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GB
Emissivity
Emissivity is a unit that describes an objects ability to emit infrared radiation = warmth.
Hotter objects emit more infrared radiation. The value for emissivity of an object can be
anything from 0 (shiny mirror, ideal reflector) to 1.0 (black body, full radiator).
Most organic materials, lacquered or oxidised surfaces have an emissivity of 0.95 - refer
to below table.
The emissivity of the imager can be adjusted from 0.01 to 1.00 to ensure accurate
measurements.
Emissivity table
Material
Emissivity
Tarmac
0.90 to 0.98
Concrete
0.94
Cement
0.96
Sand
0.90
Earth
0.92 to 0.96
Water
0.92 to 0.96
Ice
0.96 to 0.98
Snow
0.83
Glass
0.90 to 0.95
Ceramic
0.90 to 0.94
Marble
0.94
Chalk
0.80 to 0.90
Mortar
0.89 to 0.91
Brick
0.93 to 0.96
Black cloth
0.98
Human skin
0.98
The smallest possible resolution and therefore spot size that the imager can display is
3.78 mrad. This spot size is determined by pixel size divided by lens size.
The spot size on the object can be calculated as follows:
Distance to object divided by 265 (D:S of imager)
- When the imager is accurately focussed on an object in 300 cm distance, the spot size
on the object is: 300 cm / 265 = 1.132 cm.
- When the imager is accurately focussed on an object in 100 cm distance, the spot size
on the object is: 100 cm / 265 = 0.377 cm.
For the smallest possible spot size (D:S = 265:1) the imager has to be accurately focussed
on the object.
