Since 1972, the Landsat satellites have observed Earth from space, providing data that help the public and scientific community understand the state and condition of its surface through time. Users can download any of the millions of scenes in the USGS archive collected by the Landsat suite of satellites at no charge.
Currently, both Landsat 8 and Landsat 7 collect data, each following a near-polar, sun-synchronous orbit on the Worldwide Reference System (WRS-2). Each satellite has a 16-day revisit cycle, and their orbits are offset to provide 8-day repeat coverage.
Most acquired scenes are downlinked to the Landsat Ground Network and made available for download within 24 hours of acquisition. Unique scenes downlinked to International Cooperators are also ingested into the USGS global archive, and are made available upon receipt.
Landsat Level-1 standard data products are processed to standard parameters, and distributed as scaled and calibrated digital numbers (DN). The DN’s can be scaled to absolutely calibrated radiance or reflectance values using metadata distributed with the product (see conversion algorithms for Landsat 1-7 and Landsat 8).
The Landsat Science Data Users Handbooks serve as a comprehensive resource for each of the spacecraft, payloads, ground processing systems, and methodologies for using Landsat data in science studies:
Landsat product generation is in transition to a collection management scheme. The goal is to create a stable archive in which (1) sensors are cross- and absolutely-calibrated, (2) the georegistration of the scenes is known and consistent, and (3) the product format is stable. Any product improvement that would create a discontinuity within the archive will cause a new collection to be established and the archive to be reprocessed to re-establish the stability of the archive. A Landsat Product Generation system (LPGS) release, scheduled for 2016, will result in new products that will be designated as Collection 1. Information about previous releases and plans will be provided on an upcoming Collection Management webpage.
The sections below provide additional information Landsat Level-1 standard data products.
Landsat Level-1 data can be searched and downloaded at no charge. The Landsat Data Access page describes the available searching interfaces.
Landsat metadata files contain information that can be useful in locating specific data files in the archive inventory, and is also valuable to users about certain product characteristics.
Changes are occasionally made to the metadata files, in order to improve data quality and usability. The Level-1 Landsat Data Products Metadata page provides details of recent metadata and processing changes that affect the discovery and use of Landsat data, and also displays an example of a Landsat metadata (MTL.txt) file.
Landsat metadata is delivered with the Level-1 standard data products, and can be accessed in csv and xml files from the Bulk Metadata Download tool.
Data Format Control Books (DFCBs) are available for all Landsat data products. These documents describe the format and content of the Landsat data products and metadata. DFCBs are listed in the last section on the Project Documentation webpage.
Data quality measures are in place to inform users whether the integrity of Landsat data has been affected by anything from instrument artifacts to production software updates. Calibration validation is an ongoing quality check for the Landsat sensors, along with software research and development to enhance or improve the algorithms used to produce Level-1 products.
The Calibration page describes parameter updates, known anomalies, and other factors affecting data usability.
The Geometry web page provides information on the geometric accuracy, the levels of processing, and ground control point (GCP) information about the Landsat Level-1 data products.
The Landsat Quality Assessment Band web page describes how the use of Quality Assessment (QA) bits improve the integrity of science investigations, by indicating which pixels might be affected by instrument artifacts or subject to cloud contamination. The generation of a QA band is currently only available for Landsat 8 OLI/TIRS data.
The Solar Illumination and Sensor Viewing Angle Coefficient File page describes the file format and application of the angle data. The file stores the coefficients needed to convert radiances to reflectance data with solar illumination corrected. The Sensor Viewing angles are needed for the creation of some science products.
The Known Issues web page describes known artifacts that exist in the Landsat product. These artifacts vary widely between the MSS, TM, ETM+ and OLI/TIRS sensors caused by specific sensor characteristics and anomalies identified after launch.
Landsat data are systematic, geometric, radiometric, and terrain corrected to provide the highest quality data to the user communities. Occasionally, anomalies occur and artifacts are discovered that require research and monitoring.
The Landsat Calibration and Validation (Cal/Val) team investigates and tracks anomalous data. Details about a number of anomalies that have been discovered and investigated can be found on the Landsat Known Issues page.