Intensity of the Terrestrial Laser Scanning Data: Incident ...c4@87-intensity_of_the... ·...

Intensity of the Terrestrial Laser Scanning Data: Incident Angle and Surface Reflectance Effects

Verica Erić1, Martina Göring2

1Faculty of Civil Engineering, University of Belgrade, Serbia2Jade University, Oldenburg, Germany

16. Oldenburger 3D Tage | 02. Februar 2017

Motivation

Intensity of the Terrestrial Laser Scanning Data: Incident Angle and Surface Reflectance Effects | V. Erić & M. Göring 2

Target at 90° (Imager 5010C)

Devi

atio

ns fr

om p

lane

(mm

)

X (mm)

Target at 90° (API Tracker 3)

Devi

atio

ns fr

om p

lane

(mm

)

X (mm)

range of deviations: [-4.0 mm, 3.4 mm]

range of deviations: [-0.6014 mm, 0.7237 mm]

white stripewhite stripe

Motivation

Laser scanning point cloud geometrical information - X, Y, Z coordinates radiometrical information - intensity (I)

Intensity values (Z+FLaserControl) 0 – 5.000.000 (absolute values – Z+F Imager 5010C) 0 - 1 and 0 - 255 (normalized values)

Mostly used for point cloud visualisation


Motivation

Intensity values optical properties of surface hemispherical reflectance of surface from TLS data (Tan et al. 2016)

Application in the process of data estimation water surface mapping from ALS data (Höfle et al. 2007) for improving registration of point clouds (Böhm & Becker 2007) registering TLS data with digital camera images (Parmehr et al. 2014)

…

But the calibration of the obtained intensity values is needed! (Pfeifer et al. 2007, Kukko et al. 2008, Kaasalainen et al. 2009, Tan & Cheng 2016,…)


What affects intensity?

Calibration of the intensity values instrumental effects surface characteristics surface reflectance scanning geometry incident angle atmoshperic effects laser light characteristics

Intensity of the Terrestrial Laser Scanning Data: Incident Angle and Surface Reflectance Effects | V. Erić & M. Göring

Soudarissanane (2016)

5

Experiment


Z+F Imager 5010Cphase based, 1500 nm wavelength

beam divergence: < 0.3 mrad (full angle)beam diameter: approx. 3.5 mm (at 0.1 m)

Zenith LiteTM Diffuse Reflectance Target

Z+F Imager 5006iphase based, 785 nm wavelength

beam divergence: 0.22 mrad (full angle)beam diameter: 3 mm circular (at 1 m)

6

Experiment

Zenith LiteTM Diffuse Reflectance Target nearly ideal Lambertian, diffuse reflectance 4 stripes - each 5 cm x 20 cm effective spectral range: 260 – 2500 nm uniform BRDF over all angles


1500 nm (5010C)

785 nm (5006i)

white (95%) 94.660% 95.910%

light grey (50%) 41.307% 43.111%

dark grey (20%) 25.126% 23.409%

black (5%) 4.547% 4.350%

Spectral reflectance of the target (Calibration certificate, May 2015)

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Experiment

Measurement setup location: Laboratory for optical 3D measurements, Jade University, Oldenburg 2 instruments set up next to one another

Z+F Imager 5010C – extremely high resolution Z+F Imager 5006i – super high resolution

target placed at approximately 10 m distance target at approx. 90°, 80°, 70°, 60° incident angle


Data Processing


Manual selection of the target point clouds (acquired on whole target and on each stripe separately) exportedabsolute (original) intensity values (increments, 0 – 5.000.000)

SVD algorithm for best-fit plane for all target’spositions (whole target dataset) precisely estimated incident angle (normal vector = 90° incident angle)

Incident angle and surface reflectance effects on intensity values

9

Z+F LaserControl®

Incident Angle Effect


50% Reflectance

20% Reflectance

95% Reflectance

5% Reflectance

Z+F Imager 5010C

10


Strong dependence between intensity values and incident angle as incident angle decreases, intensity values for all stripes decrease

for Imager 5010C, values decreased for: 95% reflectance stripe – 23%

st. deviation - 19%

50% reflectance stripe – 20% st. deviation - 31%



distance to target ≈ 10 m


95% Reflectance StripeImager 5010C

Original Intensity Values (increments)

