetry and altimetry observations with a hydrological model ensemble, submitted to HESS, November 2013

Moore, M., S. McClusky, P. Tregoning, C. Watson and M.A. King, 2013, Empirical modelling of site specific errors in continuous GPS data, submitted to Journal of Geodesy, November 2013

White, N., J.A. Church, T. Koen, C.S. Watson, T. Pritchard, P. Watson, R.J. Burgette, M. Eliot, K.L. McInnes, B. You, X. Zhang and P. Tregoning, 2013, Australian Sea Levels - Trends, Regional Variability and Influencing Factors, Earth Sci. Rev., submitted October 2013

Memin, A., C. Watson, I.D. Haigh, L. MacPherson and P. Tregoning, 2013, Non-linear motions of Australian geodetic stations induced by non-tidal ocean loading and the passage of tropical cyclones, Earth Planet. Sci. Lett., revised 28 Mar 2014

Montillet, J.-P., P. Tregoning, A. Purcell, S.C. McClusky and S. Williams, 2014, Estimation of Co-seismic Offsets in the Far-Field of an Earthquake, J. Geophys. Res., revised 26 March 2014



Burgette, R., C.S. Watson, J.A. Church, Tregoning, P., and R. Coleman, 2013, Characterizing and minimizing the effects of noise in tide gauge time series: relative and geocentric sea level rise around Australia, Geophys. J. Int. 194(2), 719-736


Tregoning, P., R. Burgette, S.C. McClusky, S. Lejeune, H. McQueen and C.S. Watson, 2013, A decade of horizontal deformation from great earthquakes, J. Geophys. Res., 118, doi:10.1002/jgrb.50154


N. Darbeheshti, L. Zhou, P. Tregoning and S.C. McClusky, 2013, The ANU GRACE visualisation web portal, Computers and Geoscience, 52, 227-233


Montillet, J.-P., P. Tregoning, S.C. McClusky and K. Yu (2012), Extracting white noise statistics in GPS coordinate time series, IEEE Geoscience and Remote Sensing Letters 10, 563-567


P. Tregoning, A. Dehecq, S.C. McClusky, A. Purcell and E-K Potter, 2012, Separating hydrological and glacial isoststic adjustment signals: a simulation of GRACE and GPS observations Journal of Geophysical Research, revised Oct 2012

online version

Fleming, K.M., P. Tregoning, M. Kuhn, A. Purcell and H.McQueen, The effect of melting land-based ice masses on sea level around the Australian coastline, Aust. J. Earth. Sci. 59(4) , 457-467, doi:10.1080/08120099.2012.664828.


McGrath, G.S., R. Sadler, K. Fleming, Tregoning, P. and C. Hinz 2012 Tropical cyclones and the ecohydrology of Australia's recent continental-scale drought Geophys. Res. Lett. , 39, L03404, doi:10.1029/2011GL050263



Doubkova, M., RAM De Jeu, Tregoning, P. and JP Geurschman 2011. Water from space: soil moisture, groundwater and vegetation dynamics, WIRADA Science Symposium Proceedings, , p282-288, 1-5 July, Melbourne, 2011.


Tregoning, P. and S.C. McClusky 2011. Deriving groundwater estimates in Australia from GRACE observations, WIRADA Science Symposium Proceedings, , p295-300, 1-5 July, Melbourne, 2011.


Purcell, T., A. Dehecq, Tregoning, P., K. Lambeck, E-K Potter and S. McClusky 2011. Relationship between the Glacial Isostatic Adjustement and gravity perturbation observed by GRACE, Geophys. Res. Lett., 38, L18305, doi:10.1029/2011GL048624


Watson, C.S., N. White, J. Church, R. Burgette, P. Tregoning and R. Coleman (2011), Absolute Calibration in Bass Strait, Australia: TOPEX/Poseidon, Jason-1 and OSTM/Jason-2, Marine Geodesy 34:3-4,242-260.


