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Fig. B.3 Comparison of
three different methods [see
Eqs. ( B.1 )-( B.3 )] determin-
ing the mixed layer height
from optical backscatter
intensity [from Emeis et al.
( 2008 )]
Münkel ( 2007 ), and Schäfer et al. ( 2004 , 2005 ) applied the gradient method to
ceilometer data. Menut et al. ( 1999 ) took the minimum of the second derivative of
B(z) as the indication for MLH:
2 B ð z Þ oz 2
H4 IPM ¼ min
ð B : 2 Þ
o
This method is called inflection point method (IPM). It usually gives slightly
lower values for H4 than the gradient method ( B.2 ). A further approach was
suggested by Senff et al. ( 1996 ). They looked for the largest negative gradient in
the logarithm of the backscatter intensity (height of logarithmic gradient minimum
H4 LGM ):
H4 LGM ¼ min o ln B ð z Þ= oz
ð
Þ
ð B : 3 Þ
This approach usually gives the largest value for H4. According to Sicard et al.
( 2006 ) H4 IPM from ( B.2 ) is closest to the MLH derived from radiosonde ascents
via the Richardson method. The other two algorithms ( B.1 ) and ( B.3 ) give slightly
higher values. The vertical profiles shown in Fig. B.3 (taken from Emeis et al.
2008 ) give a comparison of the determination of mixed layer heights from Eqs
( B.1 )to( B.3 ).
In Emeis et al. ( 2007a ) the gradient method ( B.1 ) has been further refined and
extended to enable the calculation of up to n = 5 lifted inversions. Prior to the
determination of gradient minima the overlap and range corrected attenuated
backscatter profiles have to be averaged over time and height to suppress noise
generated artefacts. Therefore the H4 values are determined in a two-step
procedure. Between 140 and 500 m height sliding averaging is done over 15 min
and a height interval Dh of 80 m. In the layer between 500 and 2,000 m Dh for
vertical averaging is extended to 160 m. Two additional parameters have been
introduced to further reduce the number of false hits. The minimum accepted
attenuated backscatter intensity B min right below a lifted inversion is set to
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