What is a solar sun-synchronous orbit?

To achieve a sun-synchronous orbit, the satellite must pass close to, but not over, the poles — usually about 8˚ off from the pole. What this means is that the tracks of satellite data tend to be almost north-south, but not exactly so (we will see this in the practical example). These orbits are also much lower: about 500-800km (50 times closer to Earth than a geosynchronous orbit).

How it works

This time, the orbit is such that the orbit is synchronised with the Sun so that the satellite orbit always remains exactly aligned with the position of the Sun. This allows optical satellites to make observations at exactly the same time of day (the “local solar time”), usually about 10:30 am, since this is the best compromise for both low cloud cover and sufficient sunlight.

Satellite Coverage

Being so close to the surface, these satellites can only see a smaller area at any given time. However, over time, as the Earth rotates beneath their orbit, they can eventually view the entire surface. Depending on the size of the individual image coverage, the time it takes to cover the entire world can vary from as short as a day, to as long as a month. This is called the “repeat time”. In the examples we will look at in this course, this has an impact on how often we will have images of a certain kind in any given part of the world.