Real-time Wave, Tide, and Surf Prediction

Introduction: As the U.S. Navy and Marine Corps are increasingly required to operate within the littorals, there is a need to quickly set up ocean prediction models to support military planning and operations. Amphibious landings, mine countermeasures, and Special Forces operations are often required on hostile beaches. What are the expected longshore currents at a specific time on a specific beach? Will the predicted sea state prevent landing craft from operating within 48 hours? What is the ideal time for ingress/egress due to tides and currents? The Distributed Integrated Ocean Prediction System (DIOPS) provides the capability to quickly set up and perform wave, tide, and surf predictions for any worldwide location, provided adequate bathymetry is available.1

DIOPS Models: The backbone of DIOPS is the Simulating Waves Nearshore (SWAN) wave model used to predict nearshore wave conditions. SWAN includes wind-generated wave growth, the effects of refraction, shoaling, and dissipation. SWAN can receive wave energy (spectra) on its lateral boundaries from a deep-water wave model such as WAM (a DIOPS component) or WaveWatch III from the Fleet Numerical Oceanographic and Meteorology Command.

PCTIDES is a globally relocatable tidal-prediction model containing a 2-D barotropic ocean model. A 0.25° resolution global tide model, Finite Element Solutions 99 (FES99),2 is used to provide tidal conditions on open boundaries. Surface winds, pressures, and/or astronomical tides are used to force the model. Additionally, a database containing more than 4200 stations from the International Hydrographic Office can be assimilated into the model solution.

The Navy Standard Surf Model (NSSM) is the primary software for U.S. Navy operational surf forecasting. NSSM receives boundary conditions just outside the surf zone from SWAN and utilizes water levels from PCTIDES to adjust the beach profile. One-dimensional surf calculations are performed for each transect, perpendicular to the beach. Outputs include surf zone width, longshore current, breaker type (spilling, plunging, or surging), and the Modified Surf Index (MSI) that characterizes overall surf conditions used in operational planning.

DIOPS Architecture: The Dynamic Information Architecture System (DIAS), developed by Argonne National Laboratory, is the DIOPS software object framework that allows these models to work together in various context-dependent scenarios within the same simulation. DIAS is a flexible, extensible, object-oriented framework for developing and maintaining complex simulations. The object-based DIOPS framework decomposes the maritime environment from the deep ocean to the shore into classes of software objects, each with its own spatially distributed sets of attributes, and with dynamic behaviors that are implemented by the appropriate ocean physics models. The DIAS software architecture underlying DIOPS enforces the stricture that models may communicate only with domain objects, and never directly with each other. This makes it relatively easy to add or swap models without recoding. Figure 11 shows the relationship of DIOPS model components in the offshore, nearshore, and surf zone.

FIGURE 11
DIOPS domain object interactions between offshore, nearshore, and the surf zone.

The DIOPS Graphical User Interface, developed by Anteon, is divided into three functional areas using "window pane" technology. Although a standard windowing concept, this technology was leveraged from the Navy Integrated Tactical Environmental Subsystem (NITES) II Object Oriented Redesign (OOR). The DIOPS display is divided into the Task Area, Chart Area, and the Analysis Area. The operator can click and drag the windowpane to make one area larger and another smaller, but portions of each remain visible: no hidden windows. Figure 12 shows the PCTIDES model configuration for an area in the Ligurian Sea.

FIGURE 12
PCTIDES model configuration for the Ligurian Sea.

Real-time Exercise Support: DIOPS has been running at the Naval Pacific Meteorology and Oceanography Center (NPMOC) in San Diego, where a beta-test site was established since 2001. DIOPS has supported numerous military and NATO exercises, including Millennium Challenge '02 (California), Strong Resolve 2002 (Baltic Sea), Operation Iraqi Freedom '03, and most recently, Northern Lights '03 (NL03) in Luce Bay, Scotland. Figure 13(a) depicts wave conditions on September 17, 2003 in support of NL03. Figure 13(b) shows a comparison of PCTIDES water levels (top) and nested SWAN wave height (bottom) compared to in situ measurements.

FIGURE 13
(a) SWAN wave prediction for September 17, 2003. Arrows show direction to which waves are moving. White box denotes high-resolution SWAN model nest. Yellow star indicates location where measurement data are available.
(b) Time-series of (top) water levels and (bottom) wave heights at a location in Luce Bay, Scotland (yellow star). Red line denotes observation, blue line represents model prediction.

Summary: DIOPS is a relocatable wave, tide, and surf prediction system capable of operating on UNIX or PC platforms. DIOPS development is geared toward operation by junior enlisted personnel. The entire suite of models can be run at a Meteorologic and Oceanographic Command regional center with the ingestion of atmospheric forcing fields such as winds, sea-level pressure, and available bathymetry. Future efforts will link DIOPS with the Delft3D modeling system, using bathymetry from unmanned underwater vehicles to predict rip currents and 2-D surf conditions. A webservices architecture will also be developed.

Acknowledgments: The authors acknowledge Dr. Daniel Conley at the SACLANT Undersea Research Centre for providing the NL03 data.

[Sponsored by ONR and SPAWAR]