Background
In the mid-1960's, the idea of a civilian Earth resources satellite was conceived by the Department of the Interior. Later the National Aeronautics and Space Administration (NASA) embarked on an initiative to develop and launch the first Earth-monitoring satellite to meet the needs of resource managers and Earth scientists. The U.S. Geological Survey (USGS) entered into a partnership with NASA in the early 1970's to assume responsibility for archiving data and distributing data products. On July 23, 1972, NASA launched the first in a series of satellites designed to provide repetitive global coverage of the Earth's land masses. Designated initially as the "Earth Resources Technology Satellite-A" ERTS-A, it used a Nimbus-type platform that was modified to carry sensor systems and data relay equipment. When operational orbit was achieved, it was designated "ERTS-1."
The satellite continued to function beyond its designed life expectancy of 1 year and finally ceased to operate on January 6, 1978, more than 5 years after its launch date. The second in this series of Earth resources satellites (designated "ERTS-B") was launched January 22, 1975. It was renamed "Landsat 2" by NASA, which also renamed "ERTS-1" as "Landsat 1." Three additional Landsats were launched in 1978, 1982, and 1984 (Landsat 3, 4, and 5).
NASA was responsible for operating the program through the early 1980's. In January 1983, operation of the Landsat system was transferred to the National Oceanic and Atmospheric Administration (NOAA). In September 1985, the Landsat system was commercialized and the Earth Observation Satellite Company, now Space Imaging, assumed responsibility for its operation under contract to NOAA. Throughout these changes, the USGS Earth Resources Observation Systems EROS Data Center (EDC) retained primary responsibility as the Government archive of Landsat data.
The Land Remote Sensing Policy Act of 1992 (Public Law 102-555) officially authorized the National Satellite Land Remote Sensing Data Archive (NSLRSDA) and assigned responsibility to the Department of the Interior which has been delegated to the USGS EDC. In addition to its Landsat data management responsibility, the EDC investigates new methods of characterizing and studying changes on the land surface with Landsat data.
Sample Landsat Thematic Mapper image:
Glasgow, Missouri (115.7
kb)
EDC has managed the Landsat data archive for more than two decades. This archive provides a rich collection of information about the Earth's land surface. Major characteristics and changes to the surface of the planet can be detected, measured, and analyzed using Landsat data. The effects of desertification, deforestation, pollution, cataclysmic volcanic activity, and other natural and anthropogenic events can be examined using data acquired from the Landsat series of Earth-observing satellites. The information obtainable from the historical and current Landsat data play a key role in studying changes through time.
This document provides an overview of the Landsat program and illustrates the application of the data to monitor changes occurring on the surface of the Earth. Landsat multispectral scanner (MSS) data provide a historical record of the Earth's land surface from the early 1970's to the early 1990's. Landsat thematic mapper (TM) data provide land surface information from the early 1980's to the present. Yearly acquisition activity may be viewed at the SPACETRACKS website.
Characteristics of the Landsat System
Landsats 4 and 5 carry both the MSS and the TM sensors; however, routine collection of MSS data was terminated in late 1992. The satellites orbit at an altitude of 705 km and provide a 16-day, 233-orbit cycle with a swath overlap that varies from 7 percent at the Equator to nearly 84 percent at 81 degrees north or south latitude. These satellites also were designed and operated to collect data over a 185-km swath. The MSS and TM sensors primarily detect reflected radiation from the Earth's surface in the visible and near-infrared (IR) wavelengths, but the TM sensor with its seven spectral bands provides more radiometric information than the MSS sensor. The wavelength range for the TM sensor is from the visible, through the mid-IR, into the thermal-IR portion of the electromagnetic spectrum. Sixteen detectors for the visible and mid-IR wavelength bands in the TM sensor provide 16 scan lines on each active scan. Four detectors for the thermal-IR band provide four scan lines on each active scan. The TM sensor has a spatial resolution of 30 meters for bands 1 through 5, and band 7, and a spatial resolution of 120 meters for band 6.
All five of the Landsats have been in Sun-synchronous orbits with equatorial crossing times ranging from 8:30 a.m. for Landsat 1 to approximately 9:45 a.m. for Landsat 5.
Landsat Orbit (29.4 kb)
The Landsat system provides global coverage between 81 degrees north latitude and 81 degrees south latitude.
