pW

Precipitable Water - measure of the depth of liquid water at the surface that would result after precipitating all of the water vapor in a vertical column over a given location, usually extending from the surface to 300 mb.

Picowatt .

Abbreviation for picowatt. A unit of power equal to 10^-12 W, i.e., -90 dBm. Note: One picowatt is usually used as a reference level for both weighted and unweighted noise measurements. The type of measurement must be specified.