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Landsat 7

Launch date	1999-04-15 18:32:00 UTC
Launch vehicle	Delta II 7920
Launch site	Space Launch Complex 2W Vandenberg Air Force Base
Mission duration	elapsed: 13 years, 2 months and 13 days
COSPAR ID	1999-020A
Orbital elements
Reference system	WRS-2
Regime	Sun-synchronous, near-polar
Inclination	98.2°
Altitude	705 km (438 mi)
Repeat interval	16 days
Swath width	185 km (115 mi)
Equatorial crossing time	10:00 AM +/- 15 minutes

Landsat 7, launched on April 15, 1999, is the latest satellite of the Landsat program. Landsat 7's primary goal is to refresh the global archive of satellite photos, providing up-to-date and cloud-free images. The Landsat Program is managed and operated by the USGS, and data from Landsat 7 is collected and distributed by the USGS. The NASA World Wind 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, trails by one minute and follows the same orbital characteristics.

Satellite specifications[link]

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, sun-synchronous orbit, meaning it scans across the entire earth's surface. With an altitude of 705 kilometres +/- 5 kilometres, 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 gigabits (roughly 100 images). The main instrument on board Landsat 7 is the Enhanced Thematic Mapper Plus (ETM+).

Main features[link]

• A panchromatic band with 15 m (49 ft) spatial resolution (band 8)
• Visible (reflected light) bands in the spectrum of blue, green, red, near-infrared (NIR), and mid-infrared (MIR) with 30 m (98 ft) spatial resolution (bands 1-5, 7)
• A thermal infrared channel with 60 m spatial resolution (band 6)
• Full aperture, 5% absolute radiometric calibration

Scan Line Corrector failure[link]

On May 31, 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.

Following the SLC failure, an Anomaly Response Team (ART) was assembled, consisting of representatives from the USGS, NASA, and Hughes Santa Barbara Remote Sensing (the manufacturer of the ETM+ instrument). The team assembled a list of possible failure scenarios, most of which pointed at a mechanical problem with the SLC itself. Since there is no backup SLC, a mechanical failure would indicate that the problem was permanent. However, the team was unable to rule out the possibility of an electrical failure, though such a possibility was deemed remote. Nevertheless, on September 3, 2003, USGS director Charles G. Groat authorized the Landsat project to reconfigure the ETM+ instrument and various other subsystems on board Landsat 7 to use the spacecraft's redundant ("Side-B") electrical harness.

With this authorization, the USGS flight operations team at the NASA Goddard Space Flight Center uploaded a series of commands to the spacecraft, instructing it to operate using the redundant electrical harness. This operation was successful, and on September 5, 2003, the ETM+ instrument was turned on and acquired data that was sent to the Landsat ground system at EROS outside of Sioux Falls, South Dakota. It was immediately apparent that the migration to the Side-B electrical harness had not fixed the problem with the SLC. Following this, the instrument was reconfigured to use its primary electrical harness. The subsequent conclusion of the ART was that the SLC problem was mechanical and permanent in nature.

Landsat 7 continues to acquire data in this mode. Data products are available with the missing data optionally filled in using other Landsat 7 data selected by the user. To continue the Landsat legacy, studies are underway to fly an equivalent scientific sensor on a new satellite.

Satellite imagery[link]

False color IR image of Washington DC, taken by Landsat 7.

In August 1998, NASA contracted EarthSat to produce Landsat GeoCover (Geocover 2000 in NASA World Wind) — a positionally accurate orthorectified Landsat Thematic Mapper and Multispectral Scanner 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. GeoCover was later enhanced to EarthSat NaturalVue, a simulated natural color Landsat 7 derived c. year 2000, orthorectified, mosaicked and color balanced digital image dataset. Other commercial simulated true color 15-meter global imagery products built from the NASA Landsat 7 imagery include TerraColor from Earthstar Geographics, TruEarth (found in Google Earth and Google Maps) from TerraMetrics, BrightEarth from ComputaMaps, simulated natural color from Atlogis and a product of i-cubed used in World Wind.

Largest parts of the earth surface displayed on web mapping services like Google Maps/Google Earth, MSN Maps or Yahoo Maps are based on enhanced and color balanced Landsat 7 imagery.

See also[link]

• Google Earth
• NASA World Wind
• Virtual globe

External links[link]

• NASA's Landsat 7 Website
• Landsat 7 Science Data Users Handbook
• The USGS' Landsat Website
• "Landsat 7 Media Kit". Boeing. http://www.boeing.com/defense-space/space/delta/delta2/Landsat/index.html. 
• 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
• Atlogis Maps and Atlogis Meta-Maps: Online-Viewer for Landsat 5 and Landsat 7 Natural Color Mosaic
• CEOS MIM Database Landsat 7 Entry

v t e Landsat program Landsat 1 · 2 · 3 · 4 · 5 · 6 · 7 Landsat Data Continuity Mission (LDCM)

Landsat 7, launched in 1999, is the most recent addition to the Landsat program.