The current Landsat 5 platform operates from a Sun-synchronous, near-polar orbit, imaging the same 185 km (115 miles) ground swath every 16 days. The TM data are received directly from Landsat 5 by a network of 16 worldwide ground stations. The United States ground station in Norman, Oklahoma receives TM downlinks daily and records them on high density tapes (HDT). These HDTs are then sent to Space Imaging's Image Data Processing Facility located in Lanham, Maryland.
Previously, Landsat 4 and 5 TM data also were transmitted via a Tracking and Data Relay Satellite (TDRS) to a ground terminal at White Sands, New Mexico, and then relayed via a domestic communications satellite to the Space Imaging data processing facility in Norman, Oklahoma. The TM data are no longer acquired through TDRS due to K-band transmission failures on both Landsats 4 and 5.
The present acquisition status is:
- All Landsat 4 TM data acquisitions were discontinued in August 1993
due to:
- X-band transmission failure. The K-band transmission previously failed in November 1992.
- Only TDRS Landsat 5 TM data acquisitions were discontinued
in February, 1987, due to:
- K-band transmission failure.
All satellites that formerly comprised the TDRS System were in geosynchronous orbits. This configuration allowed the acquisition of TM data for nearly all of the Earth's surface except for an area between 50 degrees north and 67 degrees east by 50 degrees south and 82 degrees east. That area may have been covered in part by data recorders at the Thailand and India ground stations.
TDRS Coverage Gap - Hyderabad, India and Bangkok, Thailand Area (8.7 kb)
Space Imaging's Image Data Processing Facility in Lanham, Maryland, receives the HDTs from the Norman, Oklahoma, acquisition facility. The newly acquired data are manually and automatically screened for cloud cover and data quality through the Preprocessing and Data Classification System. The HDTs that are required for customer products continue through the image processing stream. The remaining data are stored locally for approximately six months. After temporary storage, they are archived in Jessup, Maryland until they are transferred to the NSLRSDA at EDC. When EDC places customer orders for the Landsat TM data not resident in the NSLRSDA archive, EDC must specifically request the corresponding HDTs from Space Imaging. Space Imaging then ships the requested HDTs to EDC, where the HDTs are copied and the original HDTs are returned.
There are two unique Landsat TM product generation systems, one system is at EDC and the other is at the Space Imaging facility. Both the EDC and the Space Imaging production systems generate TM systematically corrected data as follows:
- Correcting and validating the mirror scan and payload correction data
- Providing for image framing by generating a series of scene center parameters
- Synchronizing telemetry data with video data
- Estimating linear motion deviation of scan mirror/scan line corrections
- Generating benchmark correction matrices for specified map projections
- Producing along- and across-scan high-frequency line matrices
The EDC Landsat processing system is the National Landsat Archive Production System (NLAPS) System. This system replaced the EROS Digital Image Processing System (EDIPS).
A Model 107 Digital Cassette Recording System incremental (DCRSi) cassette drive is used to supply serial image data to the NLAPS. The DCRSi is a rack-mountable unit capable of recording up to 48 gigabytes on a cassette at any speed from zero to 107 megabytes per second. The built-in-Error-Correcting Code (ECC) generator and decoder provides a user Bit Error Rate (BER) of less than 1 in 1,000,000,000 bits.
The Modular Multi-Satellite Preprocessor (MMSP) receives the serial TM-A (radiometrically corrected) or TM-P (radiometrically and geometrically corrected) data from the DCRSi cassette drive. The serial data are routed to the Programmable Sync Module-2. The Sync Module searches for major and minor frame sync words, converts the serial data to parallel form, and passes the data over a 10-Byte per second dedicated bus (the High-Resolution Imagery bus) to the Demultiplexer/Subsampler (DMS/SS). The DMX/SS demultiplexes the data and writes to the memory on the MMSP CPU via the VME bus. When subsampling, the DMX/SS performs the data reduction function.
Data resampling begins after the completion of satellite orbit model generation/refinement and radiometric calibration. Data resampling consists of three distinct components; coarse resampling table generation, resampling table densification, and two-dimensional convolution resampling. Coarse table generation consists of calculating relationships between product line/pixel values at a set of grid-points and the corresponding line/pixel values in the raw data. Table densification consists of interpolating similar relationships between the remaining product line/pixel values and the corresponding raw data line/pixel values. Table densification also includes performing a number of corrections to the interpolation to account for various inaccuracies in the raw data. The convolution step involves using the fine table to convolve the output pixel values from the raw data.
