The power of satellites

Satellites play a critical role in the modern world. Navigation (powering the GPS in your smartphone or satnav) and communications (transmitting television, radio and telecommunications signals) are two obvious examples! They are also used to collect a wide range of data that is used for a huge variety of applications from meteorology to astronomy. They collect data passively, by measuring different types of radiation coming from space or the Earth, or actively, by emitting energy of a certain type and then measuring it when it bounces back.

_{Passive (left) and active (right) satellite data collection. Courtesy of William Deadman.}

These active and passive forms of data collection are together known as ‘satellite remote sensing’, often shortened to just ‘remote sensing’. The term ‘remote sensing’ refers to looking at something without physically being there. Just like a remote control allows you to operate an electrical device from a distance, remote sensing allows you to observe something from a distance.

Satellite imagery is a great example of this. Today, anyone with access to a smartphone or computer can view satellite imagery through Google Maps or similar apps. The high-resolution imagery can provide extra help to those trying to find their way around. Satellite imagery is used for much beyond personal navigation: from tracking climate change by recording seasonal ice cap levels; to military intelligence; to helping combat illegal logging and deforestation.

_{Street map and satellite imagery comparison of Hatra, Iraq. Courtesy of ESA and OpenStreetMap.}

_{What sort of things can you see in the satellite imagery that are not visible in the street map?}