The Landsat program is the longest running enterprise for acquisition of satellite imagery of Earth. On July 26, 1972 the Earth Resources Technology Satellite was launched. This was eventually renamed to Landsat.^[1] The most recent, Landsat 7, was launched on April 15, 1999. The instruments on the Landsat satellites have acquired millions of images. The images, archived in the United States and at Landsat receiving stations around the world, are a unique resource for global change research and applications in agriculture, cartography, geology, forestry, regional planning, surveillance, education and national security. Landsat 7 data has eight spectral bands with spatial resolutions ranging from 15 to 60 meters; the temporal resolution is 16 days.^[2]

History[link]

Hughes Santa Barbara Research Center initiated design and fabrication of the first three MSS Multispectral Scanners in the same year man landed on the moon, 1969. The first prototype MSS was completed within nine months by fall of 1970 when it was tested by scanning Half Dome at Yosemite National Park.

The program was called the Earth Resources Technology Satellites Program when it was initiated in 1966, but the name was changed to Landsat in 1975. In 1979, Presidential Directive 54 under President of the United States Jimmy Carter transferred Landsat operations from NASA to NOAA, recommended development of long term operational system with four additional satellites beyond Landsat 3, and recommended transition to private sector operation of Landsat. This occurred in 1985 when the Earth Observation Satellite Company (EOSAT), a partnership of Hughes Aircraft and RCA, was selected by NOAA to operate the Landsat system under a ten year contract. EOSAT operated Landsats 4 and 5, had exclusive rights to market Landsat data, and was to build Landsats 6 and 7.

A simulated-color satellite image of Kolkata taken on NASA's Landsat 7 satellite.

In 1989, this transition had not been fully completed when NOAA's funding for the Landsat program was due to run out (NOAA had not requested any funding, and Congress had appropriated only six months of funding for the fiscal year)^[3] and NOAA directed that Landsats 4 and 5 be shut down.^[4] The head of the newly formed National Space Council, Vice President Dan Quayle, noted the situation and arranged emergency funding that allowed the program to continue with the data archives intact. ^[3][4][5][6]

Again in 1990 and 1991, Congress provided only half of the year's funding to NOAA, requesting that agencies that used Landsat data provide the funding for the other six months of the upcoming year.^[3] In 1992, various efforts were made to procure funding for follow on Landsats and continued operations, but by the end of the year EOSAT ceased processing Landsat data. Landsat 6 was finally launched on October 5, 1993, but was lost in a launch failure. Processing of Landsat 4 and 5 data was resumed by EOSAT in 1994. NASA finally launched Landsat 7 on April 15, 1999.

The value of the Landsat program was recognized by Congress in October 1992 when it passed the Land Remote Sensing Policy Act (Public Law 102-555) authorizing the procurement of Landsat 7 and assuring the continued availability of Landsat digital data and images, at the lowest possible cost, to traditional and new users of the data.

Satellite chronology[link]

• Landsat 1 (originally named Earth Resources Technology Satellite 1): launched July 23, 1972, terminated operations January 6, 1978
• Landsat 2: launched January 22, 1975, terminated January 22, 1981
• Landsat 3: launched March 5, 1978, terminated March 31, 1983
• Landsat 4: launched July 16, 1982, terminated 1993
• Landsat 5: launched March 1, 1984, still functioning.^[7][8] but severe problems since Nov. 2011^[9]
• Landsat 6: launched October 5, 1993, failed to reach orbit
• Landsat 7: launched April 15, 1999, still functioning, but with faulty scan line corrector (May 2003) ^[10]

Technical details[link]

False-color composite (processed to simulate true color) image of the island of Hawaii was constructed from data gathered between 1999 and 2001 by the Enhanced Thematic Mapper plus (ETM+) instrument, flying aboard the Landsat 7 satellite. The Landsat data were processed by the National Oceanographic and Atmospheric Administration (NOAA) to develop a landcover map. The black areas on the island (in this scene) that resemble a pair of sun-baked palm fronds are hardened lava flows formed by the active Mauna Loa Volcano. Just to the north of Mauna Loa is the dormant grayish Mauna Kea Volcano, which hasn’t erupted in an estimated 3,500 years. A thin greyish plume of smoke is visible near the island’s southeastern shore, rising from Kilauea—the most active volcano on Earth. Heavy rainfall and fertile volcanic soil have given rise to Hawaii’s lush tropical forests, which appear as solid dark green areas in the image. The light green, patchy areas near the coasts are likely sugar cane plantations, pineapple farms, and human settlements.

The Multispectral Scanner had a 9" fused silica dinner-plate mirror epoxy bonded to three invar tangent bars mounted to base of a Ni/Au brazed Invar frame in a serreuire truss that was arranged with four "Hobbs-Links" (conceived by Dr. Gregg Hobbs) crossing at mid truss. This construct ensured the secondary mirror would simply oscillate about the primary optic axis to maintain focus despite vibration inherent from the 14-inch (360 mm) Be scan mirror. This engineering solution allowed the US to develop LANDSAT at least five years ahead of French SPOT which first used CCD arrays to stare without need for a scanner.

