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Figure 4 Classified Image of the SAR Image in Figure 3.
DATA DISSEMINATION
The SEACAST circulation models are run daily reinitializing
all dependent variable fields using results at -120 hours (5
days old). The models are then run forward in time
assimilating all available SST image data and a 48-hour
forecast is generated. When the SeaSonde is on-line, these
data are assimilated hourly. During an oil spill, the spill
model is run as frequently as updates are required by the
response organizations drawing current and wind input data
from the circulation models. Generally, updates are required
every few hours during the first day or two of an emergency,
and then less frequently as the response becomes organized.
When RADARSAT SAR images are obtained, they are used
to monitor the spill and reinitialize the spill model.
The output from the system consists of fields from the
hydrodynamic model—SST, salinity, surface current—and oil
slick information—volume distributions, oil volume balance,
oil properties—from the spill model. These fields are
generated at the frequency required by the user, and in the
case of the spill model this is typically every 20-30 minutes.
All fields derived from SEACAST are uniformly stored in
georeferenced, binary format and distributed to users over the
Internet. The data flow for SEACAST is illustrated in Figure
5. The digital output files are placed in password-protected
web pages and can be accessed by all entitled users at their
convenience. A data-viewing Windows program (Seainfo) is
provided to users, allowing them to display and manipulate
the model output. This system provides response
organizations and agencies responsible for monitoring oil spill
response with timely, accurate information for decision
making, taking maximum advantage of near-real time data.
An example of the Nakhodka spill model file after re-
initialization presented in Seainfo is shown in Figure 6.
Intemational Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998
Figure 6 SPILLSIM Slick Prediction Based on SAR Image
Re-initialization (Nakhodka Spill, Sea of Japan).
CONCLUSIONS
Three-dimensional circulation models have been implemented
and verified for the Canadian west coast at two scales of
resolution: a 5-km continental shelf model and a 1-km model
for the Georgia-Fuca waterway which is a large coastal sea
connected to the Pacific Ocean. Methods to successfully
assimilate near real-time sea surface temperature data from
AVHRR imagery and surface current measurements from
ground wave radars into these circulation models have been
developed and tested. Data nudging using a Gaussian
distribution in time with a 6-hour window was found to be the
most appropriate method for SST. A data blending scheme
based on weights derived from the error characteristics of the
ground wave radar (SeaSonde) systems, without time-
dependent nudging, appears optimum for current assimilation.
Assimilation of these data provides significant improvements
in surface current prediction accuracy from the models. An
oil spill trajectory and weathering model has been coupled
into the circulation model, utilizing the most recent current
data for the advective calculations. Classification techniques
for RADARSAT SAR imagery, combined with computerized
graphical editing tools, has led to practical methods for
monitoring oil slicks and parameterizing the observed slick
features into re-initialization fields for the oil spill model.
The circulation modelling system runs operationally on a 24-h
cycle on a Sun Unix workstation, computing a 5-day hindcast
with data assimilation and a 2-day forecast. Oil spill
simulations are computed as required for contingency
planning and emergency response.
The modelling systems have global applicability. Data
products, in the form of surface current, temperature and
salinity fields, as well as predicted oil slick (volume)
distributions can be distributed to users over the Internet and
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