Tregoning, P. and C. Watson, 2011. Correction to "Atmospheric effects and spurious signals in GPS analyses", J. Geophys. Res., 116, B02412, doi:10.1029/2010JB008157



Vergnolle, M., A. Walpersdorf, V. Kostoglodov, P. Tregoning, A. Santiago, N. Cotte and S. Y. Franco , Slow slip events in Mexico revised from the processing of 11 year GPS observations, J. Geophys. Res. 115, B08403, doi:10.1029/2009JB006852


Watson, C., R. Burgette, P. Tregoning, N. White, J. Hunter, R. Coleman, R. Handsworth and H. Brolsma, Twentieth Century constraints on sea level change and earthquake deformation at Macquarie Island, Geophys. J. Int. ,doi:10.1111/j.1365-246X.2010.04640.x


Brown, N. and P. Tregoning 2010. Quantifying GRACE data contamination effects on hydrological analysis in the Murray-Darling Basin, southeast Australia, Aust. J. Earth Sci. 57, 329-335.



Tregoning, P., C. Watson, G. Ramillien, H. McQueen and J. Zhang, 2009. Detecting hydrologic deformation using GRACE and GPS, Geophys. Res. Lett. 36, L15401, doi:10.1029/2009GL038718.


Tregoning, P. and C. Watson, 2009. Atmospheric effects and spurious signals in GPS analyses, J. Geophys. Res., 114, B09403, doi:10.1029/2009JB006344


Tregoning, P., G. Ramillien, H. McQueen and D. Zwartz 2009. Glacial isostatic adjustment and non-stationary signals observed by GRACE, J. Geophys. Res.114 B06406, doi:10.1029/2008JB006161


Melachroinos, S., J-M Lemoine, P. Tregoning,, R. Biancale, 2009. Quantifying aliased S2 tidal errors from multiple space-geodesy techniques, GPS and GRACE, over North West Australia, Journal of Geodesy, 83, 915-923, doi:10.1007/s00190-009-0309-2


Leblanc, M., P. Tregoning,, G. Ramillien, S. Tweed, A. Fakes, 2009. Basin scale, integrated observations of the early 21st Century multi-year drought in southeast Australia, Water Resources Res., 45, W04408, doi:10.1029/2008WR007333.

Sambridge, M, P. Tregoning, T. Bodin, H. McQueen, C. Watson, S. Bonnefoy, 2009. TerraWulf II: Many hands make light work of data analysis, Preview, 140, 23-23



The University Component of the AuScope Geospatial Team, 2008. New geodetic infrastructure for Australia, J. Spatial Sci. 53, 65-80.


Dawson, J., P. Cummins, P. Tregoning, and M. Leonard, 2008. Shallow intraplate earthquakes in Western Australia observed by InSAR, J. Geophys. Res., 113, B11408, doi:10.1029/2008JB005807


Tregoning, P., K. Lambeck and G. Ramillien , 2008. GRACE estimates of sea surface height anomalies in the Gulf of Carpentaria, Australia, Earth Planet. Sci. Lett., 271, 241-244, doi:10.1016/j.epsl.2008.04.018



Dawson, J. and P. Tregoning , 2007. Uncertainty analysis of earthquake source parameters determined from InSAR: a simulation study, J. Geophys. Res., 112, B09406, doi:10.1029/2007JB005209.


Boehm, J., P.J. Mendes Cerveira, H. Schuh, P. Tregoning, 2007. The impact of mapping functions for the neutral atmosphere based on numerical weather models in GPS data analysis, IAG Symopsium Series, P. Tregoning and C. Rizos (Eds), 130, 837-843.



Tregoning, P. and T. A. Herring, 2006. Impact of a priori zenith hydrostatic delay errors on GPS estimates of station heights and zenith total delays, Geophys. Res. Lett., 33, doi:10.1029/2006GL027706.


C. Watson, P. Tregoning, R. Coleman, 2006. The impact of solid Earth tide models on GPS time series analysis, Geophys. Res. Lett., 33(8), doi:10.1029/2005GL025538.


Walpersdorf, A., S. Baize, E. Calais, P. Tregoning and J.-M. Nocquet, 2006. Deformation in the Jura Mountains (France): First results from GPS measurements, Earth Planet. Sci. Lett., 245, 365-372.


