Deformation Analysis Based on Terrestrial Laser Scanner Measurements (TLS-Defo, FOR 5455)

Relevance: Ageing Infrastructure

Highway bridges

Germany: 5000 bridges need refurbishment
US: > 40.000 bridges structurally deficient

Water dams

59.000 large dams worldwide, majority in a critical life time
United Nations University, 2021: Ageing dams pose growing threat

We have in Germany and worldwide substantial trouble with ageing infrastructure. Substantial amount of bridges are in a critical lifetime. There are examples for severe damages and for a full closure (A45, Valley bridge Rahmede) here in North Rhine-Westphalia.

Motivation

Within geodetic deformation analyses, we statistically test geometric changes of two or more object states. A rigorous assessment of significance is needed to separate between actual geometric changes and the uncertainty influences of measurement procedures and data processing methods.

Within the current state of the art, the deformation analysis rests upon point-based measurements, acquired by e.g. total stations, Global Navigation Satellite Systems (GNSS) or extensometers. The preselection of these individual points, that should characterize the object, falls into the responsibility of the engineer. In general, this selection demands interdisciplinary collaboration. After analyzing the movement of these individual points, the movement of the complete object is gained by a spatial generalization process.

Point-wise Deformation Analysis © IGG

start-point-cloud-detection of a deformation.jpg

Pointcloud Detection of a Deformation © IGG

Approach

In order to use TLS for deformation analyses, several challenges need to be solved. These challenges are closely related to the previously mentioned demand on small measurement uncertainties and strict significance investigations that need an entirely determined uncertainty budget. The challenges are:

A surface representation of the measured object surface is needed that allows for representing object details as well as for introducing smoothness assumptions. Additionally, changes in individual parameters should be connectable to individual – if possible spatially limited – deformations (Project 1).
Calibrating the laser scanner so that systematic instrumental errors are minimized (Project 2).
Determining a realistic variance-covariance matrix of the TLS measurements for describing the measurement uncertainty (Project 3).
Quantifying the model uncertainty that originates from deviations in the surface representation of the measured object surface since this representation only approximates the real surface (Project 4).
Complement the stochastic model of TLS measurements and model uncertainty by concepts for distribution-free uncertainty modelling to take remaining systematic errors into account by sets and intervals (Project 5).