Satellite Orbit Inclination Schematic Drawing

An orbit is the gravitationally curved path of an object about a point in space (Wikipedia). Satellites orbiting around Earth are among our most valuable tools for meteorology and earth science in general. Possibilities for Earth orbits are endless, but most of our existing earth observation satellites have one of only two special orbit types: geosynchronous or sun-synchronous. The former, more commonly called geostationary, has the satellite in the equatorial plane, with an altitude chosen such that the satellite moves with the same speed as Earth rotates, so that seen from Earth the satellite seems to hover above a fixed point on the equator.

We will not consider the geosynchronous type further here, but instead focus on the other, the sun-synchronous orbit type. This is the type used by the NOAA and MetOp satellites that carry the AMSU-B and MHS instruments, used by FIDUCEO. Sun-synchronous means that these orbits are such, that the satellite passes a given point on Earth always at the same local time. These satellites have a low altitude (they are close to Earth) and a high inclination (angle between the orbit plane and the equatorial plane). The figure  shows an example. We characterize these orbits by their altitude, their inclination, and by the local time at which they cross the equator in the northward direction.