laser scanning technology for pavement monitoring - erpug · fraunhofer institute for physical...

Alexander Reiterer Fraunhofer Institute For Physical Measurement Techniques (IPM)

Laser Scanning Technology for Pavement Monitoring – A New Approach

Alexander Reiterer Fraunhofer Institute For Physical Measurement Techniques (IPM)

Laser Scanning Technology for Pavement Monitoring – A New Approach

Outline Fraunhofer IPM

Principle of a Laser Scanner

Concept of a Pavement Profile Scanner

Realized Technical Specification

Evaluation and Calibration

Examples of Implementation

Results

Conclusion and Outlook

© Fraunhofer IPM / Folie 3

Fraunhofer IPM The Institute

Services

Consulting – feasibility studies, technology-oriented market studies, technology assessment

Development – components, systems and pilot production

Support – implementing and maintenance of systems, technology transfer, coaching, workshops

Staff: 225 Employees Operating budget 2012 € 13.7 million, thereof € 4.8 million industrial proceeds

Dr. Alexander Reiterer - [email protected]


Fraunhofer IPM The Institute / Research Group “Laser Scanning LSC”

Contact Wire

Poles

Clearance Profile

Geometry

Road Pavement

Software



Pavement Monitoring Motivation

intact road infrastructure is an essential precondition for a functioning economy

One of the principal parameters of a road surface is its evenness

Based on the transverse profiles taken (generally in 1 m grids), the parameters of rut depth and theoretical water depth are calculated for the left and right wheel tracks.

→ Precise measurement / monitoring of the road surface necessary.



Pavement Monitoring (evenness, material characteristics) State of the Art

Measurement device for measurement of transverse profile with laser distance sensors mounted on a bar with a length of 3.3.m. → Dr. D. Wehrhan (Germany)

High-speed cameras, optics and laser line projectors to acquire high-resolution 3D profiles of the road. → e.g. Pavemetrics (Canada).

© Pavemetrics © Lehmann und Partner

Disadvantages: bulky, expensive and unsafe (Laser Class 3B!)

© Phoenix Scientific Inc.



Pavement Monitoring (evenness, material characteristics) State of the Art

Solution: Small, precise and safe (Laser Class 1!) device based on laser scanning technology.

Requirements:

relative precision of 0.3 mm.

max. point distance of 5 mm (transversal).

measurement independent from ambient light situation.

measurement independent from surface structure (color, roughness, etc.).

stable housing (IP67).

eye safe (laser class 1).



Laser Scanning Technology Principles

45°-Mirror Mirror as Polygon

Components of a laser scanner:

→ distance measurement module

→ angular measurement module

→ optical beam steering module




Technology (Distance Measurement)

Pros Cons

pulse-based - medium and long range (2 m – 5.000 m)

- less accurate - slower data aquisition - higher noise

phase-shift - more accurate - faster data aquisition - lower noise

- medium range only (~ 100 m)




Phase Shift Method

→ fast method for distance measurement (millions points per second)

→ precise method for distance measurement (e.g. sub-mm for distances up to 5 m)

→ method for close-range



Pavement Profile Scanner PPS Technical Specifications




relative precision of 0.3 mm.

max. point distance of 5 mm (transversal).

measurement independent from ambient light situation.

measurement independent from surface structure (color, roughness, etc.).

stable housing (IP67).

eye safe (laser class 1).




Mirror as Polygon




Polygon Mirror

Interfaces

- Modulator - DCDC-Board - FPGA - …

Laser and Detector



Pavement Profile Scanner PPS Tests and Calibration Procedure

Step 1: Evaluation of Distance Measurement Unit (Static Mode)

- Measurement section of 4 m is used as reference - Continuing measurement of distance between scanner and target - Evaluation for different reference targets (reflectivity) → functional test and evaluation of precision of the distance measurement unit.

magenta, cyan: intensity white, yellow: phase shift measurement plus distance green: difference between PPS and reference measurement




Step 2: Evaluation of Scanner (dynamic mode, step-and-go)

- Measurement section of 10 m is used as reference - Continuing measurement of distance between scanner and target - Evaluation for different reference targets (reflectivity) - Evaluation of angular values (evaluation of the encoder) - Evaluation of the internal reference phase → calibration: non-linearity is considered by a lookup-table.

blue, magenta: distance (mean, standard deviation) red: intensity green: difference between PPS and reference measurement

Distance

Std




Step 3: Evaluation of Scanner (dynamic mode, mounting height)

- Measurement of vertical profiles of different reflectivity - Continuing measurement of distance between scanner and target - Reference values are measured by a Laser Tracker (AT901) - Evaluation of reference and scanner values → calibration: non-linearity depending on angular values are considered by a higher-order (4th) polynomial function.

- Functional test under different light situation - Evaluation of air-sealed housing → functional test under real conditions.

Step 4: Indoor/Outdoor Test of the Scanner




Calibration Protocol

PPS 101, SN: 114308-8 Light Grey 35% and 80% (*) Mean Grey 20% (*)

Noise (std. dev. < 0.2 – 0.3mm)

@ middle 0 deg. 0.17 mm 0.16 mm @ side 35 deg. 0.24 mm 0.24 mm

(*) on norm target, reference system = Leica Laser Tracker AT901B



Pavement Profile Scanner PPS Possible Implementations

Lehmann und Partner Germany




Lehmann und Partner Germany




Austria Institute of Technology Austria



Pavement Profile Scanner PPS Example (Schematic)



Pavement Profile Scanner PPS Results




- 2,5 %

- 2,3 %

- 2,0 %



Pavement Profile Scanner PPS Conclusion and Outlook

laser scanning device which is able to monitor the pavement with an (relative) precision of 0.1 – 0.3 mm.

eye safe technology (laser class 1).

robust technology.

used as a reference instrument by the German Federal Highway Research Institute (BASt)

Summery

Outlook

improvement of resolution of intensity channel (~1 mm).

improvement of measurement frequency up to 2 MHz.

→ measurement device for both geometry and crack monitoring.



Visit us on the Internet at www.ipm.fraunhofer.de/laserscanning

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laser scanning technology for pavement monitoring - erpug · fraunhofer institute for physical...

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