sar interferometry applications for emergency mapping · 07 june 2016 ©e-geos2016 – 6 product 2:...

07 June 2016 ©e-GEOS2016 – www.e-GEOS.it 1

SAR interferometry applications for emergency mapping

D.Grandoni (e-GEOS S.p.A.)

Copernicus EMS Annual User Workshop

Ispra, June 21st 2017

http://www.e-geos.it/




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





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.





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





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)





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





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





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





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





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





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





MultiTemporal Coherence (MTC) – PRE/PRE

Detection of roads

Detection of water areas

Detection of built up area


PRE-PRE



Coherence (06-24 June 2016)

Woody area

Detection of grassland divided by edge rows





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



Coherence (27-28 August 2016)





Pescara del Tronto

Grisciano

Accumoli

Colle

COSMO-SkyMed

08/06/2016 24/06/2014 26/06/2016

Amatrice


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






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


08/06 – 24/06 pre-pre Coherence

24/06 – 26/08 pre-post Coherence

Mosicchio

S. Benedetto

Colli

Sommati

Prato





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)





SAR Interferomtric products on Amatrice





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





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.





Damage assessment – Open data

Damage assessment map generated less 24 hours after

the event by analyzing and georeferencing information

from open data (tweets, video,…)





Damage assessment – Optical

Damage assessment map generated based on

WorldView-1 image acquired on May 22nd, 2013





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





Damage assessment – SAR/Optical

Combination of SAR based damage assessment with

Optical based damage assessment.





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

sar interferometry applications for emergency mapping · 07 june 2016 ©e-geos2016 – 6 product 2:...

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