Oceanographic Applications of ALOS PALSAR Imagery to the Coast of the Korea Peninsula- A Case Study of the Hebei Spirit Oil Spill -

Duk-jin Kim1, Jinho Kang2, Younsoo Kim2, Hoonyol Lee3, and Wooil M. Moon1,4

1. School of Earth and Environmental Sciences, Seoul National University, Korea2. Korea Aerospace Research Institute (KARI), Korea3. Kangwon National University, Korea4. Geophysics, University of Manitoba, Canada

A massive oil spill occurred on the coast of Yellow Sea in South Korea, on December 7th, 2007

More than 10,000 tons of crude oil was spilled in the sea after a barge collided with the anchored Hebei Spirit oil tanker.

The spill contaminated ecologically pristine regions as well as polluted the western coastline of the Korean Peninsula

The Korean government declared the state of emergency in the coastal regions.

Introduction

The Synthetic Aperture Radar (SAR) is commonly used today to monitor oil spills due to its wide area coverage and also a capability to observe oceans all-weather conditions

After the oil spill occurred, available SAR sensors (ALOS PALSAR, ENVISAT ASAR, ERS-2, RADARSAT-1, and TerraSAR-X) collected imageries over the area from December 9th to December 25th.

SAR Acquisition

SAR Images

SAR imaging of oil slicks

• Bragg scattering: the NRCS (normalized radar cross section), σ0, can be written as [Romeiser et al., 1997]

)(cos16244

0 bije kgk ±Ψ⋅= θπσ

: Scattering coefficient for ij polarization (i.e., ij=HH, VV, VH, and HV): Spectral power density of the Bragg waves

2ijg

)( bk±Ψ

0=−−+= bvnw SSSSdtdN

: Action spectral density of the sea surface wave

: Source terms of energy input by the wind, nonlinear wave-wave interaction,and of energy loss by viscous dissipation and wave breaking, respectively

• Action balance equation [Elfouhaily et al., 1997]

⎟⎠⎞

⎜⎝⎛ Ψ=

kN ω

bvnw SSSS and,,,

• Damping ratio: the ratio of the normalized radar cross section of a slick-free and a slick-covered sea surface [Gade et al., 1998]

cb

cn

fb

fn

gff

gcc

c

f

c

f

c

f

SSSS

c

c

kNkN

kk

−

−

Δ−

Δ−==

ΨΨ

=2

2

)()(

)()(

0

0

β

β

σσ

Symbols f and c are for slick-free and slick covered sea surface, respectively: wind wave growth rate : group velocity of the sea wave: viscous damping coefficient

β

gcΔ

n

n

gff

gcc

c

f

c

f

gk

umcc

kk

Δ

−Δ

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛⋅

Δ−

Δ−=

ΨΨ

=φ

ββ

σσ cos

222

)()(

*4

0

0

• Wind speed dependent damping ratio [Gade et al., 1998]

: the wind friction velocity and the angle between the wind and wave direction: the reduction of the friction velocity and of the wave breaking, respectively

,*u

SAR imaging of oil slicks

φ,m nΔ

Pre-Processing

Radiometric Calibration

• The procedure to convert the digital numbers (DN) into backscattering coefficient (σ°)

• This procedure depends on SAR sensors and data type*

Speckle Reduction

Geometric Correction

• Multi-sensor and multi-temporal SAR images were used in this study

• Geo-rectification process was performed to achieve a map projection and registration images

ERS-2 : H. Laur, P. Bally, P. Meadows, J. Sanchez, B. Schaettler, E. Lopinto, and D. Esteban, “ERS SAR Calibration: Derivation of the backscattering coefficient σ° in ESA ERS SAR PRI products,” ES-TN-RS-PM-HL09, Issue 2, Rev. 5f, 2004.ENVISAT ASAR : B. Rosich and P. Meadows, “Absolute calibration of ASAR Level 1 Products Generated with PF-ASAR,”Technical Note, ENVI-CLVL-EOPG-TN-03-0010, Issue 1, Revision 5, 2004.RADARSAT-1 : S. Srivastava and N. Shepherd, “Extraction of Beta Naught and Sigma Naught from RADARSAT CDPF Products,”RReport No.: AS97-5001, Rev.2-22 May, Contract No.:9F005-6-0025/001/SN, 1998.TerraSAR-X : T. Fritz, et al., “TerraSAR-X Ground Segment: Level 1b product format specification,” Doc.:TX-GS-DD-3307, Issue, 1.3, pp. 1-257, 2007.ALOS PALSAR : JAXA, “ALOS/PALSAR Level 1.1/1.5 product Format description, NEB-070062A, Rev. K, 2008.

