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1. Hurricanes are the most devastating natural hazard
affecting the populated US East and Gulf coasts.
One of the major threats associated with hurricanes is
stormsurge.Thestormsurgecandamagebuildingsand
infrastructure, block escape routes, and drown people
by flooding low-lying coastal areas. More than 8,000
people were killed largely from storm-surge flooding
when a hurricane made landfall at Galveston, Texas, in
1900.ThedeathtollintheUSfromstorm-surgehazards
has declined drastically over the last several decades
because of a low hurricane activity and implementation
of timely evacuation from storm-surge zones. The evac-
uation zones are determined through a combination of
near-shore elevations and storm surge predicted by the
numerical model Sea, Lake, Overland Surges from
Hurricanes (Slosh)1
developed by the National Oceanic
and Atmospheric Administration (NOAA). As coastal
populations grow and decades of increased hurricane
activity occur,2
the risk of drowning thousands of peo-
ple living in low-lying areas, such as South Florida and
New Orleans, Louisiana, increases as demonstrated by
Hurricanes Katrina and Rita in 2005. Several hundred
people were killed along the Mississippi coast by the
storm-surge flooding induced by Katrina.
Coastalresidentsarewarnedandadvisedaboutevac-
uations by the National Hurricane Center (NHC) of
NOAA through the media such as TV, Web, radio, and
newspapers. However, due to a lack of first-hand expe-
rience of hurricane impact, many coastal residents tend
to overlook the danger of storm surge and choose not to
evacuate. This could cause loss of life and injury that
could be avoided.
On the other hand, some residents choose to evacu-
ate even though they are not in an evacuation zone.
Overevacuation not only brings an inconvenience to
evacuees, but also increases traffic and consequently
slows down the evacuation process.
A major reason for under- and overevacuation is that
people don’t properly relate the 2D maps of the evacu-
ation zones to their 3D life experience. Currently, TV
meteorologistsuseacolorlinebufferoveramaporsatel-
lite image to display hurricane warning and watch
zones. This information, in combination with 2D evac-
uation maps, raises the public’s awareness of following
the evacuation order. However, hurricane warning and
evacuation maps don’t provide coastal residents with a
detailed account on the effect of storm surge on people
and property.
Three-dimensional computer visualization and ani-
mation can provide a substitute for coastal residents’
lack of personal experience with hurricane-surge flood-
ing. Tremendous progress has been made in 3D anima-
tion in the last decade, which movies such as Perfect
Storm and TheDayAfterTomorrow have demonstrated.
However,the3Dvisualizationandanimationsystemfor
storm-surge flooding differs from those in Hollywood
movies in three aspects.
First, objects such as buildings, roads, and trees in a
synthetic 3D visualization environment not only have
to be able to duplicate the real-world feature visually,
but also be georeferenced so users can find real loca-
tionsthroughaddressesorspatialcoordinates.Thesizes
and shapes of buildings and trees have to be accurate so
users can sense the severity of flooding by comparing
the water level with heights of familiar objects.
Second,themagnitude,extent,andprocessofstorm-
surge flooding have to be accurate enough to represent
the real situation. This information has to be based on
hydrodynamics of storm surge.
Third,thedamageextentofapropertycausedbystorm
surgeandwaves,suchasthecollapseofahouse,mustbe
determined by engineering rules. Recent advances in
high-resolution remote-sensing technology and numer-
ical modeling make it possible to provide accurate data
fortheearth’ssurfacefeaturesandstorm-surgeflooding.
Objectives and goals
Here, we present a prototype 3D visualization and
animation system for storm-surge flooding. Our system
includes three major components:
■ a 3D synthetic visualization environment represent-
ing terrain, buildings, roads, vegetation, and the sea;
■ a module for animating surge flooding and waves;
and
■ a high-resolution storm-surge model to serve as an
engine to drive the animation of flooding (see
Figure 1).
