-1-Barcelona, June 27th, 20132nd ITFG Workshop

THz Signal & Image Processing

-2-Barcelona, June 27th, 20132nd ITFG Workshop

Outline

• SECTION 1: Alternative configurations

– Wide beam configuration (synthetic aperture processing)

– Tomographic configuration (tomosynthesis processing)

• SECTION 2: Challenge of data size

– Enhanced visualisation

– (Semi-) Automatic defect detection

-3-Barcelona, June 27th, 20132nd ITFG Workshop

Outline

• SECTION 1: Alternative configurations

– Wide beam configuration (synthetic aperture processing)

– Tomographic configuration (tomosynthesis processing)

• SECTION 2: Challenge of data amount

– Enhanced visualisation

– (Semi-) Automatic defect detection

-4-Barcelona, June 27th, 20132nd ITFG Workshop

Wide beam configuration

THz

THz

dept

h

azimuth

lenses

material under test

focusedbeam

unfocusedbeam

Top / overhead view

THz

THz

Beamwaist

• Small focused beam• Diffraction-limited• Data already focused• Lateral resolution: 1-3 mm

THz

dept

hazimuth

material under test

Top / overhead view

unfocusedbeamT

Hz

THz

THz

• No lenses needed• Wide unfocused beam (16º)• Data is focused in software• Lateral resolution: 4-7 mm

in-depthdefects

Focused FMCW Synthetic Aperture (SA) FMCW

-5-Barcelona, June 27th, 20132nd ITFG Workshop

3-D synthetic aperture imagery

Inserts - A-sandwich

100 GHz – Side A

Near surface

Rohacell core Honeycomb core

-6-Barcelona, June 27th, 20132nd ITFG Workshop

Debonds - A-sandwich - honeycomb core

Near surface

In depth

100 GHz – Side A

3-D synthetic aperture imagery

-7-Barcelona, June 27th, 20132nd ITFG Workshop

100 GHz – Side B

150 GHz – Side B

Near surface

Near surface

Debonds - A-sandwich - Rohacell core

3-D synthetic aperture imagery

-8-Barcelona, June 27th, 20132nd ITFG Workshop

Near surface

Debonds - C-sandwich - honeycomb core

100 GHz – Side B

150 GHz – Side B

3-D synthetic aperture imagery

-9-Barcelona, June 27th, 20132nd ITFG Workshop

100 GHz – Side A

Near surface

Impact (30 J) - Solid laminate - fibre glass

x-axis in mm

y-ax

is in

mm

20 40 60 80 100

10

20

30

40

50

60

70

80

90 0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

x-axis in mm

y-ax

is in

mm

20 40 60 80

10

20

30

40

50

60

70

80

90 0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

100 GHz – Side B

3-D synthetic aperture imagery

-10-Barcelona, June 27th, 20132nd ITFG Workshop

Tomographic configuration

Data procedure for 3-D imaging

• Technique for structural reproduction of object

• In THz the beam is close to a Gaussian distribution

• Information from reflected or transmitted beam

Process of acquisition/reconstruction

• Acquisition composed of a set of projections

• Modeled by the Radon transform

Tomosynthesis in transmission mode

-11-Barcelona, June 27th, 20132nd ITFG Workshop

Tomographic configuration

Tomosynthesis in reflection mode

View A

View B

View C• Reconstruction of internal

structure with more accuracy than unique reflection image

• Allow to converge to diffraction limit for BOTH lateral and longitudinal resolution

-12-Barcelona, June 27th, 20132nd ITFG Workshop

Tomosynthesis

Inserts – Solid laminate – Glass fibre

100 GHz – Side A

Images at different depths

-13-Barcelona, June 27th, 20132nd ITFG Workshop

Outline

• SECTION 1: Alternative configurations

– Wide beam configuration (synthetic aperture processing)

– Tomographic configuration (tomosynthesis processing)

• SECTION 2: Challenge of data size

– Enhanced visualisation

– (Semi-) Automatic defect detection

-14-Barcelona, June 27th, 20132nd ITFG Workshop

Challenge of data size

FMCW system

3-D data set – spatial information

TDS

3-D data set – spatial information 3-D data set – frequency information

CHALLENGE FOR THE OPERATOR

DOTNAC

• Enhanced visualisation for flat and curved samples• (Semi-) Automatic defect detection

-15-Barcelona, June 27th, 20132nd ITFG Workshop

Defect visualisation

Raw image representation Processed image representation

Water inclusion- A-sandwich - Honeycomb core

-16-Barcelona, June 27th, 20132nd ITFG Workshop

Defect visualisation

Impact (30 J) - Solid laminate - fibre glass

-17-Barcelona, June 27th, 20132nd ITFG Workshop

Automatic defect detection

Inserts - Solid laminate - fibre glass

Global Background

Input Denoised Image

Objects Boundaries

Mask Area of Interest

Foreground/Object Target

Classification

Segmentation

-18-Barcelona, June 27th, 20132nd ITFG Workshop

Automatic defect detection

Inserts - Solid laminate - fibre glass

-19-Barcelona, June 27th, 20132nd ITFG Workshop

3-D Visualisation

In-situ test on radome

3-D In-depth viewing 1 screenshot

Imaging with FMCW system

-20-Barcelona, June 27th, 20132nd ITFG Workshop

Questions?

-21-Barcelona, June 27th, 20132nd ITFG Workshop 21

Questions?

-22-Barcelona, June 27th, 20132nd ITFG Workshop

2nd ITFG Workshop

BFP: Backprojection of Filtered Projections

W0 corresponds to the projection P filtered by a ramp filter to increase details

A is the weight coefficient between the projection (θ;ρ) and the pixel (i; j)

We sum the filtered projections crossing each point

March 6th 2012

Reconstruction methods: BFP

-23-Barcelona, June 27th, 20132nd ITFG Workshop

2nd ITFG Workshop

SART: Simultaneous Algebraic Reconstruction Technique

OSEM (Ordered Subsets Expectation Method) Make initiak guess Check how well it corresponds

to the measured data Calculate the difference

between the result and real measurement

Correct the values Repeat until results satisfying

Iterative methods