Applications - Surface Based Remote Sensing of the Atmospheric Boundary Layer - page 137

Acoustic remote sensing is still alive also because it can quite easily be enhanced
to a RASS by adding a pair of electromagnetic antennas to a SODAR. This allows
directly detecting the temperature profile as well. The temperature profiles are valu-
able for the investigation of the static stability of the lower part of the ABL and
can be employed to secure the assessment of the mixing-layer height in case of
ambiguous acoustic information from the SODAR component of the instrument.
Optical remote sensing is presently the most rapidly developing part of the
ground-based remote-sensing technology. The greatest deficiency of this technol-
ogy, which used to be the rather large height of the first range gate, has nowadays
been overcome by enhanced laser technology and electronics. Today, Doppler wind
LIDARs which cover the height range between 20 m and 200 m are available and
are increasingly used for wind energy assessments. The worldwide need for an
enhanced usage of renewable energies has fostered the market for these small wind
LIDARs.
In addition to the variables accessible by acoustic methods including RASS
(wind, turbulence, temperature, mixing-layer height), optical remote sensing is well
suited to observe aerosol, humidity, and other trace gas profiles as well. This has
large relevance for precipitation, air quality, and climate impact studies. The further
emergence of Raman LIDAR technology has made it possible to derive even pro-
files of aerosol properties. Optical and acoustic sensing technologies taken together
now allow for a nearly complete probing of all major properties of the ABL.
Electromagnetic remote sensing with windprofilers has been continued in the
past decades. Such profilers, which cover more or less the whole troposphere includ-
ing the ABL, increasingly substitute the classical radiosonde soundings, because
they can be operated in an automized mode. Like SODARs, many windprofilers
have been complemented by an acoustic component to transfer them into RASS as
well. By this, wind and temperature profiles can be obtained simultaneously.
Passive remote sensing with radiometers offers less vertical resolution due to
the employment of weighting functions. Therefore, these instruments do not have
so much relevance for genuine boundary layer research. They are used more for
obtaining profiles throughout the whole troposphere and even from the stratosphere.
The development of remote sensing technologies in the past decades has led to
a revival of boundary layer meteorology. In addition to the surface layer investiga-
tions by in situ instrumentation, now profiling of the whole depth of the boundary
layer has become possible. This has relevance for basic studies of the dynamics and
thermodynamics of the atmosphere as well as for air quality studies, assessments
of renewable energy potentials, and climate change impact studies. The separated
descriptions of the surface or Prandtl layer and the Ekman layer must now be
combined in a more general description of the whole ABL.
References
Al-Sakka, H, Weill A, Le Gac C, Ney R, Chardenal L, Vinson J-P, Barthels L, Dupont E (2009)
CURIE: a low power X-band, low atmospheric boundary layer Doppler radar. Meteorol Z
18:267-276