TerraSAR-X2007/12/12

(X-band, VV)

TerraSAR-X2007/12/20

(X-band, VV)

ENVISAT2007/12/11

(C-band, VV)

ENVISAT2007/12/14

(C-band, VV)

ERS-2 SAR2007/12/14

(C-band, VV)

RADARSAT-12007/12/11

(C-band, HH)

ALOS PALSAR2007/12/09

(L-band, HH)

ALOS PALSAR2007/12/11

(L-band, Full)

ALOS PALSAR2007/12/15

(C-band, HH)

wind speed/direction

6.1 m/s/ 327.5o

(NNW)

5.1 m/s/ 349.0o

(N)

5.3 m/s/ 10.1o

(N)

6.6 m/s/ 346.8o

(NNW)

6.6 m/s/ 344.6o

(NNW)

5.9 m/s/ 12.7o

(NNE)

2.1 m/s/ 11.0o

(N)

1.6 m/s/ 27.2o

(NNE)

9.2 m/s/ 332.6o

(NNW)

incidenceangle

(at oil slicks)34 deg. 35 deg. 34 deg. 25 deg. 25 deg. 37 deg. 39 deg. 11 deg. 23 deg.

wavenumber(at oil slicks) 227 rad/m 233 rad/m 124 rad/m 94 rad/m 94 rad/m 134 rad/m 34 rad/m 10 rad/m 21 rad/m

damping ratio 7.1 dB 3.3 dB 6.9 dB 2.2 dB 3.4 dB 4.5 dB 0.0 dB 1.5 dB (HH) 1.4 dB

Measured Damping ratios

][][ 00 dBdB cf σσ −

)()()( kkyk fc Δ⋅=Δfc umu ** ⋅=

Marangoni damping

22)sin(cos21sin)sin(cos1)(

XXYXYXky

+−+−+−+

=θθ

θθθ

ηρω3

2

2

kEX =

ηω4kE

Y =

n

n

gff

gcc

c

f

c

f

gk

umcc

kk

Δ

−Δ

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛⋅

Δ−

Δ−=

ΨΨ

=φ

ββ

σσ cos

222

)()(

*4

0

0

2

3

3

235

81.91015.1

1038s107.3τ

deg. 220θN/m 0.0001E

smgsPa

mkgm

=

⋅×=

=

×=

=

=

−

−

η

ρ

Theoretical Damping Ratio

RADARSAT-1 (C-band)

ENVISAT (C-band)TerraSAR-X (X-band)

sm /4

sm /5

sm /6

sm /7

sm /8sm /9

[rad/m]r WavenumbeBragg

Dam

ping

Rat

io [d

B]

ERS-2 (C-band)

ALOS (L-band)

4290.Δn.m

==

Damping Ratio Comparison

MeasuredComputed

ALOS PALSAR (L-band, HH)2007/12/09 14:03 [UTC]

Local time [UTC +9h]

L-band Wind Retrieval

Backscattering Coefficient (σ°) Image

Level 1.1 :Level 1.5 : CFDNdB

CFQIdB

+⋅=

−++⋅=2

100

2210

0

log10][

0.32log10][

σ

σ CF : Calibration Factor(in Radiometric Data Record)

L-band Wind Comparison

Wind Retrieval Results2007/12/09 14:03 [UTC]

L-band Wind Retrieval Model[Isoguchi and Shimada, 2007]

55

44

33

2210 RaRaRaRaRaa +++++=θLevel 1.1 : incidence angle:

Level 1.5 : incidence angle:

)5,...,0(

Local time [UTC +9h]

=iai: incidence angle polynomial coefficient

(in dataset summary record)),,,( yxHf c ΔΔ= θθ

L-band Wind Comparison

Wind Retrieval Results2007/12/15 02:10 [UTC]

ALOS PALSAR (L-band, HH)2007/12/15 02:10 [UTC]

Backscattering Coefficient (σ°) Image 0m/s 35m/s

Monitoring of Oil Slick Migration

Oil Slick Detection• Land Masking (using DEM)• Adaptive Thresholding (k [dB])• Clustering and Classification

SAR dataacquisition date

Oil slickcovered area

ENVISAT2007/12/11

1400 km2

RADARSAT-12007/12/11

700 km2

TerraSAR-X2007/12/12

400 km2

ENVISAT2007/12/14

350 km2

ERS-2 SAR2007/12/14

340 km2

TerraSAR-X2007/12/20

>410 km2

ENVISAT ASAR2007/12/11 01:40

RADARSAT-12007/12/11 09:31

TerraSAR-X2007/12/12 21:44

Monitoring of Oil Slick Migration

ERS-2 SAR2007/12/14 02:15

ENVISAT ASAR2007/12/14 01:45

30-minutetime difference sm

hkm /7.0

5.025.1

≈

For the Hebei Spirit oil spill accident, which occurred in December 7th, 2007, the spilled oils were captured by TerraSAR-X, ENVISAT ASAR, RADARSAT-1, ERS-2 SAR, and ALOS PALSAR sensors.

With multi-frequency SAR images, the damping ratios were calculated and analyzed with measured wind speed and radar frequency.

From the acquired multi-temporal SAR images, the movement of oil slicks was monitored and traced; oil slicks in near-dormant motion were rapidly migrated to south on December 14th due to strong winds and currents.

This research is still in progress, where additional field data are to be integrated for further analyses and damage assessments in a nearfuture.

Summary