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.
For the exploration of gas hydrate resources by measuring the dissolved methane concentration in seawater, a continuous-wave cavity ringdown spectroscopy (CW-CRDS) experimental setup was constructed for trace methane detection. A current-modulation method, rather than a cavity-modulation method using an optical switch and a piezoelectric transducer, was employed to realize the cavity excitation and shutoff. Such a current-modulation method enabled the improvement of the experimental setup construction and stability, and the system size and stability are critical for a sensor to be deployed underwater. Ringdown data acquisition and processing were performed, followed by an evaluation of the experimental setup stability and sensitivity. The obtained results demonstrate that great errors are introduced when a large fitting window is selected if the analog-to-digital converter has an insufficient resolution. The ringdown spectrum of methane corresponding to the 2ν 3 band R(4) branch was captured, and the methane concentration in lab air was determined to be 2.06 ppm. Further experiments for evaluating the quantitative ability of this CW-CRDS experimental setup are underway from which a high-sensitivity methane sensor that can be combined with a degassing system is expected.
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