Satellite images (also Earth observation imagery, spaceborne photography, or simply satellite photo) are s 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 (105 km), these photos were from five times higher than the previous record, the 13.7 miles (22 km) by the Explorer II balloon mission in 1935.The First Photo From Space , Tony Reichhardt, Air & Space Magazine, November 01, 2006 The first satellite (orbital) 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.
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.
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 includes 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 information.
Usage Satellite images are used in many fields of activity — agriculture, geological and hydrological research, forestry, environmental protection, territorial planning, educational, intelligence and military purposes. Such images can be made in the visible part of the spectrum, as well as in the ultraviolet, infrared and other parts of the range. There are also various terrain maps made using radar surveys.
Currently, the decryption and analysis of satellite images is increasingly performed using automated software systems such as ERDAS Imagine or ENVI. At the beginning of the development of this industry, some of the types of image enhancements commissioned by the US government were performed by contractor firms. For example, ESL Incorporated has developed one of the first two-dimensional Fourier transforms for digital image processing.
Satellite image analysis is actively used to protect the environment, for example, the "Visual satellite search for illegal landfills" method has identified more than 200 unauthorized municipal solid and household waste landfills on the territory of 5 subjects of the Russian Federation,.Bezugly, T. A. The use of satellite imagery to identify the problem of unauthorized landfills in the Chelyabinsk region / T. A. Bezugly, A. R. Sibirkina // Use and protection of natural resources in Russia. – 2023. – № 2(174). – Pp. 58–62., URL: https://www.elibrary.ru/item.asp?id=54356689Bezugly, T. A. "Visual satellite search of illegal landfills": an algorithm for searching illegal landfills of solid household and construction waste using satellite images / T. A. Bezugly. Chelyabinsk : ANO "Center of Ecopathology", 2022. 49 p., URL: https://www.elibrary.ru/item.asp?id=49202156 In France, satellite imagery has been used to spot private swimming pools, limiting evasion from a tax on swimming pools.URL: https://immobilier.lefigaro.fr/fiscalite-immobiliere/guide-de-la-fiscalite-immobiliere/2852-piscine-reperee
The purchase of private imagery is also a common practice among the open-source intelligence (or OSINT) community. For example, it enables the estimation of the remaining soviet military hardware in storage that can be refitted in the context of the War in Ukraine.
Disadvantages
Because the total area of the land on Earth is so large and because resolution is relatively high, satellite databases are huge and image processing (creating useful images from the raw data) is time-consuming. Preprocessing, such as image destriping, is often required. Depending on the sensor used, weather conditions can affect image quality. For example, it is difficult to obtain images for areas of frequent cloud cover such as mountaintops. For such reasons, publicly available satellite image datasets are typically processed for visual or scientific commercial use by third parties.
Commercial satellite companies do not place their imagery into the public domain and do not sell their imagery; instead, one must acquire a license to use their imagery. Thus, the ability to legally make derivative works from commercial satellite imagery is diminished.
Privacy concerns have been brought up by some who wish not to have their property shown from above. Google Maps responds to such concerns in their FAQ with the following statement: "We understand your privacy concerns... The images that Google Maps displays are no different from what can be seen by anyone who flies over or drives by a specific geographic location."Catherine Betts told the Associated Press (2007)
Data characteristics
There are five types of resolution when discussing satellite imagery in remote sensing: spatial, spectral, temporal, radiometric and geometric. Campbell (2002)Campbell, J. B. 2002. Introduction to Remote Sensing. New York London: The Guilford Press defines these as follows: Spatial resolution is defined as the pixel size of an image representing the size of the surface area (i.e. m2) being measured on the ground, determined by the sensors' instantaneous field of view (IFOV). Spectral resolution is defined by the wavelength interval size (i.e. the size of discrete segments of the electromagnetic spectrum) and the number of intervals that the sensor is measuring. Temporal resolution is defined by the amount of time (e.g. days) 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 (e.g. contrast) and to the effective bit-depth of the sensor (number of grayscale levels) and is typically expressed as 8-bit (0–255), 11-bit (0–2047), 12-bit (0–4095) or 16-bit (0–65,535). 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). 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 (GeoEye 1) 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 (CIA) 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 (AFT&FWD) for capturing stereoscopic 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 (at coarser spatial resolution than the optical data). 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 (SAR imaging), Sentinel-2 (decameter optical imaging for land surfaces), and Sentinel-3 (hectometer optical and thermal imaging for land and water) have already been launched.
ASTER The ASTER is an imaging instrument onboard Terra, the flagship satellite of NASA's Earth Observing System (EOS) launched in December 1999. ASTER is a cooperative effort between NASA, Japan's Ministry of Economy, Trade and Industry (METI), and Japan Space Systems (J-spacesystems). 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