Variability of the Deepwater Horizon Surface Oil Spill Extent and Its Relationship to Varying Ocean Currents and Extreme Weather Conditions - Mathematical Modelling and Numerical Simulation of Oil Pollution Problems - page 6

shelf break of the northern portion of the West Florida Shelf (WFS) at about 250km
off the coast [ 21 ]. The northern intrusions of the LC may occur in any season with
periods ranging from 6 to 17 months, but tend to be more frequent during the spring
months [ 15 , 20 , 34 ]. Results derived from hydrographic and satellite observations
show that large, warm-core anticyclonic rings, referred to as LCRs, are usually shed
from the LC and propagate westward at mean translation speeds of approximately
4km/day and have mean lifetimes of days to around a year [ 12 , 23 , 34 , 37 ]. These
LCRs have radii of about 150km and may reach depths of 800m [ 25 ].
1.3 Main Data Sets and Methods
1.3.1 Surface Oil Extent
During the DWH response, the NOAA Office of Response and Restoration's Emer-
gency Response Division provided daily forecasts of the movement of surface oil,
predicting movement over 24, 48 and 72h intervals [ 17 ]. In previous incidents, the
primary dataset used to initialize oil distributions for modelling purposes was derived
from overflight observations, which would ideally delineate the oil slick boundary
and provide detailed descriptions of the distribution and percent coverage of differen-
tial oil thickness. However, even with multiple overflights per day being conducted
from several locations along the Gulf Coast, the areal magnitude of this oil spill
made it difficult for visual overflight observations to provide a comprehensive and
complete picture of the oil distribution.
Two primary data types were used to monitor oil at the ocean surface from space:
(a) surface roughness from microwave radiation; and (b) Visible and Near Infrared
(VNIR) data. By the second week of the incident, the experimental Marine Pollution
Surveillance Reports (MPSRs) provided by NOAA National Environmental Satel-
lite, Data, and Information Service (NESDIS) were an integral dataset used in the
model initialization. These analyses [ 32 ] provided an outer boundary for the extent
of the surface oil in a time frame that allowed use by the command posts to direct
operations, including overflights. The MPSRs delineated the extent of surface oil
using satellite imagery from both active and passive sensors and from other supple-
mentary information such as overflights and in situ observations. During the incident,
the MPSRs were rapidly made available, providing information about the surface oil
location after each satellite pass. The MPSRs were used in this study in combina-
tion with surface current fields to examine potential links between the GOM surface
dynamics and the surface oil extent (Fig. 1.2 ).
Synthetic Aperture Radar (SAR) sensors have been the traditional approach used
for assessing surface roughness for oil spill detection [ 2 ] since they are all-weather,
day and night, active sensors that emit microwave pulses and measure the backscat-
ter radiation reflected by the sea surface, which is a function of the sea surface
roughness. The constellation of space-borne SAR sensors (onboard satellites such as