Thestorm-surgemodel(seethe“FurtherReading”side-
bar) that we used in our study is an improvement of
NOAA’s Slosh model, which enables us to refine the spa-
Keqi Zhang,
Shu-Ching Chen,
Peter Singh,
Khalid Saleem,
and Na Zhao
Florida
International
University
A 3D Visualization System for Hurricane
Storm-Surge Flooding ______________________________
Applications
Editor: Mike Potel
http://www.wildcrest.com
18 January/February 2006 Published by the IEEE Computer Society 0272-1716/06/$20.00 © 2006 IEEE

2. tial resolution of surge modeling from the kilo-
meter to the hundred-meter scale. We built the
3D visualization environment and animation
components, which are the focus of this article,
based on the Virtual Terrain Project (VTP; see
http://www. vterrain.org) using OpenGL.
The major goals of our storm-surge flooding
visualization system are to perform
■ near-real-time animation for forecasted hur-
ricanes and
■ offlineanimationforhypotheticalhurricanes.
The NHC issues public advisories that contain
forecasted storm positions and intensity for
three and five days in advance. There is con-
siderable uncertainty in forecasting hurricane
tracks and intensity, which are inputs of
storm-surge models, because of our limited
scientific knowledge of hurricanes. The longer
the forecast period is, the larger the un-
certainty.
The uncertainty of forecasted hurricane
tracks is displayed as a cone on TV with the best
prediction in the center. Usually, the NHC
releases a public advisory every 6 hours during
a storm event and every 2 to 3 hours near land-
fall. The location, size, and shape of the fore-
casted cone are updated and improved as a
hurricaneapproachestheshore.Thisrequiresa
near-real-time modeling and animation of
storm-surge flooding to present the public with
themostrecentinformation.Also,thescenarios
for most severe, most possible, and slightest
flooding have to be produced based on the
uncertainty in the hurricane track and intensi-
tyforecasttoprovidethepublicwithacomplete
picture of possible storm-surge flooding. In
addition to informing the public, the real-time
prediction and visualization of a storm surge
lets emergency managers plan and respond to
hurricane impacts more effectively.
We used offline visualization and anima-
tion to simulate the effect of storm-surge
flooding from a hypothetical hurricane. These simu-
lations display what the effect of storm-surge flood-
ing would be if a hypothetical hurricane makes a
landfall at a designated area. Offline visualization is
useful for planning and education purposes by dis-
playing the possible impact of a storm surge on exist-
ing and future coastal development.
We selected two study sites—South Beach and the
Rickenbacker Causeway, located in Miami, Florida—to
applyour3Dvisualizationandanimationsystem.Miami
is constantly battered by hurricanes in terms of the his-
torical record. South Beach is part of a barrier island
chain facing the Atlantic Ocean. It’s a typical sample of
important coastal tourism sites that are vulnerable to
storm-surge flooding. The Rickenbacker Causeway is a
highway connecting Virginia Key and Key Biscayne and
is the only available escape route for island residents
during a hurricane.
IEEE Computer Graphics and Applications 19
Lidar
measurements
Feature extraction
Data assimilation and representation
Digital terrain
model
Building Vegetation Road
Photographs GIS databases
Visualization environment
Animation component Numerical models
1 Framework for 3D visualization and animation of storm-surge flooding.
Further Reading
For more information on key aspects of our system, please see
the following articles:
■ Storm-surge modeling: C. Xiao, K., Zhang, and J. Shen, A Three-
Dimensional Numerical Model for Storm Surge Flooding, Part I:
Model Description and Tide Simulation, tech. report, Int’l
Hurricane Research Center, 2004, p. 30.
■ Lidar data classification: K. Zhang et al., “A Progressive
Morphological Filter for Removing Non-ground Measurements
from Airborne LIDAR Data,” IEEE Trans. Geoscience and Remote
Sensing, vol. 41, no. 4, 2003, pp. 872-882.
■ Tree animation: P. Singh et al., “Tree Animation for a 3D
Interactive Visualization System for Hurricane Impacts,” Proc.
IEEE Int’l Conf. Multimedia and Expo (ICME), IEEE Press, 2005,
pp. 598-601.

