Letters

Development of a Road Disaster Monitoring
System Using Optical Fiber Sensing Technology
Kazuhiko Fujihashi, Hideki Uehara†, Masaru Okutsu,
and Koji Komatsu
Abstract
NTT Access Network Service Systems Laboratories has developed a system for monitoring road disasters by using optical fiber sensing technology. This technology allows linear measurement over longdistances, which is advantageous when the length to manage is long and risk locations are difficult todetermine in advance. This article describes various sensors developed for monitoring road disasters andsoftware for controlling the measuring devices, processing data, and performing other tasks.

1. What is optical fiber sensing technology?
Optical fiber sensing technology is for measuring
strain, temperature, optical loss, and other phenomena by inputting a laser beam into an optical fiber andanalyzing the characteristics of the reflected or trans† NTT Access Network Service Systems Laboratories
Tsukuba-shi, 305-0805 Japan
E-mail: h-uehara@ansl.ntt.co.jp

Measurement method

mitted light. It covers several methods. NTT has
developed the Brillouin optical time domain reflectometer (BOTDR) and currently uses it [1], [2]. Thismethod allows continuous measurement of the strain
along an optical fiber based on the characteristic thatthe frequency distribution of the Brillouin scattered
light, which is one type of backward scattered light
generated when an optical pulse is input into an optical fiber, shifts in proportion to the axial strain of theoptical fiber (Fig. 1). On the other hand, the OTDR

Optical pulse input

Optical fiber

Scattered light power

ε1

Str
ε2

Detection of Brillouinscattered lightain
ε1

BOTDRZ1
DistanceZ2

νB2yencequht frLigFeaturesMeasurement along the optical fiber can be performed:• continuously (the entire optical fiber is the sensor)• over long distances (approximately 10 km)

νB1

The frequency shift of the Brillouin scattered
light is proportional to the strain.

Suitable for monitoring civil and architectural
structures (large structures)

Fig. 1. Overview of system using the BOTDR method.

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system measures the optical power of the Rayleighscattered light, making it possible to measure loss in
the longitudinal direction of the optical fiber, determine connection point positions, and calculate theoptical fiber length, etc.

the Ministry of Land, Infrastructure and Transportand other road managers are currently installinginformation boxes alongside roads and are laying
optical fibers for road management. If this opticalfiber network is used as the basic infrastructure, theoptical fibers can be branched for sensors at the necessary locations, which should be advantageous forconstructing a system covering a wide area. Thisdevelopment project was undertaken by NTT AccessNetwork Service Systems Laboratories (AS Labs).

2. Development background and current themes
Japan is a mountainous country with a harsh natural environment that includes typhoons, snowfall, andearthquakes, so it regularly experiences various disasters. Roads can be affected and disasters can have aserious impact on people’s lives and the economy.
Countermeasures have been implemented in someareas, but the lengths to manage are long and it is difficult to determine the locations of risks, so thesemeasures cannot be considered complete. Remotemonitoring using sensors and other devices is performed in some places, but most management relies
on human inspectors, so this is insufficient in terms ofsafety and speed of response. Furthermore, sensor
and other monitoring data is intermittent, maintenance and renewal cycles are short, and running costs
are a burden. To resolve these issues, NTT started todevelop a system using optical fiber sensing technology, which allows remote and linear monitoring overlong distances and which has superior weather andenvironmental resistance. This technology is thought
to be suitable for monitoring road disasters because
Various sensors*

3. System overview
The road disaster monitoring system includes fourfunctions for monitoring the collapse of sloping surface layers, disasters involving snow and ice, bridges,and tunnels (Fig. 2). Various sensors were developed;
installation methods, workability, and durability wereinvestigated; and software for controlling measuring
devices, processing data, and performing other tasks
was developed, as described below.
3.1 Monitoring the collapse of a sloping surface
layer
Sloping surface layers can collapse in various different ways depending on the topography, soil quality, vegetation, and other conditions. Locations wherecollapse might occur are difficult to determine. Optical fiber sensing technology should be able to cover a
Monitoring station

Observation station

Slope

Communicationinterface

Measuring devices
Snow and ice

NetworkBridge

Meteorological Agency
Weather

Subject of this development project

Sensor information
Weather information

Under normal circumstances

Optical fiber

Measurement data

Data
processing unit

Communicationinterface

TunnelDisplay unit*
Road information(Alarms, road closed, work, etc.)

