The most common types are Earth-imaging satellites, which take satellite images, analogous to aerial photographs; some EO satellites may perform remote sensing without forming pictures, such as in GNSS radio occultation.
Types of EOS
EO satellites can be divided into two types based on how they capture imagery: passive and active.
Passive satellites detect radiation reflected off the Earth’s surface, such as visible light and infrared. In general, passive satellites are not able to work through clouds.
Active satellites transmit energy towards the Earth and measure the returned signal which provides information about the Earth’s surface. In general, active satellites can see through the cloud.
How earth observational satellites collect data
Earth Observational Satellites travel on a range of different orbits, offering varying perspectives of the Earth. Most satellites do not continuously collect data due to limitations in power and memory. Some offer regular and reliable data acquisition while others collect in small quantities over a period of time. Data is stored on-board the satellite until it is in sight of a ground station to downlink the data. The time between an image being taken and being available to download can range between a month to a few minutes and is getting faster as technology progresses. As satellites are owned by different companies there are several data providers, each with their own pricing structure.
Isro has launched many operational remote sensing satellites. Currently, thirteen operational satellites are in sun-synchronous orbit and four in Geostationary orbit. The data from these satellites are used for several applications covering agriculture, water resources, urban planning, rural development, mineral prospecting, environment, forestry, ocean resources and disaster management.
