What is temporal resolution?
To understand the concept of temporal resolution, we first need to understand two different types/classes of satellites: polar orbiting and geostationary. A polar orbiting satellite orbits around the earth from one pole to other with earth rotating beneath it. Orbiting nature of polar orbiting satellites allows them to capture data of the whole planet. A geostationary satellite, on the other hand, remains stationary with respect to earth and only observes the same portion of earth at all times.
For a geostationary satellite, temporal resolution can be defined as the duration of time between capturing two consecutive images. For example, a geostationary satellite, METEOSAT-11, captures imagery at every 15 minute interval. As a result, its temporal resolution is 15 minutes.
Same definition of temporal resolution can be applied to polar orbiting satellites. But defining it more precisely, temporal resolution for a polar orbiting satellite is the amount of time that the satellite takes to revisit and recapture a particular site. It is also commonly referred to as a satellite’s revisit period. For example, temporal resolution of a single SENTINEL-2 satellite is 10 days. This means one SENTINEL-2 satellite takes 10 days to revisit and recapture a particular site.
One confusing aspect of temporal resolution can be in interpretation of high and low temporal resolution. These are relative terms. The lower the period of time between two consecutive captures of the same area, the higher the temporal resolution. Higher temporal resolution simply means that the satellite revisits and captures data of a specific site more frequently. A satellite with temporal resolution of 1 day is said to have a higher temporal resolution relative to a satellite with temporal resolution of 15 days.
Sometimes multiple polar orbiting satellites are used to improve the temporal resolution. SENTINEL-2 mission consists of two SENTINEL satellites with each having a revisit period of 10 days. Together, this constellation of two satellites provides data of a particular site every five days making the effective temporal resolution 5 days.
Importance of multi-temporal satellite data
The ability to capture imagery and record data of the same site at different periods of time can be leveraged for multiple purposes. Some applications of multi-temporal satellite imagery are listed below:
- Monitoring changes in vegetation and crops
- Monitoring processes like deforestation, urbanization, electrification
- Daily, weekly, monthly weather studies and forecasting
- Tracking natural and man-made disasters and recovery that follows
- Observing changes in the surface of earth over time
- Clouds can sometimes affect the readings recorded by a satellite and so the ability to capture imagery of the same place at multiple instances in time can help to obtain a clear, cloud-free composite.
Temporal resolution of some popular satellites
|Mission||Number of satellites||Temporal resolution (single satellite)||Temporal resolution (constellation)|
|SENTINEL-1||2||12 days||6 days|
|SENTINEL-2||2||10 days||5 days|
|LANDSAT 7||1||16 days||16 days|
|WorldView-3||1||1 day||1 day|
|Terra||1||16 days||16 days|