# How To Simulate An Ocean

## Making water look realistic in computer simulations is devilishly hard. Now computer scientists reveal how the tricks of the trade have changed in the last 30 years

Oct 4, 2011

One of the trickiest parts of any computer simulation is making water look realistic. So imagine the programmer’s task when it comes to simulating entire oceans.

Today, Emmanuelle Darles at the University of Limoges in France and a couple of friends survey the state of the art in ocean simulation and reveal the various tricks used to make the results look realistic. They also identify a number of outstanding challenges in this area.

The basic challenge in ocean simulation is to reproduce the shape of the water’s surface as well as the way it reflects light. There are essentially three approaches, say Darle and co.

The first is to measure the behaviour of the surface of real water using buoys or satellite measurements, develop a mathematical model that describes this behaviour and then use this to bound the behaviour of water “particles” in a computer model.

The second uses wave equations to compute the size and distribution of waves on a flexible surface.

The third is known as computational fluid dynamics and computes the behaviour of the entire body of fluid using the Navier-Stokes equations.

The first and second methods work best in the deep ocean where the surface has a clean oscillatory motion. But closer to the shore, the waves begin to interact with the ocean bottom, causing them to break. That kind of behaviour is much harder to reproduce and needs to be calculated from scratch using computational fluid dynamics. Even then, the calculations are hard so various approximations are needed.

And creating a seamless join between the deep and shallow water simulations is also tricky

Then there are the ocean’s complex optical properties, which are complicated by factors such as spray, foam and the presence of sand or organisms in the water.

That can be hard to reproduce. And Darle and co point to various gaps in the simulator’s tool box. “To or knowledge, there is no work dealing with realistic foam created by breaking waves,” they say.

All this makes oceans hard to simulate well.

Nevertheless, there are impressive simulations around, the best of which tend to exploit a variety of techniques to achieve their goals.

To show off some of these, here’s a gallery of images from the paper in order of the date they were generated. Clearly significant progress has been made since the first image above, which dates from 1986.

To find out more about the techniques used to create them, go to the paper:

A Survey Of Ocean Simulation And Rendering Techniques In Computer Graphics: arxiv.org/abs/1109.6494

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