3. Constructing a 3D synthetic
visualization environment
A realistic and georeferenced 3D visualization envi-
ronment needs to be built for animating and displaying
the effect of storm-surge flooding. The major compo-
nents of the visualization environment include a digital
terrain model, buildings (location and 3D shapes), veg-
etation(type,location,height,size,anddensity),roads,
rivers, lakes, and oceans. The data required for buiding
these components can be derived through remote-sens-
ingtechnology,groundsurveys,andexistinggeographic
information system (GIS) databases.
Airborne Lidar measurements, feature
extraction, and texture derivation
High-resolution measurements of the terrain and the
earth’s surface objects are essential to constructing a
realistic 3D visualization environment. Until recent
advancesinairbornelightdetectionandranging(Lidar)
technology,ithasbeendifficulttoobtainmeasurements
of the earth’s surface topography and objects over large
areas with sufficient resolution for realistic 3D visual-
ization.AirborneLidarisanactiveremote-sensingtech-
nology. A typical airborne Lidar mapping system
consists of three basic components: a laser scanner, a
kinematic GPS, and an inertial measurement unit
(IMU)—see Figure 2. The laser scanner determines the
range from the aircraft to an object on the ground using
thetraveltimeofemittedandreflectedlaserpulses.The
GPS and IMU record the aircraft position and orienta-
tion. We can determine an object’s 3D coordinates (x, y,
and z) —referenced to the earth’s center—by combing
the laser range, GPS, and IMU data.
With vertical accuracies up to 15 cm and a submeter
horizontal resolution, Lidar measurements provide
accurate and detailed geometric information of the ter-
rain, buildings, and trees for constructing a synthetic
visualization environment (see Figure 3). However, air-
borne Lidar systems derive irregularly spaced 3D point
measurements of objects scanned by the laser beneath
the aircraft. To construct a 3D synthetic visualization
environ- ment, we have to extract geometric informa-
tion for the terrain, buildings, and trees from volumi-
nous point data.
Wehavedevelopedaframeworkthatincludesaseries
of methods to extract the features from Lidar measure-
ments.Underthisframework,measurementsfortheter-
rain and nonground objects are first classified using a
progressive morphological filter (see the “Further
Reading” sidebar). Then, buildings and vegetation are
furtherseparatedfromnongroundmeasurementsusing
parameters of a fitting plane to Lidar measurements
withinalocalwindow(seeFigure4).Withclassifiedter-
rain, building, and vegetation Lidar measurements, we
generate the digital terrain model by interpolating
groundmeasurements,extractingthefootprintsand3D
shapes of buildings, and deriving the locations and
heights of trees from nonground measurements.
Applications
20 January/February 2006
2 Schematic
diagram show-
ing data acquisi-
tion parameters
for a Lidar
system. We
obtained the
point spacings
from a scanner
with an oscillat-
ing mirror and a
forward aircraft
speed of 50
meters per
second. We can
achieve a high
point density by
setting a low
flying altitude,
slow flying
speed, and
narrow scan
angle and per-
forming over-
lapping surveys.
500-m flight
altitude 320-m-
wide
scan
swath
13-cm-wide
laser footprint
33-kHz laser
pulse rate
0.7 m
36˚ scan
angle
1.4 m
GPS satellites
GPS ground
station
Differential
GPS
navigation
Inertial
measurem
unit

4. Furthermore, we extract shape data for roads, coast-
lines, canals, and lakes from existing GIS databases.
Combining these data together, we can construct
wireframes of 3D objects for visualization. However,
object wireframes, like the skeleton of the human body,
only represent the shape of 3D objects. To make objects
look realistic, we have to provide real-life skin (texture)
over a wireframe. We obtained the texture for buildings
and trees from color aerial and ground photographs.
3D models for buildings and trees
We have to create 3D building and tree models based
on wireframe and texture data to develop a 3D visual-
ization environment in the VTP. Unfortunately, the
VTP system can only read digital terrain model (usu-
ally stored as binary files) and GIS shape files for roads
directly and generate corresponding visual represen-
tations using its C++ libraries. It does not have the
capability to create complex 3D building and vegeta-
tion models, but provides an API to read files (.3DS)
from the commercial 3D model creation software,
Autodesk’s 3ds Max. We created building and plant
models in two steps in 3ds Max. First, we created geo-
metric skeletons of objects using primitive parts such
as boxes and cylinders and their transformations in
terms of geometric data from Lidar measurements.
