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Image: Boston Harbor (220.7 kb)
The U.S. Geological Survey's (USGS) EROS Data Center (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 of 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 plays a key role in studying surface 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.
Brief History of the Landsat Program
The idea of a civilian Earth resources satellite was conceived in the Department of Interior in the mid-1960's. 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 USGS entered into a partnership with NASA in the early 1970's to assume responsibility for the archive management and distribution of Landsat 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 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 to Landsat 1. Three additional Landsats were launched in 1978, 1982, and 1984 (Landsats 3, 4, and 5, respectively). Each successive satellite system had improved sensor and communications capabilities.
Through the early 1980's, NASA was responsible for operating the Landsat satellites. In January 1983, operations of the Landsat system were transferred to the National Oceanic and Atmospheric Administration (NOAA). In October 1985, the Landsat system was commercialized. Throughout these changes, the 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 and assigned responsibility to the Department of Interior. 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.
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Image: Boston Harbor (220.7 kb)
Characteristics of the Landsat System
Landsats 1 through 3 operated in a near-polar orbit at an altitude of 920 km with an 18-day repeat coverage cycle. These satellites circled the Earth every 103 minutes, completing 14 orbits a day. Eighteen days and 251 overlapping orbits were required to provide nearly complete coverage of the Earth's surface with 185 km wide image swaths. The amount of swath overlap or sidelap varies from 14 percent at the Equator to a maximum of approximately 85 percent at 81 degrees north or south latitude. Landsats 1 through 3 satellites carried return beam vidicon (RBV) cameras and the MSS sensor. The RBV cameras did not achieve the popularity of the MSS sensor. The MSS sensor scanned the Earth's surface from west to east as the satellite moved in its descending (north-to-south) orbit over the sunlit side of the Earth. Six detectors for each spectral band provided six scan lines on each active scan. The combination of scanning geometry, satellite orbit, and Earth rotation produced the global coverage necessary for studying land surface change. The resolution of the MSS sensor was approximately 80 m with radiometric coverage in four spectral bands from the visible green to the near-infrared (IR) wavelengths. Only the MSS sensor on Landsat 3 had a fifth band in the thermal-IR wavelength.
MSS Scanning Arrangement (86.6 kb)
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 were also designed and operated to collect data over a 185 km swath. The MSS sensors flown aboard Landsats 4 and 5 are identical to the ones that were carried on Landsats 1 and 2. The MSS and TM sensors primarily detect reflected radiation from the Earth's surface in the visible and IR wavelengths, but the TM sensor provides more radiometric information than the MSS sensor. The wavelength range for the TM sensor is from the visible (blue), 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 the visible, near-IR, and mid-IR wavelengths and a spatial resolution of 120 meters for the thermal-IR band.
All of the Landsats have been in sun-synchronous orbits with equatorial crossing times ranging from 8:30 a.m. for Landsat 1 to 9 a.m. for Landsat 2 to 9:45 a.m. for Landsat 5.
The Landsat system provides for global data between 81 degrees north latitude and 81 degrees south latitude.
The Landsat platforms operate from a Sun-synchronous, near-polar orbit imaging the same 185 km (115 miles) ground swath every 16 days (formerly 18 days on Landsats 1 through 3). The MSS data were received directly from Landsats 4 and 5 by a network of 16 worldwide ground stations. Also, data were transmitted via a Tracking and Data Relay Satellite (TDRS) to its ground terminal at White Sands, New Mexico, and then relayed via a domestic communications satellite (DOMSAT) to the data processing facility. The MSS digital data were radiometrically corrected and relayed by DOMSAT to the EDC for storage, reproduction into digital and film formats, and distribution to users.
The TDRS System (TDRSS) satellites are in geosynchronous orbits. This configuration allowed the acquisition of MSS 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 be covered in part by data recorders at the Thailand and India ground stations.
