Using airborne laser scanning and historical aerial photos to identify Modern Age fortifications in the Minho valley, Northwest Iberia

Abstract

In the Institute of Heritage Sciences (Incipit), Spanish National Research Council (CSIC), we have developed a transdisciplinary research project to study the Modern Age (17th century) fortified landscapes in the Galician-Portuguese border. In recent years, different techniques based on geospatial technologies for landscape analysis have allowed us, among other things, to identify and visualize some of these fortifications, to analyse their conservation status and to understand their relationship with other fortified elements. Among these techniques, we include the photogrammetric restitution of historical aerial photos and airborne laser scanning data.

The research of this fortified landscape was based on documentary and bibliographic sources, archaeological prospection, architectural survey, photo-interpretation, the formal analysis of archaeological space, where we include the movement and perception analysis, the stratigraphic analysis or the use of a number of representation systems. Many of these fortifications from the Minho valley present significant conservation problems, since in some cases they are built on earth, wholly or partially destroyed after the war or hidden under dense vegetation.

Some of these fortified structures were identified in the documentary sources,but are not visible nowadays or in the field or even on recent aerial photos. In these cases, the archaeological work has been done with the photointerpretation of historical aerial photos from the 1950s and the use of airborne laser scanning data.

This poster will summarize the workflow and results of the application of these geospatial technologies to the Galician-Portuguese border fortified landscape. For our purposes, the application of airborne laser scanning data has allowed us to identify the archaeological features that were hidden by vegetation. We were then able to document the exact location of some fortifications, to check their condition and, above all, to make them visible, enhancing the visualization of certain structures. Similarly, the use of historical aerial photos, has allowed us to identify some fortifications that are now disappeared, or to check the deterioration that many have suffered from the 1950s to the present.

The landscape is a complex construction in which different meanings, different human actions and various historical layers intersect on a natural space. For its identification, documentation and assessment is necessary to use multidisciplinary approaches and to apply different tools. In this case,conventional archaeological work has been combined with other strategies that have improved our understanding of the Galician-Portuguese border fortified landscape, recovering the memory of some of the fortifications that form part of it and that were apparently lost.