U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2011–3017

March 2011

RESEARCH AT THE USGS WESTERN GEOGRAPHIC SCIENCE CENTER

Using Terrestrial Light Detection and Ranging (Lidar) 

Technology for Land-Surface Analysis in the Southwest

Until relatively recently, aerial-photo interpretation and traditional surveying techniques were the primary methods used to 

conduct three-dimensional (3- D) analysis 

of the Earth’s surface. Such analyses were 

significantly improved with the advent of 

airborne lidar and highly accurate Global 

Positioning System (GPS) data and instruments, which allow scientists to study 

areas of the Earth’s surface at a finer scale 

and higher precision. These technologies 

have continued to evolve and improve the 

quality of scientific work, but in recent 

years they have also given rise to new scientific tools, specifically terrestrial lidar.

In contrast to airborne systems, 

terrestrial lidar instruments are portable, 

mounted on tripods, and provide higherprecision measurements. They are active 

sensors that emit pulses of light and use 

the time delay of the reflection of light 

from target surfaces to measure distance. 

Terrestrial lidar can provide very precise 

data (millimeter accuracy) to enable 

scientists to build high-resolution threeto four-dimensional models of objects 

of interest. The fourth dimension is a 

measurement of point intensity, which 

USGS Western Geographic Science Center scientists are using terrestrial lidar to understand the consequences of landscape change in the desert Southwest. In this photograph a terrestrial lidar scanner and 

high-precision GPS are being used to investigate how wind processes influence erosion patterns and sediment transport in the Navajo Nation. (USGS photo by Miguel Velasco.)

can be useful for characterizing landsurface properties and to classify land 

use or land cover. Terrestrial lidar units 

have advantages over traditional surveying techniques and airborne instruments, 

including:

• Less expensive to deploy, schedule, 

and operate.

• Able to provide a significant increase in 

spatial resolutions.

• Able to map features otherwise obscured 

from the air, such as overhanging cliff 

faces, caves, and forest understory.

• Optimal for rapid damage assessments, 

long-term geomorphic change monitoring, and precision modeling.

Using Lidar

 Terrestrial lidar scanners are highly 

automated devices, based on laser 

rangefinding systems, and are often 

mounted on robotic pan-and-tilt heads. 

Data is generally collected from an 

merging technologies provide 

scientists with methods to 

measure Earth processes in 

new ways. One of these technologies—ultra-high-resolution, 

ground-based light detection and 

ranging (lidar)—is being used 

by USGS Western Geographic 

Science Center scientists to 

characterize the role of wind and 

fire processes in shaping desert 

landscapes of the Southwest 

United States.

E

instrument mounted on a stationary tripod, 

and the instrument can automatically 

survey as much as a 360-degree field 

of view around the instrument out to a 

distance of 1,500 m (~1 mile). It is often 

necessary to perform multiple scans from 

various locations to collect information 

from the shadows and backsides of 

objects in a scene. Sophisticated software 

for aligning scan data—a series of 

coordinates called “point clouds”—is 

required to assemble multiple clouds 

from different vantage points into a single 

coherent scene.

Once completed, the alignment of scans can 

provide a 3-D model of the object of interest 

with subcentimeter precision. Terrestrial scans 

not only have ultrafine spatial resolutions, 

but also allow data collection at enhanced 

temporal resolutions. By rescanning a scene 

or an object over a period of time, information 

on the morphology of physical features (size, 

shape, or location) can be collected and 

analyzed to understand how natural systems 

and processes of change are influencing the 

landscape and environment.
Measuring Sand-Dune Movement 

in the Southwest

Scientists with the U.S. Geological Survey’s (USGS) Western Geographic Science 

Center are using terrestrial lidar to measure 

sand-dune movement in the Southwestern 

United States. Arid lands in the Southwest 

can be very sensitive to climate changes. 

