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SAR interferometry applications for emergency mapping
D.Grandoni (e-GEOS S.p.A.)
Copernicus EMS Annual User Workshop
Ispra, June 21st 2017
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Introduction: SAR Interferometric coherence (1/2) Interferometric coherence is generated from the analysis of phase information of two SAR images collected in interferometric mode. It displays, with a color scale ranging from black to white, the coherence of each pixel in the two images. • White pixel, with high coherence, are related to stable target, such as buildings, rocks, infrastructures, bare
soil. • Progressively darker pixels, indicating medium to low coherence, are related to unstable targets, such as
vegetation and water
First SAR image – SAR Amplitude Second SAR image – SAR Amplitude
SAR Interferometric Coherence
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Introduction: SAR Interferometric coherence (2/2) Coherence map; 8 days, Mekong delta, Vietnam Coherence map; 8 days, Qom, Iran
Mean value 0.81; Max value 0.96 Mean value 0.24; Max value 0.59
Coherence map can be seen as the comparison in amplitude and phase between the two signals received during two consecutive acquisitions with the same orbit pass, look direction, incidence angle and polarization (i.e. interferometric acquisitions) over the same area.
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SAR interferometric products
Multi-Coherence Map (MCM)
MultiTemporal Coherence (MTC)
Damage Proxy Map (DPM)
Product name Image sample Short description
MultiTemporal Coherence (MTC) combines one pair of SAR images acquired in interferometric mode and is useful both for change detection and for thematic mapping as the use of coherence facilitates the detection of some land cover classes (e.g. urban, water, vegetation)
Multi-Coherence Map (MCM) combines two pairs of SAR images acquired in interferometric mode and is useful for change detection associated to significant coherence losses/gains (e.g. building destruction/construction)
Damage Proxy Map (DPM) is a derived product from the Multi-Coherence Map where coherence difference values are normalized, filtered and classified to generate a proxy map of damage assessment
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Product 1: MultiTemporal Coherence (MTC)
PETRANA – COSMO Spotlight-2 27/08/16
PETRANA – COSMO Spotlight-2 28/08/2016
PETRANA–COSMO Spotlight-2 Coherence 27/08/2016 - 28/08/2016
PETRANA – COSMO Spotlight-2 MTC 27/08/2016 - 28/08/2016
The product is generated by composing an RGB images with the following base images: • COSMO amplitude, collected on the first date (red channel) • COSMO amplitude, collected on the second date (green channel) • Coherence between the two COSMO images (blue channel)
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Product 2: Multi-Coherence Map (MCM)
SOMMATI – PRE/PRE CSK HI Coherence 06/06/2016 – 24/06/2016
The product is generated by composing an RGB images with the following base data: • COSMO coherence between two pre-event acquisitions (red channel) • COSMO coherence between one pre-event and one post event acquisitions (green channel and blue channel)
SOMMATI – PRE/POST CSK HI Coherence 24/06/2016 – 26/08/2016
SOMMATI – CSK HI MCM 06/06/2016 - 24/06/2016 – 26/08/2016
SOMMATI – PRE/POST CSK HI Coherence 24/06/2016 – 26/08/2016
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Product 3: Damage Proxy Map
• Damage Proxy Map is a point map obtained by analyzing the coherence between two pairs of COSMO SkyMed images - Pair 1: PRE-PRE; Pair 2: PRE-POST
• Damage Proxy Map is generated with the following steps:
• In the coherence from image pair 1 are extracted all pixels with higher coherence
• For all these pixels is analyzed the coherence from image pair 2. Only pixels with high coherence decrease are extracted and inserted in the Damage Proxy Map
• The process includes also histogram matching to make the two coherenc ehistograms comparable
• Damage Proxy Map is a vector product from the Multi-Coherence Map, obtained by discretizing the RGB imagery
Coherence from image pair 1 PRE-PRE Coherence from image pair 2 PRE-POST with high coherence decrease points
Damage Proxy Map
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Satellite input data requirements
1. Interferometric acquisitions = same sensor, same geometry, same polarization - Sentinel-1A/B acquire interferometric pairs every 5 days (systematically) - COSMO-SkyMed constellation acquires interferometric pairs every 4 days (on average, on demand, but with a large
background acquisition mission e.g. over all cities pop.> 200.000 worldwide)
2. Timeliness = availability of pre and post event images close to the event date (short temporal baseline) - one (or more) pre-event images and one (or more) post event images - Time interval between the acquisitions (1, 3, 4, 8, …. days)
3. Geometric fit = orbital distance between the two passes (short spatial baseline)
- This influences the quality of interferometric coherence estimation
4. Geometric resolution = level of detail of detectable changes - Normally interferometric coherence is estimated after a multilooking process (3-4 looks) to reduce noise - This means that Sentinel-1 is processed @30m, while COSMO-SkyMed Stripmap @5m
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Case Study #1 – Earthquake in Central Italy
Event description:
In the first hours of 24th August 2016 an
earthquake occurred in the centre of Italy
involving a very large territory including several
Regions (Lazio, Abruzzo, Umbria) and
Municipalities. After the main shock several
others occurred in the areas producing
casualties and damages on structures and
infrastructures.
