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Section 1 - Introduction

1.1 Foreward

The Landsat Project has provided over 45 years of calibrated high quality moderate  spatial resolution data of the Earth's surface to a broad and varied user community. This user community includes agribusiness, global change researchers, academia, state and local governments, commercial users, national security agencies, the international community, decision-makers, and the public. Landsat images provide information that meets the broad and diverse needs of business, science, education, government, and national security.

The mission of the Landsat Project is to provide repetitive acquisition of moderate-resolution multispectral data of the Earth's surface on a global basis. Landsat represents the only source for global, calibrated, moderate spatial resolution measurements of the Earth's surface that are preserved in a national archive and freely available to the public. Data from the Landsat spacecraft constitute the longest record of the Earth's continental surfaces as seen from space. It is a record unmatched in quality, detail, coverage, and value.

Launched in 1999, Landsat 7 was the latest National Aeronautics and Space Administration (NASA) satellite in a series that has produced an uninterrupted multispectral record of the Earth's land surfaces since 1972. The most recent satellite in the series, Landsat 8, was launched in 2013 and orbits in an eight-day offset with Landsat 7. Landsat 7’s space-borne data acquisition combines with the U.S. Geological Survey's (USGS) archival and distribution systems, which includes the data processing techniques required to render Landsat 7 data into a scientifically usable format. With Landsat 7, special emphasis has been placed on periodically refreshing the global data archive, maintaining an accurate instrument calibration, providing data in accordance with national policy directives, and ensuring there is a data processing system that creates publically accessible products of superior quality.

The Landsat satellites carry a variety of components, including remote sensing systems, data relay systems, attitude-control and orbit-adjustment subsystems, a power supply, and receivers and transmitters for ground station communications.

The Landsat 7 Observatory offers these features:

  • Data Continuity: Landsat 7’s launch in 1999 continued the unbroken series of land remote sensing satellites which began in 1972 with the launch of the Earth Resources Technology Satellite (ERTS-1, later renamed Landsat 1). Landsat 7 is the first on-orbit satellite in the series not to carry the Multispectral Scanner (MSS) instrument. Landsat 7 with its Enhanced Thematic Mapper Plus (ETM+) provides seamless temporal continuity between Landsat 5 (launched in 1984) and the most recent mission, Landsat 8 (launched in 2013).
  • Global Survey Mission: Landsat 7 data are acquired systematically to build and periodically refresh a global archive of sun-lit, substantially cloud-free images of Earth's landmasses.
  • Free Standard Data Products: Landsat 7 data products are available through the USGS Earth Resources Observation and Science (EROS) Center at no charge since 2008.
  • Absolute Radiometric and Geometric Calibration: Data from the Landsat 7’s ETM+ will be calibrated to better than five percent uncertainty, providing an on-orbit standard for other missions.
  • Responsive Delivery: On average, products are generated within 24 hours of receipt of the data at EROS and are then available for download online

The continuation of the Landsat Project is an integral component of the U.S. Global Change Research Program. Landsat 7 was the continuation of a joint initiative between the USGS and NASA. It was initially part of a global research program known as NASA's Earth Sciences Enterprise, an evolving long-term program studying changes in Earth's global environment. The goal of Earth Sciences Enterprise was to provide a better understanding of natural and man-made environmental changes. In the Landsat Project's long tradition, Landsat 7 is an important component of NASA’s Earth Observing System (EOS) and the USGS National Land Imaging (NLI) Program, and continues to provide critical information to those who characterize, monitor, manage, explore, and observe the land surfaces of the Earth over time.

1.2 Background

1.2.1 EOSAT Era and Basis in Law for Landsat

In the mid-1980s, U.S. Government agencies, including NASA and the National Oceanic and Atmospheric Administration (NOAA), were directed to attain their commercial space objectives without the use of direct federal funding by entering into appropriate cooperative agreements with private sector corporate entities to encourage and advance private sector basic research, development, and operations.

The implementation of this policy required the transfer of government-developed space technology to the private sector in such a manner as to protect its commercial value, which included retention of technical data rights by the private sector. Commercial sector space activities developed under this mandate were to be supervised or regulated by federal agencies only to the extent required by law, national security, international obligations, and public safety.

