Publishers version - DTU Orbit

This method gives a good accuracy (about 0.5 K for accuracy of brightness temperature
measurement better than 0.1 K) but sometimes results are not stable.
A more stable solution, having approximately the same accuracy, is given by a second
method, which uses a variation of linear statistical retrieval (Turchin, 1967; Westwater et al.,
1998). To implement this algorithm, it was constructed a covariance matrix which describes
the brightness temperature differences at equally spaced zenith angles ranging from 0 to
90 ◦ with the in situ temperature. After having performed an eigenvector analysis on this
covariance matrix a stable solution of the inverse problem is achieved. Other more modern
frequently used method in radiometry include neural network inversion and Kalman filtering.
A complete work on the most part of possible inversion methods is given in Janssen (1993).
14.5 An angular scanning temperature profile radiometer
A commercial example of an angular scanning temperature profiler radiometer is shown in
Fig. 181 and was produced by the Russian scientific company ATTEX in cooperation with
the Dutch company Kipp & Zonen: a polar regions version of the radiometer was realized
in 2001 with improved vertical resolution and was called MTP-5P (P stands for polar). The
MTP-5P has a microwave radiometer with the center frequency at about 60 GHz which
measures the radio brightness temperature of the atmosphere with a high sensitivity (0.04 K
at 1 s of integration time) at different discrete elevation angles. On the base of this discrete
measurement, it is always possible to retrieve the discrete atmospheric temperature profile
from the ground level around 5 m until to 600m(instrument’s intrinsic superiorlimit) with an
accuracy 0.5 K at a vertical resolution at lowerquotas of 10–20 m. The MTP-5P’s electronics
and parabolic antenna – beam aperture width of 0.5degrees – are housed into a thermostatic
trailer (see Figure 182) whose temperature is controlled to within 5 K: over a year’s time, the
internal radiometer’s receiver temperature should vary by less than 1 K.
Figure 181: Meteorological temperature profiler (polar version) MTP- 5P
Internal calibration of the instrument is achieved by sequentially switching between the antenna
and a reference blackbody’s radiation source (as a current controlled resistive dummy).
The complete radiometer’s technical specifications are reported in Table 20.
The brightness temperature data Tb(θ) for an angular scanning, MTP-5 radiometer has the
previousintegral form ofEq. (347)where atmosphericmolecularoxygenabsorptioncoefficient
in weighted function W ν0 (z,θ) was calculated from Rosenkranz (1992) and upper limit of
integration is H = 1 km. The statistical a priori database used for the setting up of the
inversion process was a 2-year dataset of radiosonde’s temperature profiles data from Russian
upperairstationnetwork.Innormaloperationtemperature profilesT(z)are typicallyprovided
every 3 min.
Calibration factors require infrequent updating, perhaps once a year. External calibration
DTU Wind Energy-E-Report-0029(EN) 269