Pasquale Poggi

Infrasonic waves and volcanic tremor at Stromboli

The origin of the volcanic tremor is still under debate. Many theories have been proposed in the last years, but none has yet been completely accepted. In 1993, highly sensitive pressure sensors (2.175 Pa/Volt) used to monitor the explosive activity at Stromboli have revealed unexpected correlation between small spike-shaped pressure signals (1–2 Pa) and volcanic tremor. These pressure pulses repeat regularly in time with a recurrent period of ca. 1 s. Video camera images allowed us to correlate the pressure pulses with small gas bursts occurring at one of the active vents. The striking correlation (0.971) between infrasonic and seismic energy fluctuations is particularly meaningful in the frequency domain. Infrasonic and seismic signal share the same spectral content (3 Hz) for every station within a range of 700 m around the craters. Correlations in time and frequency domain remained unaltered during the 1994 field experiments. Moreover, during 1994, the increased degassing activity has been followed by an increase in pressure release (7–8 Pa) and by a shift towards higher frequencies (8 Hz) both in the infrasonic and seismic records. Infrasonic waves and volcanic tremor show similar energy fluctuations and frequency contents, appearing therefore to be produced by the same dynamical process. On this basis, we claim that volcanic tremor at Stromboli originates by continuous outbursting of small gas bubbles in the upper part of the magmatic column.

Imaging live humans through smoke and flames using far-infrared digital holography

The ability to see behind flames is a key challenge for the industrial field and particularly for the safety field. Development of new technologies to detect live people through smoke and flames in fire scenes is an extremely desirable goal since it can save human lives. The latest technologies, including equipment adopted by fire departments, use infrared bolometers for infrared digital cameras that allow users to see through smoke. However, such detectors are blinded by flame-emitted radiation. Here we show a completely different approach that makes use of lensless digital holography technology in the infrared range for successful imaging through smoke and flames. Notably, we demonstrate that digital holography with a cw laser allows the recording of dynamic human-size targets. In this work, easy detection of live, moving people is achieved through both smoke and flames, thus demonstrating the capability of digital holography at 10.6 μm.

Seismic, acoustic, and thermal network monitors the 2003 eruption of Stromboli Volcano

The date 28 December 2002, heralded the onset of a 7-month-long effusive eruption at Stromboli volcano in Italy. The onset was accompanied on 30 December by a large landslide (Figure 1). This landslide produced a tsunami that damaged the villages on Stromboli and affected coastal zones around the southern Tyrrhenian Sea [Pino et al., 2004]. Following the landslide, the eruption was mostly characterized by effusive activity with lava flows extending from vents between 500 and 650 m above sea level. Simultaneously, Strombolis typical explosive activity died out, with no explosions from the summit craters during the initial months of the eruption. However, a major explosive event on 5 April 2003 caused considerable alarm.

Optical reconstruction of digital holograms recorded at 10.6 μm: route for 3D imaging at long infrared wavelengths

We demonstrate the optical reconstruction in the visible range (0.532 microm) of digital holograms recorded at long IR wavelengths (10.6 microm) by means of a spatial light modulator. By using an integrated recording-reconstruction system, it is, in fact, feasible to achieve direct imaging of holograms acquired outside the visible range, i.e., in the IR spectrum. By choosing a Fourier recording configuration, the reconstructed image, obtained at about a 20 times shorter wavelength than the acquisition image, exhibits minor aberrations, which do not significantly affect the optical reconstruction. The high NA achievable at a long IR wavelength allows us to image large objects at reasonable distances.

Tracking Pyroclastic Flows at Soufrière Hills Volcano

Explosive volcanic eruptions typically show a huge column of ash and debris ejected into the stratosphere, crackling with lightning. Yet equally hazardous are the fast moving avalanches of hot gas and rock that can rush down the volcanos flanks at speeds approaching 280 kilometers per hour. Called pyroclastic flows, these surges can reach temperatures of 400°C. Fast currents and hot temperatures can quickly overwhelm communities living in the shadow of volcanoes, such as what happened to Pompeii and Herculaneum after the 79 C.E. eruption of Italys Mount Vesuvius or to Saint-Pierre after Martiniques Mount Pelee erupted in 1902.

Volcano seismicity and ground deformation unveil the gravity-driven magma discharge dynamics of a volcanic eruption

Effusive eruptions are explained as the mechanism by which volcanoes restore the equilibrium perturbed by magma rising in a chamber deep in the crust. Seismic, ground deformation and topographic measurements are compared with effusion rate during the 2007 Stromboli eruption, drawing an eruptive scenario that shifts our attention from the interior of the crust to the surface. The eruption is modelled as a gravity-driven drainage of magma stored in the volcanic edifice with a minor contribution of magma supplied at a steady rate from a deep reservoir. Here we show that the discharge rate can be predicted by the contraction of the volcano edifice and that the very-long-period seismicity migrates downwards, tracking the residual volume of magma in the shallow reservoir. Gravity-driven magma discharge dynamics explain the initially high discharge rates observed during eruptive crises and greatly influence our ability to predict the evolution of effusive eruptions.

Reliability of 3D Imaging by Digital Holography at Long IR Wavelength

Digital Holography (DH) in the infrared (IR) range presents some peculiar aspects compared with the more common DH in the visible range. The current major drawback is due to the size of the pixel pitch of presently available thermal cameras, which is rather large compared to what would be optimal, and what is possible with analog films. However, since the

New high-resolution IR-color reflectography scanner for painting diagnosis

{\hbox{CO}}_{2}

Tracking dynamics of magma migration in open-conduit systems

laser wavelength is 15 times longer than average visible wavelength, a much higher stability, a wider view angle, and shorter acquisition distances are achievable, allowing easier acquisition of large object holograms.

Infrared digital holography for large objects investigation

Infrared reflectography is a prominent optical technique for non-destructive diagnostics of paintings, which allows the visualisation of details hidden by the paint layers, because of their transparency characteristics to IR radiation. High-resolution reflectography was introduced around the end of the 80s by the Istituto Nazionale di Ottica Applicata, where a prototype of an innovative scanner device was developed. This technique was recently improved with the introduction of a new optical head, able to acquire simultaneously the reflectogram and the colour image, perfectly superimposing. The technical characteristics of the IR-colour scanner guarantee: a high spatial resolution (16 points/mm2), a high tonal dynamics (thousands of grey levels), a uniform lighting of the scanned area and the punctual superimposition of the colour and IR images. Moreover we can print distortion-free reflectograms, false-colour and colour images of paintings on a 1:1 scale. The quality of the acquired reflectogram is presently higher than that obtainable with any traditional detection system, like CCD or Vidicon cameras. The point-by-point comparison between the reflectogram and the colour image of the painting, along with digital processing of the recorded images, open new possibilities for the analysis of the reflectogram. Some examples of application to the study of ancient paintings are shown.