With the passage of Public Law 98-365, the "Land Remote Sensing Commercialization Act of 1984", NOAA was directed to delegate management of the Landsat 4 and Landsat 5 satellites and their data distribution to the private sector. In addition, NOAA was to pursue procurement of future remote sensing products and services, including Landsat from the private sector.

In 1985, NOAA solicited bids to manage the existing Landsat satellites in orbit and to build and operate future systems. The Earth Observation Satellite Company (EOSAT), a joint venture between the Radio Corporation of America and Hughes Aircraft, later called Space Imaging Corporation, won the competitive bidding process in August 1984 and took over operation of the Landsat system on September 27, 1985.

From 1985 to 1994, EOSAT retained exclusive sales rights to all Landsat 4 and Landsat 5 Thematic Mapper (TM) data until July 1994, at which time it was planned that Landsat data over ten years old would become available from the National Archive at EROS (now called the National Satellite Land Remote Sensing Data Archive (NSLRSDA)). This agreement between Landsat Project management and EOSAT Corporation defined cost and reproduction rights for Landsat 4 and Landsat 5 TM data. EOSAT also won the competition to produce the next satellite in the series, Landsat 6.

By 1992, it had become clear that the high cost of commercially-provided Landsat data had greatly restricted its use in research and other public sector applications. In response, the U.S. Congress passed H.R. 6133, the "Land Remote Sensing Policy Act of 1992", into law in September of that year. This law established a new national land remote sensing policy that:

  • Abandoned full commercialization of the Landsat Project
  • Returned management of the Project to the Government
  • Established a data policy of distributing Landsat data at the Cost of Fulfilling a User Request (COFUR*) (*superceded in 2008)
  • Directed that preliminary work begin on a new Landsat 7
  • Fostered development of advanced land remote sensing systems and opportunities for commercialization

The loss of Landsat 6 during its launch in October 1993, and the ages of Landsat 4 and Landsat 5, suddenly made the new Landsat 7 mission imperative. In May 1994, a Presidential Decision Directive (National Science and Technology Council, NSTC-3) defined the original Landsat 7 Data Policy, as well as program management strategies and implementation guidelines. Subsequent NASA and NOAA memoranda in the summer of 1994 brought the current Landsat 7 mission into existence.

Additional legislation relevant to Landsat history:

  • HR1275  Short title: "Civilian Space Authorization Act, Fiscal Years 1998 and 1999"
  • HR1278  Short title: "National Oceanic and Atmospheric Administration Authorization Act of 1997”
  • HR1702  Short title: "Commercial Space Act of 1998"

1.2.2 Previous Missions

Landsat satellites have been providing multispectral images of the Earth continuously since the July 23, 1972 launch of Landsat 1. A unique 45+ year data record of Earth's land surface now exists. This unique retrospective portrait of Earth has been used across disciplines to achieve improved understanding of the planet's land surfaces and the impact of humans on the environment. Landsat data have been utilized in a variety of government, public, private, and national security applications. Examples include land and water management, global change research, oil and mineral exploration, agricultural yield forecasting, deforestation monitoring, land surface change detection, and cartographic mapping.

With the successful launch of Landsat 8 in 2013, Landsat 7 is now the oldest operational satellite in this series. The first satellite was launched in 1972 with two Earth-viewing imagers - a Return Beam Vidicon (RBV) and an 80-meter MSS. Landsat 2 and Landsat 3, launched in 1975 and 1978 respectively, were similarly configured. In 1982, Landsat 4 was launched with the MSS and a new instrument called the TM. Instrument upgrades included improved ground resolution (30 meters) and three new spectral channels or bands. In addition to using an updated instrument, Landsat 4 made use of the Multi-mission Modular Spacecraft (MMS), which replaced the Nimbus-based spacecraft design employed for Landsat 1-3. Landsat 5, a duplicate of Landsat 4, was launched in 1984 and after providing data for almost 28 years, well beyond its five-year design life, was decommissioned in 2013. Landsat 6, equipped with a 15-meter panchromatic band and an Enhanced Thematic Mapper (ETM) sensor, was lost immediately after launch in 1993. Landsat 7's ETM+ instrument is an improved version of Landsat 6's ETM sensor.

Table 1-1 lists key mission characteristics of the Landsat Project while Table 1-2 compares the sensors carried aboard these satellites. Details on the Landsat Timeline are also available.

