Lorenzo Palombi

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.

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.

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.

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.

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.

Experimental tests and radiometric calculations for the feasibility of fluorescence LIDAR-based discrimination of oil spills from UAV

Abstract This paper presents experimental tests and radiometric calculations for the feasibility of an ultra-compact fluorescence LIDAR from an Unmanned Air Vehicle (UAV) for the characterisation of oil spills in natural waters. The first step of this study was to define the experimental conditions for a LIDAR and its budget constraints on the basis of the specifications of small UAVs already available on the market. The second step consisted of a set of fluorescence LIDAR measurements on oil spills in the laboratory in order to propose a simplified discrimination method and to calculate the oil fluorescence conversion efficiency. Lastly, the main technical specifications of the payload were defined and radiometric calculations carried out to evaluate the performances of both the payload and the proposed discrimination method.

Passive remote sensing of solar-induced fluorescence spectra of crude oil

The solar-induced fluorescence (SIF) of a simulated oil slick is remotely retrieved from the infilling of the solar Fraunhofer lines of its radiance spectrum acquired by means of a sub-nanometric spectral resolution fluorescence lidar operated in passive mode (i.e. as a spectroradiometer). SIF data, retrieved from the infilling of several Fraunhofer lines selected in the 390–660 nm range, were exploited to reconstruct the oil fluorescence spectrum. This spectrum was finally compared with laser-induced fluorescence spectra acquired on the same oil slick by using the fluorescence lidar. The results open new prospects for the remote sensing of oils and their classification.

An advanced fluorescence LIDAR system for the acquisition of interleaved active (LIF) and passive (SIF) fluorescence measurements on vegetation

Fluorescence is regarded as a valuable tool to investigate the eco-physiological status of vegetation. Chlorophyll a, which emits a typical fluorescence in the red/far-red region of the e.m. spectrum, plays a key role in the photosynthetic process and its fluorescence is considered an effective proxy of photosynthetic activity of plants. Laser Induced Fluorescence (LIF) has been studied for several decades both at leaf- and canopy-level by means of optical fibers-coupled instrumentation and fluorescence LIDAR systems. On the other hand, Solar-Induced Fluorescence (SIF) has been the object of several scientific studies quite recently, with the aim to investigate the feasibility of measuring the fluorescence of vegetation using passive spectroradiometers in view of global scale monitoring from satellite platforms. This paper presents the main technical features and preliminary tests of a fluorescence LIDAR, recently upgraded to acquire maps of interleaved LIF and SIF measurements at canopy level. In-house developed electronics and software permits the acquisition of interleaved LIF and SIF spectra by switching on/off the laser, the selection of the suitable grating, the setting of the integration time and the synchronization of the Intensified CCD (ICCD) gate opening time. For each pixel of the map, a fluorescence dataset can be acquired containing a LIF spectrum – from 570 nm to 830 nm with a spectral resolution of 0.5 nm - and radiance spectra from 685.53 nm to 690.30 nm with subnanometric spectral resolution containing the molecular oxygen O2-B telluric absorption band. The latter can be exploited for polynomial regression data fit and SIF retrieval.

Implementation of a hyperspectral image simulation tool and analysis of the impact of instrumental noise on vegetation fluorescence retrieval using the telluric O2-A and O2-B lines

This paper presents an analysis of the main artifacts introduced by the non- uniformity of the instrumental characteristics in an image dataset simulated by taking into account the main technical features of the FLORIS sensor. The dataset was produced by using a hyperspectral image simulation tool – named FLISM (Fluorescence Image Simulator for space Missions) – specifically implemented to produce images of fluorescent and non-fluorescent targets acquired by a pushbroom hyperspectral instrument. In this specific case, the available technical specifications of the FLORIS sensor were taken into account to investigate some critical issues concerning Solar Induced Fluorescence (SIF) retrieval in vegetated areas by means of the FLD (Fraunhofer Line Discriminator) method, which relies on the telluric O2-A and O2-B lines to decouple the weak SIF signal of vegetation from the backscattered radiance.