Multispectral Imaging for the Analysis of Materials and Pathologies in Civil Engineering, Constructions and Natural Spaces

Resum

Multispectral imaging is a non-destructive technique that combines imaging and spectroscopy to analyse the spectral behaviour of materials and land covers through the use of geospatial sensors. These sensors collect both spatial and spectral information for a given scenario and a spectral range, so that, their graphical representation elements (pixels or points) store the spectral properties of the radiation reflected by the material sample or land cover. The term multispectral imaging is commonly associated with satellite imaging, but the application range extends to other scales as close-range photogrammetry through the use of sensors on board of airborne systems (gliders, trikes, drones, etc.) or through their use at ground level. Its usefulness has been proved in a variety of disciplines from topography, geology, atmospheric science to forestry or agriculture. The present thesis is framed within close-range remote sensing applied to the civil engineering, cultural heritage and natural resources fields via multispectral image analysis. Specifically, the main goal of this research work is to study and analyse the radiometric behaviour of different natural and artificial covers by combining several sensors recording data in the visible and infrared ranges of the spectrum. The research lines have not been limited to the 2D data analysis, but in some cases 3D intensity data have been integrated with 2D data from active (terrestrial laser scanners) and passive (multispectral digital cameras) sensors in order to analyse different materials and possible associated pathologies, getting more comprehensive products due to the metric that 3D brings to 2D data. Works began with the radiometric calibration of the active and passive sensors used by the vicarious calibration method. The calibrations were carried out through MULRACS, a multispectral radiometric calibration software developed for this purpose (see Appendix B). After the calibration process, active and passive sensors were used together for the discretization of sedimentary rocks and detecting pathologies, as moisture, in façades and in civil structures. Finally, the Doctoral Thesis concludes with a theoretical book chapter in which all the know-how and expertise arising during this research stage have been compiled.