Distributed fibre optic sensing: strain and temperature continuously along the fibre

With distributed fibre optic sensing, an optical cable becomes a sensor over its entire length. We plan the measuring system, install the sensing cables in piles, embankments, dikes and tunnels and monitor the readings continuously.

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Up to 80 km of fibre
A reading every 5 cm
Strain and temperature

Sensing cable in the structure Strain profile Local strain peak

Your benefits

One cable replaces thousands of individual sensors

Point sensors show what happens at their location. The fibre shows the whole component, including the spot where nobody would have placed a sensor.

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Continuous instead of point by point

The optical fibre itself is the sensor. Measurement covers the entire length, so a strain peak between two measuring points does not stay hidden.

Kilometres with one interrogator

One measuring unit covers lengths from a few metres to several tens of kilometres. Several cables can be read one after another via a switch.

Passive and robust

There is no electronics and no power supply at the measuring location. The fibre is immune to electromagnetic interference and lightning.

Permanently in the structure

Permanently installed sensing cables are maintenance-free, designed for a long service life and need no recalibration once calibrated.

The basics

What is DFOS?

DFOS stands for distributed fibre optic sensing. An optical fibre becomes the sensor itself and measures strain or temperature at every point along its length. Instead of individual measuring points, you get a continuous profile across the component, structure or terrain.

Measuring principle

An interrogator sends light into the fibre and analyses the Brillouin scattering. Its frequency shifts with strain and temperature, at every point along the fibre.

Strain or temperature

The cable decides which quantity is measured: in a strain cable the fibre is firmly bonded to the sheath, in a temperature cable it lies loose and stays free of strain.

Loop or single end

With both fibre ends connected to the interrogator, as a loop, the measurement is most accurate and reaches furthest. If only one end is accessible, the unit measures single-ended.

How it works

From sensing cable to strain profile

The interrogator stands protected at the edge of the structure, while only the passive cable lies in the structure. Every measurement delivers the complete profile over the full length.

01
Plan and install the cable

We define the cable type and routing and install the sensing cable: in concrete, in the ground, on the pile or in a groove on the surface.
02
Baseline measurement

After installation, the interrogator records the initial state along the entire fibre. This is the reference for every later change.
03
Measure the profile

Every measurement produces a complete profile of strain or temperature over the whole cable length, with readings a few centimetres apart.
04
Evaluate and report

The data are transmitted and evaluated automatically. Changes can be assigned to a location along the fibre and linked to limit values.

Technical data

The measuring system we use, in figures

Range, spatial resolution, accuracy and measurement time are linked. In the monitoring concept, we match them to the structure and the task.

Manufacturer data under favourable conditions. The achievable values depend on configuration, sensing cable and installation.

Measured quantities: Strain and temperature, depending on the sensing cable
Measuring principle: Brillouin scattering, frequency-domain measurement
Sensing length: A few metres up to 80 km of fibre, depending on the version
Spatial resolution: 0.5 m to 16 m selectable, down to 20 cm on lengths up to 2 km
Sampling interval: 5 cm along the fibre
Repeatability: Around 2 µm/m strain and 0.1 °C in loop measurement
Measurement time: About 1 minute for 2 km of fibre
Channels: Up to 32 sensing cables via a switch
Configuration: Loop measurement or single-ended measurement

Applications

Where distributed fibre optic sensing shows its strengths

Foundations

Piles and foundations

Strain distribution over the entire pile length, during installation, during the load test and in later operation.

Earthworks

Embankments, dikes and dams

One cable along the full length of an earth structure shows where settlement, sliding or erosion is developing.

Tunnels

Tunnels and shafts

In the shotcrete lining or on the inner lining, the fibre records deformation during excavation and in operation.

Slopes

Slopes and ground movement

Laid in the ground or integrated into geotextile, the fibre makes ground movement visible over large areas.

Installation

How the fibre gets into the structure

The installation method determines how well deformation is transferred to the fibre. We choose it to suit the structure, construction sequence and measured quantity.

Embedded in concrete, for example in piles, walls and tunnel linings
In a groove on the component surface, fixed with epoxy or cement
Laid directly in the ground or in a micro-trench
Integrated into geogrid or geotextile, for large areas
Attached to rock nails, anchors or surfaces where the ground is not accessible

DFOS complements other methods in geotechnical monitoring, such as automated total stations at the surface or tilt and settlement monitoring on individual components. Vibration is captured by vibration monitoring.

All from a single source

From cable planning to evaluation

We plan the fibre optic measuring system, install the sensing cables, operate the measurement and evaluate continuously. One contact for the whole project.

DFOS monitoring for your structure

Whether pile, dike, embankment or tunnel: we assess where a fibre shows more than individual sensors, and plan cable, installation and evaluation.

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Benedikt Seuss

Data platform

All readings on one platform

The sensors transmit their readings wirelessly to the data platform, where they are evaluated, documented and continuously checked against your thresholds.

AI-assisted data analysis
User-focused reporting
Continuous evaluation
Warning and alarm thresholds
Alerts by email and text message
Remote access around the clock

Frequently asked questions about DFOS monitoring

What is DFOS monitoring?

DFOS stands for distributed fibre optic sensing. The optical fibre itself is the sensor: an interrogator measures strain or temperature continuously along the entire fibre, over lengths from a few metres to many kilometres. Instead of individual measuring points, you get a continuous profile.

What exactly does an optical fibre measure?

With the Brillouin method used here, strain and temperature are measured. Which of the two is captured depends on the cable. In a strain cable the fibre is firmly bonded to the cable sheath and follows every deformation. In a temperature cable it lies loose and stays free of strain.

How long can the sensing length be?

Depending on the version, one interrogator covers up to 80 km of fibre. For most structures, lengths from a few hundred metres to a few kilometres are sufficient. Range, spatial resolution, accuracy and measurement time are linked and are balanced in the monitoring concept.

How fine is the spatial resolution?

The spatial resolution is selectable, typically between 0.5 m and 16 m. On lengths up to 2 km it can be refined to 20 cm. Readings are available every 5 cm along the fibre.

Does DFOS also measure vibration?

The Brillouin method used here measures strain and temperature, not vibration. For vibration we use dedicated sensors, for example in vibration monitoring and in construction vibration monitoring to DIN 4150-3.

Can existing fibre optic cables be used?

Existing telecommunications fibres are usually only suitable for temperature measurement. Strain measurement requires a cable in which the fibre is firmly bonded to the sheath, so that deformation is transferred to the fibre.

How is the sensing cable installed?

Depending on the structure, the cable is cast into concrete, bonded into a groove on the surface, laid directly in the ground or in a micro-trench, integrated into geogrid or geotextile, or attached to anchors and rock nails. We define cable routing and protection in the monitoring concept.

What happens if the fibre is damaged?

A damaged fibre can be repaired, or the cable is replaced. To prevent this in the first place, we plan cable routing, transitions and protection in the monitoring concept and support the installation.

Project inquiry

Let’s talk about your measurement task

Tell us about the structure, the length of the sensing section and the task. You will receive an initial assessment of cable type, installation and monitoring concept shortly.

+49 6742 8599600 DE +41 41 670 00 11 CH [email protected]