Landsat 7

Last updated

Landsat 7
Landsat7photo.jpg
Landsat 7 before launch
Mission type Satellite imagery
Operator NASA  / USGS
COSPAR ID 1999-020A OOjs UI icon edit-ltr-progressive.svg
SATCAT no. 25682
Mission duration5 years (planned)
25 years, 3 months, 7 days (in progress)
Spacecraft properties
Bus TIROS-N
Manufacturer Lockheed Martin Space Systems
Launch mass1973 kg
Dimensions4.04 metre long
2.74 metre diameter
Power1550 watts
Start of mission
Launch date15 April 1999, 18:32:00 UTC
Rocket Delta II 7920
Launch site Vandenberg, SLC-2W
Contractor Boeing
Entered service1999
Orbital parameters
Reference system Geocentric orbit [1]
Regime Sun-synchronous orbit
Altitude705 km
Inclination 98.21°
Period 98.83 minutes
Repeat interval16 days
Landsat-7 Mission Patch.png  

Landsat 7 is the seventh satellite of the Landsat program. 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 Landsat program is managed and operated by the United States Geological Survey, and data from Landsat 7 is collected and distributed by the USGS. The NASA WorldWind 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, 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. [2] Landsat 7 was built by Lockheed Martin Space Systems.

Contents

In 2016, NASA announced it planned to attempt the first ever refueling of a live satellite by refueling Landsat 7 in 2020 with the OSAM-1 mission; [3] [4] [5] [6] however after multiple delays, NASA announced the cancellation of OSAM-1 in March 2024. [7]

Satellite specifications

Landsat 7 Schematic Landsat7schematic.png
Landsat 7 Schematic

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 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 image sensor.

Instruments

Scan Line Corrector failure

The effect of the SLC on ETM+ scans. Landsat-7 Scan Line Corrector operation.jpg
The effect of the SLC on ETM+ scans.

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. [8]

A month after the SLC failure, the USGS compiled an assessment of the degraded data produced with the failed SLC. The assessment included input from scientists from USGS, NASA, 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. [9]

Satellite imagery

False color IR image of Washington, D.C., taken by Landsat 7. Lan7 washington dc.jpg
False color IR image of Washington, D.C., taken by Landsat 7.

In August 1998, NASA contracted EarthSat to produce Landsat GeoCover (Geocover 2000 in NASA WorldWind) — 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 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 and Google Maps) from TerraMetrics, BrightEarth from ComputaMaps, simulated natural color from Atlogis and a product of i-cubed used in NASA WorldWind.

Large 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.

Orbit lowering

Landsat 7 required regular orbital maneuvers to ensure that the local mean time (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. [10]

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 was suspended and the image sensor was placed into standby mode as the satellite's orbit was lowered. [10]

NASA is exploring the possibility of using NASA's OSAM-1 robotic servicing mission to refuel Landsat 7, [3] 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. [11]

On May 5, 2022, imaging was once again resumed, to assess the utility of imagery collected at the new lower orbit and earlier equatorial crossing time. [12]

See also

Related Research Articles

<span class="mw-page-title-main">Digital elevation model</span> 3D computer-generated imagery and measurements of terrain

A digital elevation model (DEM) or digital surface model (DSM) is a 3D computer graphics representation of elevation data to represent terrain or overlaying objects, commonly of a planet, moon, or asteroid. A "global DEM" refers to a discrete global grid. DEMs are used often in geographic information systems (GIS), and are the most common basis for digitally produced relief maps. A digital terrain model (DTM) represents specifically the ground surface while DEM and DSM may represent tree top canopy or building roofs.

<span class="mw-page-title-main">Landsat program</span> American network of Earth-observing satellites for international research purposes

The Landsat program is the longest-running enterprise for acquisition of satellite imagery of Earth. It is a joint NASA / USGS program. On 23 July 1972, the Earth Resources Technology Satellite was launched. This was eventually renamed to Landsat 1 in 1975. The most recent, Landsat 9, was launched on 27 September 2021.

The Earth Observing System (EOS) is a program of NASA comprising a series of artificial satellite missions and scientific instruments in Earth orbit designed for long-term global observations of the land surface, biosphere, atmosphere, and oceans. Since the early 1970s, NASA has been developing its Earth Observing System, launching a series of Landsat satellites in the decade. Some of the first included passive microwave imaging in 1972 through the Nimbus 5 satellite. Following the launch of various satellite missions, the conception of the program began in the late 1980s and expanded rapidly through the 1990s. Since the inception of the program, it has continued to develop, including; land, sea, radiation and atmosphere. Collected in a system known as EOSDIS, NASA uses this data in order to study the progression and changes in the biosphere of Earth. The main focus of this data collection surrounds climatic science. The program is the centrepiece of NASA's Earth Science Enterprise.

Orbital Sciences Corporation was an American company specializing in the design, manufacture, and launch of small- and medium- class space and launch vehicle systems for commercial, military and other government customers. In 2014, Orbital merged with Alliant Techsystems (ATK) to create a new company called Orbital ATK, which in turn was purchased by Northrop Grumman in 2018.