These landscapes, which are often largely 

comprised of fine-grained sand, are prone 

to wind mobilization when not stabilized 

by soil crusts or plant cover. Because of 

warming and drying trends from a changing 

climate or long-term drought, the interconnections between plant cover, precipitation, temperature, and sediment movement 

change over time. Consequently, the features 

found in arid regions can enter a cycle of 

increasing sediment mobility and decreasing 

plant-cover stabilization. These factors can 

lead to a constantly moving landscape with 

little or no plant cover, conditions that could 

have long-term and potentially significant 

impacts on agriculture, transportation, and 

human health for the Southwest.

Terrestrial lidar surveys are an effective 

approach to precisely measure and record the 

mobilization and geomorphic change of sand 

dunes in the desert Southwest. Ground-based 

lidar instruments make it possible to create 

detailed volumetric models of sampled dunes 

and compare the magnitudes and forms of 

change over short periods of time. These 

morphological studies can be integrated into 

detailed models of plant cover and climatic 

variability, and help predict potential future 

vulnerabilities in the landscape to drought or 

long-term changes in climate patterns.

Recording Desert-Soil 

Microtopography

In desert shrublands, soil mounds surrounding perennial shrubs are important 

because they are nutrient rich and contain 

organic matter, serving as sources of plant 

fertility. Fire can change the chemical 

composition of the soils in these mounds, 

but the resulting changes in the microtopography and volume of soils has not been 

quantified previously due to technological limitations. In the Pakoon Basin of the 

Mojave Desert in Grand Canyon-Parashant 

National Monument, Arizona, terrestrial 

lidar is being used by USGS scientists to 

quantify the differences between burned 

and unburned areas by creating a series of 

high-resolution bare-earth surface models 

for sample plots. Lidar scans were collected 

from unburned and previously burned sites 

with similar vegetation and soil-landform 

characteristics 10 years after experimental 

fires were conducted. Mound measurements 

indicate that the presence of fire affects the 

volume and surface roughness of mounds in 

the Pakoon Basin. Observations also show 

that the reduction in plant canopy cover in 

previously burned areas has contributed to 

a larger reduction in mound volume as a result of water and (or) wind erosion. Through 

this research, ground-based lidar is helping 

determine how fires are shaping desert shrubland landscapes in the Southwest.

The work of Western Geographic Science 

Center (WGSC) scientists using terrestrial 

lidar for land-surface analysis in the desert 

Southwest is only part of the WGSCs efforts to better understand the causes and 

consequences of land-cover change. WGSC, 

supported by the USGS Geographic Analysis 

and Monitoring Program, is also working 

with communities to help provide them the 

crucial geographic, economic, and natural 

hazards information they need to make decisions about interactions between people and 

their environment to reduce unnecessary risk.

Christopher E. Soulard and Rian C. Bogle

Edited by James W. Hendley II

Graphics and layout by Judy Weathers

For more information contact:

Christopher E. Soulard

U.S. Geological Survey

345 Middlefield Road, MS 532

Menlo Park, CA 94025

Tel. (650) 329-4317

csoulard@usgs.gov

http://geography.wr.usgs.gov/

This Fact Sheet and any updates to it are available 

online at http://pubs.usgs.gov/fs/2011/3017/

Repeat data collections with terrestrial lidar allow 

surface dimensions and movements to be tracked 

over time. In some areas, wind erosion leaves 

relic “yardangs” where sand dunes used to exist. 

Yardangs are made up of cohesive rock material 

that persists after softer material is eroded away by 

wind processes. USGS scientists are using repeat 

data collection to understand how continued wind 

abrasion weathers these rare geologic features. 

This image shows a raw lidar “point cloud” of a 

yardang from the Mojave Desert of Arizona (see 

arrow on photo; USGS photo by Rian Bogle).

Using terrestrial lidar, Western 

Geographic Science Center 

scientists scanned unburned and 

previously burned study plots in the 

Grand Canyon-Parashant National 

Monument, Arizona. Plots were 

scanned from different positions to 

get a 360-degree view of the surface 

and vegetation, resulting in more 

than 4 million point measurements 

per plot. Vegetation was separated 

from the bare-earth surface 

points using advanced software 

to create unique mound and plant 

measurements. Mound volumes and 

plant dimensions were found to be 

reduced in previously burned plots.

(USGS photo by Dave Bedford.)