Boehm, J., A. E. Niell, P. Tregoning, H. Schuh, 2006. The GMF: A new empirical mapping function based on numerical weather model data, Geophys. Res. Lett., 33(7), doi:10.1029/2005GL025546.



Tregoning, P. and T. van Dam, 2005. Atmospheric pressure loading corrections applied to GPS data at the observation level, Geophys. Res. Lett., 32, doi:10.1029/2005GL024104.


O. Titov and P. Tregoning, 2005. Effect of post-seismic deformation on Earth Orientation Parameter estimates from VLBI observations: a case study at Gilcreek, Alaska, J. Geodesy, doi:10.1007/s00190-005-0459-9.


Tregoning, P., M. Sambridge, H. McQueen, S. Toulmin and T. Nicholson, 2005. Tectonic interpretation of aftershock relocations in eastern Papua New Guinea using teleseismic data and the Arrival Pattern method, Geophys. J. Int., 160(3), 1103-1111.


Tregoning, P. and T. van Dam., 2005. The effects of atmospheric pressure loading and 7-parameter transformations on estimates of geocenter motion and station heights from space-geodetic observations, J. Geophys. Res., 110, doi:10.1029/2004JB003334.



O. Titov and P. Tregoning , 2004. Post-seismic motion of Gilcreek geodetic sites following the November, 2002 Denali earthquake, International VLBI Service for Geodesy and Astrometry 2004 General Meeting Proceedings, edited by N. R. Vandenberg and K. D. Baver, 496-500.


Tregoning, P. and A. Gorbatov, 2004. Evidence for active subduction at the New Guinea Trench, Geophys. Res. Lett., 31, doi:10.1029/2004GL020190.


Tregoning, P., P. J. Morgan and R. Coleman, 2004. The effect of receiver firmware upgrades on GPS vertical timeseries, Cahiers du Centre Européen de Géodynamique et de Séismologie, 23, 37-46.



P. Tregoning, 2003. Is the Australian Plate deforming? A space geodetic perspective, Geol. Soc. Aus Special Publication, 22 and Geol. Soc. Am Special Publication, 372, 41-48.



Beavan, J., P. Tregoning, M. Bevis, T. Kato and C. Meertens, 2002. The motion and rigidity of the Pacific Plate and implications for plate boundary deformation, J. Geophys. Res., 107, doi:10.1029/2001JB000282.


Tregoning, P., 2002. Plate kinematics in the western Pacific derived from GPS observations, J. Geophys. Res., 107, 10.1029/JB2001000406.



Tregoning, P. and H. McQueen, 2001. Resolving slip vector azimuths and plate motions along the southern boundary of the South Bismarck Plate, Papua New Guinea, Aust. J. Earth Sci., 48, 745-750.



Tregoning, P., McQueen, H., Lambeck, K., Jackson, R., Little, R., Saunders, S., and Rosa, R. 2000. Present day crustal motion in Papua New Guinea . Earth Planets Space, 52 , 727-730.


Tregoning, P., Welsh, A., McQueen, H. and Lambeck, K. 2000. The search for postglacial rebound near the Lambert Glacier, Antarctica . Earth Planets Space, 52 , 1037-1041.


Featherstone, W.E., M.P. Stewart, C. Rizos, S. Han, R. Coleman, P. Tregoning, 2000. A new facility to enhance Australian GPS-geodetic research, The Australian Surveyor, 45, 20-30.



Tregoning, P., R. Jackson, H. McQueen, K. Lambeck, C. Stevens, R. little, R. Curley and R. Rosa,, 1999. Motion of the South Bismarck Plate, Papua New Guinea, Geophys. Res. Lett., 26, 3517-3520.


Zwartz, D., P. Tregoning, K. Lambeck, P. Johnston and J. Stone, 1999. Estimates of present-day glacial rebound in the Lambert Glacier region, Antarctica, Geophys. Res. Lett., 26, 1461-1464.


Tregoning, P.,  and R. Jackson, 1999. The Need for Dynamic Datums, Geomatics Research Australasia, 71, 87-102.