<span class="mw-page-title-main">NASA WorldWind</span> Open-source virtual globe

NASA WorldWind is an open-source virtual globe. According to the website, "WorldWind is an open source virtual globe API. WorldWind allows developers to quickly and easily create interactive visualizations of 3D globe, map and geographical information. Organizations around the world use WorldWind to monitor weather patterns, visualize cities and terrain, track vehicle movement, analyze geospatial data and educate humanity about the Earth." It was first developed by NASA in 2003 for use on personal computers and then further developed in concert with the open source community since 2004. As of 2017, a web-based version of WorldWind is available online. An Android version is also available.

<span class="mw-page-title-main">Satellite imagery</span> Images taken from an artificial satellite

Satellite images are images of Earth collected by imaging satellites operated by governments and businesses around the world. Satellite imaging companies sell images by licensing them to governments and businesses such as Apple Maps and Google Maps.

<span class="mw-page-title-main">Landsat 5</span> American Earth-observing satellite launched in 1984 as part of the Landsat program

Landsat 5 was a low Earth orbit satellite launched on March 1, 1984, to collect imagery of the surface of Earth. A continuation of the Landsat Program, Landsat 5 was jointly managed by the U.S. Geological Survey (USGS) and the National Aeronautics and Space Administration (NASA). Data from Landsat 5 was collected and distributed from the USGS's Center for Earth Resources Observation and Science (EROS).

<span class="mw-page-title-main">Landsat 4</span> American Earth-observing satellite launched in 1982 as part of the Landsat program

Landsat 4 is the fourth satellite of the Landsat program. It was launched on July 16, 1982, with the primary goal of providing a global archive of satellite imagery. Although the Landsat Program is managed by NASA, data from Landsat 4 was collected and distributed by the U.S. Geological Survey. Landsat 4 science operations ended on December 14, 1993, when the satellite lost its ability to transmit science data, far beyond its designed life expectancy of five years. The satellite housekeeping telemetry and tracking continued to be maintained by NASA until it was decommissioned on June 15, 2001.

<span class="mw-page-title-main">Landsat 3</span> American Earth-observing satellite launched in 1978 as part of the Landsat program

Landsat 3 is the third satellite of the Landsat program. It was launched on March 5, 1978, with the primary goal of providing a global archive of satellite imagery. Unlike later Landsat satellites, Landsat 3 was managed solely by NASA. Landsat 3 decommissioned on September 7, 1983, beyond its design life of one year. The data collected during Landsat 3's lifetime was used by 31 countries. Countries that cannot afford their own satellite are able to use the data for ecological preservation efforts and to determine the location of natural resources.

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, Maryland, and finally to Rockville, Maryland, in the late 1980s. In 2001, EarthSat was acquired by MacDonald, Dettwiler and Associates Ltd. (MDA) of Vancouver, British Columbia. In August 2005, EarthSat was incorporated as MDA Federal Inc., the U.S. operation of MDA Geospatial Services.

<span class="mw-page-title-main">TerraSAR-X</span> German Earth observation satellite

TerraSAR-X, is an imaging radar Earth observation satellite, a joint venture being carried out under a public-private-partnership between the German Aerospace Center (DLR) and EADS Astrium. The exclusive commercial exploitation rights are held by the geo-information service provider Astrium. TerraSAR-X was launched on 15 June 2007 and has been in operational service since January 2008. With its twin satellite TanDEM-X, launched 21 June 2010, TerraSAR-X acquires the data basis for the WorldDEM, the worldwide and homogeneous DEM available from 2014.

<span class="mw-page-title-main">Landsat 2</span> American Earth-observing satellite launched in 1975 as part of the Landsat program

Landsat 2 is the second satellite of the Landsat program. The spacecraft originally carried a designation of ERTS-B but was renamed "Landsat 2" prior to its launch on January 22, 1975. The objective of the satellite was to acquire global, seasonal data in medium resolution from a near-polar, Sun-synchronous orbit. The satellite, built by General Electric, acquired data with the Return Beam Vidicon (RBV) and the Multispectral Scanner (MSS). Despite having a design life of one year, Landsat 2 operated for over seven years, finally ceasing operations on February 25, 1982.

<span class="mw-page-title-main">Landsat 8</span> American Earth-observing satellite launched in 2013 as part of the Landsat program

Landsat 8 is an American Earth observation satellite launched on 11 February 2013. It is the eighth satellite in the Landsat program; the seventh to reach orbit successfully. Originally called the Landsat Data Continuity Mission (LDCM), it is a collaboration between NASA and the United States Geological Survey (USGS). NASA Goddard Space Flight Center in Greenbelt, Maryland, provided development, mission systems engineering, and acquisition of the launch vehicle while the USGS provided for development of the ground systems and will conduct on-going mission operations. It comprises the camera of the Operational Land Imager (OLI) and the Thermal Infrared Sensor (TIRS), which can be used to study Earth surface temperature and is used to study global warming.

