David Lognoli

Hyperspectral fluorescence lidar imaging at the Colosseum, Rome

Fluorescence lidar techniques offer considerable potential for remote, non-invasive diagnostics of stone cultural heritage in the outdoor environment. Here we present the results of a joint Italian-Swedish experiment, deploying two hyperspectral fluorescence lidar imaging systems, for the documentation of past conservation interventions on the Colosseum, Rome. Several portions of the monument were scanned and we show that it was possible to discriminate among masonry materials, reinforcement structures and protective coatings inserted during past conservation interventions, on the basis of their fluorescence signatures, providing useful information for a first quick, large-scale in situ screening of the monument.

Experiments on stony monument monitoring by laser-induced fluorescence

Abstract The use of remote sensing techniques for the monitoring of historical buildings is attractive, since it can allow a fast monitoring of large surfaces without the use of scaffolding and, in addition, a thematic mapping which is easier to read. The studies on fluorescence lidar monitoring of buildings started a few years ago and are still in progress. Interesting results were obtained in biodeteriogen monitoring and in the identification of stones. The possibility of detecting fluorescence thematic images of large areas was demonstrated on both artificial targets and historical buildings. This paper describes the current state of the art on fluorescence lidar monitoring of buildings and the research trends for the near future.

A fluorescence LIDAR sensor for hyper-spectral time-resolved remote sensing and mapping

In this work we present a LIDAR sensor devised for the acquisition of time resolved laser induced fluorescence spectra. The gating time for the acquisition of the fluorescence spectra can be sequentially delayed in order to achieve fluorescence data that are resolved both in the spectral and temporal domains. The sensor can provide sub-nanometric spectral resolution and nanosecond time resolution. The sensor has also imaging capabilities by means of a computer-controlled motorized steering mirror featuring a biaxial angular scanning with 200 μradiant angular resolution. The measurement can be repeated for each point of a geometric grid in order to collect a hyper-spectral time-resolved map of an extended target.

Detection and characterization of biodeteriogens on stone cultural heritage by fluorescence lidar

Biodeteriogens are an important cause of the weathering of a monument, particularly those made of stone, and their detection at an early stage of development helps to protect the monument from deterioration. Frequent mapping of biodeteriogen accumulation is therefore highly necessary. The use of fluorescence lidar for this purpose was introduced in 1995 and has been developed in subsequent years. Three main aspects emerged during this research: the possibility of discriminating between different biodeteriogen strains, the minimum detectable quantity of biodeteriogens, and the control of the efficiency of biocide treatments. We describe the results of a laboratory experiment devoted to clarifying these three aspects of biodeteriogen monitoring by means of fluorescence lidar.

In vivo real-time recording of UV-induced changes in the autofluorescence of a melanin-containing fungus using a micro-spectrofluorimeter and a low-cost webcam

An optical epifluorescence microscope, coupled to a CCD camera, a standard webcam and a microspectrofluorimeter, are used to record in vivo real-time changes in the autofluorescence of spores and hyphae in Aspergillus niger, a fungus containing melanin, while exposed to UV irradiation. The results point out major changes in both signal intensity and the spectral shape of the autofluorescence signal after only few minutes of exposure, and can contribute to the interpretation of data obtained with other fluorescence techniques, including those, such as GPF labeling, in which endogenous fluorophores constitute a major disturbance.

Fluorescence LIDAR remote sensing of oils: merging spectral and time-decay measurements

In this paper we present hyperspectral and time resolved laser induced fluorescence spectra of oil slicks remotely sensed by means of a new fluorescence LIDAR prototype. The sensor provides both sub-nanometric spectral resolution and sub-nanosecond time resolution. The fluorescence induction is achieved by means of a frequency-tripled pulsed Nd:YAG laser @355 nm. The light is collect by a 250-mm diameter telescope and the fluorescence spectra are measured by a spectrometer and a 512-spectral channels gateable intensified CCD camera. The temporal resolution is achieved by sequentially delaying the gating time to obtain fluorescence data, which are resolved both in the spectral and temporal domains. Measurements were performed in the lab on three artificial 100-μm thick oil films at a distance of 10 m. The oils were a crude oil and two different types of diesel fuel.

