Name: Landsat 7
Satellite number: 25682
Mission: Earth science/observation
Launch date: 1999
Type of orbit: Sun-synchronous near-polar low-Earth orbit
Period: 99 minutes
Perigee: 702 km
Apogee: 704 km
Dr Allan McInnes
What do land surveying satellites do? As the name suggests, they survey the land. Like a lot of satellites that are meant for observing the Earth, they’re going to tend to be in lower orbits. Landsat 7, which is one of the big land surveying satellite programmes, tends to be in Sun-synchronous orbits, which means that they always get the same lighting conditions every time of day. So they’ll be around 500 or 700 kilometres high, looking down at the Earth, usually capturing visible light images of the Earth.
But you might also do what’s called multi-spectral imaging, which is where you’re getting not just visible light but also infrared and ultraviolet. The advantage of doing all those additional parts of the electromagnetic spectrum is that you can learn more about what’s going on, and obviously if you have infrared, you can get information about where heat sources are. Scientists can use all that additional data to learn more about the land underneath them.