Remote Sensing of Boundary Layer Structure and Height - Wind Energy Meteorology: Atmospheric Physics for Wind Power Generation - page 172

Table B.1 Overview on methods using ground-based remote sensing for the derivation of the
mixed layer height mentioned in this Appendix (see rightmost column for section number in this
Appendix)
Method Short description Section

Acoustic ARE Analysis of acoustic backscatter intensity B.1.1

HWS Analysis of wind speed profiles B.1.2

VWV Analysis of vertical wind variance profiles B.1.3

EARE Analysis of backscatter and vertical wind variance profiles B.1.4

Optical threshold Detection of a given backscatter intensity threshold B.2.1

Gradient Analysis of backscatter intensity profiles B.2.2

Idealised
backscatter

Analysis of backscatter intensity profiles B.2.3

Wavelet Analysis of backscatter intensity profiles B.2.4

Variance Analysis of backscatter intensity profiles B.2.5

Acoust./electro-magn. RASS B.3

SODAR-RASS and windprofiler-RASS B.3.1

/in situ SODAR-RASS plus surface heat flux data B.3.2

Acoust./electro-magn. SODAR plus windprofiler B.4.1

Acoustic/optical SODAR plus ceilometer B.4.2

B.1 Acoustic Detection Methods

Acoustic methods for the determination of MLH either analyze the acoustic
backscatter intensity, or, if Doppler shifts in the backscattered pulses can be
analyzed, features of vertical profiles of the wind components and its variances as
well. The acoustic backscatter intensity is proportional to small-scale fluctuations
in atmospheric temperature (usually generated by turbulence) or by stronger
vertical temperature gradients. The latter feature may be an indication for the
presence of temperature inversions, which can often be found at the top of the
mixed layer (Fig. B.1 ).
Beyrich ( 1997 ) listed possible analyses which can mainly be made from
acoustic backscatter intensities measured by a SODAR. Later, Asimakopoulos
et al. ( 2004 ) summarized three different methods to derive MLH from SODAR
data: (1) the horizontal wind speed method (HWS), (2) the acoustic received echo
method (ARE), and (3) the vertical wind variance method (VWV). We will mainly
follow this classification here and finally add a fourth method, the enhanced ARE
method (EARE), in Sect. B.1.4 .

B.1.1 Acoustic Received Echo Method

The acoustic received echo method (ARE) is the oldest and most basic method of
determining MLH from acoustic remote sensing. Most of the methods listed in