The detailed three-dimensional 

characterization of site topography is 

critical to many geomorphologic studies. 

Whether it’s a matter of glacial advance 

and retreat, coastal-seacliff landsliding, 

river-sandbar accretion and erosion, 

or the failure of civil infrastructure 

during disasters, understanding how 

these changes progress over time 

depends directly on detailed collection 

of topographic data. A new terrestrial 

(land based) laser system used by the 

U.S. Geological Survey (USGS) exploits 

advancements in light-detection-andranging (lidar) technology to collect an 

unprecedented amount of data in a very 

short time. For rapidly changing natural 

environments, such as rivers, landslides, 

and beaches, sites can now be efficiently 

surveyed repeatedly over a period of 

months, days, or even hours. The high 

resolution of lidar data, in combination 

with the ability to obtain multiple data–

sets over a short period of time, allows 

researchers to more fully understand 

the mechanics of these dynamic natural 

phenomena and to calibrate models for 

predicting future change.

Land-Based Lidar Mapping—a New Surveying 

Technique to Shed Light on Rapid Topographic Change

T

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 2006–3111

2006

and measure the returning signal in a 

highly efficient manner, such that millions 

of data points are collected in a matter 

of minutes. With this technology, a laser 

beam pulses along a constantly changing, 

but precisely measured, trajectory and 

is reflected back to the lidar device in 

a process termed “laser scanning.” By 

timing the round trip of each laser pulse, 

Methodology—Data Collection and 

Processing 

Terrestrial lidar technology is based 

on the laser rangefinder systems and 

electronic distance meters (EDMs) 

commonly used in surveying, such as 

those often observed along roadways. 

Lidar improves upon EDM techniques by 

being able to rapidly generate, transmit, 

he rate of natural change in 

such dynamic environments 

as rivers and coastlines 

can sometimes overwhelm 

the monitoring capacity of 

conventional surveying methods. 

In response to this limitation, 

U.S. Geological Survey (USGS) 

scientists are pioneering new 

applications of light detection 

and ranging (lidar), a laserbased scanning technology that 

promises to greatly increase our 

ability to track rapid topographic 

changes and manage their 

impact on affected communities.

Palm tree

Palm tree

The upper photograph shows a U.S. Geological Survey tripod-mounted lidar scanner positioned 

to scan the coast at Pleasure Point in Santa Cruz, California. The scanner is fixed with respect to 

the ground at a location, and a three-dimensional array of points is obtained from a rapidly pulsing 

laser beam to collect data in vertical lines, while the head of the scanner pans in the horizontal 

direction. The lower image shows typical raw data (“point cloud”) obtained from a lidar scan of 

the coastline above.
the precise range is determined for each 

scan position, and a series of coordinates 

are recorded (generally referred to as a 

“point cloud”). As the laser pulses are 

reflected back from objects at various 

distances from the scanner, point 

measurements are collected that define 

each object’s shape. To gather panoramic 

data at a given scene, the scanner slowly 

pans about a fixed base in the horizontal 

plane, while a rotating mirror reflects the 

laser at various trajectories in the vertical 

plane.

The USGS terrestrial lidar system 

uses a near-infrared, pulsed-laser diode 

to transmit and receive laser signals. In 

addition, a true-color sensor included in 

the lidar system automatically assigns 

each point a color value on the basis of 

field lighting conditions. The system 

is portable and designed for rapid 

acquisition of high-resolution threedimensional imagery under outdoor 

conditions. From a fixed station, a single 

lidar scan can sweep as much as 336° 

in the horizontal plane and 80° in the 

vertical plane. The laser can sense targets 

at a range as far as 1,100 feet (350 m) 

under the best atmospheric conditions, 

depending on the reflectivity of the given 

target. The range accuracy is consistently 

about half an inch (15 mm).

Data are collected at acquisition rates 

of approximately 500,000 points per 

minute, providing the ability to quickly 

image the topography of extremely 

complex natural surfaces in detail. The 

data points are converted to surface 

models after postprocessing to remove 

foreign objects (birds, people, vehicles, 

and such) and filtering to a regularly 

spaced network, typically with a minimum 

point separation of 4 to 20 inches (10 to 

50 cm). The points are then registered 

either to a local coordinate system, using 

fixed control points located within the 

scans, or to a global coordinate system, 

using a highly accurate differential global 

positioning system (GPS) or standard 

survey equipment to fix the location of 

each scanner setup. After processing of 

consecutively scanned surfaces of the 

same area at different times, linear and 

volumetric changes between the surfaces 

are measured and analyzed.

