U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2008–3024

December 2008

TerraLook: GIS-Ready Time-Series of Satellite Imagery for 

Monitoring Change

TerraLook is a joint project of the U.S. Geological Survey 

(USGS) and the National Aeronautics and Space Administration (NASA) Jet Propulsion Laboratory (JPL) with a goal of 

providing satellite images that anyone can use to see changes in 

the Earth’s surface over time. Each TerraLook product is a userspecified collection of satellite images selected from imagery 

archived at the USGS Earth Resources Observation and Science 

(EROS) Center. Images are bundled with standards-compliant 

metadata, a world file, and an outline of each image’s ground 

footprint, enabling their use in geographic information systems 

(GIS), image processing software, and Web mapping applications. TerraLook images are available through the USGS Global 

Visualization Viewer (http://glovis.usgs.gov).

Images in a TerraLook collection are rendered in simulated 

natural color and distributed in JPEG format. The JPEG file 

format and simulated natural color scheme were selected 

to make TerraLook images accessible to a wide audience. 

TerraLook JPEG files are small, which makes them quick to 

download and display using Web browsers and other commonly 

available software packages. Simulated natural colors are generally easy to interpret and understand. The simulated natural 

colors in TerraLook images are consistently processed so that 

images from four time periods—circa 1975, 1990, 2000, and the 

present—can be compared through time.

TerraLook images are drawn from two data sets archived 

at the USGS EROS. One is the Tri-Decadal Landsat Orthorectified data, a set of preselected, nearly cloud-free images for the 

1975, 1990, and 2000 time periods. Data were recorded by three 

different Landsat sensors: the Multispectral Scanner (MSS) on 

Landsats 1, 2, and 3; the Thematic Mapper (TM) on Landsats 4 

and 5; and the Enhanced Thematic Mapper Plus (ETM+) on 

Landsat 7. TerraLook’s second data source is the collection of 

over 1.5 million Advanced Spaceborne Thermal Emission and 

Reflection Radiometer (ASTER) images stored and distributed 

by the USGS EROS.

TerraLook viewer software has been developed to allow 

users to view, compare, and annotate TerraLook images. The 

bilingual (Spanish and English), open source TerraLook viewer 

is available from Source Forge (http://terralook.sourceforge.

net). The viewer allows images to be displayed by selecting 

an image footprint. The TerraLook viewer has special tools 

that make it easy to study the Earth through time and construct 

virtual mosaics. Layers can be created interactively to store 

annotation and map data, such as park or urban boundaries, or 

new information, such as the location of sample sites.

TerraLook builds on the success of NASA JPL’s Protected 

Area Archive project (http://asterweb.jpl.nasa.gov/paa.asp) 

with additional support from The Nature Conservancy, the 

World Bank Development Grant Facility Program’s InterAmerican Biodiversity Information Network Connectivity 

Development near Baltimore, Maryland, and Washington, 

D.C., intensified between 1972 and 2005. The Dulles 

International Airport west of Washington, D.C., opened in 

1962. In 1972, it was still surrounded by farmland and forest.

Tri-Decadal MSS

October 11, 1972

Tri-Decadal TM

May 16, 1987

Tri-Decadal ETM+

October 5, 2001

ASTER

March 22, 2005
Project, the U.S. State Department, the Gordon and Betty 

Moore Foundation Amazon Protected Area Network project, 

and the International Union for the Conservation of Nature and 

Natural Resources (IUCN; the World Conservation Union). 

Feedback from the conservation community guided the development of the TerraLook product and viewer, which will continue 

to evolve as the project reaches out to an even wider user 

community.

To Search and Order TerraLook Data:

USGS Global Visualization Viewer (GloVis): 

http://glovis.usgs.gov/

For More Information on TerraLook and the USGS EROS:

TerraLook Web site: http://terralook.cr.usgs.gov/

USGS EROS Web site: http://eros.usgs.gov/

Economic development 

near the confluence 

of the Iguazú and 

Paraná Rivers in 

Paraguay and Brazil involves 

a mixture of hydropower, conversion of the 

Paranaense forest into farmland, and tourism associated with 

the national parks near Iguazú Falls.

Tri-Decadal MSS

February 23, 1973

Tri-Decadal TM

April 19, 1989

Tri-Decadal ETM+

July 6, 2000

ASTER

September 17, 2003

In this December 

2006 ASTER image, 

the city of Banjul, 

Gambia, is at the 

tip of the peninsula 

that extends into the 

Gambia River. Banjul is 

bounded on the west by a forested wetland. Urban 

growth gradually encircled the wetlands between 1972 and 

2006. Protected areas can be seen as sharply delineated green 

areas in the upper-right part of the three Landsat images.

U.S. Geological Survey 

Earth Resources Observation 

and Science (EROS) Center

47914 252nd Street

Sioux Falls, SD 57198

Phone: (800) 252-4547

Phone: (605) 594-6151

TDD: (605) 594-6933

Fax: (605) 594-6589

E-mail: custserv@usgs.gov

Any use of trade, product, or firm names is for descriptive purposes only and 

does not imply endorsement by the U.S. Government.

Tri-Decadal MSS

November 5, 1979

Tri-Decadal TM

February 9, 1986

Tri-Decadal ETM+

November 6, 2000

ASTER

December 22, 2006