The Taylor Energy Oil Spill: Time-Series Of PolSAR Data To Support Continuous And Effective Observation
2018
Satellite Synthetic Aperture Radar (SAR) has been proved to be a key tool for a broad
range of environmental applications in the context of oceans and coastal areas monitoring,
including ship detection, coastline extraction, land use/cover classification, oil spill observation
and sea surface parameters retrieval. In particular, the capability of satellite SAR measurements
to support operational activities in case of natural disasters and environmental hazards as the
Deepwater Horizon oil spill accident occurred in the Gulf of Mexico in 2010 or the most recent
Sanchi accidental oil spill occurred off the eastern coast of China.
In this study, we focused on one of the richest areas in offshore oil seepages, i. e, the northern
part of the Gulf of Mexico near the Mississippi river delta, where the Taylor Energy oil drilling
platform is located (28°56’17’’N,88°58’16’’W). The platform was destroyed by the Hurricane
Ivan in 2004 and, since then, the underwater wells were continuously leaking oil. It was
estimated that more than 100 oil gallons enters into the marine environment from the Taylor
Energy platform site. This results in surface oil slicks whose average thickness and life–time are
about 1 μm and 4 days, respectively.
The area was continuously observed from satellite SAR platforms since the accidental oil spill
occurred. Space-borne SAR imagery witness that this coastal area was almost persistently
affected by this anthropogenic oil seep as the slicks were detected in about 80% of the data
collected over the site. Even if strictly speaking this leakage cannot be considered as a natural oil
seep, the underwater origin of the oil seep together with the involved weathering and aging
processes are fairly the same.
Hence, it represents a good opportunity to have a large and consistent time series of SAR
imagery that covers a well-known oil seepage. A large time series of dual-polarimetric copolarized TerraSAR-X high-resolution (1.2 x 6.6 slant range x azimuth nominal spatial
resolution) SAR imagery, collected in StripMap mode between July 2011 and April 2016 in a
wide range of incidence angles (25° - 45°) and sea state conditions (low-to-moderate wind
conditions applied, i. e., 1.5 m/s – 8.5 m/s), is exploited.
In this study, despite of the rather high noise floor that characterizes TerraSAR-X StripMap SAR
imagery (an estimated noise equivalent sigma zero, NESZ, in the range -20 dB – -23 dB), the
time series is effectively exploited to monitor the Taylor Energy oil spill. A multi-polarization
analysis, that includes co-polarized intensity and phase difference information, is undertaken on
which the oil spill detection and characterization is grounded.
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