Measuring Changes in the Natural 

Environment—from Alaskan Glaciers to 

Grand Canyon Sandbars

One application of terrestrial lidar 

technology is to measure changes in the 

natural environment, such as glaciers and 

river sandbars, both of which have been 

the focus of recent scientific studies by 

the USGS Coastal and Marine Geology 

program. Exit Glacier, near Seward, 

Alaska, is an example of a glacier that 

has significantly retreated over the past 

century. With its easily accessible terminus 

and high retreat rate, this glacier presents 

the opportunity to study a landscape in 

motion and to model the mechanics of 

glacial retreat. Lidar data collected at this 

site in July 2004 have shown the large 

magnitude and spatial distribution of ice 

tension cracks within the glacier terminus 

and the complex three-dimensional 

interactions between the retreating glacier 

and underlying bedrock landforms.

Understanding sandbar evolution 

in rivers is another area of study in 

which terrestrial lidar technology is 

revolutionizing existing methods of 

measuring change. In Grand Canyon 

National Park, USGS scientists are 

studying how sandbars move through 

erosion and accretion cycles, depending 

on the flow rate of the Colorado River. 

Sandbar surveys performed with standard 

survey techniques are time consuming and 

require scientists to walk on the sandbar 

being studied, a procedure that can 

sometimes degrade sandbar bedforms, 

especially near the edges of the sandbar. 

Aerial lidar surveys require extensive 

logistics and are relatively expensive, 

and so they are not a feasible option for 

monitoring short-term change. Terrestrial 

Terrestrial lidar is an effective means of imaging complex, inaccessible terrain. These images 

show a lidar setup at the toe of Exit Glacier near Seward, Alaska. The large tension cracks 

visible in the photograph (top) were formed as an overhanging section of ice moved away from 

the main body of the glacier. Computer-processed lidar data (bottom) from the glacier allow 

measurement of the crack patterns and dimensions for understanding glacial processes.

6.5 feet (2 m)
Lidar scanning in Grand Canyon National Park allows a better understanding of the evolution 

of river sandbars. This series of images shows a photograph (top), the raw lidar point 

data (middle), and the finished topographic surface model (bottom) of a sandbar along the 

Colorado River. Repeated surveys of this area will provide vital information on how sandbars 

accrete and erode in response to fluctuating riverflow and windblown sediment deposition 

below Glen Canyon Dam. After the passage of Hurricane Katrina in New 

Orleans in 2005, mobile lidar surveys enabled 

rapid data reconnaissance of overtopped levee 

walls. In this photograph, a lidar scanner is 

mounted to the roof of a vehicle to extend the 

field of view over floodwalls and into scour 

trenches formed by water overtopping the 

walls. Even on the sloping ground shown here, 

the lidar scanner can easily be leveled on its 

fixed tripod base to assist in accurate data 

processing.

lidar surveys, however, are easily 

repeatable and provide a noninvasive 

technique to quickly obtain the data 

required by river scientists. During the 

2004 Glen Canyon Dam High Flow Test, 

researchers obtained terrestrial lidar 

datasets of several areas, including a large 

fluctuating sandbar, and were successful 

in demonstrating lidar’s usefulness in 

modeling such complex features.

Documenting the Failure Modes of New 

Orleans Levees After Hurricane Katrina

After the failure of the New Orleans 

levee system during Hurricane Katrina 

in 2005, one of the ways the USGS 

MONITORING CHANGES OF RIVER SANDBARS responded was to use a terrestrial lidar 

system to document the failure modes of 

the compromised levees. An important 

task with widespread implications, this 

emergency response collected the only 

ultra-high-resolution dataset available for 

characterization of levee deformations 

immediately after the hurricane. 

Here, terrestrial lidar technology was 

essential for determining the “as failed” 

condition of the levees for use in forensic 

investigations. Because the levees were 

repaired immediately after the city was 

pumped dry, collecting data in a timely 

and efficient manner was required. The 

portability of the USGS lidar system was 

especially valuable—the scanner was 

easily mounted to a tripod on the roof 

of a field vehicle, providing a higher 

viewing platform and allowing data to 

be collected over such cultural features 

as levee floodwalls and into flood-scour 

trenches on the land side of these same 

walls. The lidar datasets were initially 

used by independent teams of researchers 

investigating the causes of the failures, a 

report on which was submitted to the U.S. 

Congress (http://hsgac.senate.gov/_files/

Katrina/Preliminary_Report.pdf). These 

datasets have also been used by numerous 

researchers performing geotechnical 

analyses of the levee failures including 

the Independent Levee Investigation Team 

(ILIT), whose final report is available 

at http://www.ce.berkeley.edu/~new_

orleans/.