Tregoning, P., B. Twilley, M. Hendy and D. Zwartz, 1999. Monitoring isostatic rebound in Antarctica with the use of continuous remote GPS observations, GPS Solutions, 2, 70-75.



Tregoning, P., K. Lambeck, A. Stolz, P. Morgan, S. C. McClusky, P. van der Beek, H. McQueen, R. J. Jackson, R. P. Little, A. Laing, and B. Murphy, 1998. Estimation of current plate motions in Papua New Guinea from GPS observations J. Geophys, Res, 103, 12,181-12,203


Tregoning, P., F. Tan, J. Gilliland, H. McQueen and K. Lambeck, 1998. Present-day crustal motion in the Solomon Islands from GPS observations, Geophys. Res. Lett, 25 3627-3630


Tregoning, P., R. Boers, D. O'Brien, and M. Hendy, 1998. Accuracy of precipitable water vapour estimation from GPS observations, J. Geophys. Res, 103 28,901-28,910



Tregoning, P. 1996. GPS Measurements in the Australian and Indonesian regions (1989-1993). UNISURV Report S-44 , 134 pp.


Tregoning, P.F.K. Brunner, Y. Bock, S.S.O. Puntodewo, R. McCaffrey, J.F. Genrich, E. Calais, J. Rais and C. Subarya, 1994. First geodetic measurement of convergence across the Java Trench. Geophys. Res. Lett. 21 , 2135-2139.


Brunner, F.K. and P. Tregoning, 1994. Investigation of height repeatability from GPS measurements Aust. J. Photogram. Surv. , 60 , 33-48


Brunner, F.K. and P. Tregoning, 1994. Tropospheric propagation effects in GPS height results using meteorological observations Aust. J. Photo gram. Surv. , 60 , 49-65

Conference abstracts (since 2007) (top)

13. In-situ Calibration: The potential benefits of single-pass, multi-site data collection
C. Watson, N. White, J. Church, R. Burgette, P. Tregoning and R. Coleman
OST-ST Meeting, Portugal, 18-20 October, 2010

AGU Fall Meeting, 2009

11. Assessment of 3D hydrologic deformation using GRACE and GPS.
C. Watson, P. Tregoning, K. Fleming, R. Burgette, W. Featherstone, J. Awange, M. Kuhn, G. Ramillien
AGU Fall Meeting, 2009

Hydrological processes cause variations in gravitational potential and surface deformations, both of which are detectable with ever increasing precision using space geodetic techniques. By comparing the elastic deformation computed from continental water load estimates derived from the Gravity Recovery and Climate Experiment (GRACE), with three-dimensional surface deformation derived from GPS observations, there is clear potential to better understand global to regional hydrological processes, in addition to acquiring further insight into the systematic error contributions affecting each space geodetic technique.

In this study, we compare elastic deformation derived from water load estimates taken from the CNES, JPL and CSR time variable GRACE fields. We compare these surface displacements with those derived at a global network of GPS sites that have been homogeneously reprocessed in the GAMIT/GLOBK suite. We extend our comparison to include a series of different GPS solutions, with each solution only subtlety different based on the methodology used to realize site coordinates on the terrestrial reference frame. Each of the GPS solutions incorporate modeling of atmospheric loading and utilization of the VMF1 and a priori zenith hydrostatic delays derived via ray tracing through ECMWF meteorological fields.

The agreement between GRACE and GPS derived deformations is not limited to the vertical component, with excellent agreement in the horizontal component across areas where large hydrologic signals occur over broad spatial scales (with correlation in horizontal components as high as 0.9). Agreement is also observed at smaller scales, including across Europe. These comparisons assist in understanding the magnitude of current error contributions within both space geodetic techniques. With the emergence of homogeneously reprocessed GPS time series spanning the GRACE mission, this technique offers one possible means of validating the amplitude and phase of quasi-periodic signals present in GPS time series.

