The Landsat Program has provided over 36 years of calibrated high spatial resolution data of the Earth's surface to a broad and varied user community, including agribusiness, global change researchers, academia, state and local governments, commercial users, military, and the international community. Landsat images provide information meeting the broad and diverse needs of business, science, education, government, and national security.

The mission of the Landsat Program is to provide repetitive acquisition of high resolution multispectral data of the Earth's surface on a global basis. Landsat represents the only source of global, calibrated, high spatial resolution measurements of the Earth's surface that can be compared to previous data records. The 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.

The Landsat platforms carry multiple remote sensor systems and data relay systems along with attitude-control and orbit-adjust subsystems, power supply, receivers for ground station commands and transmitters to send the data to ground receiving stations.

The most recent Landsat mission, Landsat 7, offers these features:

• Data Continuity: Landsat 7 is the latest in a continuous series of land remote sensing satellites spanning 32 years.
• Global Survey Mission: Landsat 7 data will be acquired systematically to build and periodically refresh a global archive of sun-lit, substantially cloud-free images of the Earth's landmass.
• Affordable Data Products: Landsat 7 data products will be available through the EROS Data Center at the cost of fulfilling user requests (COFUR).
• Enhanced Calibration: Data from the ETM+ will be calibrated to better than 5% absolute, providing an on-orbit standard for other missions.
• Responsive Delivery: Automated request processing systems will provide products electronically within 48 hours of order.

The continuation of the Landsat Program is an integral component of the U.S. Global Change Research Program. Landsat 7 is part of a global research program known as NASA's Earth Sciences Enterprise, a long-term program that is studying changes in Earth's global environment. The goal of Earth Sciences Enterprise is to provide a better understanding of natural and man-made environmental changes. In the Landsat Program tradition, Landsat 7 will continue to provide critical information to those who characterize, monitor, manage, explore, and observe the land surfaces of the Earth over time.

1.1.1 Previous Missions

Landsat satellites have been providing multispectral images of the Earth continuously since the early 1970's. A unique 36-year data record of the Earth's land surface now exists. This unique retrospective portrait of the Earth's surface has been used across disciplines to achieve improved understanding of the Earth'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, pollution monitoring, land surface change detection, and cartographic mapping.

Landsat 7 is the latest satellite in this series. The first was launched in 1972 with two Earth-viewing imagers - a return beam vidicon and an 80 meter multispectral scanner (MSS). Landsat 2 and 3, launched in 1975 and 1978 respectively, were configured similarly. In 1984, Landsat 4 was launched the MSS and a new instrument called the Thematic Mapper (TM). Instrument upgrades included improved ground resolution (30 meters) and 3 new channels or bands. In addition to using an updated instrument, Landsat 4 made use of the multimission modular spacecraft (MMS) which replaced the Nimbus based spacecraft design employed for Landsats 1-3. Landsat 5, a duplicate of 4, was launched in 1984 and even today (2000) after 16 years - 10 years beyond its 5 year design life - is still returning useful data. Landsat 6, equipped with a 15 meter panchromatic band, was lost immediately after launch in 1993.

Table 1.1 lists key mission characteristics of the Landsat Program while Table 1.2 compares the sensors carried aboard these satellites. A detailed Landsat Program Chronology is also available.

Table 1.1 Landsat Mission Characteristics

Table 1.2 Landsat Satellites and Sensors

1.1.2 The EOSAT Era

In the mid 1980's, U.S. Government agencies, including NASA and 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 5 satellites and their data distribution to the private sector. In addition, NOAA was to pursue procurement of future remote sensing Landsat products and services from the private sector.

In 1985, NOAA solicited bids to manage the existing Landsat satellites and to build and operate future systems. The Earth Observation Satellite Company (EOSAT ), a joint venture between RCA and Hughes Aircraft, now 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 5 Thematic Mapper (TM) data until July 1994, at which time Landsat data over ten years old became available from the National Archive at the EROS Data Center (EDC). This agreement between Landsat Program management and EOSAT Corporation on cost and reproduction rights for Landsat 4 and 5 Thematic Mapper data remains in effect and was last updated in October 1996. EOSAT also won competition to produce the next satellite in the series, Landsat 6.

1.1.3 Basis in Law for Landsat 7

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 which:

• Abandoned full commercialization of the Landsat Program.
• Returned management of the Program to the Government.
• Established a data policy of distributing Landsat data at the cost of fulfilling a user request (COFUR). And last but not least,
• Directed that preliminary work begin on a new Landsat 7.
• foster development of advanced land remote sensing systems and opportunities for commercialization

The loss of Landsat 6 in October, 1993 suddenly made the new Landsat 7 mission imperative. A May 4, 1994 Presidential Decision Directive (NSTC-3) defined the new Landsat 7 data policy, program management strategies and implementation guidelines. Subsequent NASA and NOAA memoranda later that summer brought the current Landsat 7 mission into existence.

