Ground-based temperature and humidity profiling: combining active and passive remote sensors
Abstract. Thermodynamic profiles in the planetary boundary layer (PBL) are important
observations for a range of atmospheric research and operational needs.
These profiles can be retrieved from passively sensed spectral infrared (IR)
or microwave (MW) radiance observations or can be more directly measured by
active remote sensors such as water vapor differential absorption lidars
(DIALs). This paper explores the synergy of combining ground-based IR, MW,
and DIAL observations using an optimal-estimation retrieval framework,
quantifying the reduction in the uncertainty in the retrieved profiles and
the increase in information content as additional observations are added to
IR-only and MW-only retrievals. This study uses ground-based observations collected during the Perdigao field campaign in central Portugal in 2017 and during the DIAL demonstration
campaign at the Atmospheric Radiation Measurement Southern Great Plains site
in 2017. The results show that the information content in both temperature
and water vapor is higher for the IR instrument relative to the MW
instrument (thereby resulting in smaller uncertainties) and that the
combined IR  +  MW retrieval is very similar to the IR-only retrieval below
1.5 km. However, including the partial profile of water vapor observed by
the DIAL increases the information content in the combined IR  +  DIAL and
MW  +  DIAL water vapor retrievals substantially, with the exact impact
vertically depending on the characteristics of the DIAL instrument itself.
Furthermore, there is a slight increase in the information content in the
retrieved temperature profile using the IR  +  DIAL relative to the IR-only;
this was not observed in the MW  +  DIAL retrieval.