Detection and mapping of oil slicks in the sea by combined use of hyperspectral imagery and laser induced fluorescence

M. Lennon , N. Thomas, V. Mariette
SAS ActiMar – 24, Quai de la Douane – 29200 Brest – France
Phone: +33 (0)2 98 44 29 63 Fax: +33 (0)2 98 44 70 17
marc.lennon@actimar.fr

G. Mercier
GET- ENST Bretagne – CNRS FRE 2658 TAMCIC – Technopôle Brest-Iroise
CS 83818 – 29238 Brest Cedex– France

S. Babichenko
AS Laser Diagnostic Instruments – 113A Kadaka Str., 12915 Tallin – Estonia

ABSTRACT

Efficient observation means are required for supporting operational fight against oil pollutions at sea and recovery operations, including reliable choice and guidance of maritime and airborne means of fighting such occurrences. Among the suite of sensors available, the potential of airborne passive hyperspectral imagery [1] and emergent active fluorescence laser systems [2,3], for remote sensing of oil spills at sea have been studied in the past.

The potential of combining passive and active airborne optical remote sensors for quantitative mapping of oil slicks at sea and for supporting recovery operations is proposed for evaluation in this pilot project. Location, extents, geographical configuration of slicks, volume of the oil spilled and its spatial distribution are the main useful parameters to be estimated.

A hyperspectral imager (CASI) and a Fluorescent Lidar System (FLS-AU) have been installed onboard a fixed-wing aircraft (Cessna 404). Test flights have been carried out over a controlled simulated oil pollution at sea off the coast of Brittany, France, in May 2004. Three real spills at sea have been performed during a three days campaign. Different flight and sensor configurations have been tested. The data acquisition campaign has been completed by spectroscopic measurements on the slicks at sea, onboard a small inflatable boat.

CASI data allowed very high spatial resolution (1 and 2 metres) slick maps to be produced, and the polluted surface to be estimated, after illumination corrections and definition of specific colour spaces taking advantage of observed spectral phenomena. The impact of the illumination/acquisition geometry and of the sensor configuration on the segmentation quality has been quantified. A simple radiative transfer model in the water has been studied and shown to be relevant for understanding the intra-slick spectral variability.

In-lab calibration of fluorescence spectra acquired by FLS allowed thickness to be locally estimated (approximate spatial resolution of 25 metres along-track and 200 metres across-track). These measurements have been used to “calibrate” CASI data and to extend the estimation of thickness over all the CASI pixels. This data fusion procedure proved to be consistent with the radiative transfer model over a polluted water area including a thin layer of oil, and allowed a very high resolution (1 metre) thickness map to be computed. This map shows the spatial distribution of the oil thickness and allows the total volume of oil spilled to be estimated. A critical study of the methodology used and a method for estimating the error in the quantitative measurements is proposed.

This pilot project allowed us to make a step towards answering environmental concerns associated with accidents in oil storage and transportation. Passive and active hyperspectral sensors have been shown to be complementary. In particular, data fusion from both sensors allows high-resolution spatial distribution of oil volume to be geographically mapped. We think that the use of those combined sensors, as a reliable observation means for supporting operational recovering operations, is a high potential value-added application.

REFERENCES

1. M. Lennon, V. Mariette, A. Coat, V. Verbeque, P. Mouge, G.A. Borstad, P. Willis, R. Kerr, M. Alvarez (2003). Detection and mapping of the November 2002 PRESTIGE Tanker oil spill in Galicia, Spain, with the airborne multispectral CASI sensor. 3rd EARSEL Workshop on Imaging Spectroscopy, 13-16 may 2003, Oberpfaffenhofen, Germany.
2. Reuter R., Wang H., Willkomm R. and Loguay K., Hengstermann T. and Braun A. (1995). A Laser Fluorosensor for Maritime Surveillance: Measurement of Oil Spills. EARSEL Advances in Remote Sensing, 3: 152 - 169.
3. Babichenko S., Dudelzak A., Poryvkina L. (2002). Laser sensing technologies in studies of marine and coastal environment. The Seventh International Conference on Remote Sensing for Marine and Coastal Environments, Miami, Florida, 20-22 May 2002, eProceedings, Veridan, 8 p.

Last Update: 2005-04-7