Radiometric calibration is the process of converting raw digital numbers (DNs) observed by a sensor into physical units. The radiometric calibration of Landsat TM data is performed in two steps:
-
- Absolute Calibration: the recovery of radiance (as observed by the sensor)
from the raw digital number recorded. This involves modelling the characteristics
of the optics and electronics of the sensor.
-
- Relative Calibration: the removal of residual errors in the calibrated
data to improve the qualitative appearance of the imagery.
Geometric correction removes geometric distortions in an image based on knowledge of the satellite and sensor, and remaps the image to a regular grid in a standard map projection. This is accomplished by constructing a mapping between pixel coordinates in the image and geographic coordinates on the surface of the Earth. This mapping is referred to as the forward transformation.
NLAPS has the capability to produce systematially-corrected, precision-corrected, and terrain-corrected products for specified users (see Data Organization).
The Space Imaging Image Processing System (IPS) has the capability to produce precision-corrected, geocoded, mosaicked, and terrain-corrected products. Insufficient control points in the Control Point Library that first require a single-band (Band 4) tape be produced and processed on the Control Point Extraction System for control point selection. Upon successful completion, the product is reprocessed via the EIPS. Digital elevation model and digital terrain model data are ingested through IPS for terrain-corrected and mosaic products.
A 3-band digital data tape is provided with each film product request and is used in the Film Process Generation System. The 3-band digital data are ingested, Look Up Tables are constructed, and the ordered RGB (i.e., red-green-blue filtration) is assigned for output. The latent image is processed using a Colorfire-240 film recorder. Further processing is completed per customer request. These products include paper print, color positive transparency, or processed negative transparency.
Space Imaging initiated a Fast Format for TM digital data. The general formatting criteria follows:
- Field definitions strictly follow American National Standards Institute (ANSI) and International Organization for Standardization (ISO) standards.
- Only band sequential image structure is supported. Geometric corrections to the data are done one band at a time.
- Image files consist of a single band of data.
- A digital product is referred to as a volume set. Individual tapes are referred to as volumes. A volume set may have one or more volumes depending on image size and output tape density. Multi-resolution data sets have a volume set for each resolution.
Since 1972, Landsat satellites have provided repetitive, synoptic, global coverage of high-resolution multispectral imagery. The characteristics of the MSS and TM bands were selected to maximize detecting and monitoring different types of Earth resources. For example, band 1 of TM data penetrates water for bathymetric mapping along coastal areas and is useful for soil-vegetation differentiation and for distinguishing forest types. TM band 2 detects green reflectance from healthy vegetation, and TM band 3 is designed for detecting chlorophyll absorption in vegetation. TM Band 4 data is ideal for detecting near-IR reflectance peaks in healthy green vegetation and for detecting water-land interfaces. The two mid-IR red bands on TM (bands 5 and 7) are useful for vegetation and soil moisture studies and for discriminating between rock and mineral types. The thermal-IR band on TM (band 6) is designed to assist in thermal mapping, and is used for soil moisture and vegetation studies.
Typically, TM Bands 4, 3, and 2 can be combined to make false-color composite images where band 4 represents the red, band 3 represents the green, and band 2 represents the blue portions of the electromagnetic spectrum. This band combination makes vegetation appear as shades of red, brighter reds indicating more vigorously growing vegetation. Soils with no or sparse vegetation range from white (sands) to greens or browns depending on moisture and organic matter content. Water bodies will appear blue. Deep, clear water appears dark blue to black in color, while sediment-laden or shallow waters appear lighter in color. Urban areas appear blue-gray in color. Clouds and snow appear bright white. Clouds and snow are usually distinguishable from each other by the shadows associated with clouds.
A Landsat-4 or -5 TM scene has an instantaneous field of view (IFOV) of 30 meters by 30 meters (900 square meters) in bands 1 through 5 and band 7, and an IFOV of 120 meters by 120 meters (14,400 square meters) on the ground in band 6.
The resolution for the TM sensor is shown below:
Resolution
Landsats 4-5 (meters)
Band 1 30
Band 2 30
Band 3 30
Band 4 30
Band 5 30
Band 6 120
Band 7 30
Background information and status of Landsat satellites.
