interferometric and geodetic validation of sentinel-1

CEOS Calibration and Validation Workshop 2015

Interferometric and GeodeticValidation of Sentinel-1

experiences from the 1st year of operation

Yngvar Larsen

Tom Rune LauknesNorut

Zbigniew PerskiPGI

October 27-29, 2015, at ESA-ESTEC

John DehlsNGU

Petar MarinkovicPPO.labs

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Motivation: Sentinel-1 Quality Control

Recurrent research question in field of SAR/InSAR:

What is the quality of Sentinel-1 sensor for different monitoring applications?

Sub-question:

“How good is what we measure/estimate?”

Context:

“Full scale error propagation for SAR/InSAR not straightforward...”

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Objective

We need empirical error bars

“Error bars are a representation of the variability of data, or uncertainty in a reported measurement. They give a general idea of

how precise a measurement is, or conversely, how far from the reported value the true (error free) value might be. [Wikipedia]”

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Objective

This is a workshop we are presenting →

work in progress!

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Presentation Structure

● Context

● Gentle introduction to Test Sites

● Validation studies:

Part #1: Geo-Localization (amplitude)

Part #2: InSAR validation (phase)

● Summary, recommendations & future plans

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Validation in context of...

MethodologiesSAR and InSAR applications

SAR SystemsSentinel-1, TerraSAR-X, Radarsat-2, etc.

Ground equipmentlarge number of CRs deployed

In-situ measurementsGNSS, leveling, inclinometers, weather stations, ...

Test sites

Poland, Norway, 'open sourced ones' (eg Australia), ...

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Validation in context of...

MethodologiesSAR and InSAR applications

SAR SystemsSentinel-1, TerraSAR-X, Radarsat-2, etc.

Ground equipmentlarge number of CRs deployed

In-situ measurementsGNSS, leveling, inclinometers, weather stations, ...

Test sites

Poland, Norway, 'open sourced ones' (eg Australia), ...

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Sentinel-1 Validation: General Project Setup

● A number of CR validation sites 4 in total→● Three sites in Poland● One site in Norway

● CR's monitored by in-situ (GPS and leveling) and other SAR● Different CR design/size● Different design of control networks

● Specifically, here we will focus on:● Two sites in Poland● One site in Norway● Sentinel-1 validation● As a reference:

– SAR system TerraSAR-X→– GNSS campaigns over test-sites

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Sentinel-1 Validation: General Project Setup

● A number of CR validation sites 4 in total→● Three sites in Poland● One site in Norway

● CR's monitored by in-situ (GPS and leveling) and other SAR● Different CR design/size● Different design of control networks

● Specifically, here we will focus on:● Two sites in Poland● One site in Norway● Sentinel-1 validation● As a reference:

– SAR system TerraSAR-X→– GNSS campaigns over test-sites

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Poland Test Sites: Overview

● ~111 concessions for shale gas exploitation granted in PL

● Possible subsidence expected

● Monitoring required by law

● 3 sites defined for validation and methodology development

● Projects in numbers

– Duration: Jan 2013 – Dec 2016

– Number of CRs deployed: 60

– TSX, S-1, R-2

– In-situ: GNSS, leveling, weather

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Poland Test Sites: Overview

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CR Design: Babiak, PL site

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CR Design: Babiak, PL site

0.7m – 1.7m

0.6m – 1.3m

12 deg

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Norwegian Test Site: Summary

● Long term landslides monitoring (maximum 5 cm/yr LOS)

● 4 ‘Big’ CRs & 10 'Small' TSX optimized

● ‘Big’ CRs collocated with cnts GPS

● Up to 500 meters of height difference between CRs

● InSAR ongoing since ~2008

● Equipped with the snow protection● Winter scenes due to snow could be

quite problematic

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2.5 m

“symmetric trihedral”

Validation Part #1:

Absolute Geo-Localization (Amplitude)

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Methodology and Remarks

Semantics & Definitions

Offset := predicted - estimated

Assumptions

● Methodologies for peak extractions, residual bistatic correction, atmospheric contributions, datum transformations are all considered known.

SAR and auxiliary data

● Standard Level 1 products and metadata● Precise orbits● One year of SAR data (Oct'14 – Oct'15)

Focus on results!

Babiak

Lewino

150km

PL Sites in S-1 slice

Babiak Test Site

Babiak Test Site

4km

4km

Quick stats of observation setup:

● 2 x (15 +5) CRs observed over period of 1 year

● Observation period 1+ years (mid 2014 - today)

● TSX SM: 2 x 35

● S-1 IW: 1 x 25

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TSX Results: internal validation

● To establish the reference, and validate CR coordinates

● Out of box geolocalization - only annotated parameters

● Impact of datum correction

● NO DYNAMIC (EARTH TIDES) CORRECTIONS APPLIED

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TSX GeoLocalization: Out-of-Box

Rng mean/stddev [m]: -0.3056 0.0924

Azi mean/stddev [m]: -0.5359 0.0919



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TSX GeoLocalization: Datum Correction

