SAR Remote Sensing in ArgomarineM. Babiker, T. Hamre, Nansen Environmental and Remote Sensing Center (NERSC)NorwayNew Strategies and Technologies for safety of Navigations in the Mediterranean Sea 21 November 2012, Petroferraio, Italy
Outline n Backgroundn SAR remote sensing for oil spilln SAR for Argomarinen Summary
BackgroundOil spills seriously affect the marine ecosystem and cause political and scientiﬁc concernsince they have serious effects on fragile marine and coastal ecosystem. The amount ofpollutant discharges and associated effects on the marine environment are importantparameters in evaluating sea water quality. Satellite images can improve the possibilitiesfor the detection and monitoring of oil spills as they cover large areas and offer aneconomical and easier way of continuous coastal areas patrolling. http://www.myhero.com/go/hero.asp?hero=Oil_Team_cfes_US_2012
15 November 2012 Last updated at 20:11 GMT BP gets record US criminal ﬁne over Deepwater disaster BP has received the biggest criminal ﬁne in US history as part of a $4.5bn (£2.8bn) settlement related to the fatal 2010 Deepwater Horizon disaster.
ESTIMATES OF GLOBAL INPUTS OF OIL TO THEMARINE ENVIRONMENT• Natural seeps: 46% • Discharges from consumption of oils (operational discharges fromships and discharges from land-based sources): 37% • Accidental spills from ships; 12% • Extraction of oil: 3% http://oils.gpa.unep.org/facts/sources.htm
The most commonly used remotely sensed system to detect oceanpollution is Synthetic Aperture Radar (SAR) imagery. The Prestige oil spill, Spain, caused by the sinking of an oil tanker in 2002
SAR = Synthetic Aperture Radar An active instrument that transmit/receive EM radiation, store data in amplitude and phase (real and imaginary part)• Works in the presence of clouds, day and night• Operates at microwave (or radar) frequencies• Fine resolution is independent of the platform height, so images with thesame geometric resolution (order of 10 m) can be obtained from satellitesas from airplanes
z Antenna Azimuth Range Swath x y Illuminated area!A short pulse is emitted by the antenna and then the amplitude andphase of the backscattered signal is recorded as a function of time This isrepeated over again while the platform is moving Thus a 2-dimensionalimage is generated.
Advantages compared to optical remote sensingAll weather capability (small sensitivity of clouds, light rain)Day and night operation (independence of sun illumination)No effects of atmospheric constituents (multitemporal analysis)Sensitivity to dielectric properties (water content , biomass, ice)Sensitivity to surface roughness ( ocean wind speed, currents ,oil spill )Accurate measurements of distance (interferometry)Sensitivity to man made objectsSensitivity to target structure (use of polarimetry)Subsurface penetration
SAR-based oil spill monitoring in Argomarine:SAR image ordering and acquisition for the test areas The following Satellite were investigated: ENVISAT ASAR (launched March 2002) ALOS PALSAR (November 2006) TerraSAR-X (June 2007) COSMO-SkyMed (June 2007) Radarsat-2 (December 2007)
NERSC set up automatic download of images for the two test areas, usingsoftware tools developed by NERSC in other RTD projects During the project period 208 ENVISAT ASAR images were downloaded for the Tuscan Archipelago And 280 images for The National Marine Park of Zakynthos. 3 TerraSAR-X were ordered and purchased 3 Radarsat2 images ordered and purchased
SAR analysis for oil spill detection and classiﬁcationA selection of archived images from the ENVISAT ASAR (Advanced SyntheticAperture Radar) covering both study areas were analyzed. The Next ESA SAR Toolbox (NEST) was used to analyse the ASAR data.An ENVISAT ASAR Wide swath image acquired on the 7 June 2008 covering the Tuscany Archipelago (B) oil spills mapgenerated from image (a) Red is potential oil spill, light blue currents and waves black low wind speed. A conﬁrmed oil spillis demarcated with green circle.
An ENVISAT ASAR image mode image acquired on the 14 March 2008 covering Zakynthos (B) oilspills map generated from image (a) Red is potential oil spill, light blue currents and waves black lowwind speed.
Classiﬁcation of oil spills and surface phenomena in dualpolarisation images All the available methods and models for discrimination between oil spills and look-likes using polarimetric SAR are still experimental and no concrete method or model are available for that. Alternating polarizations ENVISAT ASAR image (VV/VH) acquired on the 01 August 2003 (A) VV polarization (B) VH polarization (C) RBG image from VV, VH and VV/VH (D) Wind speed and direction generated from the image.
Alternating polarizations ENVISAT ASAR image (VV/ VH) acquired on the 11 May 2007 (A) VV polarization (B) VH polarization (C) RBG image from VV, VH and VV/VH (D) Wind speed and direction generated from t h e i m a g e .Most of the surfacephenomena, oil spills andlook-alikes investigated canbe detected clearly in bothpolarizations VV and theHH, on the other hand thesame features can’t bedetected using crosspolarizations (VH, HV).
SAR estimates of wind and currentsThe CMOD4 and Doppler shift algorithms have been applied on a selectedENVISAT ASAR images from the two areas to estimate wind speed and current.An ENVISAT ASAR wide Swath (VV) of the 27 of August 2010 covering the Tuscan Archipelago.
ENVISAT ASAR wide Swath (VV) of the 15 of October 2010 covering Zakynthos Island.
Distribution and density of oil spills in the testareasSeventy two archived ENVISAT ASAR (Advanced Synthetic Aperture Radar) WideSwath images were analyzed for oil spill distribution and density. The oil spill detection algorithm was applied for all the images and only darkfeatures with high potential to be oil spill were analyzed. A density map wascreated for each study area.
Summary SAR is the most applicable spaceborne sensor for operational oil spilldetection, mostlybecause of its all-weather/all-day detection capabilities and wide coverageThe largest challenge in detection of oil spills in SAR images is accuratediscrimination between oil spills and look-alikes.For operational purposes, there is a need for coordination between satelliteoverpasses and aerial surveillance ﬂights.Future SAR missions are crucial for sustainable operational oil spill detectionservices.