Applications - Surface Based Remote Sensing of the Atmospheric Boundary Layer - page 82

Fig. 4.4 Schematic of the determination of MLH from optical sounding. Full black curve : opti-
cal backscatter intensity B in dB, dashed line : vertical derivative of B , asterisks : vertical second
derivative of B , dots : vertical derivative of the logarithm of B . Horizontal bars indicate mixing
layer heights from eqs. ( 4.5 )to( 4.7 ). From: Emeis et al. ( 2008 )

is done over 15 min and a height interval Δ h of 80m. In the layer between 500 and

2000 m, h for vertical averaging is extended to 160 m. Two additional parame-

ters 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 200 10 − 9 m − 1 sr − 1 10 − 9 m − 1 sr − 1

× in the lower layer and 250 × in the upper

layer. Additionally, the vertical gradient value ∂ B /∂ z max of a lifted inversion must

10 − 9 m − 2 sr − 1 in the lower layer and more negative be more negative than − 0.30 ×

10 − 9 m − 2 sr − 1 in the upper layer.
If B ( z ) denotes the measured attenuated backscatter intensity in the height z above
ground averaged over time and height and

than − 0.60 ×

Δ

h is the height averaging interval, then

∂ /∂

the gradient B z in the height z is calculated as

z =

B ( z

)

∂ B

∂

+

h
2

−

h
2

) − B ( z / h , (4.8)

z

A gradient minimum is characterized by a change of sign from minus to plus
of the second derivative of B ( z ). The height interval under examination is searched
from bottom to top for these gradient minima H 4 _n .