Comparison of Atmospheric Gradients Estimated From Ground-Based GNSS Observations and Microwave Radiometry

Paper in proceeding, 2019

Observations over four years from two nearby groundbased
Global Navigation Satellite System (GNSS) stations
and one microwave radiometer have been used to
estimate linear horizontal gradients in the atmosphere.
We find that gradients estimated by the radiometer have
larger amplitudes than those estimated using data from
the Global Positioning System (GPS). One reason for this
is that they are estimated, every 15 min, independently
of previous estimates, whereas the gradients from GPS
are estimated every 5 min using constraints on their variability.
We also find that the elevation cutoff angle has a
significant impact on the estimated GPS gradients. Decreasing
the cutoff angle results in smaller gradient amplitudes.
The estimated gradients are not homogeneously
distributed in all directions. When studying the largest
gradients they all occur during the warmer period of the
year, beginning in April and ending in October. Specifically,
for the 25 events with the largest gradient amplitudes
from the GPS data, we find that the vast majority of
them are associated with the passage of weather fronts.