Outlook - Surface Based Remote Sensing of the Atmospheric Boundary Layer - page 150

directly. The present state of detecting these heights has been described in Chapter 4 ,
but all the listed methods still have considerable limitations. So efforts are ongoing
to develop reliable monitoring strategies for these heights based on ground-based
remote sensing.
But also nowcasting, the weather forecast for the next hour, and monitoring of
near-surface weather features which have immediate effects on issues such as air
traffic security on airports (wind gusts, downdraughts, cross-winds, fog, snow) lead
to an ongoing development of ground-based remote-sensing techniques. Recently,
first LIDARs for wake vortex detection have been mounted on aircraft. On-board
axial detection of wake vortices is more complex than the classic ground-based
tangential approach, because the axial air speed in these vortices is low and the
atmospheric particle density is reduced, yielding a poorer signal-to-noise ratio
(Douxchamps et al. 2008 ).
Determination of the height of cloud and fog tops is a subject of current research
as well. In the abovementioned COST 720 TUC experiment, this problem has been
addressed, too. While the base layer of clouds is well measured with ceilometers, the
top of the cloud was determined in this experiment using a 78 GHz FMCW radar.
This method for cloud top determination is based on determining the height at which
the radar signal falls below a defined threshold level and is still under development
(Ruffieux et al. 2006 ).
Additionally, new monitoring techniques, which deliver nearly continuous infor-
mation on profiles of atmospheric variables over larger parts of the complete ABL,
in turn trigger the further elaboration of theoretical concepts and analytical and
numerical description of various features of the ABL. Recent updates on techniques
and methods for ground-based remote sensing are presented and discussed on meet-
ings and workshops. Especially devoted to this special subject is the biennial series
of the “International Symposium for the Advancement of Boundary Layer Remote
Sensing (ISARS)” (selected papers from the 2006 and 2008 ISARS can be found in
Meteorologische Zeitschrift (Emeis 2007 ; Mann and Emeis 2009 )). See Appendix
for more details on this conference series. But also other scientific events such
as the triennial series of the “International Symposium on Tropospheric Profiling
(ISTP)” deal with new developments in this field. The full proceedings from the last
conference of this latter series in 2009 are available online.

References

Bingöl F, Larsen GC, Mann J (2007) Wake meandering - An analysis of instantaneous 2d laser
measurements. J Phys Conf Ser 75:012059. doi: 10.1088/1742-6596/75/1/012059
Denmead OT, Raupach MR, Dunin FX, Cleugh HA, Leuning R (1996) Boundary-layer budgets
for regional estimates of scalar fluxes. Global Change Biol 2:255-264
Denmead OT, Leuning R, Griffith DWT, Jamie IM, Esler MB, Harper LA, Freney JR (2000)
Verifying inventory predictions of animal methane emissions with meteorological measure-
ments. Bound-Layer Meteor 96:187-209
Douxchamps D, Lugan S, Verschueren Y, Mutuel L, Macq B, Chihara K (2008) On-board axial
detection of wake vortices using a 2- μ m LiDAR. IEEE Trans Aerospace Electronic Sys

44:1276-1290