Two innovative laser scanning prototypes have been developed at ENEA for diagnostics of large surfaces relevant to
monumental cultural heritage. The first, based on amplitude modulation technique in the visible, is a trichromatic (Red
/Green /Blue) imaging topologic radar (RGB-ITR) specialized to collect high resolution 3D models. After proper color
calibration, it allows for hyper-realistic rendering of colored features on painted surfaces and for precise localization of
irregularities.
The second is a line scanning system, working either in reflectance or laser induced fluorescence mode, capable of fast
2D monochromatic images acquisition on up to 90 different spectral channels in the visible/UV range, which was
developed to investigate the presence of different substances onto the painted surface.
Data collected during former field campaigns on frescos by means each scanning system will be reported and discussed
extracting information of interest to conservators by means of specific data processing methodologies and respective
software tools.
Recent results relevant to paints of the Assumption on slate and canvas by Scipione Pulzone named “il Gaetano”
collected in two churches in Rome (San Silvestro al Quirinale, Bandini chapel; Santa Caterina dei Funari, Solano della
Vetera Chapel) from the late XVI century are presented in order to demonstrate the increased diagnostic capabilities
coming from data integration. From combination of reflectance data from both instruments, the first true remote
differential colorimetry has been implemented, giving a chance to test the color quality in the future from the archived
images.
KEYWORDS: Laser scanners, Calibration, Modulation, 3D scanning, Signal detection, Distance measurement, Laser sources, 3D modeling, Sensors, Cultural heritage
Since several years our laboratory in ENEA Frascati Research Center is involved in development of laser scanners for
Cultural Heritage investigation problems. Actually the best result obtained in this field by our laboratory is a 3D Red
Green Blue Laser scanner, called RGB-ITR: the main feature of this scanner, further then measuring distances (up to
20m with a sub-millimetric resolution), is the ability to capture remotely color information by three calibrated laser
sources: this information is collected for each point sampled by the instrument and is not affected by external light
sources' influence. Moreover the ability to acquire color and distance information at the same time and for each point
decrease drastically the post-production pipeline of a complete mesh. In this work the results of a complete scan of S.
Peter Martyr in Rieti are shown, highlighting the efficiency and robustness of color calibration algorithms introduced for
a correct color representation.
KEYWORDS: RGB color model, 3D image processing, Sensors, Laser scanners, Signal to noise ratio, LIDAR, Reflectivity, 3D modeling, Modulation, Signal detection
We present a new color (RGB) imaging 3D laser scanner prototype recently developed in ENEA (Italy). The sensor is
based on AM range finding technique and uses three distinct beams (650nm, 532nm and 450nm respectively) in
monostatic configuration. During a scan the laser beams are simultaneously swept over the target, yielding range and
three separated channels (R, G and B) of reflectance information for each sampled point. This information, organized in
range and reflectance images, is then elaborated to produce very high definition color pictures and faithful, natively
colored 3D models. Notable characteristics of the system are the absence of shadows in the acquired reflectance images -
due to the system's monostatic setup and intrinsic self-illumination capability - and high noise rejection, achieved by
using a narrow field of view and interferential filters. The system is also very accurate in range determination (accuracy
better than 10-4) at distances up to several meters. These unprecedented features make the system particularly suited to
applications in the domain of cultural heritage preservation, where it could be used by conservators for examining in
detail the status of degradation of frescoed walls, monuments and paintings, even at several meters of distance and in
hardly accessible locations.
After providing some theoretical background, we describe the general architecture and operation modes of the color 3D
laser scanner, by reporting and discussing first experimental results and comparing high-definition color images
produced by the instrument with photographs of the same subjects taken with a Nikon D70 digital camera.
The propagation of polarized laser beams in turbid water is a subject of relevant interest in the field of underwater
quantitative visualization with active sensors like amplitude modulated laser systems. In such devices, target range
determination is based on the measurement of the phase difference ΔΦ between the fraction of the amplitude modulated
laser beam reflected by the target and a reference signal. As water turbidity increases, the laser radiation backscattered
from the water column shined by the sounding laser beam gives rise to an optical background with detrimental effects on
the accuracy of range measurement. In this paper we analyze the possibility to increase the apparatus accuracy with a
polarimetric technique based on the adoption of polarized laser radiation and polarization selective detection scheme for
improving the underwater imaging of real scenes (e.g. archaeological sites). The method fully takes advantages of the
different polarization properties of the laser radiation backscattered by turbid water and of the Lambertian component
diffusively reflected by the target as described by the associated Mueller matrices. Measurements have been performed
by adopting both a co-polarized and cross-polarized detection scheme with linearly and circularly polarized laser
radiation. Various degrees of turbidity were realized by adding, as diffusive element, skim milk to water in order to
obtain different scattering conditions. The effect of the transition from Rayleigh to Mie scattering regime on phase
accuracy determination has been investigated together with the role played by high order scatterings as the medium
approaches the optical thickness condition.
Forest fires can be the cause of serious environmental and economic damages. For this reason considerable effort has been directed toward forest protection and fire fighting.
The means traditionally used for early fire detection mainly consist in human observers dispersed over forest regions. A significant improvement in early warning capabilities could be obtained by using automatic detection apparatus.
In order to early detect small forest fires, the use of a dial system will be considered.
A first evaluation of the lowest detectable concentration will be estimated by a numerical simulation. The theoretical model will be used also to get the capacities of a dial system in fire surveillance of wooded areas. Fixing the burning rate for several fuels, the maximum range of detection will be evaluated. The results of these simulations will be reported in the paper.
New approaches of a spectrally tunable backlighting schemes based on a spherically bent crystal are considered. In a contrary to the traditional backlighting scheme, in which the investigated objects should be placed between the backlighter and the crystal, for the considered schemes an object is placed downstream of the crystal, before the tangential or after the sagittal focus and an image of the object is recorded at the distance from the object corresponded to the needed magnification. The magnification is defined by the ratio of the distances form the sagittal focus to the detector and from the object to the sagittal focus. A ray tracing modeling and experimental images of test meshes, obtained at an incidence angles of the backlighter radiation of 10° and 22°, are presented. It is demonstrated that, at incident angles up to 22°, a linear transformation of the obtained astigmatic images allows to reconstruct them with an accuracy (5 - 15%). A spatial resolution around 10 μm in a field of view of some mm2 is achieved, for the spectral range around 9 Å. It is also demonstrated that spherically bent crystals could be used for X-ray imaging of a self emitting plasma structures with a spatial resolution at least 50 μm in a field of view of some square millimeters for angles of incidence up to 22°.
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