Landsat

In 1969, in the year of man’s flight to the moon, the first three Multispectral Scanners (MSS, Multi-Spectral-Scanners) began to be developed and manufactured at the Hughes Santa Barbara Research Center. The first MSS prototypes were manufactured within 9 months, by the fall of 1970, after which they were tested on the Half Dome granite dome in Yosemite National Park .

The original MSS optical circuit was created by Jim Kodak, an engineer for the development of optomechanical systems, who also designed the Pioneer spacecraft optical camera, which was the first optical instrument to leave the solar system .

At the time of its creation in 1966, the program was called Earth Resources Observation Satellites , but in 1975 the program was renamed. ^[2] In 1979, Presidential Directive No. 54, US President Jimmy Carter transferred control of the program from NASA to NOAA , recommending the development of a long-term system with 4 additional satellites after Landsat 3 , as well as transferring the program to the private sector. This happened in 1985 when a group of Earth Observation Satellite Company (EOSAT), Hughes Aircraft and RCA , selected NOAA to manage Landsat under a ten-year contract. EOSAT managed Landsat-4 and -5, had exclusive rights to sell the data received in the program, and built Landsat-6 and -7.

In 1989, when the transfer of the program was not yet finalized, the NOAA ran out of budget funds for the Landsat program (NOAA did not request funding, and the US Congress allocated funding for only half the financial year ) ^[3] and NOAA decided to close Landsat 4 and 5. ^{[4] The} head of the new National Space Committee ( en: National Space Council , vice president James Quail , drew attention to the situation and helped the program get extraordinary funding. ^{[3] [4] [5] [6]}

In 1990 and 1991, Congress again provided NOAA funding for only half a year, requiring other agencies using the data collected in the Landsat program to provide the remaining half of the necessary money. ^[3] In 1992, efforts were made to restore funding, but by the end of the year EOSAT had stopped processing Landsat data. Landsat 6 was launched on October 5, 1993, but lost in an accident. Data processing from Landsat-4 and -5 was resumed by EOSAT in 1994. Landsat-7 was launched by NASA on April 15, 1999.

The importance of the Landsat program was recognized by Congress in October 1992, when the Land Remote Sensing Policy Act (Public Law 102-555) was passed, which allowed Landsat 7 to continue working and guaranteed the availability of data and images from Landsat at the lowest prices, both current and new users.

• Landsat 1 (originally ERTS-1, Earth Resources Technology Satellite 1) - launched July 23, 1972, ^[7] stopped operating on January 6, 1978
• Landsat 2 (ERTS-B) - launched on January 22, 1975, stopped working on January 22, 1981
• Landsat 3 - launched on March 5, 1978, stopped working on March 31, 1983
• Landsat 4 - launched July 16, 1982, discontinued in 1993
• Landsat 5 - launched on March 1, 1984, stopped working on December 21, 2012 ^[8]
• Landsat 6 - launch on October 5, 1993, has not been launched into the target orbit
• Landsat 7 - launched April 15, 1999, is operational. In May 2003, the Scan Line Corrector (SLC) module crashed. Since September 2003, it has been used in the mode without correction of scan lines, which reduces the amount of information received to 75% of the original. ^[9]
• Landsat 8 - launched on February 11, 2013 ^[10] . On May 30, 2013, after testing and tuning were completed, it was transferred under the control of USGS. ^[eleven]

Orbit Parameters

Landsat-1, 2, 3 satellites had the following orbit parameters - solar-synchronous orbit, subpolar; the height of the orbit is 900–920 km; the inclination of the orbit to the equatorial plane is 99 °; circulation period - 103 minutes; repeatability of shooting - once every 18 days.

The Landsat-4, -5, -7 satellites had the following orbit parameters - the orbit is solar-synchronous, subpolar; orbit height - 705 km; circulation period - 98.9 minutes; repeatability of shooting - once every 16 days.

Filming equipment

The following survey systems were installed on the Landsat series satellites:

• Multispectral video cameras Return Beam Vidicon (RVB; used on Landsat-1, -2; 3 channels, 80 meters) ^[2]
• RVB panchromatic video cameras (Landsat-3; 40 meters) ^[2]
• Scanning multispectral scanner: MSS (Landsat-1, 2, 3, 4, 5) ^[2]
• Scanning thematic scanner: TM (Landsat-4, 5) ^[12]
• Improved thematic scanner: ETM (Landsat-6) ^[13]
• Improved thematic scanner plus: ETM + (Landsat-7) ^[14]

Multispectral MSS scanners of LandSat 1–5 satellites created at the Santa Barbara Research Center ( Hughes ) are designed to obtain multispectral images of all the Earth’s surfaces. The MSS is an optomechanical system with a scanning mirror (period 74 ms) and a Ritchey-Chretien reflector telescope with a mirror diameter of 22.9 cm. Spatial resolution is 80 meters, spectral ranges: 0.5 - 0.6 μm (green), 0.6 - 0.7 μm (red ), 0.7 - 0.8 μm, 0.8 - 1.1 μm. Detectors are calibrated from every 2 scans. ^[2]

The telescope's quartz mirrors are mounted on Invar rods. The system is designed so as not to lose focus even with strong vibration, which creates an oscillating 36-cm beryllium scanning mirror. Such an engineering solution allowed the United States to launch LANDSAT satellites 5 years earlier than the French remote sensing satellite SPOT (1986 ^[15] ), which first used a two-dimensional array of CCD sensors and did not require a scanning system.

The assembly in the focal plane of the MSS instrument consists of 24 dielectric waveguides (optical fibers) with extruded ends of 5 microns in size organized in a 4x6 array. A bunch of fibers brings light to 6 silicon photodiodes and 18 photomultiplier tubes. For each of the 4 spectral ranges, a set of 6 detectors was used. The radiometric resolution of each detector is 0-255. ^[sixteen]

LandSat-8

Unlike the previous satellites of the program, LandSat-8 (called Landsat Data Continuity Mission during testing), assembled in Arizona by Orbital Sciences Corporation , ^[17] does not use a scanning mirror, but uses a Push broom scanner with linear sensors (development of the ALI system tested on the Earth Observing-1 satellite. In the focal plane of the mission’s main tool, Operational Land Imager (OLI), 14 Focal Plane Modules are installed, each module has 10 linear sensors of different ranges. The OLI telescope consists of 4 fixed mirrors. The Thermal Infrared Sensor (TIRS) infrared instrument uses a similar scheme with 3 modules in the focal plane and a separate telescope of 4 lenses made of germanium and zinc selenide . ^[18]

Using the Push broom architecture requires a huge number of detectors (6.5 thousand for the multispectral and 13 thousand for the panchromatic channel) and increased focal plane sizes, but it can increase the shutter speed from about 10 μs (ETM +) to 4 ms, thereby increasing the signal-to-noise ratio . The absence of constantly moving parts increases the stability of the platform and improves the geometry of the images. ^[18]

• Earth Remote Sensing
• Terralook

• Landsat NASA homepage
• Landsat.org Home Page
• Landsat works in the Gutenberg project
  • Landsat picture of Washington, DC
• (Commercial shots) Landsat imagery
• (Free Images) Landsat imagery from GLOVIS and Global Land Cover Facility
• Atlogis Maps and Atlogis Meta-Maps : An online service that allows you to view mosaics in natural color created by Atlogis based on Landsat 5 and Landsat 7 images.
• Landsat imagery for circa 1975, 1990 and 2000 visualized in Google Earth (required GE installed)