Oil Spill Detection by means of Oil Spill Detection by means of
DualPolarized SAR DataDualPolarized SAR Data
F.Nunziata, A.Gambardella, M.MigliaccioUniversità degli Studi di Napoli “Parthenope”
Dipartimento per le Tecnologie
SummarySummary
IntroductionIntroduction
MotivationMotivation
ModelModel
ExperimentsExperiments
ConclusionsConclusions
SAR oil spill observation, under low to moderate wind conditions, is very attractive
• Day & night observation.
• Allweather capability.
• High spatial resolution.
• Wide area coverage.
• etc.
IntroductionIntroduction
Physically SAR oil spill observation is possible since an oil slick generate a low backscatter area
IntroductionIntroduction
Likely for us there are several dark areas...
MotivationMotivation
• Oil slicks.Oil slicks.• Biogenic slicks.• Low wind areas.• Rain cells.• Currents.• Internal waves.
• Dualpolarized SAR data are employedDualpolarized SAR data are employed
MotivationMotivationOil vs biogenic slick
ImagesImages
MeasurementsMeasurements
additional info
OilOLA
SAR polarimetry to assist oil spill detection
MotivationMotivation
Recently this team showed that fully polarimetric information can improve oil spill observation.
Mission Fully Dual SingleRADARSAT2 x x xALOS PALSAR x x xTERRASARX x x x
ENVISAT x xCOSMOSkyMed x x
SShh hh SShvhv
SShv hv SSvvvv
Dualpolarized SAR Dualpolarized SAR datadata
CPDCPD
Copolarized phase difference (CPD)
ModelModel
It is the phase difference between the HH and VV channels. The CPD pdf is related to the degree of correlation between the HH and VV channels.
CPD for oil spill observation
ModelModel
•Under low to moderate wind condition and for intermediate incidence angles two reference scenarios must be considered.
SLICK FREESLICK FREE
sea surfacesea surfaceSLICK COVEREDSLICK COVERED
sea surfacesea surface
CPD for oil spill observation: SLICKFREE sea surface
ModelModel
•Assuming that the smallscale roughness is wellmodelled by the Bragg scattering mechanism:
High HHVV correlation.
A narrow CPD pdf is to A narrow CPD pdf is to
be expectedbe expected
CPD for oil spill observation: SLICKCOVERED sea surface
ModelModel
Due to their different damping properties, two cases must be considered:
Oil slicksOil slicks Biogenic slicksBiogenic slicks
CPD for oil spill observation: OILCOVERED sea surface
ModelModel
An oil slick damps the Bragg resonant waves:
• A nonBragg scattering occurs.• A low backscattered signal.
• A low polarimetric entropy.
• A low HHVV correlation.
A broadening of the CPD pdf is expectedA broadening of the CPD pdf is expected
CPD for oil spill observation: BIOGENICCOVERED sea surface
ModelModel
Biogenic slick is characterized by weak damping properties:
• A Bragg scattering occurs.• A lower backscatter signals.
• An high HHVV correlation.
A similar CPD pdf for biogenicfree and biogenic coveredA similar CPD pdf for biogenicfree and biogenic covered
is expectedis expected
CPD for oil spill observation: in a nutshell
ModelModel
Sea & Biogenic
Oil
CPD
stan
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dev
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nCP
D st
anda
rd d
evia
tion
SIRC/XSAR data: Oil slick, p.n. 44327, Cband
ExperimentsExperiments
EMPHASIS EMPHASIS
FILTERFILTER
Mean std valueSea 17°Slick 40°
SIRC/XSAR data: Oil slick, p.n. 44327, Cband
ExperimentsExperiments
The oilcovered CPD pdf has been obtained considering the pixel values above the SIRC noise floor only.
SIRC/XSAR data: OLA slick, p.n. 41370, Cband
ExperimentsExperiments
DEEMPHASIS DEEMPHASIS
FILTERFILTER
Mean std valueSea 4°Slick 5.1°
SIRC/XSAR Cband data set: CPD processing results
ExperimentsExperiments
p.n. Surfactant11588 OLA 4.5° 3.5°41467 OLA 4.0° 3.6°41370 OLA 5.1° 4.0°11352 OLA 12.3° 10.3°11439 OLA 6.3° 4.7°11586 OLA 5.7° 4.7°41465 OLA 10.4° 8.7°12816 Oil 19.3° 11.2°17041 Oil 60.0° 11.2°44327 Oil 60.0° 11.2°
Mean slick Mean sea
ConclusionsConclusions• Partially polarimetric data, once properly modelled, are useful for oil spill observation, under low to moderate wind conditions.
• A model relating the CPD to the sea surface scattering mechanism with and without surface slick has been developed.
• Under low to moderate wind conditions the CPD pdf broadening is sensitive to the presence of a low backscattering area.
• CPD acts as an emphasis filter for oil spills.
• CPD acts as a deemphasis filter for biogenic films.