Second, we created textures including material prop-
erty, color, reflection, and opacity (which cover skele-
tons) from ground and aerial photographs. Figure 5
shows models for a building and palm tree in South
IEEE Computer Graphics and Applications 21
35
25
15
5
–5
Elevation (m)
4 (a) Aerial photograph for a building surrounded by trees, (b) Lidar point
measurements for the same area, (c) unit normal vectors of the fitting
plane for a Lidar point and its neighbors within a window, (d) and the sum
of squares due to elevation deviations (SSEDs) of Lidar measurements
within a window from the fitting plane. The unit normal vectors are consis-
tent and SSEDs are small for building roof points, while unit normal vectors
are variable and SSEDs are large for vegetation points.
3 Image interpolated from point Lidar measurements
for a coastal section at South Beach, Miami, Florida. The
right corner is the ocean side.
10
8
6
4
2
0
0.3
0.2
0.1
0
Elevation (m)
10
20
30
40
0
20
40
60
0
5
10
15
10
20
30
40
0
10
20
30
40
50
60
0
1
2
10
20
30
40
50
–10 0
0
10
20
30
40
50
60
70
0
1
2
(a) (b)
(c) (d)
5 (a) Building and (b) tree models created in 3ds Max.
(a) (b)

5. Beach. In addition, we developed other models includ-
ing bridges, cars, and wake effects using 3ds Max.
3D visualization environment
Weimporteddigitalterrainmodels,buildingandveg-
etation models, and road shape files to the VTP to gen-
erate a 3D synthetic environment using C++ libraries
and OpenGL APIs. Figure 6 shows a 3D visualization
environment for an area in South Beach. VTP also has a
user-friendly interface that lets users fly or walk around
the 3D environment, zoom-in or -out of a scene, as well
as select designated locations within the environment.
This provides users with an interactive way to navigate
through a 3D synthetic environment and to reach their
location of interest.
Animation of storm-surge flooding
The animation component reproduces the storm-
surge flooding processes in a synthetic 3D visualization
environment. Data for storm-surge flooding come from
numericalmodelingbasedonhurricanetrackandinten-
sity. However, animating storm-surge flooding is not
enough to produce a realistic flooding scene because
storm surge is only one of the impacts caused by hurri-
canes. High winds and heavy rain, often accompanying
a hurricane, can also alter the environment significant-
ly. To make the visualization of surge-flooding process-
ing more closely representative of a natural situation,
we constructed six different animation engines to sim-
ulate water, wind, rain, and other phenomena caused
by storms. The six animation engines are
■ flooding and wave;
■ cloud, rain, and lightning;
■ tree;
■ debris;
■ vehicle; and
■ 3D sound.
Flooding and wave animation
The water-level change due to storm surge is easy to
animate because it approximates a sine curve and is a
relativelyslowandlarge-scaleprocess.Muchmorechal-
lengingworkistoanimateocean-surfacewaves.Ocean-
surface waves in deep water caused by hurricanes have
multifrequencies that are determined by local wind
waves and swell waves propagated from the area cov-
ered by storms. In shallow coastal water, waves trans-
form due to interactions with the bottom of the ocean
and make the animation even more complicated. Many
numerical models can simulate the generation and
propagation of multispectral waves. However, the
demand on computational resources for the simulation
and rendering is tremendous. To save computational
cost, we only implemented a simple deep ocean wave
model for enhancing the visualization effect.3
The wave
animation changes as wind speeds and directions vary,
which allows representation of wave size changes dur-
ing a hurricane. Figure 7 shows a scene of flooding
animation from our system. The animation of a super-
imposed surface wave over rising water makes surge
flooding look more realistic.
22 January/February 2006
Applications
6 3D visualization environment for South Beach.
