Pulse phase thermography for characterising large historical building façades after solar heating and shadow cast – a case study

Abstract

For assessing building façades using active thermography, in case of direct solar exposure the sun itself can be used as heat source. It is shown that active thermography can be applied to large areas successfully, if a shadow cast occurs. After performing a sequence reconstruction in order to correct the temporal behaviour of shadow movement, the data could be analysed by pulse phase thermography (PPT). Compared to raw thermograms, the obtained phase images display an improved image quality with a lot of details. The frequency of the phase images is related to the probing depth. The presented case study describes the thermographic investigation of an historical building façade, where an area of 17 m × 13 m has been investigated.

Keywords:

• pulse phase thermography (PPT)
• building façade
• solar heating
• cultural heritage

Acknowledgements

The work was supported by the Research Initiative “Zukunft Bau” of the Federal Office for Building and Regional Planning, Germany (BBR AZ: SF-10.08.18.7-10.33) under the project title “Development of a time resolved 3D mapping of deformations and defects at buildings and structures”.

Special thank is given to the restorer of the cathedral, Thomas Groll, for his collaboration and helpful discussions.