Other, recent legislation relevant to Landsat:

• 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 1997"

Visit Recent and Pending Legislation Affecting the Landsat Program for detailed public law information.

1.1.4 System Operation and Management

• NASA Landsat 7 Project developed the Landsat 7 System. Specifically, it meant designing, developing, and testing the Landsat 7 spacecraft, 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. NASA is still responsible for verifying data processing integrity and assuring high image quality. The USGS Center for Earth Resources Observation and Science (EROS) manages the overall Landsat 7 Mission Operations. In this capacity EDC directs on-orbit flight operations, implements mission policies, directs acquisition strategy, and interacts with International Ground Stations. EDC captures Landsat 7 data and performs pre-processing, archiving, product generation, and distribution functions. EDC also provides a public interface into the archive for data search and ordering and handles billing and accounting procedures.

The Landsat 7 Mission Objective is to provide timely, high quality visible and infrared images of all landmass and near-coastal areas on the Earth, continually refreshing an existing Landsat database. Data input into the system will 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 7 project will continue to make Landsat data available for U.S. civil, national security, and private sector use as well as academic, foreign, and commercial uses. Another goal of the project is to expand the uses of such data.

1.2.1 Overall Mission Objectives

Landsat 7 is to have a design lifetime of five years. The overall objectives of the Landsat 7 Mission are:

• Provide data continuity with Landsats 4 and 5.
• Offer 16-day repetitive Earth coverage.
• Build and periodically refresh a global archive of Sun-lit, substantially cloud free, land images.
• Make data widely available for the cost of fulfilling a user request (called COFUR).
• Support Government, international and commercial communities.
• Play a vital role in NASA's Earth Observing System (EOS) by promoting interdisciplinary research via synergism with other EOS observations. (In particular, orbit in tandem with EOS-AM1 for near coincident observations.)

1.2.2 Specific Performance Requirements

Some specific requirements for the Landsat 7 System include the following:

• 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 0R 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 for rapid turnaround of priority acquisitions and processing.
• Supply data to users at the cost of fulfilling the user request.
• 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.

The Landsat 7 system design can best be described as robust. New and unusual system capabilities include:

• Provides for a systematic collection of global, high resolution, multispectral data.
• Provides for a high volume of data collection (averaging 250 scenes per day into the U.S. archive).
• Uses cloud cover predicts to avoid acquiring unusable data.
• Provides data available for ordering by end users within 24 hours of capture at EDC.
• Provides delivery of up to 100 scene products per day.
• Provides improved access to International Ground Station data.

1.3.1 Global Survey Mission

An important operational strategy of the Landsat 7 mission is to establish and maintain a global survey data archive. Landsat 7 will be able to image the Earth's landmass systematically every 16 days, following the same "Worldwide Reference System" used for Landsats 4 and 5.

However, unlike previous Landsat missions, Landsat 7 will endeavor to systematically capture sun-lit, substantially cloud-free images of all of the Earth's land surface. A "Long Term Plan" has being developed to define the acquisition pattern for the Landsat 7 mission in order to create and periodically update this global archive. See Chapter 5 for descriptions of the Worldwide Reference System and Long Term Acquisition Plan.

1.3.2 Rapid Data Availability

Figure 1.2 Landsat 7 Data Distribution System

The Landsat 7 data distribution system will provide access to Landsat 7 Level 0R data products within 24 hours of collection and Level 1 processed products within 48 hours of request. Product media options include Exabyte tape (8 mm 8200, 8mm 8500), CD-ROM or electronic transfer via FTP. Billing and accounting are handled vis ECS-registered prepaid accounts. New users should contact the EDC-DAAC User Services Office (605-594-6116 voice, 605-594-6963 fax, Email for assistance in setting up data purchase accounts and arranging payment method in advance.

Landsat 7 product orders may be placed electronically via the web using the ECS search and order system or over the phone with EDC-DAAC User Services.

1.3.3 Enhanced IGS Access

Imagery of foreign land masses will be recorded and downlinked to EDC yet the temporal depth will be a fraction of what's available at the international ground stations. Users of Landsat 7 data will have improved access to this data. As stipulated in the NOAA-IGS Memorandum of Understanding, each international ground station collecting Landsat 7 data is required to send periodic inventory information in the form of scene metadata to the LP-DAAC. IGS metadata is structured according to the U.S. standard and as such, is available for web-based searching using tools developed for the U.S. archive. The IGSs also have the option to send browse imagery to the LP-DAAC for viewing by interested users.

The LP-DAAC will also support access to foreign products in other ways. Users will discover on EDC's web servers internet links to IGS browse systems and information on IGS product types and ordering protocols. No IGS products will be archived at EDC. They can only be discovered and then ordered directly from the IGS data distributor(s).

Source: http://landsathandbook.gsfc.nasa.gov