Lidar remote sensing of stone cultural heritage: detection and characterization of biodeteriogens

Different kinds of organisms can grow on stone substrata. Their presence causes effects, which range from low to severe chemical and physical alterations. Up to now, methodologies are not available to investigate in situ biodeteriogens on stone monuments. The paper discusses the use of the laser- induced fluorescence for the detection and characterization of biodeteriogens on stone monuments on the base of the experiments recently carried out by the authors. Dolomitic marble samples inoculated with different cell concentrations of two biodeteriogen have been analyzed in controlled conditions. The fluorescence spectra are compared in order to investigate the possibility of detecting the biodeteriogens at an early state of development, of identifying them by the spectral signature, and of monitoring the effect of biocidal treatments. Although further investigations are necessary the results confirm the potential of this technique in the non- destructive, remote monitoring of biodeteriogen.

A fluorescence lidar combining spectral, lifetime and imaging capabilities for the remote sensing of cultural heritage assets

This paper addresses the latest advancements concerning both instrumental features and applications to the cultural heritage of a fluorescence LIDAR featuring hyperspectral and time resolution imaging capabilities. In particular, it focuses on the instrument’s technical upgrade in terms of scan speed, enhanced spatial resolution and field of view, which permitted to extend the field of application of the LIDAR technique to wall paintings and to the classification of microbial communities. It also outlines a new concept of fluorescence imaging LIDAR based on the integration of hyperspectral and fluorescence lifetime spectroscopy, which enhances the capabilities of the technique for the characterization of the materials to be investigated in cultural heritage assets. The new prototype is able to acquire full 4D datasets over a remote surface: for each pixel of the image, a 2D datum featuring fluorescence intensity versus wavelength and time is recorded. In this paper we present the results obtained in the lab for the characterization of stone samples and in the field for the investigation of ancient frescoes.

High-resolution lidar fluorescence spectra for the characterization of phytoplankton

The Laser Induced Fluorescence (LIF) technique has been widely employed for the study and the monitoring of the phytoplanktonic population in the marine environment. Herein a method for the characterization of different phytoplanktonic species by means of a high spectral resolution lidar fluorosensor is presented. The method is based on the detection of the changes in the peak position of the fluorescence of the chlorophyll a that is contained in all phytoplanktonic species. These changes are probably due to the proteic compounds that are present together with the chlorophyll in the thylakoid membranes within the chloroplasts and that vary with the phytoplanktonic species. The main advantage is that this method does not require the presence of characteristic fluorescence features of other light harvesting pigments, such as carotenoids or phycobilines, so that it can be used also with species where only chlorophyll fluorescence is present. Moreover, the light harvesting pigments usually show a weak fluorescence because of the strong resonant coupling between them.

A fluorescence imaging lidar for the control of cultural heritage

The fluorescence lidar imaging technique turns particularly useful for the control of monuments. The investigated topics range from the detection of biodeteriogens to the characterization of stones and other masonry or restoration materials, such as protective treatments. In addition, the fluorescence lidar imaging is a non-destructive technique offering the possibility of being carried out in situ without the use of scaffolding that, beside being costly, limits the access to the monument and its use. This paper presents the main technical features of a new fluorescence imaging lidar system specifically developed for the diagnostics on the cultural heritage, whose operative conditions include outdoor and indoor environments, and the possibility of monitoring vaults and ceilings. This fluorescence lidar prototype is mainly composed of a Q-switched, tripled frequency Nd:YAG laser (@355 nm), a 1 m focal length Newtonian telescope and a 300 mm focal length spectrometer coupled to an intensified, gated 512 x 512 CCD detector. Imaging is carried out via a scanning system realized with a computer controlled mirror. The lidar prototype includes also a target pointing system for referencing the acquired fluorescence images on the target.