Earth Observation in the frame of EO-MINERS - Overview of remote sensing methods, sensors and applications
Technical terms
- Revisit: the time elapsed between two possible consecutive observations of the same point on earth by a satellite. This period of time depends on the satellite's orbit, target location, the swath of the sensor and the satellite pointing capacities.
- Sun Synchronous orbit: the satellite travels between the north and the south poles as the Earth turns below it. In a sun-synchronous orbit, though, the satellite passes over the same part of the Earth at roughly the same local time each day.
- Earth Synchronous (also: geosynchronous or geostationary): When a satellite is placed on a circular orbit on the equator plane at exactly 42,164 kilometres from the centre of the Earth (about 36,000 kilometres from Earth's surface), it enters a sort of "sweet spot" in which its orbit matches Earth's rotation. Because the satellite orbits at the same speed as the Earth rotation speed, the satellite seems to stay in place over a single longitude, though it may drift north to south.
- FOV (Field Of View): The maximum angle of view which a passive electromagnetic sensor can effectively detect the electromagnetic radiation. The FOV of a sensor corresponds to the width of the image taken (swath width). For active electromagnetic sensors, the notion of FOV and IFOV are not really defined.
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IFOV (Instantaneous Field Of View): A measure of the spatial resolution of a remote sensing imaging system. For optical or thermal electromagnetic sensors, it is defined as the angle subtended by a single detector element on the axis of the optical system. IFOV has the following attributes:
- Solid angle through which a detector is sensitive to radiation. The IFOV and the distance from the target determine the spatial resolution. A low altitude imaging instrument will have a higher spatial resolution than a higher altitude instrument with the same IFOV.
- GSD (Ground Sample Distance): The size of the pixels in a digital image, expressed in ground units. For example, if an ortho-rectified image has a 1.0 m GSD, each pixel represents a ground area measuring 1 m x 1 m. For optical and thermal electromagnetic sensors, GSD of an image is a result of its IFOV and its distance from the target. For Radar systems, it is dependant, among others, of the emitted pulse characteristics.