7 (a) Ocean wave animation and (b) overland flooding animation.
(a) (b)
(a)
(b)

6. Cloud, rain, and lightning animation
The weather of a hurricane has distinct features such
as dark clouds, heavy rain, and sometimes thunder and
lightning. To make the hurricane impact look more real-
istic, these features have to be animated appropriately.
Wecreatedtwocloudpatternstorepresenttheskyinhur-
ricaneandnormalconditions.Thehurricaneskyisfilled
withdarkandthickclouds(seeFigure8),whileanormal
sky is clear with few clouds. Cloud animation provides
viewerswithasenseofsevereweatherfromahurricane.
We animated the raindrops using a particle engine.4
The engine stores a list of raindrops and updates them
at a fixed time interval. The rain animation is associat-
ed with variables including wind direction, speed, and
rain intensity. We animated the lightning by randomly
assigning depth to each lightning structure.
Tree animation
The tree animation engine displays the wind effect
ontrees.Weemployedabillboardmodelinwhichatree
isrepresentedbyplanar-texture-mappedgeometrywith
various angles (see http://www.vterrain.org/Plants/
Modelling/) to perform a simple tree animation. The
advantage of a billboard model is that it is easy to imple-
mentandconsumeslittlecomputingresources.Thedis-
advantage is that the model only allows tree bending or
swinging as a whole around a pivot point. This method
is reasonable for animating trees far away from the cen-
terofascenewherethedetailsarenotneeded.However,
themethodlacksofflexibilityanddetailstoanimatethe
trees at the scene’s center. We used a vertex weighting
technique (see the “Further Reading” sidebar) to
improvethetreeanimationatthecenterofascene.This
method allows trunk bending and branch swinging in
different directions, making tree animation more real-
istic visually. Wind speed and direction determine the
magnitude and direction of tree bending and swinging
in the tree animation engine.
Debris animation
High winds during a hurricane often cause flying
debris that can result in serious damage to unprotected
windows. The debris can be any solid object movable by
windsuchasrocksontheground,snappedtreebranch-
es, and loosened roof tiles. We used Open Dynamics
Engine (see http://www.ode.org) along with VTP for
animating flying debris. To control the animation, we
used the wind speed and direction variables. Figure 9
showsdebrisanimationaroundtheSouthBeachregion.
Vehicle animation
To display the effect of storm-surge flooding on evac-
uationtraffic,thevehicleshavetobeanimated.Vehicles
traveling on a highway or a road during or after the rain
produce a wake effect that results in splashes around
the vehicle and a trail of water behind the vehicle. We
created .3DS models rendering the wake effect around
a vehicle and manipulated its size and texture using the
VTP to animate a car movement under rain conditions.
Figure10onthenextpageshowsthewakeeffectcaused
by car movement during rain.
3D sound animation
Creating sound effects from wind, wave, rain, and
thunder make storm-surge flooding animation more
realistic. We implemented 3D sound animation using
OpenAL (see http://www.openal.org). The sound ani-
mation includes a background sound for ocean waves
and wind, which becomes louder as the wind speed
increases. The strength of sound was determined with
reference to the listener’s position, which is the camera
locationinoursystem.Wealsoblendedsoundsforthun-
der and rain into the 3D sound effect. The sound vol-
ume of thunder depends on visibility of lightning and
its distance from the listener (camera). The sound for
rain increases in volume as listeners move close to the
road or ocean.
IEEE Computer Graphics and Applications 23
8 Cloud, rain, and lighting during a hurricane. We
added the blue background to the lower portion to
make raindrops more evident.
9 Debris
animation.

7. Discussion and conclusions
Our visualization and animation system displays a
process showing that a rising storm surge can stop and
drown vehicles in sections with low elevation during a
hypothetical hurricane, leading to a blockage of the
escaperoute.Thisvividanimation,incombinationwith
a realistic 3D visualization environment, has impressed
local coastal residents in several demos (see Figure 11).