Map information* Customized foreach customer

Alarm
Proposed response
Response instructions
and execution
In the event of an emergency

Results submitted
Transmission ofinformation via
the Internet

Display on roadinformation
signboards

Road inspection
patrols

Etc.
Work
Remove snow, sprinkle snow melting
agents, remove rocks and soil

Fig. 2. Road disaster monitoring system.

Vol. 1 No. 9 Dec. 2003

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Optical fiber waterlevel sensor

Optical fiber undergrounddisplacement sensor

Optical fiber

Optical fiber
Groundwater

Immobile point

wide area and detect even small-scalecollapses, letting road managers
quickly understand the scope of disasters. Prior to this development project, AS Labs was already participating in the “Joint Research on Monitoring Roadside Slope Collapse byUsing Optical Fiber Sensors” withmore than ten other private sector
companies led by the Incorporated
Administrative Agency Public Works
Research Institute (PWRI). In thatjoint research, AS Labs worked withNTT InfraNet Co., Ltd. and AirecEngineering Corporation to develop
optical fiber slope displacement sensors, optical fiber underground displacement sensors, and optical fiber
water level sensors, and carried out
field measurements on slopes alongside national road No. 19 on the outskirts of Nagano City (Fig. 3). During
this period there were no surface layer
collapses due to rainfall or other factors, but the workability and durability were confirmed. In addition, onsite tests were conducted using
forcible displacement, and the results
confirmed excellent measurement
characteristics.

gSlidin esurfac

Optical fiber slope
displacement
sensorOpticalfiber
Fixed boxes

To themonitoring station

NetworkBOTDR

Fig. 3. Monitoring the collapse of a sloping surface layer.
Optical fiber blizzard sensor

Optical fiber avalanche sensor

Optical fiber
snowfall sensor

To the monitoring
centerNetwork

Optical fiber road surface
temperature sensor

BOTDR/OTDR

Fig. 4. Monitoring disasters involving snow and ice.
3.2 Monitoring disasters
involving snow and ice
Approximately 60% of Japan experiences snow
3.3 Monitoring bridges
and cold weather, so winter road management is an
Bridges are focal points for transport not only underimportant issue. Road upkeep management costs andordinary circumstances, but also in the event of disasenvironmental loads must be reduced while at theters. Managing their upkeep, ensuring safety, andsame time maintaining safety by appropriately
improving earthquake resistance are important
removing snow or melting it (by sprinkling snow
themes for road managers. Bridge monitoring conmelting agents or heating the road). BOTDR snowfall
sists of monitoring the deterioration of the upperand road surface temperature sensors and OTDR
structure and monitoring bridge deformation (girderavalanche and blizzard sensors were developed tomovement, bridge pier tilting, etc.) after an earthdetect avalanches and freezing road surfaces andquake. However, considering the accuracy required
report them to managers (Fig. 4). To confirm thefor each of these tasks and the accuracy of currentfunctions of these newly developed sensors, fieldmeasuring devices, deformation was selected as thetests were conducted in cooperation with the Hokkaidevelopment subject (Fig. 5). Displacement sensors
do Otaru Civil Works Field Office from December
were developed to measure and detect the magnitude2002 to May 2003 alongside prefecture road No. 998
of bridge girder movement to judge bridge soundness(Shakotan peninsula). The results confirmed that all
and the feasibility of using them to transport goods
sensors satisfied the target performance for the mostimmediately after earthquakes. Specifically, we fabpart.
ricated prototype sensors that quantitatively measuredisplacement using the BOTDR method and simulta-50

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neously use the OTDR method tojudge whether management reference values have been exceeded.
Their functions were confirmed
through indoor tests and heat cycle
tests, etc.

Optical fiber
displacement sensors

Fig. 5. Monitoring bridges.

3.4 Monitoring tunnels
Recently, incidents of concrete
peeling or dropping from railway
tunnels and other locations have beenreported. The structure monitoring
function uses optical fiber sensing
technology (BOTDR method) tomonitor these types of structuralchanges to tunnels owned by NTT
Group companies. This function wasadded to the Tunnel Management
System from fiscal year 2001. InNTT tunnels, sensor cables are fixed to the inner surface of the tunnel in the axial direction at 2-m intervals, and they mainly monitor the occurrence ofcracking. This technology has also been applied toroad tunnels. In addition, prototype water-level-type
subsidence sensors, which use optical fiber sensors tomonitor tunnel sloping, were fabricated and their performance was confirmed through indoor tests (Fig.
6).
3.5 Road disaster monitoring software
Software was developed to control the various measuring devices described above and to gather, analyze, and display the data from the various sensors(Fig. 7). The overall monitoring system consists ofthe various sensors, optical switches, the BOTDR andOTDR, a control PC, a monitor PC, and this software.
The main functions of this software are listed inTable 1.

