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Introduction

Editor's Note: This is a slightly altered version of an article published in the October 1996 issue of Geo Info Systems, Vol. 6, No. 10, and is reproduced with permission from Advanstar Communications Inc.

The earth isn't flat, and the sky isn't a ceiling. So why do weather forecasters look at the world in just two dimensions? Because technology has limited them to two-dimensional charts, graphs, and contours. Researchers in Colorado are expanding those limits, however, by developing sophisticated three-dimensional weather displays (as shown in Figure 1) for meteorologists that will be available soon.



Figure 1. Eta model forecast of Hurricane Fran off the coast of Florida valid at 0600 UTC 4 September 1996, viewed from the southwest looking northeast. Displayed is a 20 m s-1 wind speed isosurface, with a cross section of relative humidity values shown in both the volume and in a second two-dimensional view (inset).

Systems developers at FSL have been assigned the task of developing technology for high-powered, infor-mation-packed weather forecasting workstations of the future. This effort is part of the National Weather Service's technological revitalization, and the three-dimensional technology is a key component of the prototype "Weather Forecast Office (WFO)-Advanced" weather workstation developed by FSL.

Three-dimensional weather visualization will supplement existing two-dimensional weather slices - flat representations of a thin "layer" of weather - chiefly by saving meteorologists the trouble of mentally "stacking" two-dimensional images to create a three-dimensional model.

Three-dimensional weather displays also help:

• researchers comprehend new short-range weather forecasts, now produced regionally instead of just in Washington, thanks to advances in computer processing power;

• scientists gauge the validity of predictive models by crunching massive amounts of data and comparing the actual weather to the predictions; and

• scientists, researchers and others - such as forecasters and visitors to FSL - appreciate the physical principles behind the weather in a way that's impossible when viewed in two dimensions. This difference is comparable to looking at a map and actually driving down a road.

Using three-dimensional visualization, researchers can virtually surf across the country measuring weather variables, digesting more data than ever, and display them in an accessible, color-coded, high-resolution format.

Next Generation Weather Tools

The first generation of meteorologists craned their heads toward the sky. Contemporary meteorologists generally work somewhere between that method and three-dimensional visualizations, while some forecasters work with little more than wax pencils and paper. In any case, the classic approach is to study two-dimensional slices. Three-dimensional visualizations bring to meteorology what voices brought to silent films: a vivid approximation of real life.

And real life is precisely what meteorologists are trying to approximate as they collect slices of weather and mentally stack and analyze them. If you relieve meteorologists from having to do mental two-dimensional to three-dimensional calculations, they can concentrate on the actual numbers needed for forecasts. In meteorology, three-dimensional displays will not replace two- dimensional displays, but three-dimensional displays can help reduce the amount of two-dimensional data that forecasters study. Despite the efficiency of three-dimensional visualization, a few meteorologists dismiss the new technology as newfangled and glitzy, expressing the same resistance to revolutionary technology witnessed throughout the ages.

Efficiency is becoming increasingly important as the sources and volumes of data proliferate. Fortunately, computer horsepower is also increasing, and three- dimensional weather is harnessing it to display more data faster in more places. This process allows forecasters and atmospheric scientists to develop, for the first time, sophisticated mesoscale - 20 to 200 kilometers - hourly forecast models for the next 12 to 18 hours in just four hours, a fraction of the time that slower computers have taken.

Traditionally, local forecasters have relied on national forecasts and combined them with local observations to predict the local weather. They really didn't have a true regional forecast, which is important. After all, it can be snowing in Denver while it's sunny in Boulder.

Using three-dimensional technology, meteorologists are provided with finer granularity, enabling them to better predict the weather. FSL's national-scale renderings are created from grid points 60 km apart. Its regional renderings, which cover the eastern two-thirds of Colorado, or roughly 360,000 square kilometers, display a grid resolution of 10 kilometers. Locally, resolution is down to one kilometer. The smaller the area being dis-played, the higher the resolution.

Virtual Flights of Fancy

Researchers are using AVS/Express object-orientated visual intelligence software (Advanced Visual Systems [AVS], Waltham, Massachusetts) to convert millions of data points into three-dimensional images of weather phenomena such as wind, moisture, and temperature, as well as to display contour lines, wind symbols, and temperature readings. [FSL's early experimentation with AVS software is covered in two articles by Paula McCaslin and Philip McDonald in the December 1992 FSL Forum. At that time, it was the laboratory's hope that three-dimensional display applications would have a place in future meteorological workstation design.]

AVS/Express software allows researchers to actually "get into" the weather. FSL researchers have taken virtual flights around hurricanes and through clouds to sample wind speed and moisture. Even when there's no weather to speak of, there are still places to go. When FSL research associate Philip A. McDonald demonstrates the technology, he likes to take his audience on a virtual tour of Colorado (Figure 2). He flies up the Arkansas River Valley, swoops down on Denver, leapfrogs over Pikes Peak and lands in San Luis Valley.

Longer trips are possible with FSL's three-dimensional visualization system, D3D, to be part of the WFO-Advanced workstation. Researchers can soar across the United States and see the weather graphically displayed. Wind-speed data, for example, renders a zucchini-shaped form hovering over the United States. This shape repre-sents the jet stream, which carries weather systems across the country and makes West Coast-to-East Coast airline flights quicker. FSL researchers can rotate the image, drill into it, even slice it up.

