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Figure186:Temperaturebehaviour(topfigure)andtemperaturecrosssection(bottomfigure)
during the all field experiment (18 November 2002 to 15 December 2002)
shown in Fig. 185, multi channel method without scanning had a low vertical resolution at
the lowest part of the ABL (about 300 m).
Thesecondmethod(ourdiscussedcasestudy) isbasedonusinganangular-scanningsinglechannel
radiometer with the central frequency of 60 GHz. This method and the instrument
were proposed by Troitsky et al. (1993) and discussed in detail by Kadygrov and Pick (1998)
and Westwater et al. (1999).
Due to the large atmospheric absorption by molecular oxygen at 60 GHz, angular-scanning
method has some advantages for ABL temperature profiling over the multi channel method
(Kadygrov et al., 2004a), which can be summarized as follows:
• it can really to operate in all weather conditions: the measurements do not depends on
changes of water vapor density or on the presence of fog or low clouds
• better vertical resolution in the lower 300 m
• the bandwidth of the receiver is very wide which provides a high sensitivityof the receiver
(about 0.04 K at 1 s integration time);
• instrument has a small sizes, is very portable, can provide reliable automated continuous
profiling from a variety of sites and relatively small cost
However single-channel angular-scanning method, how we have seen, has its limitations in
altitude measurement. It can measures only from the ground level up to 1000 m.
Notation
Aν fraction of incident energy absorbed from a direction
Bν(T) brightness
c vacuum speed of light
dIν variation of specific intensity
ds elementary segment in the direction of propagation
dΩ solid angle element
h Planck’s constant
altitude
Hb boundary-layer height
Iν specific intensity
k Boltzmann’s constant
MPM microwave propagation model
RTE radiative transfer equation
274 DTU Wind Energy-E-Report-0029(EN)