Satellite Launch
(End of Service)
Sensor Resolution
(m)/type
Communication Alt
(km)
Rep.
(days)
Data
(Mbps)
Landsat 1 07/23/1972
(01/06/1978)
RBV 80/ms Direct downlink
+ recorders
917 181 15
MSS 80/ms
Landsat 2 01/22/1975
(07/27/1983)
RBV 80/ms Direct downlink
+ recorders
917 181 15
MSS 80/ms
Landsat 3 03/05/1978
(09/07/1983)
RBV 40/pan Direct downlink
+ recorders
917 181 15
MSS 80/ms
2401/ther
Landsat 4 07/16/1982
(06/15/20011)
MSS 80/ms Direct downlink
+TDRSS
705 162 85
TM 30/ms
1201/ther
Landsat 5 03/01/1984
(06/05/20132)
MSS 80/ms Direct downlink
+TDRSS
705 162 85
TM 30/ms
1201/ther
Landsat 6 10/05/1993
(10/05/19933)
ETM 15/pan Direct downlink
+ recorders
705 162 85
30/ms
1201/ther
Landsat 7 04/15/1999 ETM+ 15/pan Direct downlink
+SSR
705 162 150
30/ms
601/ther
Landsat 8 02/11/2013 OLI 15/pan Direct downlink
+SSR
705 162 X-band: 384
S-band: 260
30/ms
TIRS 1001/ther

Table 1-1. Key Landsat Project Mission Characteristics

  • End of service date (satellite decommissioned; 1science data downlink capability ended in 1993;  2TM data ended in 2011, MSS data ended in 2013; 3 lost during launch)
  • Sens. = Sensor(s) (RBV = Return Beam Vidicon; MSS = Multispectral Scanner; TM = Thematic Mapper; ETM = Enhanced Thematic Mapper; ETM+ = Enhanced Thematic Mapper Plus; OLI = Operational Land Imager; TIRS = Thermal Infrared Sensor)
  • Res. = Nominal visible wavelength spatial resolution (meters); 1thermal bands of Landsat 3-8 collected at various spatial resolutions and resampled to match the multispectral resolutions.
  • Type = Sensor type (pan = panchromatic, ms = multispectral, ther = thermal)
  • Communication = Data transfer and handling options (TDRSS = Tracking and Data Relay Satellite System; SSR = Sold State Recorder)
  • Alt. = Nominal altitude on orbit
  • Rep. = Landsat revisit interval (WRS = Worldwide Reference System, 1WRS-1, orbit inclined at 99.2°; 2WRS-2, orbit inclined at 98.2°)
  • Data = Data transfer rate (Megabits per second)

 

Satellite Sensor(s) Band (Wavelength (µm)) Spatial Resolution (meters)
Landsat 1, Landsat 2      
  Return Beam Vidicon (RBV) 1 (0.48 – 0.57) 80
    2 (0.58 – 0.68) 80
    3 (0.70 – 0.83) 80
  Multispectral Scanner (MSS) 4 (0.5 - 0.6) 80
    5 (0.6 - 0.7) 80
    6 (0.7 - 0.8) 80
    7 (0.8 - 1.1) 80
Landsat 3      
  Return Beam Vidicon (RBV) 1 (0.505 - 0.75) 40
  Multispectral Scanner (MSS) 4 (0.5 - 0.6) 80
    5 (0.6 - 0.7) 80
    6 (0.7 - 0.8) 80
    7 (0.8 - 1.1) 80
    8 (10.4 - 12.6) 2401
Landsat 4, Landsat 5      
  Multispectral Scanner (MSS) 4 (0.5 - 0.6) 80
    5 (0.6 - 0.7) 80
    6 (0.7 - 0.8) 80
    7 (0.8 - 1.1) 80
  Thematic Mapper (TM) 1 (0.45 – 0.52) 30
    2 (0.52 – 0.60) 30
    3 (0.63 – 0.69) 30
    4 (0.76 – 0.90) 30
    5 (1.55 – 1.75) 30
    6 (10.4 – 12.5) 1202
    7 (2.08 – 2.35) 30
Landsat 7      
  Enhanced Thematic Mapper Plus (ETM+) 1 (0.450 – 0.515) 30
    2 (0.525 – 0.605) 30
    3 (0.630 – 0.690) 30
    4 (0.775 – 0.900) 30
    5 (1.550 – 1.750) 30
    6 (10.40 – 12.50) 602
    7 (2.080 – 2.350) 30
    8 (0.520 – 0.900) 15
Landsat 8      
  Operational Land Imager (OLI) 1 (0.435 – 0.451) 30
    2 (0.452 – 0.512) 30
    3 (0.533 – 0.590) 30
    4 (0.636 – 0.673) 30
    5 (0.851 – 0.879) 30
    6 (1.566 – 1.651) 30
    7 (2.107 – 2.294) 30
    8 (0.503 – 0.676) 15
    9 (1.363 – 1.384) 30
  Thermal Infrared Sensor (TIRS) 10 (10.60 – 11.19) 1002
    11 (11.50 – 12.51) 1002

