For all the European Countries, the rail network represents a key critical infrastructure, deserving protection

in view of its continuous structure spread over the whole territory, of the high number of European citizens

using it for personal and professional reasons, and of the large volume of freight moving through it.

Railway infrastructures monitoring with COSMO/SkyMed imagery

and multi-temporal SAR interferometry (ID: 1464682)

M. T. Chiaradia1, R. Nutricato1,2, D. O. Nitti1,2, F. Bovenga3, L. Guerriero1,2

1 Politecnico di Bari, Italy, 2 Geophysical Applications Processing – GAP srl, Bari, Italy, 3 National Research Council of Italy, CNR-ISSIA, Bari, Italy

[1] F. Bovenga et al., “SPINUA: A flexible processing chain for ERS/ENVISAT long term interferometry,” in Proc. ERS-ENVISAT Symp., Salzburg, Austria, 2004.

[2] F. Bovenga et al., “Application of multi-temporal differential interferometry to slope instability detection in Urban/Peri-urban areas,” Eng. Geol., vol. 88, no. 3/4, pp. 218–239, Dec. 2006.

[3] F. Bovenga et al., “Using COSMO/SkyMed X-band and ENVISAT C-band SAR interferometry for landslides analysis”, Remote Sensing of Environment, Volume 119, 16 April 2012, Pages 272-285.

[4] D. Calcaterra et al.,"Weathering-related Slope Instabilities of The Calabrian Arc (italy)". EGS XXVII General Assembly, Nice, 21-26 April 2002, abstract #2862.

[5] L. Cascini et al., “Advanced low- and full-resolution DInSAR map generation for slow-moving landslide analysis at different scales”. Engineering Geology, 112(1–4), 29–42, 2010.

[6] M. T. Chiaradia et al., “On the COSMO-SkyMed Exploitation for InSAR DEM Generation". AGU Fall Meeting, San Francisco, California, USA, 5-9 Dec. 2011, abstract #EP41A-0574.

[7] C. Colesanti et al. "Monitoring landslides and tectonic motions with the Permanent Scatterers Technique". Engineering Geology, 68(1), 3-14, 2003.

[8] C. Del Ventisette et al., "Using ground based radar interferometry during emergency: the case of the A3 motorway (Calabria Region, Italy) threatened by a landslide". Nat. Haz. Earth Syst. Sci., 2011.

[9] A. Ferretti et al., “Permanent scatterers in SAR Interferometry”. IEEE Transactions on Geoscience and Remote Sensing, 39, pp. 8–20, 2001.

[10] R. F. Hanssen, “Radar Interferometry: Data Interpretation and Error Analysis”. Dordrecht: Kluwer Academic Publishers, pp. 308, 2001.

[11] G. Iovine et al., "Emergency management of landslide risk during Autumn-Winter 2008/2009 in Calabria (Italy). The example of San Benedetto Ullano". 18th World IMACS / MODSIM Congress, 2009.

[12] G. Ketelaar. Monitoring surface deformation induced by hydrocarbon production using satellite radar interferometry. PhD Thesis, 2008.

[13] D. Reale et al., "Postseismic Deformation Monitoring With The COSMO/SKYMED Constellation". IEEE Geoscience Remote Sensing Letters, 2011.

[14] The IIFFI Project (Italian Landslide Inventory): http://www.sinanet.apat.it/progettoiffi

[15] National Geoportal (NG) of the Extraordinary Plan of Environmental Remote Sensing (EPRS-E): http://www.pcn.minambiente.it/GN/

Acknowledgements

CSK images provided by ASI (Agenzia Spaziale Italiana) in the framework

of the project “Landslide Monitoring and Mapping System - CAR-SLIDE”

(PON 01 00536). Optical images provided by GoogleEarth and

GoogleStreet. The authors would like to thank dr. J. Wasowski (CNR-IRPI,

Bari, Italy) for helpful comments on the achieved results.

Fig.3

0 2 km 4 km

Contacts

For further details please contact:

raffaele.nutricato@gapsrl.eu

davide.nitti@fisica.uniba.it

Multi-temporal Interferometric Analysis

SPINUA (Stable Point INterferometry over Un-urbanised Areas)

is a Persistent Scatterers (PS) interferometric algorithm for multi-

temporal Differential SAR Interferometric analysis. The processing

chain is the result of a joint effort of the Remote Sensing Group of

the Department of Physics at Politecnico di Bari and the ISSIA-CNR

institute of Bari. SPINUA has been developed with the aim of

detection and monitoring of coherent PS targets in non- or scarcely-

urbanized areas [1,2]. The processing chain has been further

updated in order to deal properly with X-band data from both CSK

and TerraSAR-X.