<span class="mw-page-title-main">Earth Observing-1</span>

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 observatories that will have a significant increase in performance while also having reduced cost and mass. The spacecraft was part of the New Millennium Program. It was the first satellite to map active lava flows from space; the first to measure a facility's methane leak from space; and the first to track re-growth in a partially logged Amazon forest from space. EO-1 captured scenes such as the ash after the World Trade Center attacks, the flooding in New Orleans after Hurricane Katrina, volcanic eruptions and a large methane leak in southern California.

IRS-1A, Indian Remote Sensing satellite-1A, the first of the series of indigenous state-of-art remote sensing satellites, was successfully launched into a polar Sun-synchronous orbit on 17 March 1988 from the Soviet Cosmodrome at Baikonur. IRS-1A carries two sensors, LISS-1 and LISS-2, with resolutions of 72 m (236 ft) and 36 m (118 ft) respectively with a swath width of about 140 km (87 mi) during each pass over the country. Undertaken by the Indian Space Research Organisation (ISRO). It was a part-operational, part-experimental mission to develop Indian expertise in satellite imagery.

<span class="mw-page-title-main">Landsat 9</span> American Earth-observing satellite launched in 2021 as part of the Landsat program

Landsat 9 is an Earth observation satellite launched on 27 September 2021 from Space Launch Complex-3E at Vandenberg Space Force Base on an Atlas V 401 launch vehicle. NASA is in charge of building, launching, and testing the satellite, while the United States Geological Survey (USGS) operates the satellite, and manages and distributes the data archive. It is the ninth satellite in the Landsat program, but Landsat 6 failed to reach orbit. The Critical Design Review (CDR) was completed by NASA in April 2018, and Northrop Grumman Innovation Systems (NGIS) was given the go-ahead to manufacture the satellite.

<span class="mw-page-title-main">NOAA-21</span> NASA/NOAA satellite

NOAA-21, designated JPSS-2 prior to launch, is the second of the United States National Oceanic and Atmospheric Administration (NOAA)'s latest generation of U.S. polar-orbiting, non-geosynchronous, environmental satellites called the Joint Polar Satellite System. NOAA-21 was launched on 10 November 2022 and join NOAA-20 and Suomi NPP in the same orbit. Circling the Earth from pole-to-pole, it will cross the equator about 14 times daily, providing full global coverage twice a day. It was launched with LOFTID.

OSAM-1 was a cancelled NASA spacecraft designed to test on-orbit refilling of satellites. It was previously known as Restore-L.

References

  1. "LANDSAT 7 Satellite details 1999-020A NORAD 25682". N2YO. 25 January 2015. Retrieved 25 January 2015.
  2. EO-1 Phase F Report PD-icon.svg This article incorporates text from this source, which is in the public domain .
  3. 1 2 Kleiner, Kurt (24 February 2022). "Orbiting robots could help fix and fuel satellites in space". Knowable Magazine. doi: 10.1146/knowable-022422-1 . Retrieved 10 March 2022.
  4. Henshaw, Carl Glen; Glassner, Samantha; Naasz, Bo; Roberts, Brian (3 May 2022). "Grappling Spacecraft". Annual Review of Control, Robotics, and Autonomous Systems. 5: 137–159. doi:10.1146/annurev-control-042920-011106. ISSN   2573-5144. S2CID   242628083 . Retrieved 10 March 2022.
  5. "OSAM-1: Robotic Servicing Mission | NASA's Exploration & In-space Services". NASA NExIS. 3 July 2020. Archived from the original on 3 July 2020. Retrieved 3 July 2020.PD-icon.svg This article incorporates text from this source, which is in the public domain .
  6. "NASA's Restore-L Mission to Refuel Landsat 7, Demonstrate Crosscutting Technologies". 23 June 2016. Retrieved 21 December 2017.PD-icon.svg This article incorporates text from this source, which is in the public domain .
  7. Foust, Jeff (1 March 2024). "NASA cancels OSAM-1 satellite servicing technology mission". SpaceNews . Retrieved 2 March 2024.
  8. Storey, James; Scaramuzza, Pasquale; Schmidt, Gale; Barsi, Julia (2005). LANDSAT 7 SCAN LINE CORRECTOR-OFF GAP-FILLED PRODUCT DEVELOPMENT (PDF). Pecora 16 "Global Priorities in Land Remote Sensing".
  9. "Preliminary Assessment of the Value of Landsat 7 ETM+ Data" (PDF). USGS. Retrieved 7 May 2022.
  10. 1 2 "Landsat 7 | U.S. Geological Survey". www.usgs.gov. Retrieved 7 May 2022.
  11. "Landsat 7" . Retrieved 27 September 2021.
  12. "Landsat 7 Data Acquired at Lower Orbit Now Available" . Retrieved 14 April 2023.