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Temporal Resolution

 

Zeitliche Auflösung

 

Image data acquired by remote sensing sensors do not only differ with regard to the spatial and spectral resolution: The so-called temporal resolution is also very important. The temporal resolution provides information on the distance of time between the acquisitions of two images of the same area.
The higher the temporal resolution, the shorter the distance of time between the acquisitions of images.Many satellites have a medial temporal resolution of about 14 days. But there are also satellites with a very high temporal resolution capable of acquiring images of the same area every 15 minutes. That is because satellite sensors with a high temporal resolution such as weather satellites are geostationary satellite sensors.

Geostationary satellite systems (see first animation below) differ from the so-called polar orbiting satellites in that they do not orbit and acquire images of the whole globe. Instead, they observe the same section of the surface of the earth while permanently staying in the same place. That way, they can acquire images of the same area at short intervals of only a few minutes. As seen from earth, geostationary satellites remain in the same place as they keep turning parallel to the earth. In order to acquire images of a section as big as possible, geostationary satellites fly as high as approx. 36.000 km. In accordance, they have a lower spatial resolution than polar orbiting satellite systems.

 


Orbit and extend of image acquisition of a geostationary satellite.



Polar orbiting satellite systems (animation below) fly as high as approx. 900 km and thus have a higher spatial resolution than geostationary satellites. Even though they only observe a very small section of the surface of the earth, they fly from pole to pole on a very schiefe Bahn while the earth keeps turning beneath them. That way, they can acquire images of the whole surface of the earth within only a couple of days.

 

 

Orbit and extend of image acquisition of a polar orbiting satellite.


High temporal resolution

If you ask yourself whether you should use images of a geostationary or a polar orbiting satellite depends on the intended purpose: Do you need images with a high temporal resolution for the observation of weather phenomena? In this case you should use geostationary satellite images.
However, if you need images with a high spatial resolution for creating a map of a certain area, you should use images of a polar orbiting satellite.

You can use satellite data with a high temporal resolution in order to observe phenomena such as the tide. The tidal forces impacting on the earth are caused by the gravitational interactions between the earth and the moon as well as the earth and the sun. The tide consists of low tide (the process of water draining) and high tide (the process of water rinsing).
The swipe below shows a section of the mudflat close to the East Frisian Islands. The two satellite images help you distinguish between low tide and high tide. In the image showing high tide differences regarding the depth of sea, for example the emerging tideways, can be observed.

 

 


Low tide and high tide in the satellite image (images by courtesy of USGS/ NASA Landsat Program)

 

 

Low temporal resolution

Satellite sensors with a low temporal resolution are very useful as well since in most cases sensors which acquire images of a certain area only once or twice a month happen to have a better spatial resolution (e.g. 30m) than sensors with a resolution of, for instance, 1000m providing images once an hour. The distance of time between the two images in the swipe below is ten days. You can see the city of Gleebruk (Indonesia) before and after the tsunami of December 2004, which caused extensive damage.

 

 

Satellite image showing the ramifications of the 2004 tsunami on Banda Aceh (images by courtesy of DigitalGlobe)


 


Conclusion:

The technical term “temporal resolution” refers to the distance of time between two images of the same area. Geostationary satellites acquire images of the same section of the surface of the earth so they have a very high temporal resolution. Polar orbiting systems, in turn, have a low temporal but a high spatial resolution.