Comparison of scanning aerosol lidar and in situ measurements of aerosol physical properties and boundary layer heights

The spatiotemporal distribution of aerosol particles in the atmosphere has a great impact on radiative
transfer, clouds, and air quality. Modern remote sensing methods, as well as airborne in situ measurements by
unpiloted aerial vehicles (UAV) or balloons, are suitable tools to improve our understanding of the role of aerosol
particles in the atmosphere. To validate the measurement capabilities of three relatively new measurement sys-
tems and to bridge the gaps that are often encountered between remote sensing and in situ observation, as well
as to investigate aerosol particles in and above the boundary layer, we conducted two measurement campaigns
and collected a comprehensive dataset employing a scanning aerosol lidar, a balloon-borne radiosonde with the
Compact Optical Backscatter Aerosol Detector (COBALD), an optical particle counter (OPC) on a UAV, and a
comprehensive set of ground-based instruments. The extinction coefficients calculated from near-ground-level
aerosol size distributions measured in situ are well correlated with those retrieved from lidar measurements, with
a slope of 1.037 ± 0.015 and a Pearson correlation coefficient of 0.878, respectively. ... mehrVertical profiles measured
by an OPC-N3 on a UAV show similar vertical particle distributions and boundary layer heights to lidar mea-
surements. However, the sensor, OPC-N3, shows a larger variability in the aerosol backscatter coefficient mea-
surements, with a Pearson correlation coefficient of only 0.241. In contrast, the COBALD data from a balloon
flight are well correlated with lidar-derived backscatter data from the near-ground level up to the stratosphere,
with a slope of 1.063 ± 0.016 and a Pearson correlation coefficient of 0.925, respectively. This consistency be-
tween lidar and COBALD data reflects the good data quality of both methods and proves that lidar can provide
reliable and spatial distributions of aerosol particles with high spatial and temporal resolutions. This study shows
that the scanning lidar has the capability to retrieve backscatter coefficients near the ground level (from 25 to
50 m above ground level) when it conducts horizontal measurement, which is not possible for vertically pointing
lidar. These near-ground-level retrievals compare well with ground-level in situ measurements. In addition, in
situ measurements on the balloon and UAV validated the scanning lidar retrievals within and above the boundary
layer. The scanning aerosol lidar allows us to measure aerosol particle distributions and profiles from the ground
level to the stratosphere with an accuracy equal to or better than in situ measurements and with a similar spatial
resolution.