Remote Sensing of Boundary Layer Structure and Height - Wind Energy Meteorology: Atmospheric Physics for Wind Power Generation - page 173

Fig. B.2 Principal sketch of the EARE method for determining the mixed layer height from
vertical profiles of the acoustic backscatter intensity (bold line) and the variance of the vertical
velocity component (sigma w in m/s, dotted line). Left lifted inversion, right stable nocturnal
layer with very low mixed layer height
Beyrich ( 1997 ) belong to this method. The method does not require a Doppler shift
analysis of the backscattered signals but is based on the analysis of facsimile plots,
i.e., time-height cross-sections of the backscatter intensity. The method makes use
of the assumption that turbulence is larger in the mixed layer than in the
atmosphere above, and that this turbulence is depicted in enhanced intensity of the
acoustic backscatter. MLH is analyzed either from the maximum negative slope or
from the changing curvature of the vertical profile of the acoustic backscatter
intensity or it is analyzed from the height where the backscatter intensity decreases
below a certain pre-specified threshold value.
B.1.2 Horizontal Wind Speed Method
The horizontal wind speed method (HWS) requires a Doppler shift analysis of the
backscattered acoustic signals. The algorithm is based on the analysis of the shape
of hourly-averaged vertical wind speed profiles using the assumption that wind
speed and wind direction are almost constant within the mixed layer but approach
gradually towards the geostrophic values above the mixed layer. Beyrich ( 1997 )
listed this method in his Table 2 but did not discuss it further. The applicability of
the method is probably limited to well-developed convective boundary layers
(CBL) due to the underlying assumptions. Such CBL are often higher than the