Rng mean/stddev [m]: 0.06433 0.0924

Azi mean/stddev [m]: 0.00401 0.0919

Rng mean/stddev [m]: 0.1807 0.0982


Datum correction: ETRS89 ITRF2008→

(No dynamic correction larger stddev)→

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S-1 GeoLocalization: Out-of-box

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● Two clusters because of Center-of-Gravity correction

● Before/after May'15

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Bistatic difference:● correction applied in processor wrt center of the swath

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S-1 GeoLocalization: With corrections

Corrections:● APS model by A.Schubert / M.Jehle et al (UZH team)● Bistatic refined● CoG for old scenes (before 2015-05-01)

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Rng mean/stddev [m]: -0.2801 0.1376Rng mean/stddev [m]: -0.2801 0.1376

Azi mean/stddev [m]: 3.0671 0.6749Azi mean/stddev [m]: 3.0671 0.6749



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● axes now 1:5 for rg:az

● the same as for the resolution difference

● a circular point cloud is expected (and observed!)

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We observed ~0.7 meters offset between clouds in azimuth direction!?

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S-1 GeoLocalization: CR in Swath Overlap● In Norway we have CR in IW1/IW2 swath overlap

NB: We were very lucky!

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S-1 GeoLocalization: CR in Swath Overlap

Difference between apparent CR position in IW1/IW2

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S-1 GeoLocalization: Issues Discussion

● The same CR observed in two swaths

● Discrepancy in measured peak positions in IW1/IW2

● Offset difference

● Range:● Delta time := 0.8 sec almost the same atmosphere→● Definitely there's no 20 cm APS difference as observed

● Unexplained cause?

● Azimuth:

● Unexplained average of 1.6 meters

● Misalignment between swaths?

● Timing jitter reported & fixed, also values too small to explain this

IPF issue ?

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S-1 GeoLocalization: IPF issues?

IPF issue ?

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S-1 GeoLocalization: IPF issues?

Wild theory: what if bistatic correction in the processor NOT wrt mid-IW2, but wrt mid-swath for each swath individually?

Validation Part #2:

InSAR Quality Control (Phase)

Methodology: InSAR validation

● Closed loop validation of S-1 vs TerraSAR-X● Cross validation of double-differences● 'Raw' phases: no-unwrapping, no corrections,

preliminary qualified products● Reduced network size: working on single-arcs● On-going work

Time period: ● Oct'14 – Oct'15

Data:● S-1: 25 x IW @33 deg● TSX: 35 x SM @36deg

Network Design: Babiak, PL test site

Network Design: Babiak, PL test site

~ 200 m

Results: InSAR validation

TSX @36

S-1 @33

S-r09

T-r15T-r16

Results: InSAR validation

TSX @36

S-1 @33

Outlier: Snow in CR ?

Results: InSAR validation arc #1

TSX @36

S-1 @33

TSX stddev [mm]: 0.4873

S1 stddev [mm]: 0.6829

● 'raw' InSAR double differences● No in-processing outlier removal● Results still being refined● Dealing with APS● STDDEV wrt a smoothed version

to get rid of signal and outlier

S-r09

T-r15T-r16


TSX @36

S-1 @33



S-r09

T-r15T-r16

Norway: InSAR vs Continuous GPS @ Landslides


Unfiltered S-1 InSAR time-series


Filtered / smoothed S-1 InSAR time-series


Possible InSAR processing issues?

Ionosphere?

Filtered / smoothed S-1 InSAR time-series

Summary

● Different quality aspects of S-1 independently validated

● GeoLocalization accuracy of S-1 (ballpark)● Azimuth: ~2.5 m (with stddev of 0.7m)● Range: -0.3 m (with stddev of 0.14m)

Potential issues of swath misalignment observedHopefully(?) our findings are in an agreement with other teams?

● InSAR validation of S-1● Phase STDDEV in the ballpark of 0.7 mm

Should be ~1mm We got it in the controlled environment!→

Anyone else validating S-1 InSAR and willing to share findings?

Plans and future work

● This is an on-going validation project:

Updates at upcoming conferences and workshops

● Making work public and open source:

Plan is that parts of this work will eventually be open-sourced (algos and code) and/or results made available in coordination with funding agencies.

● Current focus on:● Assembling and interpreting of results● InSAR time series processing and validation

Acknowledgments:● Copernicus Programme, all Sentinel-1 results: “Contain modified Copernicus Sentinel

data (2014/2015)”● ESA SEOM Programme – InSARap Study● Polish Ministry of Environment● Norwegian collaborators: NVE (Norwegian Water Resources and Energy Directorate)● Nuno Miranda, ESA, for helpful pointers @Fringe15 on the initial validation results● Eelco Doornbos and Wim Simons of TU Delft (Astrodynamics and Space Missions

Department) for their clarifications of Sentinel-1 orbital dynamics

Plans and future work

● This is an on-going validation project:

Updates at upcoming conferences and workshops

● Making work public and open source:

Plan is that parts of this work will eventually be open-sourced (algos and code) and/or results made available in coordination with funding agencies.

● Current focus on:● Assembling and interpreting of results● InSAR time series processing and validation

Public version of this talk available on SlideShare

Easier to find it via my twitter stream: twitter.com/pmar

interferometric and geodetic validation of sentinel-1

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