Landsat 7 is the seventh

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope ...

of the

Landsat program The Landsat program is the longest-running enterprise for acquisition of satellite imagery of Earth. It is a joint NASA / United States Geological Survey, USGS program. On 23 July 1972, the Landsat 1, Earth Resources Technology Satellite was l ...

. Launched on 15 April 1999, Landsat 7's primary goal is to refresh the global archive of satellite photos, providing up-to-date and cloud-free images. The

is managed and operated by the

United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...

, and data from Landsat 7 is collected and distributed by the USGS. The

NASA WorldWind NASA WorldWind is an open-source (released under the NOSA license and the Apache 2.0 license) virtual globe. According to the website (https://worldwind.arc.nasa.gov/), "WorldWind is an open source virtual globe API. WorldWind allow ...

project allows 3D images from Landsat 7 and other sources to be freely navigated and viewed from any angle. The satellite's companion,

Earth Observing-1 Earth Observing-1 (EO-1) is a decommissioned NASA Earth observation satellite created to develop and validate a number of instrument and spacecraft bus breakthrough technologies. It was intended to enable the development of future Earth imaging o ...

, trailed by one minute and followed the same orbital characteristics, but in 2011 its fuel was depleted and EO-1's orbit began to degrade. Landsat 7 was built by

Lockheed Martin Space Systems Lockheed Martin Space is one of the four major business divisions of Lockheed Martin. It has its headquarters in Littleton, Colorado, with additional sites in Valley Forge, Pennsylvania; Sunnyvale, California; Santa Cruz, California; Huntsville ...

. In 2016, NASA announced plans to attempt the first ever refueling of a live satellite by refueling Landsat 7 in 2020 with the OSAM-1 mission; as of 2021, the launch date has slipped to 2025. NASA plans to decommission the satellite following the 2021 launch and activation of Landsat 9.

Satellite specifications

Landsat 7 was designed to last for five years, and has the capacity to collect and transmit up to 532 images per day. It is in a

polar Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates * Polar climate, the c ...

sun-synchronous orbit A Sun-synchronous orbit (SSO), also called a heliosynchronous orbit, is a nearly polar orbit around a planet, in which the satellite passes over any given point of the planet's surface at the same local mean solar time. More technically, it is ...

, meaning it scans across the entire Earth's surface. With an altitude of 705 km, it takes 232 orbits, or 16 days, to do so. The satellite weighs 1973 kg, is 4.04 m long, and 2.74 m in diameter. Unlike its predecessors, Landsat 7 has a solid-state memory of 378 Gbits (roughly 100 images). The main instrument on board Landsat 7 is the Enhanced Thematic Mapper Plus (ETM+), a

whisk broom scanner A whisk broom or spotlight sensor, also known as an across-track scanner, is a technology for obtaining satellite images with optical cameras. It is used for passive remote sensing from space. In a whisk broom sensor, a mirror scans across the sate ...

image sensor An image sensor or imager is a sensor that detects and conveys information used to make an image. It does so by converting the variable attenuation of light waves (as they pass through or reflect off objects) into signals, small bursts of c ...

Instruments

* A panchromatic band with 15 metre

spatial resolution In physics and geosciences, the term spatial resolution refers to distance between independent measurements, or the physical dimension that represents a pixel of the image. While in some instruments, like cameras and telescopes, spatial resolut ...

(band 8) *

Visible Visibility, in meteorology, is a measure of the distance at which an object or light can be seen. Visibility may also refer to: * A measure of turbidity in water quality control * Interferometric visibility, which quantifies interference contrast ...

(reflected light) bands in the spectrum of blue, green, red,

near-infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

(NIR), and mid-infrared (MIR) with 30 metre spatial resolution (bands 1–5, 7) * A thermal

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

channel with 60 metre spatial resolution (band 6) * Full aperture, 5% absolute

radiometric Radiometry is a set of techniques for measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power in space, as opposed to photometric techniques, which ch ...

calibration

Scan Line Corrector failure

On 31 May 2003, the Scan Line Corrector (SLC) in the ETM+ instrument failed. The SLC consists of a pair of small mirrors that rotate about an axis in tandem with the motion of the main ETM+ scan mirror. The purpose of the SLC is to compensate for the forward motion (along-track) of the spacecraft so that the resulting scans are aligned parallel to each other. Without the effects of the SLC, the instrument images the Earth in a "zig-zag" fashion, resulting in some areas that are imaged twice and others that are not imaged at all. The net effect is that approximately 22% of the data in a Landsat 7 scene is missing when acquired without a functional SLC. A month after the SLC failure, the

USGS The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, a ...

compiled an assessment of the degraded data produced with the failed SLC. The assessment included input from scientists from USGS,

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

, and the Landsat 7 science team, and concluded that the results were still usable for many scientific applications and that there were several potential approaches to compensate for the missing data.

