Remote Sensing of Boundary Layer Structure and Height - Wind Energy Meteorology: Atmospheric Physics for Wind Power Generation - page 182

optical backscatter intensity (but not the optical backscatter intensity itself) is used
to determine H4. This discrepancy in the processing of the two backscatter
intensities is due to the different scattering processes for acoustic and optical
waves: Acoustic waves are scattered at atmospheric refractivity gradients and thus
at temperature gradients (Neff and Coulter 1986 ) while optical waves are scattered
at small particles. Therefore the optical backscatter intensity is proportional to the
aerosol concentration itself. The MLH on the other hand, which we desire to derive
from these backscatter intensities, is in both cases found at heights where we have
vertical gradients of the temperature and of the aerosol concentration. Therefore,
in principle, the vertical distribution of the acoustic backscatter intensity should
look very much alike to the negative of the vertical distribution of the vertical
gradient of the optical backscatter intensity.
Simultaneous measurements with different remote sensing devices have mainly
been made in order to evaluate one remote sensing method against the other
(Devara et al. 1995 ). But one could also think of combining the results two or more
remote sensing devices for determining the structure of the ABL. Direct detection
of MLH from acoustic backscatter intensities is limited to the order of about 1 km
due to the rather high attenuation of sound waves in the atmosphere. In contrast,
optical remote sensing offers much larger height ranges of at least several
kilometres, because the attenuation of light waves in the atmosphere is small
unless there is fog, clouds or heavy precipitation.
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