Satellite imagery


Satellite images are images of Earth collected by imaging satellites operated by governments and businesses around the world. Satellite imaging companies sell images by licensing them to governments and businesses such as Apple Maps and Google Maps.

History

The first images from space were taken on sub-orbital flights. The US-launched V-2 flight on October 24, 1946, took one image every 1.5 seconds. With an apogee of 65 miles, these photos were from five times higher than the previous record, the 13.7 miles by the Explorer II balloon mission in 1935. The first satellite photographs of Earth were made on August 14, 1959, by the U.S. Explorer 6. The first satellite photographs of the Moon might have been made on October 6, 1959, by the Soviet satellite Luna 3, on a mission to photograph the far side of the Moon. The Blue Marble photograph was taken from space in 1972, and has become very popular in the media and among the public. Also in 1972 the United States started the Landsat program, the largest program for acquisition of imagery of Earth from space. In 1977, the first real time satellite imagery was acquired by the United States' KH-11 satellite system. The most recent Landsat satellite, Landsat 9, was launched on 27 September 2021.
Image:TIROS-1-Earth.png|thumb|left|The first television image of Earth from space transmitted by the TIROS-1 weather satellite in 1960
All satellite images produced by NASA are published by NASA Earth Observatory and are freely available to the public. Several other countries have satellite imaging programs, and a collaborative European effort launched the ERS and Envisat satellites carrying various sensors. There are also private companies that provide commercial satellite imagery. In the early 21st century satellite imagery became widely available when affordable, easy to use software with access to satellite imagery databases was offered by several companies and organizations.

Satellite image applications

Satellite images have numerous applications in a variety of fields.
  • Weather: They guide meteorologists in forecasting patterns, tracking storms, and understanding climate change.
  • Oceanography: By measuring sea temperatures and monitoring ecosystems, satellite images unlock insights into our oceans' health and global climate.
  • Agriculture and fishing: Satellite data helps locate fish populations, assess crop health, and optimize resource use for a thriving agricultural and fishing industry.
  • Biodiversity: Conservation efforts leverage satellite technology to map habitats, monitor ecosystem changes, and protect endangered species.
  • Forestry: Satellite data empowers sustainable forestry by tracking deforestation, assessing fire risks, and managing resources effectively.
  • Landscape: Analyzing land use patterns with satellite images supports urban planning and facilitates sustainable development initiatives.
Less mainstream uses include anomaly hunting, a criticized investigation technique involving the search of satellite images for unexplained phenomena.
The spectrum of satellite images is diverse, including visible light, near-infrared light, infrared light and radar, and many others. This wide range of light frequencies can provide researchers with large volumes of useful and rich information. In addition to the satellite applications mentioned above, these data can serve as powerful educational tools, advance scientific research and promote a deeper understanding of our environment. This shows that satellite imagery provides rich information and can promote global development.

Data characteristics

There are five types of resolution when discussing satellite imagery in remote sensing: spatial, spectral, temporal, radiometric and geometric. Campbell defines these as follows:
  • Spatial resolution is defined as the pixel size of an image representing the size of the surface area being measured on the ground, determined by the sensors' instantaneous field of view.
  • Spectral resolution is defined by the wavelength interval size and the number of intervals that the sensor is measuring.
  • Temporal resolution is defined by the amount of time that passes between imagery collection periods for a given surface location.
  • Radiometric resolution is defined as the ability of an imaging system to record many levels of brightness and to the effective bit-depth of the sensor and is typically expressed as 8-bit, 11-bit, 12-bit or 16-bit.
  • Geometric resolution refers to the satellite sensor's ability to effectively image a portion of the Earth's surface in a single pixel and is typically expressed in terms of ground sample distance. GSD is a term containing the overall optical and systemic noise sources and is useful for comparing how well one sensor can "see" an object on the ground within a single pixel. For example, the GSD of Landsat is ≈30m, which means the smallest unit that maps to a single pixel within an image is ≈30m x 30m. The latest commercial satellite has a GSD of 0.41 m. This compares to a 0.3 m resolution obtained by some early military film based reconnaissance satellites such as Corona.
The resolution of satellite images varies depending on the instrument used and the altitude of the satellite's orbit. For example, the Landsat archive offers repeated imagery at 30 meter resolution for the planet, but most of it has not been processed from the raw data. Landsat 7 has an average return period of 16 days. For many smaller areas, images with resolution as fine as 41 cm can be available.
Satellite imagery is sometimes supplemented with aerial photography, which has higher resolution, but is more expensive per square meter. Satellite imagery can be combined with vector or raster data in a GIS provided that the imagery has been spatially rectified so that it will properly align with other data sets.