10. Regional deformation from the 2004 Macquarie Ridge great earthquake, Australia-Pacific plate boundary zone
Reed Burgette, C. Watson, P. Tregoning
AGU Fall Meeting, 2009

The transpressional Australia-Pacific plate boundary south of New Zealand has produced some of the largest strike-slip earthquakes in the instrumental record, including the 23 December 2004 Mw ~8.1 earthquake. The oceanic setting of this plate boundary limits terrestrial GPS measurements to sites on Macquarie Island (the only subaerial portion of Macquarie Ridge), southeastern Australia, and New Zealand. We investigate coseismic and postseismic deformation from the 2004 earthquake by analyzing GPS data at 16 sites and compare observed GPS vertical velocity with a relative sea level dataset that spans 96 years.

We invert the horizontal displacements (24 mm at Macquarie Island, < 2 mm in Australia and North Island of NZ) for a best fitting set of fault parameters using an elastic half-space dislocation model. The modeling results are similar to those reported from seismological techniques: predominantly lateral slip occurred on a fault within the Australian plate, west of the main plate boundary, with a moment magnitude of ~8.1. Due to the symmetry of far-field elastic deformation, the geodetic data cannot discriminate between the two possible nodal planes. We prefer left-lateral slip on a NNW-striking fault based on the orientation of the aftershock pattern and fracture zones.

We observe transient postseismic horizontal velocity changes at all of the GPS sites with significant coseismic displacements. Postseismic site velocities are significantly different from the pre-earthquake tectonic velocities. Preliminary modeling suggests that most of the postseismic deformation results from viscoelastic relaxation rather than afterslip. In the four years following the earthquake, the total postseismic deformation is approximately equal in magnitude to the coseismic offset observed at each site, highlighting the broad spatial and temporal scales of effects from this earthquake. This scale of deformation has important implications for the maintenance of a mm-level geodetic reference frame.

Vertical coseismic deformation from the earthquake is within the noise of the GPS time series. The 14 year GPS record at Macquarie Island (IGS site: MAC1) shows a preseismic trend of subsidence of 2.2 +/- 0.4 mm/a. This rate is corroborated by a 96 year duration relative sea level trend of 4.8 +/- 0.6 mm/a. In contrast, late Pleistocene marine terraces suggest a long-term uplift rate of ~0.8 mm/a for Macquarie Island. Pre-earthquake horizontal velocities at MAC1 show movement at 11 mm/yr relative to the stable Pacific plate, approximately 1/3 the magnitude, and ~20 deg more convergent than the relative AUS-PAC plate motion vector. Taken together, these geodetic observations suggest that the Macquarie segment of the AUS-PAC boundary is accumulating strain that will be released in earthquakes with coseismic contraction, and emergence that exceeds the interseismic subsidence.

9. Estimation of hydrological loading effects to correct VLBI analysis
G. Estermann, P. Tregoning and Jeongho Baek
AGU Fall Meeting, 2009

Geodetic observations such as VLBI are sensitive to changes in terrestrial water storage. The few hydrological models currently available show differences in their spatial distribution, globally and also between models. Periodic seasonal variations in the models with amplitudes of up to a few tens of centimeters primarily affect the vertical component of the geodetic observation. Notably, many stations obtain agreement between the Earth response to hydrological loading and the seasonal fit of the VLBI station heights. However, correcting VLBI station heights and baseline lengths for hydrological loading effects using IVS-R1 and IVS-R4 sessions improves the root mean square deviations only marginally. One reason for the small improvement is the relatively large scatter around station heights and hence the hydrological signal is hidden. Nevertheless, it is incorporated in the geodetic signal and needs to be accounted for. It was not possible to clearly identify the best suitable numerical model and therefore a different approach is applied. GPS and GRACE derived hydrological variations are used to correct the VLBI analysis. Although this technique is not free of assumptions, it has turned out to be a very good method to correct geodetic VLBI for changes in terrestrial water storage while avoiding the highly variable numerical models.