Radiometrically corrected (spacecraft and sensor systematic parameters) MSS data were transmitted from the data processing facility to the EDC via DOMSAT. At the EDC, the data were recorded on high-density tape (HDT) using 14-track digital recorders and then archived. In the interest of long-term preservation, the HDT tapes were converted over to Digital Cartridge Tapes (DCT) tapes in the late 1980's.
Previously, the data were processed by the EROS Digital Image Processing System (EDIPS), based on user request. The EDIPS read the HDT, geometric corrections were applied, optional image enhancement processing was performed, and the processed data were recorded on high-resolution film for archive use in generating photographic reproductions.
The National Landsat Production System (NLAPS) processing system is currently used by the EDC for processing data. This system replaced EDIPS in the mid-1990's. A Digital Cassette Recording System (DCRSi) cassette drive is used to supply serial image data to NLAPS. The NLAPS produces systematic, precision, and terrain corrected digital products. The NLAPS products also offer variable pixel sizes, image orientations, resampling techniques, horizontal datums, map projections, and WRS scene center offsets.
For further information on the NLAPS MSS processing system, refer to:
Since 1972, the 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 the band's capabilities for detecting and monitoring different types of Earth resources. For example, MSS band 1 can be used to detect green reflectance from healthy vegetation, while MSS band 2 is designed for detecting chlorophyll absorption in vegetation. MSS bands 3 and 4 are ideal for recording near-IR reflectance peaks in healthy green vegetation and for detecting waterland interfaces.
MSS Bands 4, 2, and 1 can be combined to make false-color composite images, where band 4 controls the amount of red, band 2 the amount of green, and band 1 the amount of blue in the composite. This band combination makes vegetation appear as shades of red with brighter reds indicating more vigorously growing vegetation. Soils with no or sparse vegetation will range from white (sands) to greens or browns, depending on moisture and organic matter content. Water bodies 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 as bright white, and they are usually distinguishable from each other by the shadows associated with the clouds.
MSS scenes from Landsats 4 and 5 have an instantaneous field of view (IFOV) of 68 meters in the cross-track direction by 82 meters in the along-track direction (223 by 272.3 feet, respectively). To understand this concept, consider a ground scene composed of a single 82- by 82-m area. The scan monitor sensor ensures that the cross-track optical scan is 185 km at nominal altitude regardless of mirror scan nonlinearity or other perturbations of mirror velocity. Cross-track image scan velocity is nominally 6.82 meters per microsecond. After 9.958 microseconds, the 82- by 82-m image has moved 67.9 meters. The sample taken at this instant represents 15 meters of previous information and 68 meters of new information. Therefore, the effective IFOV of the MSS detector in the cross-track direction must be considered to be 68 meters which corresponds to a nominal ground area of 68 meters, by 82 meters at the satellite nadir point. Using the effective IFOV in area calculation eliminates the overlap in area between adjacent pixels.
Landsats 1 through 3 provided Earth coverage similar to Landsats 4 and 5. However, the higher altitude of Landsats 1 through 3 resulted in a different swathing pattern with the IFOV being 56 meters in the cross-track direction by 79 meters in the along-track direction (183.7 feet by 259.2 feet, respectively).
The resolution for the MSS sensor is shown below:
Landsat Orbit (29.4 kb)
TDRS Coverage Gap (8.7 kb) Landsats 1-3 Landsats 4-5 (meters)
Band 4 Band 1 79/82*
Band 5 Band 2 79/82
Band 6 Band 3 79/82
Band 7 Band 4 79/82
Band 8** 237
* As a result, the nominal altitude was 920 km for Landsats 1, 2, and 3.
Nominal altitude for Landsats 4 and 5 is 705 km. The resolutions are
approximately 79 and 82 meters respectively.