Table 1-2. Landsat Sensor Characteristics

  • Band (Wavelength (µm)) = Detector wavelength in micrometers measured at Full Width at Half Maximum (FWHM)
  • Resolution = Approximate maximum spatial resolution per band (in meters); 1 Landsat 3 included a thermal band, but the channel failed shortly after launch. 2 Landsat 4-8 thermal bands collected at various resolutions, but resampled to match multispectral band resolutions.

1.2.3 Operations and Management

The Landsat 7 project management structure changed repeatedly from 1992 through 1998, from NASA/United States Air Force / USGS to NASA / NOAA / USGS to a bi-agency NASA / USGS partnership. As described in the Landsat 7 Management Plan, NASA was responsible for the development and launch of the Landsat 7 satellite and the development of the ground system. The Landsat 7 Project Office at NASA Goddard Space Flight Center (GSFC) managed these responsibilities, with Hughes Santa Barbara Remote Sensing (SBRS) building the sensor and Lockheed Martin Missiles and Space developing the spacecraft. The USGS is responsible for operation and maintenance of the satellite and the ground system for the life of the satellite. In this role, the USGS captures, processes, and distributes the data and is responsible for maintaining Landsat 7 data within their remote sensing image archive.

The NASA GSFC Landsat 7 Project was responsible for development of the Landsat 7 system. Specifically, this involved designing, developing, and testing the Landsat 7 spacecraft, the ETM+ instrument, and the end-to-end ground system. NASA was also responsible for the satellite launch and performing a 60-day in-orbit check out before handing operations to the USGS. The USGS, collaborating with NASA and the Landsat Science Team, is responsible, decades after launch, for verifying data processing integrity and assuring high image quality.

The USGS EROS Center manages the overall Landsat 7 mission operations. In this capacity EROS directs on-orbit flight operations, implements mission policies, directs acquisition strategy, and interacts with International Ground Stations (IGS). EROS acquires Landsat 7 data from various ground receiving stations and performs pre-processing, archiving, product generation, and distribution functions. EROS also provides an accessible public interface into the archive for data search and ordering, as well as many insights on the 45+ years of Landsat data.

1.3 Landsat 7 Mission

The primary Landsat 7 mission objective is to provide timely, high-quality, visible-, infrared-, and thermal-wavelength images of all land and near-coastal areas on Earth, and to thereby continually refresh the existing Landsat archive. Newly acquired data are required to be sufficiently consistent with currently archived data in terms of acquisition geometry, calibration, coverage, and spectral characteristics to allow comparison for global and regional change detection and characterization.

The Landsat Project also continues to make all Landsat data available at no charge for U.S. civil, national security, and private sector use as well as academic, foreign, and commercial uses. An additional goal of the Landsat Project is to expand the uses of such data.

1.3.1 Overall Mission Objectives

Landsat 7 has a design lifetime of five years; it has recently begun its 18th year of operations (ca. 2017). The overall objectives of the Landsat 7 mission are:

  • Provide data continuity with previous Landsat missions
  • Offer 16-day repeat coverage of the Earth’s surface
  • Build and periodically refresh a global archive of sunlit, substantially cloud free, land area and coastal images
  • Make data widely and freely available. As of 2008, Landsat data with standard processing are available at no cost through digital access
  • Support Government, international, and commercial communities
  • Play a vital role in NASA's EOS by promoting interdisciplinary research via synergism with other EOS observations. (In particular, by orbiting in tandem with NASA’s Terra satellite to obtain near coincident observations.)

