CNR - IFAC

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.

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. © 2000 É ditions scientifiques et médicales Elsevier SAS

To stop, or at least to reduce, the weathering of the stone surface its strength is often improved by treatments of different chemical composition. The uniform distribution of the treatment and the conservation of its integrity during the years are crucial factors for a good protection of the monument. As a consequence a technique which allows a remote mapping of the treatment and its characteristics would be very attractive. This paper describes the first experiments devoted to the use of fluorescence lidars in the monitoring of protective treatments on stone surface. Although further investigations are necessary the first results demonstrate the possibility of a detection and characterisation of protective treatments by fluorescence lidars.

Remotely sensed laser-induced autofluorescence spectra of pure cultures of fungal strains (Aureobasidium pullulans, Verticillium sp.) and of bacterial strains (Bacillus sp., Pseudomonas sp.) are presented. The strains were isolated from samples collected in a Roman archaeological site (Tropaeum Traiani) near Constanta, Romania. The fluorescence spectra were detected in vivo from a distance of 25 m in the outdoor, using a high spectral resolution fluorescence LIDAR featuring a UV laser (XeCl@308 nm) as an excitation source. All the examined strains, except for the A. pullulans, showed fluorescence features such to allow their characterisation by processing data with multivariate techniques. Both Principal Component Analysis and Cluster Analysis were applied to the data set and compared to discriminate between the examined strains.

This paper illustrates a method for the remote measurement of the attenuation coefficient of natural water as a function of wavelength. This measurement is carried out with a fluorescence lidar system which has both spectral and temporal resolution, thus allowing the remote monitoring of volume targets, such as water column profiles. This fluorescence lidar has been designed and developed by the authors in view of an automatic operation from ship or buoy.

Remote imaging measurements of laser-induced fluorescence have been performed, with application towards cultural heritage. Measurement campaigns have been performed at, e.g., the Coliseum in Rome. Differences in fluorescence spectra from different points were found and images corresponding to different features could be produced for thematic mapping.

This paper presents a study devoted to investigate the feasibility of non-destructive remote sensing of biological growth on mural paintings by means of the fluorescence lidar technique. The latter is a technique that can be used to carry out fluorescence measurements without any direct contact with the investigated surface and independently from external environmental conditions like full sunlight. The study initially addressed the investigation of the effects of low-fluence pulsed UV laser radiation on different types of paint layers, prepared either with a fresco or a secco techniques and using different pigments and binders. To irradiate the samples we used a tripled-frequency Nd:YAG laser, emitting at 355 nm, and fluences ranging from 0.1 mJ/cm 2 to 1 mJ/cm 2 . Different analytical techniquescolorimetry, optical microscopy, Fiber Optical Reflectance Spectroscopy (FORS), Attenuated Total Reflectance (ATR) microscopy and gas cromatography/mass spectrometry (GC/MS) -were applied to the irradiated samples to compare the morphological and physico-chemical properties before and after laser irradiation. The outcomes of this study were used to arrange a second experiment focused on fluorescence lidar measurements on model samples inoculated with different concentrations of biodeteriogens, specifically a green alga (Apatococcus sp.) and a cyanobacterium (Chroococcus sp.). The results demonstrated the feasibility of the remote detection of cyanobacteria and algae on painted surfaces at a pre-visual stage of development by means of the fluorescence lidar technique using a laser fluence of 1 mJ/cm 2 at the target.

Abstract The CEFLES2 campaign during the Carbo Europe Regional Experiment Strategy was designed to provide simultaneous airborne measurements of solar induced fluorescence and CO2 fluxes. It was combined with extensive ground-based quantification of leaf-and canopy-level processes in support of ESA's Candidate Earth Explorer Mission 5 of the “Fluorescence Explorer”(FLEX).

We present a feasibility study for a satellite borne fluorescence Lidar. The instrument is based on technologies which are either already available, or in an advanced state of development. In particular, the laser transmitter is derived from the experience acquired in the development of the laser transmitter for the ADM-Aeolus ESA mission; the collection optics is based on recent studies on large aperture deployable mirrors (ESA projects ALC, Advanced Lidar Concept, and LATT, Large Aperture Telescope Technology).

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), on-board the European ENVIronmental SATellite (ENVISAT) launched on 1 March 2002, is a middle infrared Fourier Transform spectrometer measuring the atmospheric emission spectrum in limb sounding geometry. The instrument is capable to retrieve the vertical distribution of temperature and trace gases, aiming at the study of climate and atmospheric chemistry and dynamics, and at applications to data assimilation and weather forecasting.

