Applications - Surface Based Remote Sensing of the Atmospheric Boundary Layer - page 106

the temperature dependence of the intensity of the rotational Raman lines. Several
ground-based Raman LIDAR systems exist today (Vaughan et al. 1993 , Nedeljkovic
et al. 1993 , Behrendt and Reichardt 2000 ). Figure 4.19 shows an example obtained
by the scanning rotational Raman LIDAR of the University of Hohenheim, a mobile
system which is mounted on a truck (Radlach et al. 2008 ). The LIDAR data were
acquired with a spatial resolution of 30 m and a temporal resolution of 60 s. The low-
est range gate is about 600 m above ground. The scanning feature of the instrument
allows for height cross sections of the temperature field.
A Raman LIDAR needs to be calibrated to obtain absolute temperature data.
This is, e.g. done by comparison of the ratio of two rotational Raman signals with
temperature profiles measured with radiosondes that are close in time and space to
the LIDAR measurement. For 1 min integration time, an accuracy of the noontime
temperature of better than 1 K can be achieved for ranges of less than 1 km (Radlach
et al. 2008 ).
4.3.2.3 Passive Remote Sensing with Radiometers
This and the next subchapter demonstrate that passive remote-sensing techniques
are suited for temperature profiling as well, if the terrain possesses sufficient hor-
izontal homogeneity and some drawbacks in vertical resolution can be accepted.
Temperature profiles (see Fig. 4.20 for an example) from scanning microwave
radiometers at 5-mm wavelengths (60 GHz) gave excellent comparisons with in situ
temperature measurements during winter conditions at the Boulder Atmospheric
Observatory 300-m tower; several days of data were obtained during a snow storm,
with no degradation of the quality of the data. A limited number of comparisons with
a 915-MHz RASS above tower levels, showed the ability of the radiometer to derive
temperature profiles to about 500 m height above ground with an accuracy of about
1 ◦ C (Westwater et al. 1999 ). The maximum range of these microwave radiometers
is 600 m. The vertical resolution decreases drastically with height, being 7.5 m at 10
m, 65 m at 100 m, and 300 m at 400 m. Therefore, this passive radiometric technique
is applicable only for the lower parts of the atmospheric boundary layer.
Fig. 4.20 Temperature
profile from radiometer
sonding (ATTEX, bullets )
compared to tower ( open
squares )andRASS( full line )
data. From Westwater et al.
( 1999 )