Radiation thermometry can be extended to measuring not just the temperature at a small spot on a surface, but building up a two-dimensional image of a large area or even the complete surface.

With modern detector arrays it is possible to produce a map of the temperature with typically 380 by 290 pixels. This is presented as a picture, but because the camera operates in the infrared the image is either black and white or in false colours.

Thermal imaging is now widely used in:

• surveillance
• night vision
• search and rescue
• building and land surveying
• aircraft and missile tracking
• detecting hot spots due to failure in electrical equipment and electronic circuits
• medical thermography

These are often qualitative applications, relying only on contrast. For quantitative thermometry one must be able to convert the signals to temperatures using a calibration procedure.

Reference is made to a simple internal blackbody source, which is used to link the colours or shades to numerical temperature values. From time to time it is necessary to check this with respect to a calibrated external blackbody source, if possible with a large enough area to fill the complete field of view.

In many respects the instruments can be treated as 2-dimensional radiation thermometers and they share many features:

• may be fixed installations, portable or hand-held
• focused on distant or near objects
• prone to the same sources of error, due to emissivity and reflected radiation, size-of-source, etc.
• more affordable than a few years ago
• powerful tools in thermal and temperature measurement.

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Good practice online modules

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• Temperature measurement
  
• Introducing temperature measurement
• Types of thermometer
• Temperature measurements in healthcare
• Temperature measurement in practice