8. New Geodetic Infrastructure for Australia: The NCRIS / AuScope Geospatial Component
Paul Tregoning, Christopher S Watson, Richard Coleman, Gary Johnston, Jim Lovell, John Dickey, William E Featherstone, Chris Rizos, Matt Higgins, Russell Priebbenow
AGU Fall Meeting, 2009

In November 2006, the Australian Federal Government announced AUS$15.8M in funding for geospatial research infrastructure through the National Collaborative Research Infrastructure Strategy (NCRIS). Funded within a broader capability area titled ‘Structure and Evolution of the Australian Continent’, NCRIS has provided a significant investment across Earth imaging, geochemistry, numerical simulation and modelling, the development of a virtual core library, and geospatial infrastructure. Known collectively as AuScope (, this capability area has brought together Australian’s leading Earth scientists to decide upon the most pressing scientific issues and infrastructure needs for studying Earth systems and their impact on the Australian continent. Importantly and at the same time, the investment in geospatial infrastructure offers the opportunity to raise Australian geodetic science capability to the highest international level into the future.

The geospatial component of AuScope builds onto the AUS$15.8M of direct funding through the NCRIS process with significant in-kind and co-investment from universities and State/Territory and Federal government departments. The infrastructure to be acquired includes an FG5 absolute gravimeter, three gPhone relative gravimeters, three 12.1 m radio telescopes for geodetic VLBI, a continent-wide network of continuously operating geodetic quality GNSS receivers, a trial of a mobile SLR system and access to updated cluster computing facilities. We present an overview of the AuScope geospatial capability, review the current status of the infrastructure procurement and discuss some examples of the scientific research that will utilise the new geospatial infrastructure.

EGU Meeting, 2009

P. Tregoning and C. S. Watson,
EGU, 2009

Improvements in the analyses of Global Positioning System (GPS) observations yield resolvable mm to sub-mm differences in coordinate estimates, thus providing sufficient resolution to distinguish subtle differences in analsis methodologies. Here we investigate the effects on site coordinates of using different approaches to modelling atmospheric pressure loading deformation (ATML) and handling of tropospheric delays. The rigorous approach of using the time-varying VMF1 mapping function in conjunction with ray-traced zenith hydrostatic delays (ZHD) produces solutions with lower noise at a range of frequencies compared with solutions generated using the empiri- cal Global Mapping Function and Global Pressure and Temperature ZHD model. This is particularly evident when ATML is accounted for. We found little difference in solutions when non-tidal ATML is applied either at the obser- vation level or as a subsequent daily-averaged value. An additional finding of this study is the demonstration that failing to model tidal ATML at the diurnal and semi-diurnal frequencies can introduce anomalous aliased signals in GPS time series with a period that closely matches the GPS draconitic semi-annual period (351.4/2 days). This is evident in both stacked and single site power spectra, with each tide contributing roughly equally. The amplitude of the aliased signal reaches a maximum of 0.8 mm with a clear latitudinal dependence that is not correlated directly with locations of maximum tidal amplitude. This is the first evidence of aliased signals being produced from tidal ATML deformations.

OSTST Meeting, 2008

C Watson, N White, J Zhang, R Coleman, P Tregoning, J Church
OSTST Meeting, Nice, November 2008

The Bass Strait absolute calibration site is the sole in situ altimeter calibration facility of its kind in the Southern Hemisphere, located on the north west coast of Tasmania, Australia (40 39'S, 145 36' E). The site is situated under Jason-1/Jason-2 descending pass 088, which crosses the coast near the city of Burnie, Tasmania.

A number of changes have taken place at the Bass Strait site during the lead up to the launch of Jason-2. The primary comparison point for in-situ bias determination has been shifted north west along the descending pass to help eliminate land contamination within the radiometer data. The calibration methodology remains centered on the measurement of continuous sea surface height (SSH) at the comparison point using oceanographic moorings with high accuracy pressure gauges and associated instrumentation. We define the datum of the moorings using repeated GPS buoy deployments of 8 hours duration. The French Transportable Laser Ranging System (FTLRS) was also located in Burnie for the period November 30 2007 to April 30 2008, allowing us to directly assess orbit quality in this region. Oceanographic instrumentation was installed to coincide with the FTLRS period and extends to cover the duration of the Jason-1/Jason-2 inter-calibration period. Outside of these times, we are able to determine bias estimates from tide gauge comparisons that have been corrected for datum and tidal differences using comparison with the calibrated mooring SSH.