Triggering entity:
Italian Civil protection activated the
Copernicus EMS Rapid Mapping at 10:13 UTC
on 24/08/2016
33 areas of interest have been mapped
using both aerial and satellite data, producing
and delivering almost 60 grading maps
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COSMO SkyMed Data used for SAR Products generation
Himage (3m) 8 images (5 pre + 3 post)
Spotlight 2 (1m) 4 images (post event)
Copernicus first set of AOIs
First CSK image @17:09 UTC 24/08/2016
1
2 2
3
- 24/08 - 07/08 - 23/08 - 08/06 – 24/06 – 26/08 - 20/08 – 28/08
2
2
27/08 – 28/08 27/08 – 28/08
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Multitemporal Coherence Map (MTC) – PRE/POST
COSMO-SkyMed Himage (5m)
PRE-POST
Amplitude 24 June 2016
Amplitude 26 August 2016
Coherence (24/06 – 26/08 2016)
Concentraiton of damages in the historic center
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MultiTemporal Coherence (MTC) – PRE/PRE
Detection of roads
Detection of water areas
Detection of built up area
COSMO-SkyMed Himage (5m)
PRE-PRE
Amplitude 06 June 2016
Amplitude 24 June 2016
Coherence (06-24 June 2016)
Woody area
Detection of grassland divided by edge rows
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MultiTemporal Coherence (MTC) – POST/POST
Parking area with vehicle movement
Tents camp and vehicle movement
Vehicles and material movement
AMATRICE – COSMO Spotlight-2 MTC. Images dates 27/08/2016 – 28/08/2016
COSMO-SkyMed Spotlight-2 (2m)
PRE-PRE
Amplitude 27 August 2016
Amplitude 28 August 2016
Coherence (27-28 August 2016)
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Pescara del Tronto
Grisciano
Accumoli
Colle
COSMO-SkyMed
08/06/2016 24/06/2014 26/06/2016
Amatrice
Multi-Coherence Map (MCM)
One single pass, acquired most of the affected area Urban areas appearing in red (even of small dimensions) have been effectively affected by the earthquake
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Multi-Coherence Map (MCM)
Quick detection of changes over
urban areas
Amatrice
Over the built-up areas (small town and villages) the reddish pixel identify
buildings and infrastructures possible affected by the earthquake
COSMO-SkyMed Himage (5m)
08/06 – 24/06 pre-pre Coherence
24/06 – 26/08 pre-post Coherence
Mosicchio
S. Benedetto
Colli
Sommati
Prato
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Interferometric Coherence Himages: 08/06/2016; 24/06/2016; 26/08/2016
Co
he
ren
ce
pre
-pre
C
oh
ere
nce
P
re-p
ost
Teramo (not affected) Amatrice (affected) Illica (affected)
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SAR Interferomtric products on Amatrice
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Damage Proxy Map
• Damage Proxy Map enhances the area where has been detected, in the pre-post image pair, a strong decrease of coherence in the high coherence data in the pre-pre image pair
• Decrease can be associated with roofs large movement or building destruction
• Coherence decrease is color coded in the Damage Proxy Map, with darker area showing higher decrease
AMATRICE – COSMO SkyMed H1 Damage Proxy Map. 08/06/2016 – 24/06/2016 – 26/08/2016
Coherence Decrease
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Case Study #2 – Oklahoma City Tornado
Triggering entity:
e-GEOS has been proactively acquiring
COSMO-SkyMed images before and after the
event, generating damage assessment maps
provided to US Government.
e-GEOS has been regularly acquiring also
optical data for optical-SAR combined analysis.
Event description:
On the afternoon of May 20, a large, violent
tornado touched down west of Newcastle,
Oklahoma and impacted the town of Moore,
causing severe damage to residential areas as
well as Plaza Towers and Briarwood Elementary
schools. The Oklahoma Office of the Chief
Medical Examiner has confirmed several
fatalities, at least 200 people injured.
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Damage assessment – Open data
Damage assessment map generated less 24 hours after
the event by analyzing and georeferencing information
from open data (tweets, video,…)
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Damage assessment – Optical
Damage assessment map generated based on
WorldView-1 image acquired on May 22nd, 2013
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Damage assessment – SAR
Damage assessment map generated based the
interferometric analysis of a COSMO-SkyMed pair.
Red: Amplitude CSK May 17th, 2013
Green: Amplitude CSK May 25th, 2013
Blue: interferometric coherence
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Damage assessment – SAR/Optical
Combination of SAR based damage assessment with
Optical based damage assessment.
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Conclusions
SAR Interferometry applications can contribute operationally to satellite emergency mapping, subjec to the availability of suitable datasets
Advantages: - All-weather, day-night acquisition capabilities complementary to optical sources
- Quick overview over large areas to detect affected settlements
- High sensitivity also to «small effectes» depending on the used SAR band (in particular, X-band), coherence loss is registered also for «deformations» in the order of few centimeters
- Fully automated processing
Limitations: - Availability of suitable pre-event images necessary conditions, not always satisfied. Need for
systematic colelctions (e.g. Sentinel-1, COSMO-SkyMed background mission)
- Geometric resolution in some cases (e.g. Sentinel-1) not enough to detect damages to buildings
All COSMO-SkyMed images © ASI - Agenzia Spaziale Italiana e-GEOS S.p.A – L.O. Contrada Terlecchie snc – Matera / HQ Via Tiburtina, 965 – Roma