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       – Landsat 5: Landsat 5 delivered Earth imaging data for nearly 29 years and set the Guinness World Record for the “longest operating Earth observation satellite”. Its longevity provides a reference for time-series analysis of the Earth.

       – SPOT-1: A commercial high-resolution optical satellite initiated by CNES in the 1970s. Since 1986, the SPOT family has taken more than 10 million high-quality images, which constitute reference data.

       – SPOT-4: The second generation of the SPOT satellites. The panchromatic band is associated with four multispectral (XS) bands at 20 m resolution. The platform is three-axis stabilized, and the viewing direction is selected with a mirror.

       – Landsat 7: This satellite, launched in 1999, is considered a high-accuracy calibrated Earth-observing satellite. Its radiometric measurements are accurate compared to the same measures made on the ground. In October 2008, the USGS made all Landsat 7 data free to the public. It led to a 60-fold increase of data downloads. The satellite is still active in 2020.

       – ASTER: The ASTER instrument on the Terra satellite creates a detailed map of land surface, and scientists have made an elevation model with this data. The first global digital elevation model (GDEM) was released to the public in 2009. It covers the polar regions and complements NASA’s SRTM. The spatial resolution of pixels of 15 m is conducive to the creation of a 30 m resolution DEM. The last version of the ASTER DEM was released in 2019. Since 2016, all satellite images have been available at no charge for all users. The satellite was still active in 2020.

       – Ikonos: Ikonos was a breakthrough among the commercial satellites. The whole platform is used to point towards a geographical region. The whole satellite is agile and, consequently, the satellite weight is reduced. Commercial images with submetric resolution are available. The dynamic range of images is increased.

       – Quickbird-2: Quickbird-2 features enhanced commercial spatial resolution. It is the highest-resolution commercial satellite to date.

       – SPOT-5: Third-generation satellite of the SPOT family operated by Spot Image. It takes 2.5 m panchromatic images and 10 m multispectral ones. Pointing is done with steering mirrors. The HRS instrument is composed of two telescopes pointing around 20° forward and backward. The HRS takes native stereoscopic images with a resolution of 5 m (along track) × 10 m (across track).

       – Formosat-2: This satellite has a daily revisit for event/disaster monitoring, thanks to a body-pointing capability of ±45° in roll and pitch.

       – agility is often the reference: it simplifies the instrument and reduces use of steering mirrors;

       – operators reduce the satellite altitude in order to find a compromise between smaller aperture and better spatial resolution. Examples: Cartosat-2C and Cartosat-3A;

       – a large aperture is chosen to optimize the resolution. Examples: WorldView-3 and Gaofen-8;

       – satellite constellations are increasingly proposed: this decreases the weight of the satellite, the payload and platform complexity and the satellite unitary cost, while increasing the number of satellites (constellation) and improving the revisit time. Constellations of high-resolution satellites are used to retrieve change detection information, geo-statistics, etc. Examples: SkySat, SuperView and RapidEye;

       – usually, a focal plane is composed of several time delay integration (TDI) image sensors, mounted in staggered configuration. CCD sensors are used where ultralow noise is preferred. However, CMOS detectors with low power, high frame rate and low cost are also used. The use of matrix detectors (CCD or CMOS) adds video mode functions into the satellites. Examples: Zhuhai and BlackSky constellations.

       – Asnaro: The overall aim of this project is to develop a new generation of mini-satellite buses with high-performance characteristics. It is based on open-architecture techniques and manufacturing methodologies to reduce the cost and development period.

       – Carbonite-2: This satellite is a technology demonstration of low-cost СКАЧАТЬ