Prob

abili

ty D

ensit

y Fu

nctio

n

11

Strong dependence between intensity values and incident angle Imager 5010C – linear dependence between intensity values and incident angle for all stripes except

for 5% reflectance stripe



95% Reflectance Stripe (Imager 5010C)

Incident Angle

Orig

ina

Inte

nsity

Val

ues (

incr

emen

ts)

5% Reflectance Stripe (Imager 5010C)

Incident Angle

Orig

ina

Inte

nsity

Val

ues (

incr

emen

ts)

12


Strong dependence between intensity values and incident angle as incident angle decreases, intensity values for all stripes decrease

for Imager 5006i, values decreased for:





distance to target ≈ 10 m


95% Reflectance Stripe - Imager 5006i

Original Intensity Values (increments)

Prob

abili

ty D

ensit

y Fu

nctio

n

13

Strong dependence between intensity values and incident angle Imager 5006i – linear dependence between intensity values and incident angle for 95% and 50% but

not for for 20% and 5% reflectance stripes



95% Reflectance Stripe (Imager 5006i)

Incident Angle

Orig

ina

Inte

nsity

Val

ues (

incr

emen

ts)

5% Reflectance Stripe (Imager 5006i)

Incident Angle

Orig

ina

Inte

nsity

Val

ues (

incr

emen

ts)

14

How do surfaces of different reflectance affect intensity values?

For both TLSs and for all incident angles:

the higher the reflectance of surface is, the higher the intensity values are

the higher the intensity values are,the higher the standard deviations are

change in intensity values is not proportionalto the change in surface reflectance

lower intensity values can be measured more precisely

Surface Reflectance Effect


Z+F Imager 5010C (EHRNQ)

90° inc. angle 95% 50% 20% 5%No of points 18140 18300 18300 18300

Mean 2340582 1191041 793053 141786

St. dev. 34150 26325 24674 8642

Max - Min 216064 186880 82432 82432

Points out. ±σ 5749 5661 5793 4272

Z+F Imager 5006i (SHRNQ)No of points 732 732 732 732

Mean 924507 465672 275148 56001

St. dev. 13549 11560 7351 5121

Max - Min 87552 63488 53760 36764

Points out. ±σ 220 244 226 109

Intensity values analysis (in increments)

15

How do surfaces of different reflectance affect intensity values?

For both TLSs and for all incident angles:

the higher the reflectance of surface is, the higher the intensity values are

the higher the intensity values are,the higher the standard deviations are

change in intensity values is not proportionalto the change in surface reflectance


Intensity Values by Stripes (90°, Imager 5010C)

Horizontal Angle (°)



Inte

nsity

Val

ues [

incr

emen

t]

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Opposite effect of surface reflectance on measuring intensity values and positions of points lower surface relfectance more precise intensity values lower surface reflectance less precise measured positions of points



Target at 90° (Imager 5010C)

Devi

atio

ns fr

om p

lane

(mm

)

X (mm)

5% reflectance stripe


Intensity Values by Stripes (90°, Imager 5010C)

Horizontal Angle (°)

Inte

nsity

Val

ues [

incr

emen

t]



17

Conclusion and Outlook

Calibration of the intensity values provided by TLS is needed

Incident angle and surface reflectance affect the intensity values as incident angle decreases, intensity values also decrease – the biggest drop is for 5%

reflectance stripe (31% for Imager 5010C, 30% for Imager 5006i)

the higher the surface reflectance is, the higher the intensity values are


Opposite effect of surface reflectance on measuring intensity values and positions of points


Conclusion and Outlook

Future steps: different calibrated target-TLS distances, same incident angle

different calibrated target-TLS distances, different incident angles

estimation of surface reflectance from obtained intensity data

…


calibrated target

non-calibrated target

non-calibrated target

Baselines in Sandkrug

Thank you for your attention!

Verica Erić1: [email protected] Göring2: [email protected]

1Faculty of Civil Engineering, University of Belgrade, Serbia2Jade University, Oldenburg, Germany

mailto:[email protected]

mailto:[email protected]

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