The MSS FPA, or Focal Plane Array consisted of 24 square optical fibers extruded down to .0002"square fiber tips in a 4x6 array to be scanned across the Nimbus spacecraft path in a +/-6 degree scan as the satellite was in a 10:30 polar orbit, hence it had to be launched from Vandenberg AFB. The fiber optic bundle was embedded in a fiber optic plate to be terminated at a relay optic device that transmitted fiber end signal on into six photodiodes and 18 photomultiplier tubes that were arrayed across a 0.30-inch (7.6 mm) thick aluminum tool plate, with sensor weight balanced vs the 9-inch (230 mm) telescope on opposite side. This main plate was assembled on a frame, then attached to the silver-loaded magnesium housing with helicoil fasteners.

Key to MSS success was the scan monitor mounted on the underbelly of the Mg housing. It consisted of a diode source and sensor mounted at ends of four flat mirrors that were tilted so that it took 14 bounces for a beam to reflect length of the three mirrors from source to sender striking Be scan mirror seven times as it reflected seven times off the flat mirrors. It only sensed three positions, both ends of scan and the mid scan, but that was all that was required to determine where MSS was pointed and electronics scanning could be calibrated to display a map.

Future[link]

The Landsat Data Continuity Mission (LDCM),^[11] scheduled to be launched January 2013, will be the next satellite in the Landsat series. It is being launched on an Atlas V 401 from Vandenberg Air Force Base by the Launch Services Program. It will continue to obtain valuable data and imagery to be used in agriculture, education, business, science, and government. The new satellite is being assembled in Arizona by Orbital Sciences Corporation.^[12]

Overview of the Thermal Infrared Sensor (TIRS), one of the instruments on the Landsat Data Continuity Mission (LDCM).

A timelapse of the Thermal Infrared Sensor (TIRS) instrument for the Landsat Data Continuity Mission (LDCM) being cleaned, bagged, and packed to ship to Orbital Sciences Corp, where TIRS will be integrated with the spacecraft.

See also[link]

• Remote sensing

References[link]

External links[link]

Wikimedia Commons has media related to: Landsat or Landsat images

• Landsat homepage
• Landsat NASA homepage
• Landsat.org Home Page
• Works by Landsat at Project Gutenberg
  • Landsat picture of Washington, D. C.
• (Free) Landsat imagery from GLOVIS and Global Land Cover Facility
• Atlogis Maps and Atlogis Meta-Maps: Online-Viewer for Landsat 5 and Landsat 7 Natural Color Mosaic from Atlogis. Meta-Maps includes Google, MSN and Yahoo Maps.
• (Free) Landsat mosaic imagery from the WELD project.
• Landsat imagery for circa 1975, 1990 and 2000 visualised in Google Earth (required GE installed)

v t e Landsat program Landsat 1 · 2 · 3 · 4 · 5 · 6 · 7 Landsat Data Continuity Mission (LDCM)

v t e World Reconnaissance Satellites, excluding Russia and the United States Commercial Electro-optical Quickbird · WorldView-1 · WorldView-2 · Ikonos · GeoEye-1 · GeoEye-2 · SPOT · EO1-ALI · ASTER · LANDSAT · ALOS Synthetic Aperture Radar RADARSAT-1 · RADARSAT-2 · PALSAR International Electro-Optical Disaster Monitoring Constellation  Brazil IMINT SCD-1 · SCD-2 · CBERS-1 · CBERS-2 · SSR  China IMINT JSSW · FSW-0 · FSW-1 · FSW-2 · FSW-3 · JianBing · CBERS-2 (joint Brazil) · Yaogan SIGINT JSSW-3  · SJ-2 · DQ-1 COMM Feng Huo-1 · ShenTong-1  France IMINT Hélios 1B · Helios 2A SIGINT Cerise · Clementine  Germany IMINT SAR-Lupe COMM TerraSAR-X · TanDEM-X  India IMINT Cartosat-1  · Cartosat-2  · Cartosat-2A Other RISAT-2  · RISAT-1  Israel IMINT Ofeq -> Ofeq 5 · Ofeq 7  · Ofeq 9 COMM AMOS 1 · AMOS 2 · AMOS 3 · AMOS 4 Other Eros · TecSAR  Italy IMINT COSMO-SkyMed  Japan IMINT IGS 1A/B · IGS 2A/B · IGS 3A · IGS 4A/B · IGS 5A · IGS 6A · IGS 7A  Turkey IMINT Göktürk I · Göktürk II COMM Turksat 1A  · Turksat 1B · Turksat 1C · Turksat 2A · Turksat 3A  Taiwan IMINT - COMM Formosat-1 · Formosat-2