** Landsat 3 only.
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
*** MSS data acquisition suspended in 1992
The MSS sensors were line scanning devices observing the Earth at a right angle to the orbital track. The cross-track scanning was accomplished by an oscillating mirror; six lines were scanned simultaneously in each of the four spectral bands for each mirror sweep. The forward motion of the satellite provided the along-track scan line progression. All five Landsats have carried the MSS sensor which responds to Earth-reflected sunlight in four spectral bands. Landsat 3 carried an MSS sensor with an additional band, designated band 8, that responded to thermal (heat) infrared radiation.
The radiometric range of bands for the MSS sensor is shown below: (Handbook, 1979 and 1984, USGS).
Wavelength
Landsats 1-3 Landsats 4-5 (micrometers)
Band 4 Band 1 0.5 - 0.6
Band 5 Band 2 0.6 - 0.7
Band 6 Band 3 0.7 - 0.8
Band 7 Band 4 0.8 - 1.1
Band 8 10.4 - 12.6
Micrometers and their relationship to the electromagnetic spectrum are explained in the glossary.
Systematically corrected image data are offered to the public. (These data are radiometrically and geometrically corrected using the satellite model and platform/ephemeris information.) The image data are also rotated and aligned to a user-defined map projection.
The systematic processing level offers either a band-interleaved-by-line (BIL) or a band-sequential (BSQ) image data format.
Both the Map Registered and Terrain Corrected formats are processed in BSQ or BIL image data formats.
NLAPS-processed digital tape products include:
To place orders and to obtain additional information regarding technical details, ancillary products, and pricing schedules, contact:
Customer Services, EROS Data CenterOnline 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.
Product availability varies. Product media for the General Public include:
MSS Scene - Pierre, South Dakota (79 kb)
Applications and Related Data Sets
Landsat data have been used by government, commercial, industrial, civilian, and educational communities in the U.S. and worldwide. These data are being used to support a wide range of applications in areas such as global change research, agriculture, forestry, geology, resources 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 two decades. The types of changes that can be identified include agricultural development, deforestation, natural disasters, urbanization, and the development and degradation of water resources. The MSS archive retains over 630,000 scenes with a data volume of 20 terabytes.
Beginning in the spring of 1979, the MSS sensor flown aboard Landsat 3 began to experience a problem with proper synchronization of scan lines. NASA performed a series of tests during the period of April 8-24, 1979, in an attempt to correct the situation. However, in the fall of 1979, the problem began occurring with increasing frequency. After that period, line-start anomalies affected 20 percent to 40 percent of all Landsat 3 MSS images acquired.
The MSS sensor was equipped with a hardware feature that generated a line-start pulse to activate the MSS detectors at the beginning of each mirror sweep. The problem occurred when this start pulse was either absent or of an abnormally low amplitude. Because the detectors were not activated at the appropriate time, no data were acquired during the initial part of the scan. A second pulse did activate the detectors when the mirror was about 30 percent of the way across a scan, but the early (western) portion of the intended scan area was lost by that time.
Because there are six detectors per band, multiples of the six scan lines were involved. The number of scan lines affected in a given frame was random and depended on how many line-start pulses were missed. As many as 40 percent of the scenes are affected, and the number of affected scans varies from 10 percent to 90 percent of the scans in the image.
Before the occurrence of this problem, all scan lines were left-justified during routine processing at NASA; that is, they were aligned at the left side of the image. For every line-start pulse missed, a set of six scan lines was, thus, aligned with those that had normal start pulses. This caused that set of scan lines to shift on the ground about 48 km (29.8 miles) to the left of where they should have been.
After the first appearance of the line-start anomaly, NASA contracted to have the ground hardware modified to alleviate this problem. Basically, the hardware properly aligns the good portions of the affected scan lines with respect to the other scan lines so that the ground features line up correctly. Unfortunately, the 30 percent of the data that was missed in each scan line is lost; missing areas are represented in the image as blanks. The corrected images are technically more than 70 percent usable, meaning that much of the image area is unaffected, but their appearance is aesthetically poor. All quality code references to line-start anomaly scenes refer only to the unaffected areas. --------------6BA5F78136C--