A USAL student has developed a low-cost methodology to reveal, in a rigorous way, pathologies present in façades and buildings, without having contact with them and through new technologies.
They are living testimonies of civilisation and constitute the most valuable heritage that shapes reality and the future. They are buildings, landscapes, ruins, sculptures, churches, murals, museums, paintings and even streets. The reality is that, despite their high value, many have wounds. The sum of the passage of time or the negligence of their owners has dragged them to this point.
To put a stop to this unfortunate situation, Susana del Pozo, a student at the University of Salamanca, is immersed in a project whose goal is to develop a low-cost methodology that allows ‘rigorous’ detection of pathologies present in façades and civil constructions, without having contact with them and through the use of new technologies.
In this sense, multispectral images are emerging as a “non-destructive” alternative to the most expeditious inspection methods in the fields of civil engineering and cultural heritage. It involves remote data capture with both passive sensors –conventional and multispectral cameras– and active sensors –terrestrial laser scanners– that work within the visible infrared range of the electromagnetic spectrum. “These devices capture the light reflected by the materials and if we can determine this proportion, we will be able to know what pathology we are dealing with,” explains Del Pozo. Therefore, the challenge is to transform each value stored by each pixel of the images into a real physical reflectance value. This transformation process is called radiometric calibration.
In this project, a low-cost measurement has been chosen, such as a six-channel multispectral camera, various coloured canvases and vinyls that have been used as control surfaces, as well as various homogeneous natural and artificial surfaces such as grass, asphalt, cardboard, etc. In addition, a pioneering software has been developed –MULRACS– to assist the calibration process that is valid for any type of sensor and wavelength within the visible infrared range of the spectrum. “It allows images from each sensor to be transformed into images with reflectance values through a very intuitive interface and processing.”
At present, routine inspections are carried out visually, “with a subjective connotation” and based on the experience developed over years by the expert, without quantitative evaluations of the state of conservation in this regard, he says. That is why both a “rigorous evaluation and remote monitoring” are “key” to the conservation of these constructions, especially in the areas of greatest exposure to degradation factors.
The low-cost hardware-software combination and its own development make this proposal a “unique” methodology on the market, thanks to which studies and analyses of any type of material can be carried out, “which opens up the range” of disciplines that can benefit from it. The main advantage that sensors provide, as this woman from Avila points out, is that they provide geometry and metrics, so that any “injury” can be quantified.
This technology is based on the study of the behaviour of energy when it interacts with terrestrial materials. Specifically, it focuses on the study of the proportion of energy reflected by each surface for each wavelength of the electromagnetic spectrum, that is, obtaining the so-called ‘spectral signature’ of each material.
In this sense, the combination of different sensors –passive and active– is being used to capture the radiation reflected by the materials to be studied, in this case the facades of historic buildings and civil engineering works, and whether this radiation comes from the sun or is emitted by the devices themselves. The planning process for data collection is “crucial” to obtaining good results, highlights Susana del Pozo.
The added value of this project, which began in September 2011 linked to his doctoral thesis, is the savings resulting from the use of a low-cost methodology and processes, as well as the versatility in use both on platforms and in aerial devices such as drones or paramotors of moderate heights, for which the impact of atmospheric gases is negligible. It also offers the possibility of radiometrically calibrating any type of sensor using the software.
