 |
|
|
||||
| Earth Resources Observation and Science (EROS) |
Landsat Thematic Mapper Data (TM)
Originally, the National Aeronautics and Space Administration (NASA) was responsible for operating the Landsat satellites through the early 1980s. 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. After that date, all Landsat commercial rights became the property of Space Imaging, with exclusive sales rights to all U.S. thematic mapper (TM) data. Throughout these changes, the U.S. Geological Survey (USGS) retained primary responsibility as the Government's long-term archive of Landsat data. As of July 1, 2001, Space Imaging relinquished their commercial right to Landsat data. The Land Remote Sensing Policy Act of 1992 (Public Law 102-555) officially authorized the government and assigned responsibility to the Department of Interior delegated down to the USGS.
The idea of a civilian Earth resources satellite was conceived in the Department of Interior in the mid-1960s. 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 1970s 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 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 had improved sensor and communications capabilities. NASA was responsible for operation of the Landsats until the early 1980s.
In January 1983 operations of the Landsat system were transferred to the National Oceanic and Atmospheric Administration. The Landsat system was commercialized in 1985 and became the property of Space Imaging EOSAT (later, Space Imaging) who maintained responsibility until July 1, 200l when control was returned to the federal government.
The U.S. Geological Survey (USGS) has managed the Landsat data archive since the launch of Landsat 1. 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 to the Earths surface.
Landsat data have been used by government, commercial, industrial, civilian, and educational communities in the US 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. The types of changes that can be identified include agricultural development, deforestation, natural disasters, urbanization, and the development and degradation of water resources.
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.
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.
Landsats 1-5 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 at the USGS/EROS Data Center in Sioux Falls, SD receives TM downlinks daily and records them on high density tapes (HDT).
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 for final disposition in the National Land Remote Sensing Data Archive(NSLRSDA) at the USGS/EROS Data Center. 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 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)
The USGS/EROS Data Center receives the Landsat TM data directly from the satellite. The newly acquired data are manually and automatically screened for cloud cover and data quality. The HDTs that are required for customer products continue through the image processing stream. All Landsat TM data are resident in the NSLRSDA archive.
The USGS/EROS Data Center Landsat TM product generation system, provides the following level of services:
The EDC Landsat processing system is the National Landsat Archive Production System (NLAPS) System. This system replaced the EROS Digital Image Processing System (EDIPS) and provides radiometric and geometric correction of the TM 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:
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 systematically-corrected, precision-corrected, and terrain-corrected products for specified users (see Data Organization).
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 | June 15, 2001 | TM and MSS *** |
| Landsat 5 | March 1, 1984 | ** | TM and MSS *** |
** currently operational
*** MSS data acquisition suspended in 1992
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 Landsats 4-5 | Resolution (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 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.
NLAPS-processed digital tape products include:
For information on the TM digital product format descriptions, refer to:
The 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
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.
| Accessibility FOIA Privacy Policies and Notices | |
  |
|