COMMENTS – The achieved results indicate that multitemporal SAR interferometric techniques may represent a valid and powerful tool for a

wide-scale constant monitoring of ground deformations occurring along railway infrastructures as well as surrounding areas affected by hydro-

geological instabilities. The X-band COSMO/SkyMed constellation represents an important added value since, thanks to the higher spatial and

temporal resolution, it allows to discriminate deformation regimes, such as structural instabilities, shallow and deep mass displacements [12].

SAR interferometry is the coherent combination of two (or more) SLC

images of the same area taken from slightly different directions:

COSMO SkyMed (CSK) constellation is an Italian Space Agency (ASI) mission made of 4 satellites able to

acquire SAR images in several imaging modes. CSK SAR sensor works in X-band providing spatial resolution

one order of magnitude better than the previous available satellite SAR data, as well as short revisit time (up to

8 hours for the full constellation). Recent scientific works have shown the advantages of using CSK in the monitoring of terrain deformations

caused by landslides, earthquakes, etc [3,13]. On the other hand, thanks to the high spatial resolution, CSK appears to be very promising in

monitoring man-made structures, such as buildings, bridges, railways and highways, thus enabling new potential applications. The multi-

beam capability (off-nadir look angle may be selected from 16° to 52°), as well as the right/left look side, gives us the ability to improve their

visibility along the line-of-sight (LOS): this depends indeed on the local orientation of the area, described by the aspect and slope

(inclination), with respect to the LOS. Starting from orbit information and from an available DEM, a visibility map can be derived [5] allowing

a preliminary inspection of the territory with the aim of searching areas suitable to InSAR monitoring, on one side, and selecting the best

available geometry (ascending or descending passes) on the other side.

Barritteri Reggio Calabria

ABSTRACT – The present work investigates the potentialities of the COSMO/SkyMed (CSK) constellation for railway infrastructures

monitoring through multitemporal SAR interferometric analyses with particular attention devoted to the impact of the improved spatial

resolution with respect to the previous SAR sensors.

A dataset of 57 right-looking CSK stripmap

Single-Look-Complex (SLC) images was

ordered: the full frame entirely covers the

area of interest, i.e. the stretch of the

Tyrrhenian railway line between Palmi and

Reggio Calabria (Region: Calabria, Italy), as

shown in Fig.1. The images were acquired

by the first two sensors of the constellation

between October 2009 and April 2012

(mean rate: one acquisition every 16 days),

along ascending pass in HH polarization at

a look angle of 29 deg (beam H4-03).

Range Chirp and Doppler Bandwidths are

~120 Mhz and 2.55 kHz, respectively,

leading to a ground resolution of 3x3 m2.

Fig.2 Fig.1

CSK Dataset

Introduction

The present study has been carried out in the framework of a scientific project named CAR-SLIDE (Mapping

and monitoring system for landslides forecast), funded by the Italian Ministry of Education, Universities and

Research (MIUR), aimed at producing a diagnostic system, capable to foresee and monitor landslide events

along railway networks by integrating in situ data, detected from on board sophisticated innovative measuring

systems, with Earth Observation (EO) techniques.

Railway system traverses a wide variety of terrains and encounters a range of geo-technical conditions. The interaction of these factors

together with climatic, and seismic forcing, may produce ground instabilities that impact on the safety and efficiency of rail operations.

In such context, a particular interest is directed to the development of technologies regarding both the prevention of mishaps of

infrastructures, due to natural disasters and/or to terrorist attacks, and the fast recovery of their normal working conditions after the

occurrence of accidents (disaster managing). Both these issues are of strategic interest for EU Countries, and in particular for Italy, since,

more than other countries, it is characterized by a geo-morphological and hydro-geological structure complexity that increases the risk of

natural catastrophes due to landslides, overflowings and floods.

Particular importance is attached to the use of advanced SAR interferometry, thanks to their all-

weather, day-night capability to detect and measure with sub-centimeter accuracy ground surface

displacements that, in such context, can occur before a landslide event or after that movements [7].

Special attention is directed to the use of SAR images acquired by CSK constellation capable to

achieve very high spatial resolution and very short revisit and response time [3,13].