1] HNO 3 profiles measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument operating on the Envisat satellite are validated with balloon measurements. An agreement of ±5% is obtained. The two measurements observe HNO 3 features in different spectral regions (vibration spectra in the middle infrared and rotation spectra in the far infrared, respectively) and the agreement is obtained after that significant upgradings are made to the spectroscopic database. A stringent test of our understanding of HNO 3 spectroscopy for remote sensing measurements is obtained.

We measured the expansion coefficient of Torlon 4203 (polyamide-imide) as a function of temperature between 4.2 and 295 K. The thermal expansion is lower than that of most polymers. The thermal conductivity k between 0.1 and 5 K was also measured: below 1 K, a quadratic dependence on temperature of k was found, as predicted by the tunnelling model, while the behaviour shown by our data above 1 K suggests the presence of a plateau.

In preparation for a possible space mission, a breadboard version named REFIR-BB of the Radiation Explorer in the Far Infrared (REFIR) instrument has been built. The REFIR is a Fourier-transform spectrometer with a new optical layout operating in the spectral range 100-1100 cm Ϫ1 with a resolution of 0.5 cm Ϫ1 , a 7-s acquisition time, and a signal-to-noise ratio of better than 100. Its mission is the spectral measurement in the far infrared of the Earth's outgoing emission, with particular attention to the long-wavelength spectral region, which is not covered by either current or planned space missions. This measurement is of great importance for deriving an accurate estimate of the radiation budget in both clear and cloudy conditions. The REFIR-BB permits the trade-off among all instrument parameters to be studied, the optical layout to be tested, and the data-acquisition strategy to be optimized. The breadboard could be used for high-altitude ground-based campaigns or could be flown for test flights on aircraft or balloon stratospheric platforms. The breadboard's design and the experimental results are described, with particular attention to the acquisition strategy and characterization of the interferometer. Tests were performed both in laboratory conditions and in vacuum. Notwithstanding a loss of efficiency above 700 cm Ϫ1 caused by the poor performance of the photolithographic polarizers used as beam splitters, the results demonstrate the feasibility of using the spectrometer for space applications.

We report the most accurate measurement of the helium fine structure splitting. The 2 3 P 0 -2 3 P 1 energy splitting is 29 616 949.7 6 2.0 kHz. Laser saturation spectroscopy, heterodyne pure frequency determination, and fluorescence detection were combined in a novel experimental approach. The absence of external perturbing magnetic fields, used in earlier experiments, lends confidence to our determined value and allows us to discriminate between contradictory results previously reported. This result, when combined with expected advances in theory, should yield a new value of the fine structure a, which may help clarify a presently puzzling experimental situation. [S0031-9007(99)08416-1]

The measurement of thermal and mechanical properties of materials at cryogenic temperatures gains more and more importance in the field of the application of novel high-tech materials to aerospace industry and in developing scientific instrumentation. We present a simple and inexpensive interferometric dilatometer for the measurement of the thermal expansion of materials in the 4-300 K range. The dilatometer consists of a Michelson tilt-compensated interferometer in which the path difference is given by the variation in length of a sample enclosed in a 4 K cryostat. The compensation for misalignment permits a fast and simple operation routine that configures the instrument as a valuable tool for materials engineering.

Nitric acid (HNO 3 ) is one of the key products that are operationally retrieved by the European Space Agency (ESA) from the emission spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding (MI-PAS) onboard ENVISAT. The product version 4.61/4.62 for the observation period between July 2002 and March 2004 is validated by comparisons with a number of independent observations from ground-based stations, aircraft/balloon campaigns, and satellites. Individual HNO 3 profiles of the ESA MIPAS level-2 product show good agreement with those of MIPAS-B and MIPAS-STR (the balloon and aircraft version of MIPAS, respectively), and the balloon-borne infrared spectrometers MkIV and SPIRALE, mostly matching the reference data within the combined instrument error bars. In Correspondence to: D. Y. Wang ([email protected]) most cases differences between the correlative measurement pairs are less than 1 ppbv (5-10%) throughout the entire altitude range up to about 38 km (∼6 hPa), and below 0.5 ppbv (15-20% or more) above 30 km (∼17 hPa). However, differences up to 4 ppbv compared to MkIV have been found at high latitudes in December 2002 in the presence of polar stratospheric clouds. The degree of consistency is further largely affected by the temporal and spatial coincidence, and differences of 2 ppbv may be observed between 22 and 26 km (∼50 and 30 hPa) at high latitudes near the vortex boundary, due to large horizontal inhomogeneity of HNO 3 . Similar features are also observed in the mean differences of the MIPAS ESA HNO 3 VMRs with respect to the ground-based FTIR measurements at five stations, aircraft-based SAFIRE-A and ASUR, and the balloon campaign IBEX. The mean relative differences between the MIPAS and FTIR HNO 3 partial columns are within ±2%, comparable to the MIPAS Published by Copernicus Publications on behalf of the European Geosciences Union. 4906 D. Y. Wang et al.: MIPAS Operational Nitric Acid systematic error of ∼2%.