We will present a number of comparisons between the available altimetry data sets including Jason-1 B- and C-series GDRs, Jason-2 IGDRs, and Jason-1 GDRs with FTLRS derived orbits. We compute absolute bias estimates based on comparison with our high accuracy SSH time series from the first mooring recovered in July 2008. Estimates from GPS buoy deployments and from the tide gauge SSH are also presented.

J Zhang, P. Tregoning, C Watson, F Pierron and Ftlrs staff, R Coleman
OSTST Meeting, Nice, November 2008

View a pdf of the poster.

The Bass Strait in-situ calibration site has been involved in the calibration and validation of satellite altimeter data since the launch of TOPEX/Poseidon in 1992. The primary focus at the site has been the estimation of absolute bias in altimeter derived sea surface height (SSH) using a combination of oceanographic moorings, GPS buoy deployments, coastal tide gauge and land based GPS data. As the sole site of its kind in the Southern Hemisphere, the Bass Strait site provides important input into understanding various error sources in satellite altimetery. With an objective of improving our understanding of any geographically correlated orbit errors present in altimeter orbits, the Bass Strait site was selected as part of a collaborative French/Australian project to trial the French Transportable Laser Ranging System (FTLRS). The FTLRS was operated in Tasmania over a five month period between 1 December 2007 to 17 April 2008 jointly by French and Australian staff. The FTLRS and temporary GPS were located within the city of Burnie directly under Jason-1 descending pass 088, several kilometers from the Burnie tide gauge/CGPS and inland CGPS sites. During the Tasmanian FTLRS campaign, a total of 673 over flights from 12 different satellites were observed and a total of 9200 normal points have been computed. In this poster, we present initial results from our analysis of FTLRS data. Whilst building SLR capacity in Australia, we seek to highlight the influence of an additional tracking station in this area of the Southern Hemisphere. Our FTLRS based orbits will assist in quantifying regional or geographically correlated orbit errors present in satellite altimeter data, allowing any bias in altimetry derived SSH in this region to be estimated.

AGU Fall Meeting, 2008

4. Improved GPS Analysis Including Modelling of non Tectonic Signals Confirms Simple 4-4.5 Year Period for SSEs in Guerrero, Mexico, and Allows Prediction of the Next Event in 2010
Vergnolle, M., Walpersdorf, A., Cotte, N., Tregoning, P., Kostoglodov, V., Santiago, J.A., Franco, S
AGU Fall Meeting, 2008.

The precise knowledge of the occurrence time of aseismic slow slip events (SSEs), their spatio-temporal evolution and the amount of deformation they produce are prerequisites to any deeper understanding of the loading/unloading process on faults and thus on earthquake cycles. We re-process and re-analyze observations from permanent GPS stations located in the Guerrero subduction zone, Mexico, where the world's largest SSEs have been observed in 2002 and 2006. Our objective is to refine the characteristics of these two major SSEs as well as smaller quasi-annual SSEs that have previously been reported in this zone and that have been interpreted as climate-driven SSEs. First, we choose to process the data using a double-difference processing strategy that shows a noise reduction of $\sim$ 40\% with respect to the published PPP analysis. Second, using the VMF1 tropospheric mapping function, applying an up-to-date ocean loading model, and applying at the observation level atmospheric pressure loading corrections, the variability of the position time series reduces by $\sim$30\%. Third, we remove a posteriori elastic deformation related to surface loading of hydrologic origin to reduce the annual perturbations that remained in the vertical position time series. We generate the elastic deformations by characterizing changes in surface loads from gravity anomalies estimated from GRACE data, assuming that the anomalies were caused entirely by changes in surface hydrologic loads. Our new GPS analysis has three main results. (1) Most of the time series corrected by the modelled hydrologic loading are different from the raw time series at 80\% confidence level. (2) There is no longer clear evidence of the small, quasi-annual, periodic SSEs suggesting that the previously identified signals may actually be artifacts of the GPS analysis strategy. However, non-periodic anomalous displacements with amplitude $<$$\sim$3mm are present in some time series. (3) The large SSEs do not recover completely the accumulated strain suggesting that a part still has to be released. About the characteristics of the large SSEs, we show that the start and end of the SSEs are roughly simultaneous on the 3 GPS components for most of the stations located inland whereas for the stations located on the coast (closer to the trench and above the seismogenic part of the subduction interface) the temporal slip evolution is complex and shows three stages with different rates. Using a 1-D elastic dislocation model and the total 3D surface displacements, we invert for slip on the subduction interface and find that a large amount of slip (up to 20cm) is needed both in the seismogenic and transition zones for the 2002 and 2006 SSEs. For the 2006 SSE, the amount of slip in the transition zone is smaller than in the seismogenic zone. The models are simple and the solutions are not unique but they strongly suggest that the seismogenic zone is involved in the SSE generation and that both SSEs do not have the same slip distribution on the interface; thus are not similar. The improved constraints on the Mexican GPS position time series permit us to predict that the next SSE should occur in 2010.

