Radar interferometric techniques and data validation Terrafirma Essen, March 2011 Page 1
Agenda Introduction to InSAR technology Different radarinterferometric techniques Validation of InSAR technology Conclusions Page 2
Advancement in InSAR technology Radar satellites used by Altamira Information ERS-1 ERS-2 Radarsat-1 ENVISAT Launch: July 1991 Owner: European Space Agency Frequency: C-band Launch: April 1995 Owner: European Space Agency Frequency: C-band Launch: November 1995 Owner: Canadian Space Agency Frequency: C-band Launch: March 2002 Owner: European Space Agency Frequency: C-band New generation X-band satellites ALOS Radarsat-2 TerraSAR-X (x 2) COSMO-SkyMed (x 4) Launch: January 2006 Owner: JAXA Frequency: L-band Launch: December 2007 Owner: Canadian Space Agency Frequency: C-band Launch: June 2007 Owner: German Space Agency Frequency: X-band Launch: June & December 2007, October 2008 Owner: Italian Space Agency Frequency: X-band Page 3
Product example Average ground motion rate in Barcelona 2003-2008 Detailed view: Barcelona centre cm/year Detailed view: Barcelona airport Page 4
What does "InSAR technology" mean? InSAR and satellites First measurement Second measurement (afterwards) Results In terferometric S ynthetic A perture R adar = = Superimposition of waves to detect differences High resolution radar system Travel phase between ground and sensor gives distance with millimetric precision Difference between two measurements indicates ground movement over time Ground movement is measured with radar satellites, comparing the satellite distance from the Earth s surface at different moments in time. Page 5
Product example Average ground motion rate in Barcelona 2003-2008 Detailed view: Barcelona centre cm/year Detailed view: Barcelona airport Page 6
Ground motion analysis in the past and monitoring in the future Historical analysis with data in the past 1992-2010 (Satellites: ERS/Envisat, ALOS) Monitoring in the future 2011 -? (Satellites: TerraSAR-X, CosmoSkymed) Analysis of ground motion since 1992 Detects ground motion in the past, e.g. Natural subsidence in area of interest before cavern development Ground motion measurement with new data Regular updates every year (or more frequently) Ground motion studies can be conducted in the past and also with new data. Page 7
Agenda Introduction to InSAR technology Different radarinterferometric techniques Validation of InSAR technology Conclusions Page 8
Introduction to PSI technology What is a PS? Understanding the construction phase constructing the resolution cell of the SAR S = Pixel σ(k). e i2π R(k) λ Page 9
Introduction to PSI technology Definition of Persistent Scatterer Definition PS A PS is a target that keeps the reflection properties along the acquisitions. Its radar response is characterised by a reduced noise level allowing reliable phase measurements in repeat passes phase [rad] acquisitions d] phase [rad acquisitions Temporal changes of the scatterers, different look angle, volume scattering and other factors originate noisy phase contributions inthe resolution cell Page 10
Why not all targets exhibit PS behavior? Effect of the signal carrier frequency Different penetration of the radar signal could occur in function of the observed terrain nature and the wavelength. Depending on the ground layer the reflection properties can be kept in repeat passes X-band C-band L-band Page 11
Advancements in InSAR technology X-Band satellites: Redundancy of satellites Japanese Space Agency (JAPEX) 1992-2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 JERS-1 ALOS L-BAND European Space Agency (ESA) ERS-1 ERS-2 Envisat Sentinel-1 C-BAND Seosar Canadian Space Agency (CSA) Radarsat-1 Radarsat-2 German Space Agency (DLR) EADS Infoterra GmbH TerraSAR-X Tandem-X TerraSAR-X 2 X-BAND ItalianSpace Agency (ASI) Cosmo SKYMED New generation X-band satellites are a satellite constellation: Working with several similar satellites mitigates the risk of satellite failure. Page 12
Why not all targets exhibit PS behavior? Effect of the resolution in repeat passes Temporal and geometric decorrelation have a lower impact on high resolution data. The probability of having a PS like pixel becomes higher when increasing the resolution Slant-range res 12m Slant-range res 3m With more resolution the measurement can be obtained with more detail With more resolution only 1 pixel of 4 will loss the measurement objects on ground in SLC 1 objects on ground in SLC 2.. SAR image1 SLC 2 SAR image2 SLC 2 Page 13
Measurement points Natural Points and Reflectors Natural Points Artificial Corner Reflectors Existing Points Roofs, metallic structures that reflect the radar signal Possibility to conduct historical studies Aluminum Trihedrals Areas where there are not many natural points (areas with vegetation, snow, ongoing construction ) Allow for densification of measurements While areas with infrastructure can be measured with natural points, areas with little infrastructure require reflectors in order to guarantee measurement points. Page 14
Overview InSAR techniques Page 15
Agenda Introduction to InSAR technology Different radarinterferometric techniques Validation of InSAR technology Conclusions Page 16