Satellite Launched Decommissioned Sensors
Landsat 1 July 23, 1972 January 6, 1978 MSS and RBV
Landsat 2 January 22, 1975 February 25, 1982 MSS and RBV
Landsat 3 March 5, 1978 March 31, 1983 MSS and RBV
Landsat 4 July 16, 1982 * TM and MSS
Landsat 5 March 1, 1984 ** TM and MSS
* in standby mode used for range and command as of December 14, 1993. ** currently operational
The TM sensor is an advanced, multispectral scanning, Earth resources instrument designed to achieve higher image resolution, sharper spectral separation, improved geometric fidelity, and greater radiometric accuracy and resolution than the MSS sensor. The TM data are scanned simultaneously in seven spectral bands. Band 6 scans thermal (heat) infrared radiation.
Spectral range of bands and spatial resolution for the TM sensor are:
Wavelength Resolution
Landsats 4-5 (micrometers) (meters)
Band 1 0.45-0.52 30
Band 2 0.52-0.60 30
Band 3 0.63-0.69 30
Band 4 0.76-0.90 30
Band 5 1.55-1.75 30
Band 6 10.40-12.50 120
Band 7 2.08-2.35 30
All TM bands are quantized
as 8 bit data.
Micrometers and their relationship to the electromagnetic spectrum are explained in the glossary.
The EDC offers systematically corrected 10-year and older TM image data to the general public. These data are radiometrically and geometrically corrected, using the satellite model and platform/ephemeris information. The image data also are rotated and aligned to a user-defined map projection.
The EDC systematically processed data are offered either in a band-interleaved-by-line (BIL) or a band-sequential (BSQ) image data format.
- Other processing formats are available from the EDC to the U.S. Government and its Affiliated Users (USGAU) only. The formats are:
- Map Registered Data: These data are radiometrically and geometrically corrected using the satellite model and platform/ephemeris information. The image data are rotated and aligned to a user-defined map projection, using ground control points to improve the satellite model.
- Terrain Corrected Data: These data are radiometrically and geometrically corrected using the satellite model and platform/ephemeris information. The image data are rotated and aligned to a user-defined map projection, using ground control points and a digital terrain model. The rotation, alignment, and registration are done to improve the satellite model and to improve the geodetic inaccuracy caused by the parallax error that occurs because of local terrain elevation.
- Both the Map Registered and Terrain Corrected formats are processed in BSQ or BIL image data formats.
NLAPS-processed digital tape products include:
- Image data and the metadata describing the image
- Processing procedure, which contains information describing the process by which the image data were produced
- DEM data and metadata describing them (available only with terrain corrected products)
- "National Landsat Archive Production System (NLAPS) Systematic Format Description Document"
- "National Landsat Archive Production System (NLAPS) Precision and Terrain Corrected Formats Description Document"
The Space Imaging Fast Format volume set contains a header file, image files, and a trailer file.
The first file on each volume, a Read-Me-First file, contains header data. It is in American Standard Code for Information Interchange (ASCII) format and adheres to ANSI and ISO standards. The header file contains a single 1536-byte ASCII record. All alphanumerics are left justified, and all numerics are right justified.
All image files contain only one TM band of image pixels. There are no header records within the image file, nor are there prefix or suffix data in the individual image records. Image data may be blocked or unblocked.
The blocking factor is a procedure used to minimize the number of digital tapes required to accommodate a full-scene, seven-band image set. Image data are written to tape in individual records and between each record is an inter-record gap of 0.35 inch, separating image file records. Unblocked data contain one line of image data per tape record.
The last volume of the Fast Format image set includes a trailer file. The trailer file contains ephemeris information to compute the approximate spacecraft position for each pixel in the image. This file is in ASCII format and adheres to ANSI and ISO standards.
The structure for a single-volume and a multi-volume set are presented below. Each file is followed by an End-Of-File (EOF) marker. An End-Of-Volume (EOV) marker consists of three EOF markers.