1.3.2    Initial System Performance Requirements

Some of the initial specific requirements for the Landsat 7 ETM+ system included the following; updates to these requirements that reflect current operations (ca. 2017) are listed in Section 1.3.3.

  • Acquire, capture, and archive the equivalent of 250 ETM+ scenes per day
  • Produce browse and metadata for all full and partial scenes acquired
  • Produce the equivalent of 100 Level-0Reformated (L0R) products and 100 Level-1 products per day, with phased expansion capabilities to handle an increased processing load
  • Accept data acquisition and product requests from users
  • Provide rapid turnaround of priority acquisitions and processing
  • Supply data to users at COFUR
  • Provide communications downlinks for data capture by fixed and transportable X-Band ground stations using the Consultative Committee for Space Data Systems (CCSDS) standard protocol for communication of data

1.3.3 Current System Capabilities

The Landsat 7 ETM+ system design currently (ca. 2017) includes the following capabilities:

  • As of 2008, the entire Landsat archive is available for download at no charge
  • Acquisitions average 470 scenes per day
  • All acquisitions are processed to Level-1 products and archived
  • Acquisition requests for special circumstances are accepted
  • Provides for a systematic collection of global, moderate resolution, multispectral data
  • Uses cloud cover predictions to minimize acquisition of less desirable data
  • All acquisitions are available for user access within 24 hours of receipt at EROS
  • Provides improved access to IGS data

Figure 1 1. The current Landsat 7 data ingest and distribution system at EROS
Figure 1-1. The current Landsat 7 data ingest and distribution system at EROS

1.3.4 Global Survey Mission

An important operational strategy of the Landsat 7 mission is to establish and maintain a global survey data archive. Landsat 7 images the Earth's landmasses systematically every 16 days utilizing the same Worldwide Reference System (WRS) used for Landsat 4, 5, and 8 (WRS-2, see Table 1-1).

However, unlike previous Landsat missions, Landsat 7 endeavors to systematically capture sun-lit, substantially cloud-free images of the Earth’s entire land surface. A Long Term Acquisition Plan (LTAP) was developed to define the acquisition pattern for the Landsat 7 mission in order to create and periodically update this global archive. This enabled the creation of further Global Land Survey (GLS) products from ETM+ data. See Section 2 for a description of Landsat 7's Worldwide Reference System 2 (WRS-2) orbit and Section 4 for additional information about the Landsat 7 LTAP.

  Landsat 7 Landsat 8
Scenes/day  ~450  ~750
SSR size  378 Gbits, block-based  3.14 Terabit, file-based
Sensor Type  ETM+, whisk-broom  OLI/TIRS, pushbroom
Compression  No  ~2.1 variable rice compression
Image D/L  X-Band GXA x3  X-band, Earth coverage
Data Rate  150 Mbits/sec x3 channels/frequencies  384 Mbits/sec, CCSDS virtual channels
Encoding  Not fully CCSDS compliant  CCSDS, LDPC FEC
Ranging  S-Band 2-way doppler  GPS
Orbit  705 km sun-sun 98.2° inclination (WRS-2)  705 km sun-sun 98.2° inclination (WRS-2)
Crossing time  10:00 AM ± 15 minutes local time  10:11 AM ± 15 minutes local time

Table 1-3. Comparison of Landsat 7 and Landsat 8 Observatory Capabilities

1.3.5 Rapid Data Availability

Landsat 7 data are downlinked and processed into standard products within 24 hours of acquisition. Level-1 and LandsatLook products are available through the USGS online interfaces. All users are required to register through the EROS Registration System (ERS).

All products are accessible via the internet for download via HTTPS; there are no product media options.

As with all Landsat data, products are available at no charge to the user. Available data can be viewed through a number of interfaces:

1.3.6 Enhanced IGS Access

Landsat 7 imagery of foreign landmasses has been directly downlinked to IGSs since early in the Landsat 7 mission. Historically, much of the data held internationally were unique, relative to each station’s area of coverage, and were not duplicated in the EROS archive.

This changed when the USGS Landsat Global Archive Consolidation (LGAC) effort began in 2010, with a goal to consolidate the Landsat data archives of all IGSs. Furthermore, as stipulated in the USGS-IGS Memorandum of Understanding, each IGS is now required to provide a copy of all newly downlinked Landsat 7 data to EROS to support the LGAC effort.


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