TERRESTRIAL AND AERIAL GROUND-PENETRATING RADAR IN USE FOR THE ARCHITECTURAL RESEARCHES: ANCIENT 16TH CENTURY WATER SUPPLY AND DRAINAGE AT THE MONASTERY OF EL ESCORIAL (MADRID, SPAIN)
Remote sensing techniques in Archaeology are increasingly essential components of the methodologies used in archaeological and architectural researches. They allow uncovering unique forgotten data which are unobtainable using traditional excavation techniques, mainly because their precise location is lost. These data are still important since they can help to prevent flood effects inside the ancient building cellars and basements, as it happened periodically in El Escorial. Wide ancient drainage galleries run more than one hundred feet downhill outside the building, ensuring that rainwater and springs were adequately drained. Nowadays their plans are lost, and the lack of documents related both to the ancient water supply and drainage systems become an impediment to solve the stains of damp on the stone masonry walls and vaults, and even other occasional flooding effects. In this case, nondestructive techniques were needed to find the ancient underground passages in order to preserve the integrity of the building and its current activities. At a first stage oblique aerial infrared images taken from a helium barrage balloon helped to find easily, quickly and cheaply the buried masonry structures. Secondly, radar pulses were particularly interesting to image the subsurface as they were valuable means of assessing the presence and amount of both soil water and buried structures. The combination of both techniques proved to be an accurate and low-cost way to find the ancient drainage systems. Finally, results were produced by means of open source software.