The area density (also known as areal density, surface density, or superficial density) of a two-dimensional object is calculated as the mass per unit area. The SI derived unit is: kilogram per square metre (kg·m−2).
It can be calculated as:
or
where
-
ρA = average area density m = total mass of the object A = total area of the object ρ = average density l = average thickness of the object
A special type of area density is called columnar density; it is obtained integrating volumetric density over a vertical column:
where denotes the vertical coordinate (e.g., height or depth). An example is the Dobson unit for atmospheric ozone. Columnar density is closely related to the vertically averaged volumetric density as
where ; notice that, and have units of, e.g., grams per cubic metre, grams per square metre, and metres, respectively.
Read more about Area Density: Usage
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