Resolution

Resolution: sensor characteristic that affect what can be seen in an image

Source: NASA

• Spatial resolution
• Spectral characteristics
• Temporal characteristics
• Sensor sensitivity

SPATIAL RESOLUTION

• Spatial resolution refers to the amount of detail that can be detected by a sensor. It is the smallest unit measured;
• Images where only large features are visible are said to have coarse or low resolution. In fine or high-resolution images, small objects can be detected.
• Detailed mapping of land-use practices requires a much greater spatial resolution.
• Size of an image pixel in ground dimensions.
• Usually represented by the length of one side of a square (i.e., 30m resolution).

The spatial resolution of passive sensors depends primarily on their Instantaneous Field of View (IFOV).

The IFOV is the angular cone of visibility of the sensor (A) and determines the area on the Earth’s surface which is “seen” from a given altitude at one particular moment in time (B). The size of the area viewed is determined by multiplying the IFOV by the distance from the ground to the sensor (C). This area on the ground is called the resolution cell and determines a sensor’s maximum spatial resolution.

Spatial Resolution Advice

• Moving from detection => identification => analysis requires finer resolution.
• Rule of thumb – select resolution ~1/10th the size of the feature you want to examine.
• Rule of thumb is not very useful – strongly linked to feature characteristics (contrast, location, shape…).
• Get advice from others – experience is invaluable.
• High contrast between features allows detection of sub-pixel sized features.