The U.S. Geological Survey's Data Center 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 play 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 data provide a historical record of the Earth's land surface from the early 1970's to the early 1990's. Landsat thematic mapper data provide land surface information from the early 1980's to the present.
- A 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-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 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.
NASA was responsible for operating the Landsats through the early 1980's. 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.
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 north or south latitude. These satellites carried two sensors: a return beam vidicon (RBV) and a MSS. The RBV sensor was essentially a television camera and 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.
MSS Scanning Arrangement (86.6 kb)
Landsats 4 and 5 carry both the MSS and the thematic mapper (TM) sensors; however, routine collection of MSS data was terminated in late 1992. They 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 north or south latitude. These satellites were also designed and operated to collect data over a 185 km swath. The MSS sensors 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 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.
Landsat Orbit (29.4 kb)
All of the Landsats have been in sun-synchronous orbits with equatorial crossing times ranging from 8:30 a.m. for Landsat 1, 9 a.m. for Landsat 2, to 9:45 a.m. for Landsat 5.Extent of Coverage
The Landsat system provides for global data between 81 degrees north latitude and 81 degrees south latitude.Acquisition
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). Multispectral scanner (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 EROS Data Center for storage, reproduction into digital and film formats, and distribution to users.
The TDRS System (TDRSS) satellites 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.
TDRS Coverage Gap (8.7 kb)Processing Steps
Radiometrically corrected (spacecraft and sensor systematic parameters) MSS data were transmitted from the data processing facility to the EROS Data Center (EDC) via DOMSAT. At the EDC, the data are recorded on high-density tape using 14-track digital recorders and archived. Based on user request the data are processed by the ERO Digital Image Processing System (EDIPS). EDIPS reads the HDT's, geometric corrections are applied, optional image enhancement processing is performed, and the processed data is recorded on high-resolution film. Computer compatible tape products are also produced based upon user demand.Data Characteristics
Since 1972 these satellites have provided repetitive, synoptic, global coverage of high-resolution multispectral imagery. The characteristics of the MSS and TM bands were selected to maximize their capabilities for detecting and monitoring different types of Earth's resources. For example, MSS band 1 can be used to detect green reflectance from healthy vegetation, and band 2 of MSS 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 water-land 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. This band combination makes vegetation appear as shades of red, 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 will appear blue. Deep, clear water will be dark blue to black in color, while sediment-laden or shallow waters will appear lighter in color. Urban areas will appear blue-gray in color. Clouds and snow will be bright white and they are usually distinguishable from each other by the shadows associated with the clouds.Spatial Resolution
Landsats 4 and 5 MSS scenes have an instantaneous field of view (IFOV) of 68 meters in the cross-track direction by 82 meters in the along-track direction (223.0 by 272.3 feet, respectively). To understand this concept, consider a ground scene composed of a single 82- by 82-meter 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-meter 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:
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* 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 as a result.
** 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
The multispectral scanner (MSS) sensors were line scanning devices observing the Earth perpendicular 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
Two types of image data are offered:
A) Fully processed data with both geometric and radiometric corrections applied.
B) Partially processed data with only radiometric corrections applied.
Processing Codes Fully Processed Partially Processed MSS = CCT-P MSS = CCT-A
Both processing levels offer either a band-interleaved-by-line (BIL) or a band-sequential (BSQ) image data format.
Unlike previous Landsat CCT formats (Landsats 1 through 3), current digital tapes include a comprehensive field location and data description information superstructure. This superstructure consists of:
- a volume directory file which generally describes the data configuration and provides pointers to each data file.
- a file descriptor record for each data file which describes the data structure within the file and provides pointers to certain fields within the file.
The entire superstructure is composed of four records. Three records (volume descriptor, text, file pointer) reside in a volume directory file. The fourth record is the file descriptor record which is the first record of each data file. The four superstructure records are similar to one another in content as well as in format. The purpose of these records is to identify, describe and locate data in the data files. Thus, superstructure records primarily supply information about the data on the digital tapes rather than carry data themselves. Additional MSS data organization information is available in the following appendices:
MSS Data Organization Pre-EDIPS (BIP-2) Data Organization
Applications and Related Data Sets
Landsat data have been used by government, commercial, industrial, civilian, and educational communities in the U.S. and worldwide. They are being used to support a wide range of applications in such areas 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 more than 15 years. 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 has over 630,000 scenes with a data volume of 20 terabytes. The TM archive has over 300,000 scenes with a data volume of over 50 terabytes.
This document is an excerpt from: http://edcwww.cr.usgs.gov/glis/hyper/guide/landsat