Optical fiber
sensor cable

Optical fiber
water-level-type
subsidence sensor

Fig. 6. Monitoring tunnels.

Displaying mapsDisplaying sensor information

Displaying BOTDR data

Fig. 7. Example screen-shot of road disaster monitoring
system.

References[1]

4. Conclusion[2]

NTT Access Network Service Systems Laboratories has developed a road disaster monitoring systemusing optical fiber sensing technology. This system
was designed mainly for roads, but it can also be
applied to other civil structures. We expect NTT
group companies to continue developing it for various other fields.

Vol. 1 No. 9 Dec. 2003

Displaying processed data

H. Naruse, “Application of Optical Fiber Strain Gauge Technology toCivil Structures,” NTT Technical Journal, Vol. 11, No. 5, pp. 69-71
1999 (in Japanese).
T. Kurashima, “Non-destructive Measurement of Optical Fiber Strainand Loss from One End,” NTT Technical Journal, Vol. 9, No. 6, pp.
87-89, 1997 (in Japanese).

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Table 1. Outline of road disaster monitoring software functions.
Function

Description

Controlling measuring devices

Setting measurement conditions for each measuring device (BOTDR, OTDR) and setting the timetable for
periodic measurement

Displaying measurement data

Displaying measurement data (strain, loss), loading and displaying stored data, and converting displayed
data to .txt format

Registering and displaying
sensor information

Registering and displaying various information regarding individual sensors including sensor type, sensor
name, number of channels, route length, sensor section, compensation section, management reference
values, and calibration coefficients.

Displaying maps

Displaying maps of the monitored area (zoom in/out, move up/down/left/right) and displaying registeredsensors on the map

Processing and displaying data

Processing physical quantities (displacement, temperature, etc. ) or making various judgments based on
measured data and displaying them as time series.

Giving alarms

Displaying on the map in conspicuous colors any locations where the management reference values havebeen exceeded and sounding an alarm. “Caution” and “Warning” histories are stored.

Kazuhiko Fujihashi

Masaru Okutsu

Senior Manager, Business development group,
NTT InfraNet Corporation.
He received the B.E. and M.E. degrees in civilengineering from Waseda University, Tokyo in
1981 and 1983, respectively. In 1983, he joined
Nippon Telegraph and Telephone public corporation (now NTT corporation). From 1990 to1992, he worked in the Facility Design Section of
the Kanto Region Facility Construction Management Center. From 1992 to 1996, he worked inthe Access Network System Project Group of theAccess Network Systems Laboratories. From1996 to 1998, he worked in the Urban Civil Engineering Office of the Kyushu Region FacilityConstruction Management Center. From 1998 to2003, he worked in the Civil Engineering Projectof Access Network Service Systems Laboratories. He is now engaged in the development ofoptical fiber sensing technology and technology
sales. He is a member of the Japan Society ofCivil Engineers (JSCE) and Japan Association
for Earthquake Engineering (JAEE).

Chief examiner, Corporate planning division,Kansai branch, NTT InfraNet Corporation.
He received the B.E. and M.E. degrees in civilengineering from Waseda University, Tokyo in
1994 and 1996, respectively. In 1996, he joined
NTT Access Network Laboratories, Tsukuba,
Japan. He took up his present position in 2003.
From 1996 to 2003, he was engaged in the development of optical fiber sensing technology anddisaster prevention technology for undergroundfacilities. He is now engaged in management
planning. He is a member of JSCE and JAEE.

Hideki Uehara
Senior research engineer, Civil Engineering
Project, NTT Access Network Service Systems
Laboratories.
He received the B.E. degree in civil engineering from the University of Tokyo, Tokyo in
1983. In 1983, he joined Nippon Telegraph andTelephone public corporation (now NTT corporation). From 1997 to 2000, he worked in NTT
West Corp. corporate sales headquarters. From2000 to 2003, he worked in the customer service
section of NTT Communications Corp. He is
now engaged in the Civil Engineering Project ofthe Access Network Service Systems Laboratories. He is a member of JSCE.

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Koji Komatsu
Engineer, Civil Engineering Project, NTTAccess Network Service Systems Laboratories.
He received the B.E. and M.E. degrees in civilengineering from Waseda University, Tokyo in
1996 and 1998, respectively. In 1998, he joined
NTT Access Network Laboratories, Tsukuba,Japan. He has been engaged in the developmentof optical fiber sensing technology and disasterprevention technology for underground facilities.
He is a member of JSCE and JAEE.

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