Basic Principles of Surface-Based Remote Sensing - Surface Based Remote Sensing of the Atmospheric Boundary Layer - page 49

Fig. 3.8 Radio-acoustic sounding system (Sodar-RASS) for profile measurements of wind, turbu-
lence, and temperature. The acoustic sounder (sodar) with its three white antennas is in the middle,
the emitting radio antenna is to the left and the receiving radio antenna is to the right
sufficiently accurate approximation of the virtual air temperature. The maximum
range of a SODAR-RASS is usually less than thousand metres so that such an instru-
ment covers the lower part of the boundary layer. Due the high vertical resolution
and the low minimum range of about 30-40 m, which is comparable to the abilities
of a SODAR, a SODAR-RASS is well suited for the detection of shallow nocturnal
boundary layers.
3.5 LIDAR
A light beam emitted into the atmosphere can interfere with the air in different
ways. Alterations may occur due to elastic scattering (Rayleigh scattering at atoms
and molecules, Mie scattering at aerosols and water droplets (especially at clouds
and rain drops)), inelastic scattering (Raman scattering), fluorescence, absorption,
and Doppler shift. Based on these different interactions, five types of LIDARs
(Light detection and ranging) have been developed to actively and remotely analyse
trace substance concentrations in the atmosphere (Weitkamp 2005 ). As fluorescence
LIDARs do not have any applicability in the boundary layer, four types are of
interest here: