The main components of an Earth Observation Mission are the satellites and the sensors or instruments installed. Each mission has a specific type of constellation, orbit, data type and scope which distinguishes them from others. Innovation pushes new missions towards higher resolutions, wider coverages and increasing specific and specialized measurements.
Constellations are a first important parameter in satellite missions. A constellation of 2 or more satellites increases the coverage of the satellite, thus the temporal resolution. The type of orbit of the satellite can be polar-orbiting vs. geostationary. Geostationary satellites orbit around the equator at high altitude, while polar-orbiting satellites travel from pole to pole, typically operating at lower altitudes. They complete one orbit in around 1.5 hour, covering the complete earth surface in 24 hours. These type of satellites are used for applications like disaster, security and environment monitoring. The geostationary satellites are put in orbit at high altitude, matching the rotation speed of the earth, always remaining above the exact same point. Communication and Global Positioning satellites are typically geostationary satellites. Meteo satellites are used in both types of orbits.
Sensors and instruments (called the 'payload') determine the scope of the mission. All-weather and day-and-night capabilities are achieved using Synthetic Aperture Radar (SAR) imaging missions. Multi-spectral high-resolution mapping is used among others for detailed land monitoring, vegetation mapping, water monitoring and emergency services. Specific measuring instruments are developed to do eg. atmospheric monitoring or determine specific parameters such as sea-surface topography, sea- and land-surface temperature, ocean colour and land colour.
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