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Perth subsidence monitoring project

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Presentation on theme: "Perth subsidence monitoring project"— Presentation transcript:

1 Perth subsidence monitoring project
Funded by Perth subsidence monitoring project Mick Filmer1, Will Featherstone1, Andreas Schenk2 & in conjunction with Landgate and ARC 1Western Australian Centre for Geodesy, Curtin University 2Geodetic Institute, Karlsruhe Institute of Technology, Germany

2 Vertical land motion (VLM)
Groundwater extraction results in VLM (usually subsidence) Groundwater extraction in Perth increased ~1997 Evidence of subsidence up to ~6 mm/yr from CGNSS Left panel: Subsidence of ~9 m between 1925 and 1977 in California. From Galloway & Burbey (2011)

3 Why is it necessary to monitor VLM?
Risk of damage to physical infrastructure Houses/buildings Transport infrastructure Distortion and changes of AHD heights – Landgate is mandated to supply accurate heights Benchmarks on vertical datum (AHD) Tide gauges in Earth-centred reference frame

4 Heights change over time
AUSGeoid09 will not deliver AHD correctly, because benchmarks are moving vertically HAHD = h – AG09fitted – Δht (φ,λ,t)

5 Aims of the project Quantify subsidence of the Perth Basin
including spatial and temporal variations Combination of InSAR, CGNSS, repeat levelling InSAR delivers high spatial resolution over large area Develop vertical velocity model for Perth region provide users with corrected transformation to AHD using GNSS Correct tide gauge records for VLM Fremantle is longest record in Southern Hemisphere

6 Few knew that Perth was sinking
Lack of dedicated geodetic monitoring system – we need data! Two CGNSS stations (only since ~1993) Limited repeat GNSS observations Little repeat levelling Few archived InSAR images 10 ERS 12 Envisat I2 11 Envisat I3 21 ALOS PALSAR images, but cost $$$

7 The status quo – a lot more required
Now three CGNSS stations Extracted 1970s levelling (black) Repeat levelling (red)

8 GNSS - Gnangara Subsidence correlates with increased water extraction
At this location for : ~-5 cm height change ~-25 m water level change Top panel: GPS ellipsoidal height (m) Bottom panel: Depth (m) of water in Yarragadee aquifer

9 GNSS - Hillarys Lots of discontinuities and noise in the time series
Complicates estimating VLM trends Subsidence makes TG observed sea level rise appear faster Top panel: GPS at Hillarys (antenna is above sign) Bottom panel: GPS ellipsoidal height (m)

10 InSAR introduction Multiple radar images from repeat passes of the same satellite Interferogram is formed by differencing images pixel-by-pixel Multiple interferograms stacked to compute VLM time series Figure is of ALOS (Japanese Aerospace Exploration Agency)

11 InSAR preliminary results
Envisat I3 deformation map Contaminated by atmospheric signal Short time-series (1 year) and only 11 InSAR images PROBLEM: not enough data Envisat data provided by European Space Agency (ESA)

12 InSAR preliminary results
TerraSAR-X deformation map Oct 2012-April 2013 12 images, but acquisitions continuing until end of 2013 up to 36 images not enough yet… TerraSAR-X data supplied by the German Space Centre (DLR) under GA-Curtin-Landgate-KIT science project

13 VLM by levelling Advantages Disadvantages
High precision – proven for detecting VLM Repeatable along same traverse Archived data can extend back over time of deformation – data available, but in hardcopy Disadvantages Low spatial resolution Relatively slow – usually low temporal resolution

14 Repeat levelling Compare 1970s ΔH to 2011 re-levelled ΔH between Hillarys and Fremantle; Hillarys to Gnangara E-W profile will compare 2013 re-levelling with s ΔH Re-levelling will be used to validate TerraSAR-X and CGNSS time-series

15 The outlook Perth’s water shortage woes will continue, especially as our population increases Monitoring of Perth’s subsidence needs serious and ongoing $$$ commitment over time We need lots of good data over a long time period: more CGNSS stations dedicated to VLM more InSAR [long, well sampled time-series – large image stack] Expand re-levelling program

16 The outlook Current project is funded by the Australian Research Council, Landgate, and Curtin University Project ends December 2013 Without additional funding, it will cease Heights in Perth will degrade over time Ongoing monitoring and solutions to the problem are dependent on the project continuing…

17 Acknowledgements We would like to thank
European Space Agency, German Space Agency, Landgate, Geoscience Australia and the WA Department of Water for supplying data Australian Research Council, Landgate and Curtin University for project funding Andy Hooper (StaMPS), TUDelft (Doris), JPL/Caltech (roi_pac) for freely available InSAR software Nigel Penna (Newcastle University, UK)

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