Western Pacific Geophysics Meeting, 2008

3. Present-day crustal deformation in Papua New Guinea
P. Tregoning, H. McQueen, D. Zwartz, K. Lambeck, R. Rosa and S. Tiki
Western Pacific Geophysics Meeting, Cairns, August 2008.

Papua New Guinea is one of the most active tectonic regions in the world, containing every type of plate boundary. From nearly two decades of GPS observations, we will present a comprehensive assessment of the tectonic motion that is occurring today, spanning most of the country, encompassing five or more rigid regions and several deforming zones. New observations and better analysis procedures have permitted more accurate estimates of the rigid plate velocities, indicating the extent of indentation of the Australian Plate along the western border, subduction-related deformation along the northern coast, co- and post-seismic deformation related to the 2002 Wewak earthquake and likely deformation of the Papuan Peninsula relative to the Australian Plate.

2. Drought detection in the Murray-Darling basin from space gravity and hydrologic observations
M. Leblanc, G. Ramillien,P. Tregoning,, S. Tweed and A. Fakes
Western Pacific Geophysics Meeting, Cairns, August 2008.

GRACE geoid data were used to monitor and analyse the severe multi-year drought of Murray-Darling river basin in Australia for the recent period (08/2002-07/2007). The GRGS/CNES 10-day solutions up to degree 50 (i.e., spatial resolution of ~400 km) were used to estimate time-series (and associated uncertainties) of water volume change over this ~1 x 106 km2 region and revealed a significant decrease of water mass versus time of ~100 km3. Annual averages of GRACE-derived water storage were compared to in-situ observations of surface waters and showed a correlation of 98%. In this semi-arid region of Australia, groundwater represents the larger part of the total water loss (70%) during the drought, thus showing the capability of GRACE to detect and monitor the variations of shallow groundwater.

1. Detecting Hydrological Loading Effect variations from GRACE/GPS over the Amazon basin
S. Melachroinos, G. Ramillien, J.-M. Lemoine, R. Biancale, F. Perosantz and P. Tregoning
Western Pacific Geophysics Meeting, Cairns, August 2008.

As an aquifer is charged or discharged the effective stress on the pore crustal skeleton changes and may lead to variations in surface elevations of the crust. We asses the ability of GRACE satellite gravimetry to detect these time-variable Hydrological Loading Effects (HLE) due to regional water storage redistributions. Radial displacements of the Earth's surface due to hydrological mass load were derived from the latest GRGS release of 10-day GRACE solutions (08/2002-06/2007, spatial resolution of ~400 km). We predict HLE by the implementation of a spherical harmonic predictions in the spectral domain as well as by a surface point-wise integration of Green's functions, gridded amplitudes and local phases of equivalent water height (EWH) variations. To validate our predictions at seasonal time scales, time-series of these vertical HLE displacements are interpolated and compared to the GPS station height estimates available in the Amazon basin. Analysis of errors on estimated changes of vertical displacement from the GRACE solutions are also made and then compared to the GPS precision.

Last modified: Thurs 11 September 2008