Resolutions

When using remote sensors to measure the Earth, there are
four different types resolutions that need to be considered depending on the
target of interest and purpose. These resolutions particularly refer to
satellites however can also refer to the operations of other platforms, such as
drones and aircraft. These need to be selected depending on what you actually
want to observe.

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Spatial resolution refers to the smallest area on Earth that
a satellite can observe, depending on the size of the objects on the Earth that
you are collecting data about. The lower the spatial resolution, the larger the
area that will be detected. Temporal resolution refers to the frequency a
satellite observes the same area on Earth. The higher the temporal resolution,
the shorter the interval is between when the images are taken. Spectral
resolution determines the wavelengths in the electromagnetic spectrum that the
sensor measures. Black and white film still extends over most if not all of the
visible portion of the electromagnetic spectrum however with a fine or coarse
spectral resolution, the sensor records information about a smaller wavelength
range for a particular channel. Whereas colour film is sensitive to the visible
electromagnetic spectrum. A high spectral resolution will mean that it will be
individually sensitive to the blue, green and red wavelengths, so features with
various colours can be distinguished. Multi and hyper spectral sensors are able
to detect multiple narrow spectral bands over the electromagnetic spectrum. The
extremely high spectral resolutions of these sensors allow it to differentiate
between different targets more accurately.2 Finally, the radiometric
resolution refers to the sensitivity of the sensor to detect slight differences
in energy. The finer the radiometric resolution of a sensor is, the more
sensitive it is to detecting minor differences in energy.

 

Types of
satellites

There are two types of satellite remote sensing platforms –
geostationary and polar satellites which orbit the Earth in different ways; these
are matched to the capability and objective of the sensors they carry. Orbits
can vary in altitude and rotation relative to the Earth. Most remote sensing
platforms follow near polar orbits1

 

Geostationary
orbits

Satellites at high altitudes, which view the same portion of
the Earth’s surface at all times have geostationary orbits. These satellites
revolve at speeds which match the rotation of the Earth, so they seem
stationary in relation to their position over the Earth’s surface. These
satellites are used when information needs to be collected continuously over a
specific area. Satellites used for weather and communication purposes often
have these types of orbits. The high altitude also enables some satellites to
monitor weather and cloud patterns covering an entire hemisphere of the Earth.2
The high altitude also means that the resolution of the images taken is low. The
pattern of the orbit is illustrated in the diagram below:

1 http://www.nrcan.gc.ca/node/9283