ResolutionsWhen using remote sensors to measure the Earth, there arefour different types resolutions that need to be considered depending on thetarget of interest and purpose. These resolutions particularly refer tosatellites however can also refer to the operations of other platforms, such asdrones and aircraft.

These need to be selected depending on what you actuallywant to observe. Spatial resolution refers to the smallest area on Earth thata satellite can observe, depending on the size of the objects on the Earth thatyou are collecting data about. The lower the spatial resolution, the larger thearea that will be detected. Temporal resolution refers to the frequency asatellite observes the same area on Earth. The higher the temporal resolution,the shorter the interval is between when the images are taken. Spectralresolution determines the wavelengths in the electromagnetic spectrum that thesensor measures.

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Black and white film still extends over most if not all of thevisible portion of the electromagnetic spectrum however with a fine or coarsespectral resolution, the sensor records information about a smaller wavelengthrange for a particular channel. Whereas colour film is sensitive to the visibleelectromagnetic spectrum. A high spectral resolution will mean that it will beindividually sensitive to the blue, green and red wavelengths, so features withvarious colours can be distinguished. Multi and hyper spectral sensors are ableto detect multiple narrow spectral bands over the electromagnetic spectrum. Theextremely high spectral resolutions of these sensors allow it to differentiatebetween different targets more accurately.

2 Finally, the radiometricresolution refers to the sensitivity of the sensor to detect slight differencesin energy. The finer the radiometric resolution of a sensor is, the moresensitive it is to detecting minor differences in energy.  Types ofsatellitesThere are two types of satellite remote sensing platforms –geostationary and polar satellites which orbit the Earth in different ways; theseare matched to the capability and objective of the sensors they carry. Orbitscan vary in altitude and rotation relative to the Earth. Most remote sensingplatforms follow near polar orbits1 GeostationaryorbitsSatellites at high altitudes, which view the same portion ofthe Earth’s surface at all times have geostationary orbits. These satellitesrevolve at speeds which match the rotation of the Earth, so they seemstationary in relation to their position over the Earth’s surface.

Thesesatellites are used when information needs to be collected continuously over aspecific area. Satellites used for weather and communication purposes oftenhave these types of orbits. The high altitude also enables some satellites tomonitor weather and cloud patterns covering an entire hemisphere of the Earth.2The high altitude also means that the resolution of the images taken is low.

Thepattern of the orbit is illustrated in the diagram below:1 http://www.nrcan.gc.ca/node/9283