U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2005-3114

November 2005

Advanced Very High Resolution Radiometer

Normalized Difference Vegetation Index Composites

Printed on recycled paper

The Advanced Very High Resolution Radiometer 

(AVHRR) is a broad-band scanner with four to six bands, 

depending on the model. The AVHRR senses in the visible, 

near-, middle-, and thermal- infrared portions of the electromagnetic spectrum. This sensor is carried on a series of National 

Oceanic and Atmospheric Administration (NOAA) Polar

Orbiting Environmental Satellites (POES), beginning with the 

Television InfraRed Observation Satellite (TIROS-N) in 1978.

Since 1989, the United States Geological Survey (USGS) 

Center for Earth Resources Observation and Science (EROS) 

has been mapping the vegetation condition of the United States 

and Alaska using satellite information from the AVHRR sensor. 

The vegetation condition composites, more commonly called 

greenness maps, are produced every week using the latest

information on the growth and condition of the vegetation.

One of the most important aspects of USGS greenness

mapping is the historical archive of information dating back 

to 1989. This historical stretch of information has allowed the 

USGS to determine a “normal” vegetation condition.

As a result, it is possible to compare the current week’s

vegetation condition with normal vegetation conditions. An 

above normal condition could indicate wetter or warmer

than normal conditions, while a below normal condition

could indicate colder or dryer than normal conditions. The

interpretation of departure from normal will depend on the 

season and geography of a region.

Characteristics of AVHRR

 The greenness maps are representations of the Normalized Difference Vegetation Index (NDVI). The NDVI has been 

utilized for many years to measure and monitor plant growth 

(vigor), vegetation cover, and biomass production from

multispectral satellite data.

Figure 3. Greenness map for Alaska,

August 10 - 23, 2005.

Figure 1. The AVHRR sensor aboard the NOAA POES Satellite. Image 

courtesy of NOAA.

Figure 2. Greenness map for the conterminous United States,

August 10 - 23, 2005.
 NDVI is computed daily from spectral bands observed by 

NOAA’s AVHRR sensor. The two bands acquire data in the red 

(RED: 0.6-0.7μm) and near-infrared (NIR: 0.7–1.1μm) regions 

of the electromagnetic spectrum.

NDVI is computed as follows:

NDVI = (NIR - RED) / (NIR + RED)

Weekly and biweekly NDVI composites are produced 

from multiple AVHRR observations that have been composited 

together to create a nearly cloud-free image showing

maximum greenness. Each pixel in a greenness image shows 

the maximum condition of vegetation for a 1 x 1 km segment

of land for a weekly or biweekly period. The vegetation

condition can change quite rapidly during the growing season. 

Since rapid changes are often more important, biweekly images 

are updated every week using the current and previous week’s 

composite data.

Applications of AVHRR Data

USGS greenness maps can be used to evaluate the

vegetation condition of a region by showing the health and 

vigor of the vegetation. Generally, healthy vegetation

is considered an indicator of favorable climatic and environmental conditions, while poor vegetation condition is indicative 

of droughts and diminished productivity. The greenness maps 

are produced at a scale that is most useful for national,

statewide, and regional evaluation of vegetation condition.

The greenness maps are used by government agencies and 

private industry for a wide variety of applications including 

agricultural assessment, grazing land management, grassland 

and forest fire danger assessment, and drought monitoring.

Data Access

The AVHRR composites are available as 7- or 14-day

composites from 1989 to the present for the conterminous

Figure 4. AVHRR Fire potential index for August 12, 2001. On this day, there was 

a major outbreak of fires occurring in the western United States.

United States and Alaska. Composites can be ordered at a

minimal cost on media or via FTP.

The greenness maps include all acquired AVHRR bands, 

NDVI, and ancillary bands at 1 km resolution. The projection is 

Lambert Azimuthal Equal Area for the United States and Albers 

Equal-Area Conic for Alaska.

AVHRR NDVI composites are currently available for search 

and order on Earth Explorer at:

http://earthexplorer.usgs.gov.

Further Information:

For additional information on AVHRR NDVI composites,

contact USGS Center for Earth Resources Observation and

Science (EROS) Customer Services.

USGS/EROS

Attn: Research

47914 252nd Street

Sioux Falls, SD 57198-0001

Tel: 800-252-4547

Tel: 605-594-6151

TTY/TDD: 605-594-6933

Fax: 605-594-6589

E-mail: custserv@usgs.gov

Resources for AVHRR:

AVHRR U.S. Greenness Viewer:

http://gisdata.usgs.net/website/ivm/viewer.php

AVHRR Level 1B product page:

http://edc.usgs.gov/products/satellite/avhrr.html

NOAA Satellite Archive:

http://www.ncdc.noaa.gov

For information on other USGS products and services,

call 1-888-ASK-USGS, or visit http://ask.usgs.gov or

http://www.usgs.gov.