Deformation Monitoring with Terrestrial SAR Interferometry

Transcription

1 Lisbon, 12 October 2009 Deformation Monitoring with Terrestrial SAR Interferometry Michele Crosetto Institute of Geomatics Castelldefels (Barcelona) 1 Content Introduction: Satellite-based SAR interferometry Ground-based SAR: Fundamentals Data acquisition characteristics Examples of monitoring campaigns Real-aperture-radar 2 1

2 Satellite-based SAR interferometry S M - If S M: Φ Int = Φ S Φ M = Φ Mov Φ M - If S M: Φ S Φ Int = Φ S Φ M = P = ΦTopo + Φ Mov = P 3 Satellite-based SAR: Envisat 4 2

3 Satellite-based SAR: TerraSAR-X -25 mm/yr 25 5 Ground-based SAR Key characteristics: It s a radar-based imaging sensor Range resolution Cross-range resolution - SAR Coherent radar Interferometric capabilities 6 3

4 GBSAR: range resolution R n-th range bin RAR Antenna boresight Range profile, where the targets are resolved with a given range resolution Range (m) Source: IDS course 7 Cross-range resolution: SAR The Synthetic Aperture Radar technique enables us to get high crossrange resolution exploiting the movement of the antenna The SAR processing of the data collected during the sensor movement of 2 m allows the system to get a cross-resolution of: λ ϕ = = 4.3mrad 2 L 8 4

5 Cross - Range direction Pixel Range direction Radar position Source: IDS course 9 Interferometric phase We exploit the phase of the signal. In particular, we exploit the difference of phase measured in two or more acquisitions. First acquisition TX RX ϕ 1 d λ d = 4π ( ϕ ϕ ) 2 1 Second acquisition TX RX ϕ 2 Source: IDS course 10 5

6 Hardware: example of IBIS-L Sensor Module Power Supply Module Linear Scanner PC 11 GB-SAR data acquisition Robust, day/night, all weather. High degree of automation Range capabilities: 3-4 km Intrinsically precise: mm, sub-mm Resolution: - ex. Ku-band: range = 0.5 m; cross-range = rad Nominal coverage: - ex. Ku-band: 30-40º Line-of-sight measurement Heavy instrument 12 6

7 4 km 30º 13 Deformation monitoring example: Formigal landslide (Pyrenees) 14 7

8 Formigal landslide (Spanish Pyrenees) 3 TLS campaigns: July 06, October 06, June 07 1 continuous GBSAR campaign: October-November 06 Several topographic campaigns: total station & D-GPS 15 TLS data coverage: Formigal Test Site July scan intensity image ( ) 8

9 TLS data coverage: Formigal Test Site July scan intensity image ( ) Good point = 60% of total TLS data coverage: Formigal Test Site October scan intensity image ( ) 9

10 TLS data coverage: Formigal Test Site October scan intensity image ( ) Good point = 36% of total GB-SAR Line-of-sight displacements; 5 October -21 November 06; Max distance = 1350 m 10

11 GB-SAR Point cm 5 th October 21 st November distance = 550 m Technical issues coherence over time 22 11

12 GBSAR coherence Continuous GBSAR acquisiton 5 October 21 November 2006 Coherence threshold = GBSAR coherence Non-continuous GBSAR acquisition 5 October 21 November 2006 Coherence threshold = 0.9 The spatial sampling density and coverage are reduced The monitoring feasibility has to be assessed on each site 24 12

13 Artificial Reflectors 25 Reflector artificial (triedre) 26 13

14 Technical issue: validation

15 Validation D isplacem ent m easured (m m ) 14,00 12,00 10,00 8,00 6,00 4,00 2,00 Tripod corner reflector evolution 0,00 0-2, Measure number Reference displacement (micrometer) Displacement mesured by GBSAR Difference Sensor to target distance = 44 m 29 Validation Validation error (reference- GBSAR) 0,20 0,10 Difference (mm) 0,00-0,10-0, ,30-0,40 Measure number Sensor to target distance = 44 m Measurements not corrected for (linear) atmospheric effects 30 15

16 Real Aperture Radar (RAR) 31 Real aperture radar 32 16

17 RAR 33 RAR 34 17

18 RAR 3,3 Hz 35 RAR: Cadore bridge Cadore Bridge (Belluno) lenght: 128m Radar position 36 18

19 RAR: Cadore bridge Spectral analysis mm/hz First resonance frequency Hz 37 19