This feature article, written by members of the UN Operational Satellite Applications (UNOSAT) programme, outlines how satellite technology can improve emergency relief after a natural disaster.

UNOSAT uses satellite data to produce maps and damage reports for nongovernment organisations, intergovernmental agencies and disaster managers in emergency situations. The authors describe how the process works — from receiving a relief agency's phone call to collecting and analysing relevant satellite data.

They argue that satellite data, when combined with ancillary data such as road maps or population distribution, can help aid workers navigate affected areas and provide estimates of the number of people likely to be affected by, for example, floods or landslides.

The authors describe the range of satellite sensors used by UNOSAT, explaining the advantages of different types of data depending on the disaster. For example, radar imagery, which is unaffected by cloud, is particularly useful to monitor flooding, whereas high resolution optical data is better for earthquake damage assessment.