Imaging satellites

Public domain

Satellite imaging of the Earth surface is of sufficient public utility that many countries maintain satellite imaging programs. The United States has led the way in making these data freely available for scientific use. Some of the more popular programs are listed below, recently followed by the European Union's Sentinel constellation.

CORONA

The CORONA program was a series of American strategic reconnaissance satellites produced and operated by the Central Intelligence Agency Directorate of Science & Technology with substantial assistance from the U.S. Air Force. The type of imagery is wet film panoramic and it used two cameras for capturing stereographic imagery.

Landsat

Landsat is the oldest continuous Earth-observing satellite imaging program. Optical Landsat imagery has been collected at 30 m resolution since the early 1980s. Beginning with Landsat 5, thermal infrared imagery was also collected. The Landsat 7, Landsat 8, and Landsat 9 satellites are currently in orbit.

MODIS

MODIS has collected near-daily satellite imagery of the earth in 36 spectral bands since 2000. MODIS is on board the NASA Terra and Aqua satellites.

Sentinel

The ESA is currently developing the Sentinel constellation of satellites. Currently, 7 missions are planned, each for a different application. Sentinel-1, Sentinel-2, and Sentinel-3 have already been launched.

ASTER

The ASTER is an imaging instrument onboard Terra, the flagship satellite of NASA's Earth Observing System launched in December 1999. ASTER is a cooperative effort between NASA, Japan's Ministry of Economy, Trade and Industry, and Japan Space Systems. ASTER data is used to create detailed maps of land surface temperature, reflectance, and elevation. The coordinated system of EOS satellites, including Terra, is a major component of NASA's Science Mission Directorate and the Earth Science Division. The goal of NASA Earth Science is to develop a scientific understanding of the Earth as an integrated system, its response to change, and to better predict variability and trends in climate, weather, and natural hazards.
  • Land surface climatology—investigation of land surface parameters, surface temperature, etc., to understand land-surface interaction and energy and moisture fluxes
  • Vegetation and ecosystem dynamics—investigations of vegetation and soil distribution and their changes to estimate biological productivity, understand land-atmosphere interactions, and detect ecosystem change
  • Volcano monitoring—monitoring of eruptions and precursor events, such as gas emissions, eruption plumes, development of lava lakes, eruptive history and eruptive potential
  • Hazard monitoring—observation of the extent and effects of wildfires, flooding, coastal erosion, earthquake damage, and tsunami damage
  • Hydrology—understanding global energy and hydrologic processes and their relationship to global change; included is evapotranspiration from plants
  • Geology and soils—the detailed composition and geomorphologic mapping of surface soils and bedrocks to study land surface processes and Earth's history
  • Land surface and land cover change—monitoring desertification, deforestation, and urbanization; providing data for conservation managers to monitor protected areas, national parks, and wilderness areas

    Meteosat

The Meteosat-2 geostationary weather satellite began operationally to supply imagery data on 16 August 1981. Eumetsat has operated the Meteosats since 1987.
  • The Meteosat visible and infrared imager , three-channel imager: visible, infrared and water vapour; It operates on the first generation Meteosat, Meteosat-7 being still active.
  • The 12-channel Spinning Enhanced Visible and Infrared Imager includes similar channels to those used by MVIRI, providing continuity in climate data over three decades; Meteosat Second Generation.
  • The Flexible Combined Imager on Meteosat Third Generation will also include similar channels, meaning that all three generations will have provided over 60 years of climate data.