Zenith Wet Delays (ZWD)

The Zenith Wet Delay (ZWD) is the component of the atmospheric delay experienced by a radio signal traveling from a satellite to a receiver, caused by water vapor in the atmosphere. Unlike the hydrostatic (dry) delay, ZWD is highly variable in time and space and cannot be accurately predicted from surface pressure alone. Precise modelling or estimation of ZWD is essential in GNSS applications to achieve high-accuracy positioning and geodetic measurements.

More Info: https://geodesy.science/item/lower-neutral-atmosphere/