Geoscience Reference
In-Depth Information
Fig. 2. Brightness distributions within ±4° from the center of beam direction at the altitudes
from 1.4 km to 9.8 km (Palmer et al., 1998). Red color corresponds to highest brightness.
Images on the left and right of each pair were obtained with the Fourier-based method and
the Capon method, respectively.
2.1.2 Measurement results
An example of high-angle-resolution measurement using CRI is presented. Fig. 2 shows
brightness distributions within ±4° from the center of beam direction measured by the Middle
and Upper Atmosphere radar (MU radar). MU radar is a MST radar installed at Shigaraki MU
Observatory, Japan (34.85°N, 136.10°E; Fukao et al., 1990). CRI successfully produces fine-scale
angular distributions of backscattered clear-air echo power within the two-way half-power full
beam width of 2.5°. Such high angular resolution cannot be attained without CRI. It is noted
that the Capon method exhibits better resolution than the Fourier-based method. Using data
collected by a VHF radar installed at Tourris, France (43.08°N, 6.01°E), Hélal et al. (2001)
showed a fine-scale angular distribution of backscattered clear-air echo power using the
Capon and MUSIC methods. Chau and Woodman (2001) also showed the angular distribution
using the Fourier-based method, Capon method, MEM, and the fitting technique. Using the
characteristic that raindrop fall velocity is much greater than vertical wind velocity, Palmer et
al (2005) demonstrated that fine-scale angular distributions of backscattered power from clear
air and that from raindrops are able to be obtained separately. From a CRI measurement by
TEP, Pollard et al. (2000) demonstrated that horizontal distribution of refractive index
structure function is able to be measured.
