Non-invasive analyses of a multi-stratified archaeological and historical site: the Crypta Balbi case-study

Abstract

Abstract A number of non-invasive techniques were used to study the state of conservation of an important archaeological site in the centre of Rome, the Crypta Balbi (part of the Museo Nazionale Romano), so-called after proconsul Lucio Cornelio Balbo, who in the year 13 BC built here a theatre in the Campus Martius [1]. Excavations are still ongoing, so new relevant archaeological findings could still be discovered. At the same time, this involves that each new finding must be conserved and preserved. To this aim, extensive monitoring campaigns are essential. The reconstructions in Figure 1 and 2 show the structure of the monument during the II century (imperial age) and after, until the 15th century [1]. Figure 3 shows the studied site as it is today. The theatre and the Crypta (a kind of courtyard) are located within the red dotted circles. Today it is close to a tramway in the city centre, that induces air pollution and vibrations potentially putting at risk this unique archaeological site. In order to study its various layers, a number of non-invasive techniques have been used. Among them: infrared cameras for the thermographic analysis, velocimeters to evaluate impact of vibrations, microclimatic parameters acquisition, kinematic analysis, digital video elaboration by motion magnification method. Substantially, this monitoring campaign was based on non-contact investigations in order to eliminate any danger to damage the elements of the monument, which provided useful insights. Thermal images of the monument were captured using a Flir T440 thermal infrared camera. Microclimatic parameters and data of weather stations were collected for correlation to experimental ambient vibration and NDTs data. In particular, air temperature and humidity were monitored by two MSR145 mini data loggers. Seismographs type SL06 SARA Instruments digital recorders equipped with SS02 triaxial velocimeters were used for the vibration monitoring. Each seismograph is independent and provided with battery for the energy supply and with a GPS antenna for synchronization, so that data from different instruments can be compared in the time domain. The instrumentation is very accurate, in fact the sensitivity is 400 V/m/s and the frequency range from 0.2 to 50 Hz, sampling frequency set at 200 Hz. Data were acquired from 10:00 a.m. to 12:00 a.m. Motion Magnification (MM) is a recently developed video processing methodology [2, 6, 5]. MM [2 - 6] acts like a microscope in digital videos, magnifying motions hardly visible with the naked eye, but leaving unchanged the topology of the images.