Colorado River
UNDERSTANDING COASTALBLUFF LANDSLIDING

ANALYZING LEVEE FLOODWALL FAILURES

For more information, contact:

U.S. Geological Survey

Western Coastal and Marine Geology

345 Middlefield Road

Menlo Park, CA 94025

650–329–5042

http://walrus.wr.usgs.gov/

This Fact Sheet and any updates to it

are available online at

http://pubs.usgs.gov/fs/2006/3111/

Terrestrial lidar monitoring of seacliff erosion 

along the Pacific coastline has allowed 

researchers to analyze the failure modes 

of coastal-bluff landslides. These three 

model views, each from a slightly different 

perspective, show temporally consecutive 

lidar scans of a coastal-bluff section in 

Pacifica, California, where 33 feet (10 m) of 

crest retreat occurred between October 2002 

(blue) and May 2003 (orange). The orientation 

scale on each image shows Z, vertical; N, 

north; and E, east.

Brian D. Collins and Robert Kayen

Edited by

George A. Havach

Graphic design by

Jeanne S. DiLeo

Printed on recycled paper

Analyzing Coastal-Bluff (Seacliff) 

Landslides from Storm-Induced Erosion

The Pacific coastline of California, 

Oregon, and Washington is one of 

the most dynamic environments in 

the United States. Along this heavily 

populated coast, land development 

and civil infrastructure are commonly 

threatened by erosion caused by large 

winter storms. Especially in central 

California, extensive coastal-bluff erosion 

and landsliding occur almost every 

winter. The USGS has been monitoring 

several stretches of the coast south of San 

Francisco both to document changing 

bluff conditions and to analyze and 

predict landslide events. Efficient use 

of terrestrial lidar surveys allows steep 

coastal-bluff areas to be monitored on a 

monthly or even daily basis, as needed. 

In contrast to aerial lidar surveys, which 

are better suited for studies over longer 

(for example, semiannual or annual) 

baselines, terrestrial lidar surveys are 

easily deployed to quickly collect the 

high-resolution data needed to understand 

both beach and bluff (seacliff) processes. 

Along the Pacifica, California, coastline, 

lidar surveys measured as much as 33 feet 

(10 m) of coastal-bluff retreat in less than 

a single month during the 2002–2003 

winter storm season—a telling statistic, 

considering the close proximity of homes 

and roads to the ocean. Lidar data have 

been used to demonstrate a direct link 

between changing coastal-bluff geometry 

and the likelihood of bluff failure and 

land loss at the crest, making continued 

monitoring important in establishing 

thresholds for landslide prediction along 

these bluffs.

The Future of Terrestrial Lidar Surveying

With the recent introduction of such a 

powerful surveying technique as terrestrial 

lidar, USGS scientists are just beginning 

to push its limits. Already, new lidar 

surveys are under way along several 

stretches of the Pacific coast, while repeat 

surveys of many sites are performed 

periodically throughout the year. Among 

the most recent uses of this technology 

are lidar-scanning the headwalls of glacial 

cirques to evaluate rockfall potential and 

measure erosion, collecting landform 

data to monitor erosion of archeological 

sites in the Grand Canyon, and continued 

application as both a change-detection and 

a disaster-response tool for learning about 

our constantly changing world. 

The development and use of new 

surveying techniques, like terrestrial lidar, 

is only a part of USGS efforts to protect 

people’s lives and property from geologic 

and environmental hazards in the coastal 

zones and other areas of the United States.

This cross section (view northward) was 

developed from lidar datasets of the breached 

17th Street Canal in New Orleans after 

Hurricane Katrina in 2005. Lateral movement 

of the soil levee and its concrete floodwall, 

as measured by displacement of a chainlink 

fence, was approximately 46 feet (14 m). The 

cross section shows the original position of 

the concrete floodwall (now destroyed) and 

the emergency-repair embankment that was 

constructed after the hurricane to prevent 

additional flooding and to allow pumping out 

of the city. Inset photograph shows a lidar 

scanner set up on the emergency-repair 

embankment in front of displaced earth blocks.

Emergency

repair

embankment

Displaced earth

blocks with fence

Original

position

of fence

Vegetation

Original location

of canal flood wall

46 feet (14 m)

Beach level

Beach level

Crest

Crest

Crest

Beach level

Bluff height

79 feet (24 m)

33 feet (10 m)

N

E

Z

N E

Z

E

Z