GeoRadar Division IBIS range PRODUCTS APPLICATIONS · GeoRadar Division IBIS-FS measured scenario...

GeoRadar Division

Static and Dynamic Monitoring of Civil Engineering Structures by Microwave

Interferometry

Garry Spencer and Mark Bell

1

GeoRadar Division

LANDSLIDE & DAM MONITORINGIBIS - FL

SLOPE STABILITY IN MININGIBIS - FM

STRUCTURE MOVEMENTSIBIS - FS

IBIS rangeAPPLICATIONSPRODUCTS

2XXV International Federation of Surveyors

Congress, Kuala Lumpur, Malaysia, 16 – 21

June 2014

GeoRadar Division

XXV International Federation of Surveyors


June 2014

3

GeoRadar Division

IBIS FS Hardware



June 2014

GeoRadar Division

Techniques behind the IBIS FS system

1. Frequency Modulated - Continuous Wave (FM-CW) technique for obtainingthe 1-Dimensional Range Profile with Range Resolution.

The IBIS FS product utilises two radar techniques:



June 2014

17.1 – 17.3 GHz

Single Transmit & Receive Burst

2. Interferometric technique

GeoRadar Division

The interferometric analysis provides data on object displacement bycomparing phase information, collected in different time periods, of reflectedwaves from the object, providing a measure of the displacement with anaccuracy of less than 0.01mm (intrinsic radar accuracy in the order of 0.001mm.)

Interferometric Technique

TX

RX

TX

RX

d

TX

RX

TX

RX

d

First acquisition

Second acquisition

1ϕ

2ϕ

( )124ϕϕ

πλ −−=d



June 2014

GeoRadar Division

The displacement is measured in the direction of the line of sight of the system.

Rh

d

dp

α

h

Rdd p ⋅=

R

h=)sin(α)sin(α

pdd =

To calculate the real displacement is needed to know the acquisition geometry

The distance Ris measured

by IBIS-S

1-D Interferometric technique



June 2014

GeoRadar Division

IBIS-FS measured scenario is determined by

• Antenna beamwidth (depending on the model, from 10° to 50°).

• User’s defined maximum range (up to 1 Km)

The measured scenario is divided into range bins, whose number depends on the range resolution (0.75 m minimum, constant with distance). Two targets at the same distance from the radar fall on the same range bins.

IBIS

-FS

n-thrange bin

Range profile

Distance (m)

IBIS-FS Acquisition Mode

Range resolution



June 2014

GeoRadar Division

IBIS-FS installed at the turbine pillar base (height 60m)

Welding lines are good reflective points

Range Profile: one dimensional image with 0.5m range resolution

IBIS-FS: 1-dimensional range profiles



June 2014

GeoRadar Division

Measurement accuracy: IBIS vs. Total Station

Test objective: comparison between IBIS-S results and a high-performance TotalStation in measuring a target displacement

Target distance: 33mForced displacement:• 3 x 1mm step towards IBIS-S and -3mm back• 2 x 0.5mm step towards IBIS-S and -1mm back• 5 x 0.1mm step towards IBIS-S and -0.5mm back



June 2014

GeoRadar Division

Measurement accuracy : IBIS vs. Total Station

0 500 1000 1500 2000-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

time [sec]

Rad

ial D

ispl

acem

ent [

mm

]1mm displacements

1 mm displacement

-0,0035

-0,0030

-0,0025

-0,0020

-0,0015

-0,0010

-0,0005

0,0000

0,0005

0 20 40 60 80 100 120

Measure Number

Dis

plac

emen

t (m

)

0 200 400 600 800 1000-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

time [sec]

Rad

ial D

ispl

ace

men

t [m

m]

0.5 mm displacement

0,5 mm displacement

-0,0015

-0,0010

-0,0005

0,0000

0,0005

60 80 100 120 140 160 180

Measure Number

Dis

plac

emen

t (m

)

IBIS-S results Total station results

1mm

ste

ps0.

5mm

ste

ps



June 2014

GeoRadar Division

0 500 1000 1500 2000 2500 3000 3500 4000 4500

-0.50

-0.40

-0.30

-0.20

-0.10

0.00

0.10

time [sec]

Rad

ial D

ispl

acem

ent [

mm

]

0.1 mm displacement

0,1 mm displacement

-0,0008

-0,0005

-0,0003

0,0000

0,0003

120 140 160 180 200 220 240 260 280 300 320 340 360 380 400

Measure Number

Dis

plac

emen

t (m

)

IBIS-S results Total station results

0.1m

m s

teps

Measurement accuracy : IBIS vs. Total Station



June 2014

GeoRadar Division

Static Monitoring

Load positionCorners

IBIS-FS



June 2014

GeoRadar Division

IBIS-FS corner reflectors

BEAMS

CORNERREFLECTORS

From the structure plan is possible to determine whether reflectors are needed or not.



