investigations with the sentinel-1 interferometric wide swath...

Investigations with the Sentinel-1 Interferometric Wide Swath Mode Pau Prats-Iraolaa, Matteo Nanninia, Rolf Scheibera, Francesco De Zana, Steffen Wollstadta , Federico Minatib, Francesco Vecchiolib, Mario Costantinib, Andrea Bucarellib ,

Sven Borgstromc , Thomas Walterd, Michael Foumelise, Yves-Louis Desnosf

a b c d f e

German Aerospace Center Microwaves and Radar institute

Outline

• Introduction • TOPS InSAR Chain • TOPS Special Considerations

– LOS variation – Considerations for PSI processing

• Sentinel-1 Results • Conclusion


Introduction • INSARAP: Sentinel-1 InSAR Performance

Evaluation with TOPS Data • Pilot Sites:

– Campi Flegrei/Vesuvius (1xasc/2xdesc) – Istanbul (1xasc/2xdesc) – Mount Etna (1xasc,1xdesc) – Mexico City (2xasc/2xdesc)


TOPS InSAR Chain • Particularities of the TOPS signal

– Azimuth-dependent Doppler centroid – Doppler variation larger than azimuth

sampling frequency – Burst mode (synchronization required,

burst-wise processing)

• Critical InSAR processing steps – Accurate azimuth offset computation for coregistration (1 cm ⇒ 0.001 azimuth

samples) – Interpolation – Azimuth spectral filtering

• Selected strategy – Geometric coregistration + global offset estimation – Valid for stationary scenarios (or scenarios with slow deformation rates, e.g., PSI)


TOPS InSAR Chain • Main Workflow [1]

– Backgeocoding

– Coregistration

• Global offset (overlap areas, ESD in azimuth)

• Nominal from geometry [2] (interpolation)

– Interferogram generation

• Spectral filtering (optional)

• TOPS specific processing

– ESD, interpolation, spectral filtering

– Burst-wise processing

– Debursting and mosaicking performed at the end (for interferogram generation)

[1] P. Prats, R. Scheiber, L. Marotti, S. Wollstadt, A. Reigber, “TOPS Interferometry with TerraSAR-X,” IEEE Trans. on Geosci. and Remote Sens., vol. 50, no. 8, Aug. 2012. [2] E. Sansosti, P. Berardino, M. Manunta, F. Serafino, G. Fornaro, “Geometrical SAR Image Registration,” IEEE Trans. on Geosci. and Remote Sens., vol. 44, no. 10, Oct. 2006.

Enhanced Spectral Diversity (ESD)

Update of range and azimuth offsets

Coregistration (interpolation)

Spectral filtering

Interferogram generationCoherence estimation

Debursting and sub-swath mosaicking

Filtered SLCs

Backgeocoding

Coregistered SLCs

Master SlaveOrbit DEM

Range and azimuth offsetsSlant phase

Interferometric products (burst-wise)

Mosaicked interferometric products

Interferogram generationInterferogram generation

CoregistrationCoregistrationIncoherent Cross

Correlation

More details under (INSARAP Workshop): http://seom.esa.int/insarap/page_participation.php

http://seom.esa.int/insarap/page_participation.php


TOPS Special Considerations • TOPS has a varying line of sight! [1]

– And due to the burst operation, the LoS vector experiences jumps – Azimuth phase jumps should be expected at burst edges in the presence of

azimuthal motion: They simply reveal azimuth components of the motion, sensed by a sudden change in Doppler centroid. ∆𝑥𝑥

∆𝑦𝑦

sin (𝛽𝛽) co

s𝛽𝛽

𝛽𝛽

∆𝑟𝑟 = ∆x ∙ sin 𝛽𝛽 + ∆𝑦𝑦 ∙ cos (𝛽𝛽)

Δ 𝜙𝜙 = 2 𝜋𝜋 ⋅ 𝑓𝑓dc ⋅ Δ𝑡𝑡

= 𝑓𝑓dc =2𝑣𝑣𝜆𝜆 sin 𝛽𝛽

= 4𝜋𝜋𝜆𝜆 ⋅ Δ𝑥𝑥 ⋅ sin𝛽𝛽

[1] F. De Zan et.al., Interferometry with TOPS: coregistration and azimuth shifts, EUSAR 2014, Berlin, Germany.

www.DLR.de/HR > SEOM INSARAP • INSARAP Workshop • December 10, 2014 > Slide 7 Phase Discontinuities over Pine Island Glacier

azimuth →


Simulated Earthquake Signature 80

km

(4 b

urst

s)

(Azim

uth)

+ =

Zero-Doppler phase Along-track motion phase TOPS interferogram

+ =

Max disp.: 1.23 m Max phase: +/-150º

Max disp.: 37 cm Max phase: +/-45º

[1] A. Hooper, Sentinel-1 for Geo-Dummies, Wegener 2014, Leeds, Sep. 2014.


Simulated Earthquake Signature • Rationale:

– Processing should be straightforward for small earthquakes (just the “usual” phase unwrapping problems due to decorrelation).

– For large earthquakes: • Follow rationale as in [1][2]:

– First estimation of azimuth offsets with cross-correlation – Refinement with spectral diversity at burst level and exploiting overlap areas – Removal of azimuthal phase component – Unwrapping – Insertion of removed azimuthal components

• Model-based computation of earthquake signature (with a priori info from previous step) [3]. Residual should be small and unwrappable.