Researchers have also developed dramatic models for aviation: pink shapes looming over a map of the United States warn of potential icing conditions at specific elevations. The system also dramatically displays turbulence, cloud ceilings, and visibility.

In its current design, the WFO-Advanced workstation will display images in both two and three dimensions. The three-dimensional images will be used primarily to display high resolution local data and forecasts of the Local Analysis and Prediction System (LAPS).



Figure 2. Virtual Tour of Colorado.
Shown in the above image is an overhead view of the LAPS analysis of surface pressure (hPa) over the Colorado domain at 2100 UTC, 26 November 1996. The pink line indicates a user-defined flight path. Shown in the image below is a view along the user-defined flight path approaching Denver. This scene includes surface winds (m s-1) and cloud liquid water (.02g m-3)



State of the Art

Traditionally, when meteorologists examined a cloud they viewed a two-dimensional display depicting a horizontal slice at a given elevation, with contour and moisture readings. Using three-dimensional weather visualization, the cloud is rendered in its full volume, and meteorologists can manipulate it into two-dimensional planes for a detailed view.

A vertical probe tool allows researchers to wade into a weather system, click on a single point in that volume and sample data from the ground to a point about 10 miles high, from 21 different elevations. This method is similar to launching a virtual weather balloon, only this "balloon" doesn't drift - it goes straight up.

Instead of being outside the data and looking down at them or viewing them obliquely, researchers can actually get into the volume and explore them. They can even add a fourth dimension. By displaying forecasts for half-hour periods in rapid-fire succession, meteorologists can observe the development of a storm, rather than seeing only a snapshot.

How it Works

Data pour into weather offices from weather balloons, ground stations, radar, aircraft and satellites. Researchers used the AVS software to build an application converting those millions of data points into three-dimensional images. Since 1990, FSL has used the software mainly for meteorological model verification.

Color choice is critical to three-dimensional visualization because the wrong choice can mislead the viewer. FSL chose a greenish-brown color for the earth, blue for the ocean, and a rainbow color scale to depict temperature, pressure, and other variables.

Wind speed is displayed according to meteorological tradition, with wind barbs. In wind-barb code, a long dash means 10 knots, a short one means 5 knots, and a flag shape means 50 knots. FSL's three-dimensional displays can show wind barbs simultaneously with contour lines, colors, shapes, and numbers.

The three-dimensional weather visualization application is being developed on a Hewlett-Packard (Palo Alto, California) 715 workstation with a 24-bit, true color display controller and graphics accelerator in a UNIX environment. The WFO-Advanced workstation's D3D interface includes a graphical user interface, a three-button mouse, and a keyboard. Menu bars offer the user intuitive choices of file, model, data and source, while icon buttons allow the user to zoom, pan, and rotate the displayed image.

Whither Two-Dimensional?

Not all meteorologists are ready to abandon two-dimensional technology for three-dimensional technology, but the two technologies can complement each other. Traditionally, meteorologists have looked at one slice or data layer in the atmosphere at a time. They may examine a half dozen significant slices regularly. Typically, meteorologists view slices from overhead. Slices may have contours on them, or perhaps a sheet of colors, and they may be combined with satellite images. The meteorologists look at this numerical information and try to imagine the structure, ultimately a three-dimensional one, in their minds.

Not only is three-dimensional visualization more comprehensive, it can reduce the meteorologists' workload. For instance, if nothing is going on but a lot of blue sky, there's not much to look at. But somewhere in that blue sky a meteorologist may spot something that indicates the potential for severe weather. The three-dimensional display shows them the whole sky at once, not just a slice. Meteorologists can click on a current area, pop up a cross section and pull out a two-dimensional slice with all the quantitative information needed.

With weather models generating more data, more parameters, and higher resolution in both space and time, forecasters will be inundated with information. "The mesoscale model produces enormous amounts of data, and there's no way a forecaster can look at every single field or cross section in time to get the forecast out," said FSL meteorologist John Snook. "The three-dimensional visualization gives you a snapshot of the whole picture very rapidly. Then the forecaster can look at it and say, 'That's where it looks like it's going to rain today. I can start concentrating on that area.'"

What Next?

FSL researchers are already sold on three-dimensional imagery, but meteorologists will probably need training to reap the benefits of having more information and more flexibility at their fingertips. Forecasters have deadlines, and if they're not getting the information they need when they need it, it's useless.

"Ultimately, we can generate products that the public can understand much easier instead of looking at more sophisticated things the forecaster might use to formulate the forecast," Snook said.

But for now, the goal is to get the technology out of the laboratory and into the forecasters' hands. FSL conducts daily weather briefings, and forecasters there are using D3D in an experimental environment. Researchers are asking them to experiment with and evaluate D3D. If the forecasters find that the system is lacking a certain feature, the system developers will try to create it so that D3D displays precisely the weather phenomena meteorologists want to see - the way they want to see it. The technology will continue to improve. As early as 1997, forecasters at the Denver Weather Service Forecast Office could be viewing weather the way it really happens - in three dimensions.

FSL's three dimensional weather displays can be found on the World Wide Web at http://www.fsl.noaa.gov/frd-bin/LAPS.homepage.cgi .

(Paula McCaslin is a computer analyst in FSL's Forecast Research Division, headed by John A. McGinley. Philip A. McDonald is a research associate in the Systems Development Division, headed by U. Herbert Grote. Steve McGrath is a writer with Beaupre & Co. Public Relations.)