Our understanding of global warming depends on the accuracy with which the atmospheric components that modulate the Earth's radiation budget are known. Many uncertainties still exist as regards the radiative effect of water in the different spectral regions, among which is the far infrared, where very few observations have been made. An assessment is shown of the atmospheric outgoing flux obtained from a balloon-borne platform with wideband spectrallyresolved nadir measurements at the top of the atmosphere over the full spectral range, from 100 to 1400 cm −1 , made by a Fourier transform spectrometer with uncooled detectors. From these measurements, we retrieved 15 pieces of information regarding water vapour and temperature profiles and surface temperature, with a major improvement in our knowledge of water vapour in the upper troposphere. The retrieved atmospheric state made it possible to calculate the emitted radiance also at frequencies and zenith angles that have not been observed and to determine the outgoing spectral radiation flux. This proves that spectrally resolved observations can be used to derive accurate information on the integrated flux. While the retrieved temperature was in agreement with ECMWF analysis, the retrieved water vapour profile differed significantly; depending on the time and the location, the derived flux in the far infrared (20-600 cm −1 ) differed by 2-3.5 W/m 2 from that calculated using ECMWF. The error with which the far infrared flux is determined by REFIR-PAD is about 0.4 W/m 2 and is caused mainly by calibration uncertainties, while detector noise has a negligible effect. This proves that uncooled detectors are adequate for top-of-the-atmosphere radiometry.

A spectroradiometer has been developed for the characterisation of the atmospheric emission in the 100-1100 cm-1 spectral range with a resolution of 0.5 cm-1 and a signal-to-noise ratio of 100. This instrument has been studied in the framework of the REFIR (Radiation Explorer in the Far InfraRed) space project, which addresses the need for new data in a range not yet covered by any current or planned space mission for improving our knowledge of the distribution of the atmospheric components that modulate the Earh's emission, such as mid and upper tropospheric water vapour and clouds. The spectroradiometer is a based on a Fourier transform polarising interferometer with a new optical scheme that makes use of four polarising beam splitters and room-temperature pyroelectric detectors. It provides all the desired features including broad spectral coverage, two separated input ports and two output ports, optical compensation for tilt errors in the moving mirror unit, measurement of the overall input signal (both planes of polarization) on the same detector. This optical configuration maximizes the reliability of the spectrometer in particular for long lifetime space operations or for field campaigns and optimizes its performances with room temperature operations. The spectroradiometer is a compact instrument designed both for laboratory applications and for field campaings. In particular it has been designed for operations in high-altitude ground-based campaigns and on a stratospheric balloon platform. This work describes the design and fabrication of this instrument, the results of the spectroscopic characterisation performed in laboratory conditions and under vacuum, and possibly the first tests on atmospheric measurements scheduled for the beginning of 2004 in the South of Italy.

The SAFIRE-A airborne spectrometer, provides an unique combination of different measuring schemes and parameters, including limb, nadir and space direction line of sight, variable spectral resolution up to 0.004 cm-1, two spectral channels in the region from 10 to 250 cm-1, with bandwidth from 1 to several cm-1, and the possibility of operating both atmospheric radiance and polarization measurements. In the high spectral resolution radiance operating mode, SAFIRE-A has been deployed in several campaigns, amongst which a mid-latitude and a polar campaign aimed to the validation of MIPAS-ENVISAT and the APE-GAIA Antarctic campaign with the objective of the study of the southern polar vortex region. In these campaigns the instrument provided 2-D maps of volume mixing ratio of trace atmospheric constituents with higher spatial resolution with respect to spaceborne instruments, thus providing a valuable tool for validation and for study of local phenomena involved in atmospheric chemistry. An accurate estimation of the vertical resolution has been performed, based on calculation of the averaging kernel and tested by comparing SAFIRE-A limb profiles with simultaneously measured in-situ data, as well as of other instrument parameters. Moreover, the combination on a single instrument of the capabilities for high spectral resolution measurements and for detection of atmospheric polarization effects can offer an unique opportunity to investigate processes that require a precise characterization both of the chemical field and of clouds and particles distribution and properties, such as Polar stratospheric Clouds formation and denitrification mechanisms occurring in the polar lower stratosphere. As a future development, lower spectral resolution (0.1 cm-1) and broadband measurement capabilities of a Nadir looking configuration of the instrument could be exploited to retrieve information on structure and properties of high cirrus clouds and to make a contribution to the study of their role in both Earth's radiation budget and upper tropospheric chemistry. In this framework an interesting possibility is the synergy that is provided by an instrumentation package including also a broadband nadir-looking spectroradiometer operating in the 100-1100 cm-1 region, of which a prototype has been developed recently by our group.