Geoscience Reference
In-Depth Information
spacing by off-line signal processing. On the other hand, on-line sampling interval in cases
of short pulse transmission must be equivalent or shorter compared with the range
resolution determined by transmitted pulse width. On-line sampling interval in cases of
FMCW transmission also must be equivalent or shorter compared with the range resolution
determined by sweep range of transmitted frequency.
Fig. 6. Time-altitude plots of (a) brightness and (b) vertical wind velocity. Data were
collected using vertically-pointing beam of the MU radar operated with the RIM observation
mode (Fukao et al., 2011). The region within the black rectangular is plotted in panel (b). The
thick black contours in panel (b) show 46 dB brightness level. The figure is reproduced with
permission from the Royal Meteorological Society.
2.3 Further applications
2.3.1 High-resolution measurement using both spaced antennas and multiple
frequencies
By using spaced receivers and multiple frequencies simultaneously, radar resolution is able
to be improved both in angle and range, which leads to realize a three-dimensional (3-D)
imaging. Signal processing procedures of the 3-D imaging are described by Yu & Palmer
(2001). In 2004, the MU radar was upgraded for the 3-D imaging capability with 5
frequencies across a 1 MHz bandwidth and 25 intermediate frequency (IF) digital receivers
(Hassenpflug et al., 2008). Using the 3-D imaging with the Capon method, Hassenpflug et al.
(2008) showed a 3-D structure of radar echoes associated with billows of KH instability.
Chen et al. (2008) applied the 3-D imaging to data collected by the MU radar in order to
investigate relations between the angular distribution of clear-air echo power and tilted
refractive-index layers caused by KH instability. The 3-D imaging technique is also able to
be used for clutter mitigation. Using the MU radar, Yu et al. (2010) showed that the 3-D
imaging provides comparable or better performance of both echo layer reconstruction and
clutter mitigation compared to RIM.