Satellite imagery

In August 1998,

contracted

EarthSat Earth Satellite Corporation (EarthSat), an American company, was a pioneer in the commercial use of Earth observation satellites. Founded in 1969, EarthSat was first headquartered in Washington, D.C., and later moved its offices to Bethesda, Mar ...

to produce Landsat GeoCover (''Geocover 2000'' in

) — a positionally accurate orthorectified Landsat

Thematic Mapper A Thematic Mapper (TM) is one of the Earth observing sensors introduced in the Landsat program. The first was placed aboard Landsat 4 (decommissioned in 2001), and another was operational aboard Landsat 5 up to 2012. /sup> TM sensors feature seven ...

and

Multispectral Scanner The Multispectral Scanner (MSS) is one of the Earth's observing sensors introduced in the Landsat program. A Multispectral Scanner was placed aboard each of the first five Landsat satellites. : "The Multispectral Scanner System", NASA Official: Dar ...

imagery covering the majority of the Earth's land mass. The contract was part of the NASA Scientific Data Purchase which was administrated through NASA's

John C. Stennis Space Center The John C. Stennis Space Center (SSC) is a NASA rocket testing facility in Hancock County, Mississippi, United States, on the banks of the Pearl River at the Mississippi–Louisiana border. , it is NASA's largest rocket engine test facility. ...

GeoCover Earth Satellite Corporation (EarthSat), an American company, was a pioneer in the commercial use of Earth observation satellites. Founded in 1969, EarthSat was first headquartered in Washington, D.C., and later moved its offices to Bethesda, Mar ...

was later enhanced to EarthSat NaturalVue, a simulated natural color Landsat 7 derived circa year 2000, orthorectified, mosaicked and color balanced digital image dataset. Other commercial simulated true color 15-metre global imagery products built from the NASA Landsat 7 imagery include TerraColor from Earthstar Geographics, TruEarth (found in

Google Earth Google Earth is a computer program that renders a 3D computer graphics, 3D representation of Earth based primarily on satellite imagery. The program maps the Earth by superimposition, superimposing satellite images, aerial photography, and geog ...

and

Google Maps Google Maps is a web mapping platform and consumer application offered by Google. It offers satellite imagery, aerial photography, street maps, 360° interactive panoramic views of streets ( Street View), real-time traffic conditions, and rou ...

) from TerraMetrics, BrightEarth from ComputaMaps, simulated natural color from Atlogis and a product of i-cubed used in

. Large parts of the Earth surface displayed on

web mapping Web mapping or an online mapping is the process of using maps, usually created through geographic information systems (GIS), on the Internet, more specifically in the World Wide Web (WWW). A web map or an online map is both served and consumed, ...

services like

, MSN Maps or

Yahoo! Maps Yahoo! Maps was a free online mapping portal provided by Yahoo! Functionality included local weather powered by The Weather Channel, printing maps, and local reviews powered by Yelp. It shut down on June 30, 2015. For a time in 2019, Yahoo! Maps ...

are based on enhanced and color balanced Landsat 7 imagery.

Decommissioning

Landsat 7 required regular orbital maneuvers to ensure that the

local mean time Local mean time (LMT) is a form of solar time that corrects the variations of Solar time#Apparent solar time, local apparent time, forming a uniform time scale at a specific longitude. This measurement of time was used for everyday use during the ...

(LMT) data acquisitions were maintained. The final such maneuver took place on February 7, 2017. From that point forward, the satellite's orbit began to slowly degrade (lower) such that by 2021 it had faded from the desired 10:00 AM LMT to about 9:15 AM. With the September 27, 2021 launch of Landsat 9, Landsat 7 is to be decommissioned. Its orbit has degraded such that Landsat 9 can move into the 705-km ) “standard” orbit altitude, and take Landsat 7's place in an orbit that allows data to be collected eight days out of phase with Landsat 8 (with two satellites in orbit, a Landsat scene is collected over every location on Earth every eight days). Landsat 7's 9:15 AM LMT acquisition will preclude acquiring high-quality and heritage-continuing data. On April 6, 2022, the science mission ended and the image sensor was placed into standby mode as the satellite's orbit was lowered. NASA is exploring the possibility of using NASA's Restore-L Robotic Servicing Mission 27 to refuel Landsat 7, primarily to ensure successful decommissioning, but also to provide the possibility of turning the satellite into a transfer radiometer. This would allow it to act as a calibration instrument for Landsats 8 and 9, and perhaps even extend its scientific utility.

References

External links

NASA's Landsat 7 Website

The USGS' Landsat Website
*
NASA's World Wind Project
*
List of Landsat layers available in World Wind

NASA Applied Sciences Directorate
website for free viewing/download of Landsat GeoCover band 742 mosaics
University of Maryland Global Land Cover Facility
for free viewing/download of individual Landsat images, GeoCover mosaics, and other earth imagery data
Harris GLOBE15
- Harris Corporation Geospatial website (includes 15m global data set details)
EarthSat's NaturalVue 2000: Global natural color satellite imagery coverage (resolution 15 m), based on Landsat 7 data acquired between 1999 and 2001

TerraColor.Net
- TerraColor 15m imagery website
TruEarth
15m imagery website
ICEDS Webserver
a free WMS compliant webserver, serving a variety of Geographic data including Landsat images

an

Online-Viewer for Landsat 5 and Landsat 7 Natural Color Mosaic
CEOS MIM Database Landsat 7 Entry
{{Orbital launches in 1999 Spacecraft launched in 1999 Spacecraft launched by Delta II rockets Landsat program Earth observation satellites of the United States NASA satellites orbiting Earth