Displaying and animating 3D objects is an extensive
computationandmemory-consumingtask.Thecurrent
prototype—running on a PC workstation with a 3.2-
GHz processor, 2 Gbytes of RAM, and a 256-Mbyte
graphiccard—hasachievedacceptableperformancefor
a coastal area extending several kilometers, but has dif-
ficulty in rendering large-scale visualization. We can
improve the performance for a large-scale 3D visual-
ization and animation in several ways. First, we can
increase the animation speed by optimizing many
graphics-rendering algorithms. Pyramid algorithms
need to be introduced into the system to compress com-
ponents for a large-scale animation.
Second, we can improve the animation speed by run-
ningthesysteminacomputercluster.Todothisrequires
breaking down the large-scale project into many small-
scale components, and the corresponding parallel algo-
rithms have to be developed.
Third, if resources are limited for visualizing and ani-
mating the entire area impacted by storm surge, we can
perform visualization and animation for landmark
buildings, evacuation bottlenecks, and key locations
instead of the whole area. The public can derive the
impression of storm-surge impact by watching the ani-
mation at landmarks close to their living areas.
We designed our current prototype for real-time
visualization and animation for storm-surge flooding,
which has higher requirements for computing power
than a non-real-time visualization. An emphasis on
real-time visualization and animation limits the detail
of the 3D visualization environment. A real-time ani-
mation is not required for answering what-if questions
for the possible impacts of hypothetical hurricanes hav-
ing different intensities. These questions are best
addressed in offline animations, which can take hours
to produce frames through a batch mode. Greater
details of the 3D environment and flooding processes
can be included in the offline visualization and ani-
mation. Therefore, we must treat real-time and off-line
animation separately.
Our 3D visualization and animation system is based
on real measurements and georeferenced data. By
inputting the address or spatial coordinate for a specif-
ic house, users can view the impact of storm surge on
their property. Users can also view the spatial changes
of storm-surge flooding by flying or walking through an
animated environment. Therefore, this system can help
emergency managers educate coastal residents to take
appropriate evacuation action by allowing coastal resi-
dents to view the potential impact and damage of storm
surge to their living environment. This system is also
usefulforperformingoptimalurbanplanningandflood
damage mitigation by simulating possible storm-surge
impact. Moreover, we can extend the current system to
visualize and animate fresh-water flooding and wind
damage to buildings. Georeferenced 3D synthetic visu-
alization environments created for hurricane impact
animation can also be used for other animation tasks
such as routine traffic visualization. ■
Applications
24 January/February 2006
11 Flooding
and traffic
animation
for the
Rickenbacker
Causeway
during a hypo-
thetical hurri-
cane. Right
panel shows a
traffic blockage
due to storm-
surge flooding.
10 Water
wake effect
animation.

8. Acknowledgments
This work was partially supported by a grant from the
Federal Emergency Management Agency and by the
Florida Hurricane Alliance Research Program spon-
sored by the NOAA. This article is based on our paper
from the Proceedings of the IEEE International
Conference on Multimedia and Expo 2005 (see the side-
bar for the complete reference). We thank Mike Potel,
associate editor in chief of IEEE Computer Graphics and
Applications, for reviewing our article and providing
valuable comments.
References
1. C.P. Jelesnianski, J. Chen, and W.A. Shaffer, Slosh: Sea,
Lake and Overland Surges from Hurricanes, tech. report,
Nat’l Oceanic and Atmospheric Administration, 1992,
p. 71.
2. S.B. Goldenberg et al., “The Recent Increase in Atlantic
Hurricane Activity: Causes and Implications,” Science, vol.
293, no. 5529, 2001, pp. 474-479.
3. A. Fournier and W.T. Reeves, “A Simple Model of Ocean
Waves,”Proc.Siggraph,vol.4,ACMPress,1986,pp.75-84.
4. W.T. Reeves, “Particle System—A Technique for Modeling
a Class of Fuzzy Objects,” ACM Trans. Graphics, vol. 2, no.
2, 1983, pp. 91-108.
Readers may contact Keqi Zhang at zhangk@fiu.edu.
Readers may contact editor Mike Potel at potel@
wildcrest.com.
IEEE Computer Graphics and Applications 25
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