Considering the increase of atmospheric pollution levels in our cities, due to emissions from vehicles and domestic heating, and the growing threat of terrorism, it is necessary to develop instrumentation and gather know-how for the automatic detection and measurement of dangerous substances as quickly and far away as possible. The Multi- Wavelength DIAL, an extension of the conventional DIAL technique, is one of the most powerful remote sensing methods for the identification of multiple substances and seems to be a promising solution compared to existing alternatives. In this paper, first in-field tests of a smart and fully automated Multi-Wavelength mini-DIAL will be presented and discussed in details. The recently developed system, based on a long-wavelength infrared (IR-C) CO<sub>2</sub> laser source, has the potential of giving an early warning, whenever something strange is found in the atmosphere, followed by identification and simultaneous concentration measurements of many chemical species, ranging from the most important Greenhouse Gases (GHG) to other harmful Volatile Organic Compounds (VOCs). Preliminary studies, regarding the fingerprint of the investigated substances, have been carried out by cross-referencing database of infrared (IR) spectra, obtained using in-cell measurements, and typical Mixing Ratios in the examined region, extrapolated from the literature. First experiments in atmosphere have been performed into a suburban and moderately-busy area of Rome. Moreover, to optimize the automatic identification of the harmful species to be recognized on the basis of in cell measurements of the absorption coefficient spectra, an advanced multivariate statistical method for classification has been developed and tested.
Recently surveying large areas in an automatic way, for early detection of harmful chemical agents, has become a strategic objective of defence and public health organisations. The Lidar-Dial techniques are widely recognized as a cost-effective alternative to monitor large portions of the atmosphere but, up to now, they have been mainly deployed as ground based stations. The design reported in this paper concerns the development of a Lidar-Dial system compact enough to be carried by a small airplane and capable of detecting sudden releases in air of harmful and/or polluting substances. The proposed approach consists of continuous monitoring of the area under surveillance with a Lidar type measurement. Once a significant increase in the density of backscattering substances is revealed, it is intended to switch to the Dial technique to identify the released chemicals and to determine its concentration. In this paper, the design of the proposed system is described and the simulations carried out to determine its performances are reported. For the Lidar measurements, commercially available Nd- YAG laser sources have already been tested and their performances, in combination with avalanche photodiodes, have been experimentally verified to meet the required specifications. With regard to the DIAL measurements, new compact CO<sub>2</sub> laser sources are being investigated. The most promising candidate presents an energy per pulse of about 50 mJ typical, sufficient for a range of at least 500m. The laser also provides the so called "agile tuning" option that allows to quickly tune the wavelength. To guarantee continuous, automatic surveying of large areas, innovative solutions are required for the data acquisition, self monitoring of the system and data analysis. The results of the design, the simulations and some preliminary tests illustrate the potential of the chosen, integrated approach.
The PBL is the lower layer of the atmosphere that is sensitive to the effect of the Earths surface, it controls the flow of
heat and momentum between the surface and the free atmosphere, thus playing a key role in atmospheric circulation.
At University of Rome "Tor Vergata", Quantum Electronic and Plasma Laboratories (EQP), two mobile Light Detection
and Ranging (LIDAR) systems have been developed. With these systems the monitoring of the Planetary Boundary
Layer (PBL) has been performed.
The first mobile Lidar system is based on a pulsed Nd:YAG Q-Switched laser source operating at three wavelengths:
1064 nm, 532 nm and 355 nm. Acquiring the elastic backscattered signals, it has been possible to estimate the aerosolitic
backscattering coefficient at the aim to reconstruct the vertical aerosol profiles.
The second one is a Differential Absorption Lidar system (DIAL), composed by a CO2 laser, working in the window
spectral range between 9 and 11μm. With this system it has been estimated the water vapour concentration in the PBL
region using the two wavelengths 10R20 (10.591 μm) and 10R18 (10.571 μm), which represent, respectively, the
absorbing wavelength and non-absorbing one of the water molecule. The comparison of the backscattered radiation at
these wavelengths yields the trace gas number density as a function of distance along the field-of-view of the receiving
Diurnal and nocturnal measurements have been performed simultaneity using the two Lidar/Dial systems. Vertical
profiles of the aerosolitic backscattering coefficient and water vapour concentration profiles have been estimated. The
results and their comparison will be present in this work.
Forest fires can be the cause of environmental catastrophe, with the natural outcomes of serious ecological and
economic damages, together with the possibility to endanger human safety. At the aim to reduce this catastrophe
several author have been shown that the Laser light scattering can be uses to reveals the particulate emitted in the
smoke. Infact experimental and theoretical investigations have shown that lidar is a powerful tool to detect the tenuous
smoke plumes produced by forest fires at an early stage. In early 90's Arbolino and Andreucci have shown the
theoretical possibility to detect the particulate emitted in atmosphere from smoke forest fire. Vilar at all have shown
experimentally the possibility to measure the density variation in atmosphere due to plume emitted in forest fire event.
Gaudio at all. have already shown that it is possible to evaluate water vapor emitted in smoke of vegetable fuel using a
CO<sub>2</sub> dial system.
In this paper a theoretical model to evaluate the capabilities of a lidar system in fire surveillance of wooded areas will
be presented. In particular we intend propose a technique to minimizing the false alarm in the detection of forest fire by
lidar based on a measurement of second components emitted in a combustion process. Usually to detect a fire alarm a
rapid increase of aerosol amount is measured. If the backscattering signal report a peak, the presences of a forest fire
will be probable. Our idea to confirm this hypothesis is measure the second components emitted in a forest fire at the
aim to minimize the false alarm. The simulated measurements of the humidity amount within the smoke plume will be
carried out by means of Raman analysis. Fixing the burning rate of the vegetable-fuels, the maximum range of
detection will be evaluated.
The quick increase of terrorism and asymmetric war is leading towards new needs involving defense and security.
Nowadays we have to fight several kind of threats and use of chemical weapons against civil or military objectives is one
of the most dangerous.
For this reason it is necessary to find equipment, know-how and information that are useful in order to detect and identify
dangerous molecules as quickly and far away as possible, so to minimize damage.
Lidar/Dial are some of the most powerful optical technologies. Dial technology use two different wavelengths, in order
to measure concentration profile of an investigated molecule. For this reason it is needed a "fingerprint" database which
consists of an exhaustive collection of absorption coefficients data so to identify each molecule avoiding confusion with
interfering ones. Nowadays there is not such a collection of data in scientific and technical literature.
We used an FT-IR spectrometer and a CO<sub>2</sub> laser source for absorption spectroscopy measurements using cells filled with
the investigated molecules. The CO<sub>2</sub> source is the transmitter of our DIAL facility. In this way we can make a proper
"fingerprint" database necessary to identify dangerous molecules. The CO<sub>2</sub> laser has been chosen because it is eye safe
and, mainly, because it covers a spectral band where there is good absorption for this kind of molecules. In this paper IR
spectra of mustard will be presented and compared to other substances which may interfere producing a false alarm.
Methodology, experimental setup and first results are described.