Time-resolved laser fluorosensors: a laboratory study of their potential in the remote characterization of oil

Concentration-Emission Matrix (CEM) Spectroscopy Combined with GA-SVM: An Analytical Method to Recognize Oil Species in Marine

The establishment and development of a set of methods of oil accurate recognition in a different environment are of great significance to the effective management of oil spill pollution. In this work, the concentration-emission matrix (CEM) is formed by introducing the concentration dimension. The principal component analysis (PCA) is applied to extract the spectral feature. The classification methods, such as Probabilistic Neural Networks (PNNs) and Genic Algorithm optimization Support Vector Machine (SVM) parameters (GA-SVM), are used for oil identification and the recognition accuracies of the two classification methods are compared. The results show that the GA-SVM combined with PCA has the highest recognition accuracy for different oils. The proposed approach has great potential in rapid and accurate oil source identification.

A novel method for detection of camellia oil adulteration based on time-resolved emission fluorescence

In this study, time-resolved emission fluorescence (TRES) combined with chemometrics was developed and employed for adulteration analysis of camellia oil. TRES was first decomposed by parallel factors analysis (PARAFAC). Next, an artificial neural network (ANN) model was built for the adulteration analysis. A linear range of 5–50%, a limit of detection (LOD) of 3% and root mean square error of prediction (RMSEP) values lower than 3% were achieved. Compared with the steady-state measurement, easy access to the information from fluorophores of low concentration was shown to be an intrinsic advantage of the time-resolved measurement; this advantageous characteristic was helpful for optimizing adulteration analysis. It was demonstrated that TRES combined with chemometrics was a simple, rapid and non-intrusive method for adulteration analysis of vegetable oil.

A New Approach of Oil Spill Detection Using Time-Resolved LIF Combined with Parallel Factors Analysis for Laser Remote Sensing

In hope of developing a method for oil spill detection in laser remote sensing, a series of refined and crude oil samples were investigated using time-resolved fluorescence in conjunction with parallel factors analysis (PARAFAC). The time resolved emission spectra of those investigated samples were taken by a laser remote sensing system on a laboratory basis with a detection distance of 5 m. Based on the intensity-normalized spectra, both refined and crude oil samples were well classified without overlapping, by the approach of PARAFAC with four parallel factors. Principle component analysis (PCA) has also been operated as a comparison. It turned out that PCA operated well in classification of broad oil type categories, but with severe overlapping among the crude oil samples from different oil wells. Apart from the high correct identification rate, PARAFAC has also real-time capabilities, which is an obvious advantage especially in field applications. The obtained results suggested that the approach of time-resolved fluorescence combined with PARAFAC would be potentially applicable in oil spill field detection and identification.

Fiber-optic laser-induced fluorescence probe for the detection of environmental pollutants

Laser-induced fluorescence (LIF) spectroscopy in combination with fiber optics is shown to be a powerful tool for qualitative and quantitative diagnostics of environmental pollutants in water and soil. Timeintegrated data accumulation of the LIF signals in early and late time windows with respect to the excitation pulse simplifies the method so that it becomes attractive for practical applications. Results from field measurements are reported, as oil contaminations under a gas station and in an industrial sewer system are investigated. A KrF-excimer laser and a hydrogen Raman shifter can be applied for multiwavelength excitation. This allows a discrimination between benzene, toluene, xylene, and ethylbenzene aromatics and polycyclic aromatic hydrocarbon molecules in the samples under investigation. For a rough theoretical approach, a computer simulation is developed to describe the experimental results.

Fluorescence response of mineral oils: spectral yield vs absorption and decay time

The fluorescent emission from film samples of representative oils has been investigated by means of two independent experiments: (i) time-resolved fluorosensing at a fixed excitation frequency, by which the spectral emission yield and the associated decay times, tau(lambda), were determined, and (ii) monitoring of the integrated fluorescence in a fixed spectral band as a function of film thickness, from which extinction coefficients alpha(lambda) were derived at a number of excitation frequencies. After checking the good mutual consistency of corresponding emission data obtained in the two types of experiments, a unified analysis was elaborated in terms of a renormalized conversion efficiency, i.e., correcting the measured spectral yields for the ratio (tau/alpha). This quantity can be shown by an ppropriate model to be typical of the emitting fluorophores but independent of absorption or quenching effects due to the complex oil medium. This was indeed found to be the case for a large variety of oils, in spite of extreme variations in their absolute emission yield.

Lidar fluorosensing of mineral oil spills on the sea surface

Airborne fluorosensor measurements over maritime oil spills show that this method enables a sensitive classification and quantification of surface films having a thickness in the 1-microm range. However, significant changes of the optical signature of oil occur in the presence of submicrometer films which are not yet fully understood. Possible reasons for this effect are discussed and the limitations of laser fluorosensing of small oil discharges are outlined.

Measurement of fluorescence decay of crude oil: a potential technique to identify oil slicks

The single photon counting technique has been used to measure the decay time for several Kuwaiti crude and refined oils. Fluorescent characteristics of two different bunker oils from widely separate geographic areas have been studied. Laser induced fluorescent data for the crude oil samples are compared with the decay time results to evaluate the potential of these techniques for the identification of oil sticks in the marine environment. Response of the oil film thickness to various excitation wavelengths from a CW Ar ion laser and a pulsed xenon lamp has been investigated.

Field performance of a laser fluorosensor for the detection of oil spills

An airborne laser fluorosensor is described that was designed to detect and identify targets by means of the characteristic fluorescence emission spectrum. The first field trials of the sensor over marine oil and dye spills are reported. A correlation technique has been developed that, when applied to the data collected during these field trials, clearly differentiated among dye, the two crude oils, and the general fluorescence background of ocean water.

Time-resolved fluorimetry via a new cross-correlation method

A new instrument for the measurement of short fluorescence lifetimes is discussed and characterized. The instrument is basically an implementation of the cross-correlation between the excitation source and the induced fluorescence response. Such an approach, with a mode-locked argon-ion laser as the source, is shown to be capable of measuring lifetimes as short as 80 psec with a precision of 10 psec.

Teledetection of the thickness of oil films on polluted water based on the oil fluorescence properties

A method is described of determining the thickness of oil films on polluted water by remote sensing of oil fluorescence radiation. For this purpose the oil is excited at two wavelengths, one in the UV (337 nm) and one in the red (633 nm), while a third intermediate excitation wavelength (490 nm) can be used to extend the measuring range. With this set of excitation wavelengths, measuring ranges of several tens to hundreds of micrometers are demonstrated in the laboratory for thirty-two different crude and heavy fuel oils.

Effect of sea-state on the performance of laser fluorosensors

The effect of the sea-state on the performance of laser fluorosensors operating in both spectral and temporal modes is estimated. For the spectral mode, calculations of the dependence of reflective losses on the angle of incidence show that the attenuation of the fluorescence return is not significantly affected for the range of sea-states expected in deep water. In the temporal mode the return signal is distorted by the sea-state. Fortuitously this distortion does not significantly alter the full width at half maximum (FWHM), a parameter from which decay times can be estimated.