June 2014

GeoRadar Division

0 10 20 30 40 50 60 7030

40

50

60

70

80

90CB

G

HD

EF

A

SNR

(dB

)

Ground-Range (m)

Range profile of P2-S – P3-S span

IBIS-FS installation

Bridge testing: static live load test

: Linear Variable Differential Transformer to measure displacement



June 2014

GeoRadar Division

LVDT

0 200 400 600 800 1000 1200 1400-30

-20

-10

0

10

B D F H

disp

lace

men

t (m

m)

time (s)

LC1


: Linear Variable Differential Transformer



June 2014

GeoRadar Division

LVDT

0 200 400 600 800 1000 1200 1400-30

-20

-10

0

10 IBIS-S LVDT

-20.50-15.62

-8.84

disp

lace

men

t (m

m)

time (s)

LC1


: Linear Variable Differential Transformer



June 2014

GeoRadar Division

P1P3 P4

P2

Static settlements of bridge’s pier and beam

5 m6,5 m

P4

P3

P2

P1

-0,6

-0,5

-0,4

-0,3

-0,2

-0,1

0

0,1

0,2

0 500 1000 1500 2000 2500 3000 3500 4000

tempo [s]

spos

tam

ento

[mm

]

P1

P2

P3

P4

Vertical movements of the 4 points



June 2014

GeoRadar Division

Dynamic Monitoring

Corners

IBIS-FS



June 2014

GeoRadar Division

Measurement objective: comparison with accelerometers, resonancefrequencies and modal shape retrieval

Central arch length (m): 62.5



June 2014

Dynamic Monitoring: Capriate bridge

GeoRadar Division

To make a comparison between theresults of IBIS-S system andaccelerometers system 6 corner reflectorwere installed at the same position ofaccelerometers



June 2014


GeoRadar Division

Bridge photograph and range profile



June 2014


GeoRadar Division

Velocity comparison for Test Point 22

Vel

ocity

[mm

/sec

]V

eloc

ity [m

m/s

ec]

Time [sec]

Time [sec]

IBIS-S

accelerometer

Zoom on the first 15 sec – direct comparison

IBIS-S

acc



June 2014


GeoRadar Division

Frequency analysis comparison on

3000sec acquisition duration

IBIS- FS

acc

Acc detected frequency

IBIS-S detected frequency

Percentage error

Hz Hz %

2,617 2,595 0,84

3,164 3,182 -0,57

6,641 6,608 0,50

8,086 8,077 0,1124XXV International Federation of Surveyors


June 2014


GeoRadar Division

f = 2.617 Hz

f = 6.641 Hz f = 8.086 Hz

f = 3.164 Hz

Modal shape obtained by accelerometer data




June 2014

GeoRadar Division

Modal shapes comparison

0 23 46 69 92 115-1.2

-0.6

0.0

0.6

1.2 Accelerometer IBIS-S sensor

Nor

mal

ized

Mod

e S

hape

Distance along deck (m)

0 23 46 69 92 115-1.2

-0.6

0.0

0.6


Nor

mal

ized

Mod

e S

hape


f=2.617Hz

f=3.164Hz




June 2014

GeoRadar Division

f=6.641Hz

f=8.086Hz

0 23 46 69 92 115-1.2

-0.6

0.0

0.6


Nor

mal

ized

Mod

e S

hape


0 23 46 69 92 115-1.2

-0.6

0.0

0.6


Nor

mal

ized

Mod

e S

hape

Distance along deck (m)Modal shapes comparison




June 2014

GeoRadar Division



June 2014

28

In Summary: • Interferometry deflection measurements were measured

and compared with accelerometer and Linear VariableDifferential Transformer fully validating the instrumentresults.

• The IBIS-FS can be rapidly deployed for short-termdisplacement and vibration monitoring with completemeasurement and set up time being less than one hour

• A great deal of information can be captured from a numberof points on a variety of structures very quickly making theunit an excellent alternative for economical static anddynamic surveys

GeoRadar Division



June 2014

29

Questions ?

Thanks for your attention

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GeoRadar Division IBIS range PRODUCTS APPLICATIONS · GeoRadar Division IBIS-FS measured scenario...

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