Assimilation of GNSS zenith total delay in NAVGEM

The observable is the ground-based zenith total delay (ZTD) at each ground station. This ground-based GNSS ZTD represents the tropospheric delay of the propagation of GNSS radio L-band signal between the transmitters and the ground stations after correcting for ionospheric effects.

Here, we present the implementation procedure, quality control, single observation test, bias correction scheme, and data impact assessment. One of the critical elements in the quality control scheme is to correct for the difference between the observing ground station elevation and the numerical model terrain. A single observation test shows comparable impact from this new data source to a single radiosonde observation at a single level.