USING OF A WATER RAMAN BACKSCATTERING SIGNAL FOR REMOTE SENSING OF OIL POLLUTION ON THE SEAWATER. Abstract

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Emilia Wójcik
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1 VIOLETTA DOZDOWSKA 1 & TADEUSZ KÓL 2 1 Institut of Oceanology Polish Academy of Sciences Powstańców Warszawy 55, PL Sopot, Poland drozd@iopan.gda.pl 2 Department of Physics Faculty of Marine Engineering, Marine Academy Morska 81-87, PL Gdynia, Poland USING OF A WATE AMAN BACKSCATTEING SIGNAL FO EMOTE SENSING OF OIL POLLUTION ON THE SEAWATE Abstract emote sensing methods are more and more widely applied in studies dealing with the upper seawater layer. The fluorescing lidar system FLS-UV, designed and developed by LDI Ltd. in Tallinn, Estonia, was used to detect and identify the oil substances on the water surface. The lidar records the laser-induced return signal excited by the UV light beam, 299 nm, in four channels which correspond to, respectively, λ maximum of aman scattering of laser beam light on water molecules, λ 10 nm, λ + 10 nm and λ + 20 nm. Laboratory experiment for calibration of the oil film thickness measurements, relying on adding the small dozes of oil, proved a very good (0,95) correlation with the results obtained by the lidar method. In the years several lidar sea-experiments aimed at detection and estimation oil slicks on water surface were carried out, during research cruises of r/v Oceania on the Baltic Sea. The results revealed that the biggest oil pollution of the water surface occurs in coastal water areas and Gulf of Gdansk and in the vicinity of river outlets. Introduction The Southern Baltic constitutes a part of a semi-enclosed sea extending along the northern coastline of Poland. This ecosystem is known for high temporal and spatial variability of 1

physical, chemical and biological parameters, caused by mainly freshwater run-off, winds, bathymetry and vicinity of ports and shipping lines (Piskozub et al., 1998).

2 physical, chemical and biological parameters, caused by mainly freshwater run-off, winds, bathymetry and vicinity of ports and shipping lines (Piskozub et al., 1998). Detection and quantification of oil spills on water surface is one of the most important task in the field of environmental protection because the oil film on the water surface effects the character of aquatic and atmospheric processes. In order to estimate the amount of oils spilled into seawater the marine, in situ, and laboratory experiments were designed and executed with the purpose of building a database for a calibration / validation exercise of lidar FLS-UV (Figure 1). Figure 1. The lidar FLS-UV set-up on the r/v Oceania during marine experiments. Methods The remote sensing of oil spills on water surface is based on detection of pollutant fluorescence response (Hengsterman & euter, 1990), oil characterization using its fluorescence signal and estimation of oil spill thickness using suppression of water aman signal by an oil film. (Figure 2). The equation for the oil film thickness d calculations is the following: d = 1 I ln a I 0 where: 0 I, I - water aman intensities measured through the oil slick and clean water surface correspondingly, a - extinction coefficient of an oil. 2

3 Figure 2. The suppression of water aman signal by an oil film is used to measure the thickness of oil spill spread over water. esults Calibration laboratory experiment To provide the quantitative measurements, the calibration of water aman scattering spectral peak attenuated by an oil product concentration has to be used. The calibration procedure comprises adding the small and known quantities of oil. Then, the dependency of water aman intensity on the concentration can be derived to create the calibration curve.(figure 3). Figure 3. Dependence of water aman scattering signal intensity on oil film thickness (n=18); Petrobaltic Oil. 3

4 Typically such a calibration can work well only as long as the composition of water contamination is not changed. This calibration is also useful when no specific oil products are expected to be present in a sample, and a mixture of oil products is to be diagnosed (Babichenko, 2001). Marine experiments Three cruises were conducted at different seasons from 1997 to 2002 according to collect the data. The graphs in Figure 4 demonstrate the variability of the oil film thickness on the seawater surface in different seasons and areas of the Southern Baltic. The relationship between an oil pollution and the vicinity of river outlets and drilling platforms and ports shows a high spatial identity (Figure 4 and 5). Figure 4. The results of the oil film thickness measurements obtained during different cruises. 4