[1] R. Scheiber, et. al. , Speckle Tracking and Interferometric Processing of TerraSAR-X TOPS Data for Mapping Nonstationary Scenarios, IEEE JSTARS, early access paper available. [2] F. De Zan et.al., Interferometry with TOPS: coregistration and azimuth shifts, EUSAR 2014, Berlin, Germany. [3] A. Hooper, Sentinel-1 for Geo-Dummies, Wegener 2014, Leeds, Sep. 2014.

http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6926747&url=http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6926747








PSI Processing • One straightforward solution is to discard half of the overlap area per burst/sub-swath.

• However, overlap areas might contain slightly different PSs due to the different observation geometries (scientific experiments possible).

• Operationally, overlap areas can be used mainly for quality check purposes.

• Such PSs can be also exploited ⇒ larger PS density at overlap areas!

burst 1

burst 2

common

ca. 20% of points are

detected in both bursts


Sentinel-1 Results


Std.Dev. Burst mis: 1.8 ms Std.Dev. 𝐵𝐵⊥ = 75 m Std.Dev. Doppler = 20 Hz

Statistical Analysis with Sentinel-1 Interferograms

-10.00-8.00-6.00-4.00-2.000.002.004.006.008.00

10.00

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

Burst mis-synchronization [ms]

-250.00

-200.00

-150.00

-100.00

-50.00

0.00

50.00

100.00

150.00

200.00

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

Perpendicular baseline [m]

-40.00-30.00-20.00-10.00

0.0010.0020.0030.0040.0050.0060.00

07/1

0/20

14

19/1

0/20

14

31/1

0/20

14

12/1

1/20

14

24/1

1/20

14

06/1

2/20

14

18/1

2/20

14

30/1

2/20

14

11/0

1/20

15

23/0

1/20

15

04/0

2/20

15

16/0

2/20

15

28/0

2/20

15

12/0

3/20

15

Doppler centroid [Hz]


Mexico City: Descending (Dawn) 15.10.2014 – 08.03.2015 𝑁𝑁𝑖𝑖𝑖𝑖𝑖𝑖 = 12 Far range

08.10.2014 – 13.03.2015 𝑁𝑁𝑖𝑖𝑖𝑖𝑖𝑖 = 13 Near range


Mexico City: Ascending (Dusk) 23.10.2014 – 16.03.2015 𝑁𝑁𝑖𝑖𝑖𝑖𝑖𝑖 = 12 Far range

18.10.2014 – 11.03.2015 𝑁𝑁𝑖𝑖𝑖𝑖𝑖𝑖 = 12 Near range


Mexico City: Cross-Comparison

vs

vs

vs

Comparison confirms expectations: - APS main responsible for observed

differences - Ascending acquisitions (dusk) more affected

by APS - Best cross-result between descending

configurations (0.056 cm/month = 6.7 mm/year) with just 5 months of acquisitions


e-GEOS’ PSP-IFSAR Processing Chain [1]

[1] M. Costantini et al., Persistent Scatterer Pair Interferometry: Approach and Application to High-Resolution COSMO-SkyMed SAR Data, IEEE JSTARS, vol. 7, no. 7, 2014.

Very high PS density! PSP temporal coherence threshold = 0.9 Graph connectivity = 6


Campi Flegrei: GPS Measurements

January - June 2014 July - September 2014

Start of time series beginning of October

~2 cm

Horizontal and Vertical GPS deformation pattern at Campi Flegrei (2014)


Campi Flegrei: Descending 07.10.2014 – 12.03.2015 𝑁𝑁𝑖𝑖𝑖𝑖𝑖𝑖 = 10

Uplift confirmed by in-situ measurements


Campi Flegrei: Ascending 20.10.2014 – 13.03.2015 𝑁𝑁𝑖𝑖𝑖𝑖𝑖𝑖 = 11

Strong APS signal (dusk)


Campi Flegrei: Preliminary Validation

*Measurement validation kindly provided by Prospero de Martino, INGV-Vesuvius Observatory

RITE

ACAE


• Triplets analsyis [1] No phase consistency, i.e., Φ123= arg < 𝐼𝐼1𝐼𝐼2∗ >< 𝐼𝐼2𝐼𝐼3∗ >< 𝐼𝐼3𝐼𝐼1∗ > ≠ 0, is related

to the presence of two or more scatterers (volume, moisture [2]). [1] F. De Zan et.al., Lack of triangularity in SAR interferometric phases, EUSAR 2014, Berlin, Germany. [2] F. De Zan et.al., A SAR Interferometric Model for Soil Moisture, IEEE TGRS, Vol. 52, No. 1, Jan 2014

Triplets & Moisture VV polarization

VH polarization

F. De Zan, M. Zonno, P. Lopez-Dekker, A. Parizzi, “Phase inconsistencies and water effects in SAR

interferometric stacks” Tuesday @ 9:20, Big Hall


Conclusion • TOPS InSAR requires more processing effort, but everything is

solvable. • Validation results presented over two pilot sites

– Cross-validation over Mexico City – Validation with in-situ measurements over Campi Flegrei – On-going work: cross-check of the two PSI chains

• The evaluated results confirm the excellent interferometric capabilities of the Sentinel-1 satellite: – Excellent burst synchronization and antenna pointing performance – Capability to build up stacks in short time spans (time series require

large stacks to achieve millimeter accuracy due to APS) – Reduced repeat-pass cycle & wide swath (≥ 2 LOS vectors within 12

days)


Thank you for your attention!

investigations with the sentinel-1 interferometric wide swath...

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