In this context, a stack of 57 CSK stripmap images has been acquired, covering the Calabria's Tyrrhenian

coast, between the towns of Palmi and Reggio Calabria. The imaged area is of strategic importance since

The two towns are connected by a stretch of the Tyrrhenian railway line, a fundamental line (as classified

by RFI, the Italian Rail Network) belonging to the TEN-T network, i.e. the trans-european transport network

defined since early '90 by the European Commission. Moreover, Calabria region is a challenging area where carrying on an analysis on

weathering-related slope movements [4]. In Calabria, on 2009 the geo-hydrological crisis was so severe that the Italian Government had to

declare the state of emergency [8,11]. This work concerns the processing of the CSK dataset through multi-temporal InSAR techniques.

Displacement maps derived on the area of interest are presented and commented with particular attention to the potential impact that such

EO-based product can have on the railway networks monitoring, threatened by local failures as well as landslide phenomena [8].

Fig.4a

Fig.4b

Multi-temporal interferometric techniques have been developed with

the aim of tackling the effects of critical error sources, such as that

associated with the interaction between the microwave signal and the

atmosphere [10], that may limit the accuracy of topography estimation

and detection of small movements. By processing stacks of SAR

images, several differential interferograms are generated and properly

combined to allow identifying and monitoring targets on the ground that

remain coherent to a sufficient degree through time [9]. For these

targets it is possible to provide time series of accurate displacements,

as well as very precise topographic corrections to the reference

topography thus allowing also precise geographic localization even at

the highest (full) sensor resolution.

Here we report the results obtained by processing through SPINUA

algorithm the CSK stripmap dataset in Fig.2. Figure 3 shows the

displacement rate map for the entire investigated area, delimited by the

gray-shaded area. The density of the measurable coherent targets

depends on the ground coverage, and it is maximum (even > 40K

PS/km2) over urban areas thanks to the abundance of artificial

structures with coherent backscattering. It drops abruptly, instead, over

vegetated areas (because of the poor penetration depth of the radar

signal, especially in X-band) or along slopes affected by layover and

shadow. These results are in line to those obtained on other sites [6].

Refe

ren

ces

Normal Baselines span around 1.8 km, as shown by the spatial and temporal baseline distribution of Fig. 2.

ErrATMMOV

INT hr

B

sin

4

0

Topography Atmospheric

artifacts Movement

Processing errors

(noise, orbital inaccuracy)

Figure 4 refers to the stretch of the

TEN-T railway line between

Bagnara Calabra and Favazzina,

two small towns along the

Calabria’s Thyrrenian coast. Fig.4a

refers to the displacement rate

map, while the refined topographic

information (w.r.t. a reference

SRTM 90-m DEM) is shown in Fig.

4b. The entire stretch is densely

covered by PS, thus allowing a

constant and uniform monitoring.

Further examples are shown in the

insets below (Figures 5÷9).

Due to its complex orography and litography [4],

many case studies of infrastructures threatened

by landslides have been documented in the

Calabria Region [8]. Fig.7 shows moving PS over

all the extension of the “Giambarelli” viaduct (A3

highway), close to Barritteri town, due to ground

instabilities also reported in the IFFI web

catalogue [14]. Our results are in line with low-

resolution ascending ASAR C-band velocity

maps provided by [15] for the period 2002-2009.

A stretch of the TEN-T Calabrian

railway fundamental line between

Scilla and Favazzina towns, along the

Thyrrenian shoreline. The measured

linear PS density along the railway

line is close to the full SAR sensor

resolution (3m) for all tracks in

visibility (no tunnels) and not affected

by strong SAR distortions due to the

surrounding slopes.

The inset on the left shows

many moving coherent

scatterers (such as those

labeled PS_A and PS_B in

Fig.5b/c) along the old

elevated railway due to local

instabilities, while the

underlying breakwater seems

to be stable. Measured ground

mean velocities are close to

7÷8 mm/yr. Local inspections

are ongoing in the area.

Scilla-Favazzina Fig.5a

Fig.5b

Fig.7 Figures 8 and 9 refer to the Reggio Calabria urban area.

These test sites have been selected as further example of

the high density of coherent scatterers achievable over

man-made structures (buildings, railway lines, highways

and airports) with high resolution X-band SAR satellite

sensors, thus encouraging new potential applications, as

intra-building deformation mapping.

Fig.4

Fig.5

Fig.7

Fig.8

Fig.6

Fig.9

Fig.9b

Fig.9a Fig.8

“Tito Menniti”

Airport (REG)

R.C. Central

Railway Station

Railway Station

R.C. S.Gregorio

IFFI

Archi Another example of ground

instabilities affecting the

Thyrrenian railway line.

Local inspections are

ongoing in the area.

Fig.6

Fig.5c

PS_A PS_B

PS_B PS_A