Validation Project (2006-2008) Alkmaar : rural area of forest, dunes, beaches and villages. Amsterdam : urban area including autonomous and spatially uncorrelated terrain-motion over the 9.5km route of the new N-S metro line. Page 17
Validation Project (2006-2008) Outcome: Process and product validation confirmed quality of Terrafirma products Process comparison: Estimated standard deviations for each OSP were 0.40 0.53mm/year for velocities, 1.1 4.0mm for time series, and 2.14 4.71m for topographic corrections. Comparison with groundtruth Alkmaar: Direct velocity validation against the leveling shows RMS error ranges from 1.0 1.5mm/year for ERS, and 1.3 1.8mm/year for Envisat. Direct time-series validation shows RMS error ranges from 6.2 8.7 mm for ERS and 3.6 4.8 mm for Envisat. Amsterdam: The absolute standard deviation of the double difference in velocity ranges from 1.0 to 1.2mm/year. The average RMS errors of single deformation measurements in the time series range from 4.2 to 5.5mm. Page 18
InSAR validated with Geodetic measurements (Spain) Project description Monitoring of dike in Barcelona's port: historical subsidence measurement between 1995 to 2002 Comparison with geodetic reference points, taken by topographic service InSAR measurement points Validation results Geodetic reference points Subsidence [cm] InSAR subsidence in line with reference 0-1 -2-3 -4-5 -6-7 0895_7331 V=-1.31 cm/yr S0896_7331-8 V=-1.37 37cm/yr -9 0894_7331 V=-1.39 cm/yr InSAR Geodetic point V= -1.42 cm/yr -10 0892_7331 V=-1.40 cm/yr -11 Reference measure -12 ene-95 may-96 sep-97 feb-99 jun-00 nov-01 mar-03 Page 19
InSAR validated with extensometres (Southern Spain) Project description Validation results Historical monitoring of southern Spanish city in waterpomping area Comparison of PS-InSAR results with extensometres InSAR stable point measurements Measurement results of extensometres Page 20
InSAR validated with GPS (Eastern Europe) Project description Historical PS-InSAR subsidence measurement in a city in Eastern Europe Comparison of PS-InSAR results with GPS Validation results GPS-PSI Comparison GPS avg subsidence/ year: 2.634 mm InSAR avg subsidence/ year: 3.047 mm Page 21
Combining different datasets Definition of the different acquisition geometries ASC/DESC The satellite can overpass the area of interest in a descending or ascending mode The incidence angle is different depending on the mode Ascending track Descending track Duration of complete orbit: 100 min Earth rotation A D Images are acquired from very different point of view. The Scatterers response are completely different Page 22
Combining different datasets Definition of the different acquisition geometries different tracks Envisat can vary its incidence angle in 7 positions (I1 to I7) therefore the same area of interest can be "viewed" from several tracks I7 I6 I5 I4 I3 I2 I1 Flight direction Flight direction 100 km I1 I2 I3 I4 I5 I6 I7 485 km 100 km Page 23
Combining different datasets Review of the benefits in PSI processing PSI measurements are in Instrument geometry. Not N/S and E/W oriented PSI analysis are done independently within every track MAJOR BENEFITS: increasing the PS density redundancy to the estimations D HIGLIGHTS: a reduced number of targets supports a multi-track analysis the detected deformation magnitudes and patterns could slightly differ Decomposition of the East-West and the Up-Down components A Example of combination of 4 tracks with ENVISAT Page 24
Combining different datasets Increasing of the final PS density Combination of 4 tracks with ENVISAT Page 25
Combining different datasets Redundancy of the performed estimates ENVISAT DESC Track 151 +1 cm/year -1 cm/year Page 26
Combining different datasets Redundancy of the performed estimates ENVISAT DESC Track 380 +1 cm/year -1 cm/year Page 27
Combining different datasets Redundancy of the performed estimates ENVISAT ASC Track 244 +1 cm/year -1 cm/year Page 28
Combining different datasets Redundancy of the performed estimates ENVISAT ASC Track 473 +1 cm/year -1 cm/year Page 29
Agenda Introduction to InSAR technology Different radarinterferometric techniques Validation of InSAR technology Conclusions Page 30
Conclusions Advantages of radar satellite technology High precision of measurements Average vertical precision: 1 mm Vertical precision between two measurements: 3 mm Possibility to measure the past Possibility to analyse movement in the past, data available from 1992 until present High frequency of updates New measurement data every 4 days Possibility to increase frequency if necessary Guaranteed measurement points Cost and time efficiency Reflectors guarantee measurements in any environment Robust and simple solution, requires no maintenance Measurements made from space, eliminating need for on-site work (Only intervention: Installation of reflectors) First movement results available in only 4 months Radar technology allows to measure ground movements with very high precision minimizing in-situ interventions. Page 31
VIELEN DANK! MERCI, GRACIAS Johanna Granda, Director Sales and Marketing johanna.granda@altamira-information.com Alain Arnaud, CEO Barcelona Calgary C/ Córcega, 381-387387 Bankers Hall, West Tower, 10 th floor E - 08037 Barcelona, Spain 888 3 rd Street SW Calgary AB T2P 5C5, Canada T.: +34 93 183 57 50 T.: +403 444 6861 www.altamira-information.com Page 32