Single Volume Multi Volume
Volume Set Volume Set
Volume 1 Volume 2
Header File Header File Header File
EOF EOF EOF
Band 1 Band 1 Band 5
EOF EOF EOF
Band 2 Band 2 Band 6
EOF EOF EOF
Band 3 Band 3 Band 7
EOF EOF EOF
Band 4 BAND 4 EOV
EOF EOF Trailer File
Band 5 EOV
EOF Trailer File
Band 6
EOF
Band 7
EOF
EOV
Trailer File
Data Availability
To place orders and to obtain additional information regarding technical details, ancillary products, and pricing schedules, contact: Customer Services, EROS Data Center
Online requests for these data can be placed via the USGS Global Land Information System (GLIS) interactive query system. The GLIS system contains metadata and online samples of Earth science data. With GLIS, you may review metadata, determine product availability, and place online requests for products.
The EROS Data Center offers TM digital products on Compact Disc Recordables and 8-mm cartridge tapes. Space Imaging offers thematic mapper data products of black and white and color film and paper products and various digital products.
The General Public has access to 10-year and older data and all of these data physically reside in the NSLRSDA at EDC; therefore, no HDT access fee applies. An HDT access fee may apply to newer data obtained from Space Imaging. For information on the products offered by the EDC and Space Imaging to the General Public, refer to:
The USGAU is comprised of U.S. Government agencies, U.S. Government contractors, researchers involved with the U.S. Global Change Research Program and its international counterpart programs, and other researchers and international entities that have signed a cooperative agreement with the U.S. Government involving the use of Landsat data for noncommercial purposes. For information on the products offered by the EDC to the, refer to:
U.S. Government and its Affiliated Users
Additional ordering instructions include:
- Scenes 10 years (from today's date) and older are priced the same as Space Imaging scenes.
- TM Scenes acquired before or on October 28, 1992 will have no HDT access fee.
- Scenes acquired after October 28, 1992, will require an HDT access fee equal to $70 times the number of scenes on each HDT purchased from Space Imaging plus a 5 percent brokerage fee. The only time this does not apply is when the same scenes were previously purchased by another customer, then no HDT access fee or 5 percent brokerage fee will be applied.
- Access to and distribution of TM data are referenced in the table below or at the "Current Status and Summary of Agreement Between Landsat Program Management and Space Imaging Corporation on Cost and Reproduction Rights for Landsat 4/5 Thematic Mapper Data" Web site.
+-----------------+----------------------+
| | |
| July 16, 1982 | 10 years ago |
| to | to |
| 10 years ago | Present |
+---------------+-----------------+----------------------+
|General Public | USGS/EDC | Space Imaging |
+---------------+-----------------+----------------------+
| USGAU | USGS/EDC | USGS/EDC |
+---------------+-----------------+----------------------+
Applications and Related Data Sets
Landsat data have been used by governmental, commercial, industrial, civilian, and educational communities in the United States and worldwide. These data are being used to support a wide range of applications in such areas as global change research, agriculture, forestry, geology, resource management, geography, mapping, water quality, and oceanography. Landsat data have potential applications for monitoring the conditions of the Earth's land surface. The images can be used to map anthropogenic and natural changes on the Earth over periods of several months to several years. Examples of changes that can be identified include agricultural development, deforestation, natural disasters, urbanization, and the development (see sample image below) and degradation of water resources. The Landsat TM archive has over 300,000 scenes with a data volume of over 50 terabytes.
Sample Landsat TM image that reflects water resource development of a portion of the Missouri River:
Image northwest of Oahe Dam and
Pierre, South Dakota (59.2 kb)
- Earth Observation Satellite Company, 1985, User's guide for Landsat
thematic mapper computer-compatible tapes: Lanham, Md., Earth Observation
Satellite Company [variously paged].
- Earth Observation Satellite Company, 1994, Landsat system status report--September 1994: Lanham, Md., Earth Observation Satellite Company, p. 1-11.
- National Aeronautics and Space Administration, 1981, Draft Landsat-D worldwide reference system (WRS) users guide: [Greenbelt, Md.], National Aeronautics and Space Administration [variously paged].
- National Oceanic and Atmospheric Administration, 1983, Landsat data users notes: [Sioux Falls, S. Dak.], National Oceanic and Atmospheric Administration [variously paged]
- U.S. Geological Survey and National Oceanic and Atmospheric Administration, 1984, Landsat 4 data users handbook: [Washington, D.C.], U.S. Geological Survey and National Oceanic and Atmospheric Administration [variously paged].
- Earth Observation Satellite Company, 1994, Landsat system status report--September 1994: Lanham, Md., Earth Observation Satellite Company, p. 1-11.