5 The increase of oil pollution was found near the river outlets (Vistula, Zn2, and Leba, L7, L8) and the harbours: Gdansk, Leba, Wladyslawowo (Z, L7, 6) and occurred in the vicinity of the shipping lines connected with oil transport and storage: (11., 16., c). Figure 5. The oil film thickness space-distribution obtained during three research cruises of r/y Oceania. Sharply increase of oil concentration was detected in the area located around the oil drilling platform (PETOBALTIC). (1.-10.). Conclusions In general, the remote sensing strategy chosen for this estuary allowed observations of oil pollution distributed in central and western part of Southern Baltic ecosystem. 5

6 The sensing wavelength, 299 nm, used in lidar experiments is effective to excite the fluorescence of oils as well as dissolved organic matter. While the DOM concentration displays rather high values in the Southern Baltic its presence contributes probably the significant fluorescence emission that overlaps on the oil fluorescence spectrum recorded by the lidar. Therefore for the more precise interpretation of the oil film thickness results the study of DOM composition and luminescent properties should be carried out simultaneously. To provide the correct diagnostic of oil pollution such processes as dissolving, evaporation, mixing, chemical and biological degradation of pollutant have to be taken into account. eferences Babichenko S., 2001 (7). Spectral fluorescent signatures in diagnostics of water environment, Institute of Ecology, Tallinn Pedagogical University. Hengsterman T. & euter., Lidar fluorescensing of mineral oil spills on the sea surface, Appl. Opt., 29, Piskozub J., Drozdowska V. & Irczuk M., A water extinction lidar system for detecting thin oil spills preliminary results of field tests, Oceanologia 40(1),

7 VIOLETTA DOZDOWSKA 1, TADEUSZ KÓL 2 1 Zakład Dynamiki Morza Instytut Oceanologii, PAN Sopot 2 Katedra Fizyki Wydział Mechaniczny Akademia Morska, Gdynia ZASTOSOWANIE OSŁABIONEGO SYGNAŁU 0ZPOSZENIA AMANOWSKIEGO WODY DO SZACOWANIA GUBOŚCI FILMU OLEJOWEGO NA POWIEZCHNI MOZA. Streszczenie Zdalne i bezkontaktowe metody pomiarowe znajdują różnorakie zastosowania w badaniach powierzchni mórz. Jednym z narzędzi służących do zdalnego wykrywania i identyfikowania substancji ropopochodnych znajdujących się w górnej warstwie morza jest lidar fluorescencyjny. Prezentowany tutaj lidar FLS-UV został zaprojektowany i wykonany LDI Ltd. w Tallinie, Estonia. Zasada działania lidaru FLS-UV opiera się na rejestracji sygnału powrotnego wzbudzonego laserowym światłem UV o długości fali 299 nm. Widmo powrotne rejestrowane jest w 4 kanałach odpowiadających długością fal odpowiednio λ maksimum rozproszenia amanowskie wiązki światła lasera na molekułach wody, λ 10 nm, λ + 10 nm oraz λ + 20 nm. Laboratoryjny eksperyment kalibracyjny pomiaru grubości filmu olejowego, polegający na dodawaniu ściśle określonych ilości oleju, wykazał bardzo dobrą (0,98) korelację z wynikami otrzymanymi przy pomocy lidaru FLS-UV. W latach przeprowadzono szereg lidarowych eksperymentów morskich mających na celu wykrywanie i szacowanie grubości filmu olejowego na powierzchni morza podczas rejsów badawczych r/y Oceania na Morzu Bałtyckim. Wyniki tych badań wykazały, że największa ilość substancji ropopochodnych występuje w pobliżu portów i ujść rzek. 7

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