This document summarizes validation studies of Sentinel-1 data from its first year of operation. Validation was conducted using test sites in Poland and Norway with corner reflectors monitored by GPS and other sensors. Initial validation results show Sentinel-1 geo-localization accuracy of approximately 2.5 meters in azimuth and -0.3 meters in range, with potential issues observed between swaths. InSAR validation shows phase standard deviation of about 0.7 mm compared to TerraSAR-X data. Ongoing work includes refining results and validating InSAR time series to further assess Sentinel-1 quality for monitoring applications.

1. CEOS Calibration and Validation Workshop 2015
Interferometric and Geodetic
Validation of Sentinel-1
experiences from the 1st
year of operation
Yngvar Larsen
Tom Rune Lauknes
Norut
Zbigniew Perski
PGI
October 27-29, 2015, at ESA-ESTEC
John Dehls
NGU
Petar Marinkovic
PPO.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...
Methodologies
SAR and InSAR applications
SAR Systems
Sentinel-1, TerraSAR-X, Radarsat-2, etc.
Ground equipment
large number of CRs deployed
In-situ measurements
GNSS, leveling, inclinometers, weather stations, ...
Test sites
Poland, Norway, 'open sourced ones' (eg Australia), ...

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Validation in context of...
Methodologies
SAR and InSAR applications
SAR Systems
Sentinel-1, TerraSAR-X, Radarsat-2, etc.
Ground equipment
large number of CRs deployed
In-situ measurements
GNSS, 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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Norwegian Test Site: Summary

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Norwegian Test Site: Summary
2.5 m
“symmetric trihedral”

17. 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!

20. Babiak
Lewino
150km

21. PL Sites in S-1 slice

22. Babiak Test Site

23. Babiak Test Site

24. Babiak Test Site
4km
4km

25. 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
Rng mean/stddev [m]: -0.1893 0.0982
Azi mean/stddev [m]: -0.5981 0.1520

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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
Azi mean/stddev [m]: -0.0581 0.1520
Datum correction: ETRS89 ITRF2008→
(No dynamic correction larger stddev)→

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S-1 GeoLocalization: Out-of-box

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S-1 GeoLocalization: Out-of-box
●
Two clusters because of Center-of-Gravity
correction
●
Before/after May'15

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S-1 GeoLocalization: Out-of-box
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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S-1 GeoLocalization: With corrections
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
Rng mean/stddev [m]: -0.2501 0.1475
Azi mean/stddev [m]: 2.2986 0.6826

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S-1 GeoLocalization: With corrections
Rng mean/stddev [m]: -0.2801 0.1376
Azi mean/stddev [m]: 3.0671 0.6749
Rng mean/stddev [m]: -0.2501 0.1475
Azi mean/stddev [m]: 2.2986 0.6826
●
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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S-1 GeoLocalization: With corrections
Rng mean/stddev [m]: -0.2801 0.1376
Azi mean/stddev [m]: 3.0671 0.6749
Rng mean/stddev [m]: -0.2501 0.1475
Azi mean/stddev [m]: 2.2986 0.6826
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?

41. Validation Part #2:
InSAR Quality Control (Phase)

42. Methodology: InSAR validation
●
Closed loop validation of S-1 vs TerraSAR-X
●
Cross validation of double-differences
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'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

43. Network Design: Babiak, PL test site

44. Network Design: Babiak, PL test site
~ 200 m

45. Results: InSAR validation
TSX @36
S-1 @33
S-r09
T-r15
T-r16

46. Results: InSAR validation
TSX @36
S-1 @33
Outlier: Snow in CR ?

47. 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-r15
T-r16

48. Results: InSAR validation arc #2
TSX @36
S-1 @33
TSX stddev [mm]: 0.5622
S1 stddev [mm]: 0.6805
S-r09
T-r15
T-r16

49. Results: InSAR validation arc #3
TSX @36
S-1 @33
TSX stddev [mm]: 0.6025
S1 stddev [mm]: 0.7674
S-r09
T-r15
T-r16

50. Norway: InSAR vs Continuous GPS @ Landslides

51. Norway: InSAR vs Continuous GPS @ Landslides
Unfiltered S-1 InSAR time-series

52. Norway: InSAR vs Continuous GPS @ Landslides
Filtered / smoothed S-1 InSAR time-series

53. Norway: InSAR vs Continuous GPS @ Landslides
Possible InSAR processing issues?
Ionosphere?
Filtered / smoothed S-1 InSAR time-series

54. 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 observed
Hopefully(?) 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?

55. 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

56. 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