Geoscience Reference
In-Depth Information
Recent development in radar interferometry techniques provides means for enhancing radar
resolution and improving data quality. In radar interferometry, spaced receiver antennas are
used to improve angular resolution, and multiple carrier frequencies are used to improve
range resolution. The former is referred to as coherent radar imaging (CRI) or spatial
domain interferometric imaging (SDI; Palmer et al., 1998; Hassenpflug et al., 2008), and the
latter is referred to as range imaging (RIM; Palmer et al., 1999) or frequency-domain
interferometric imaging (FII; Luce et al., 2001). Hereafter the abbreviations CRI and RIM are
used. Though development of the radar interferometry technique have decades of history
(Hocking, 2011), CRI and RIM, which have been intensively developed for the last decade,
are presented in section 2.
Wind profiling radars operated at approximately 50 MHz frequency (50-MHz wind
profiling radars) are not sensitive for small-sized cloud particles. Therefore 50-MHz wind
profiling radars are able to measure vertical and horizontal wind velocities in both the
clear air and cloudy regions. Millimeter-wave radars, which use near 35-GHz or 95-GHz
frequency (i.e., 8-mm or 3-mm wavelength) and hence are able to detect echoes scattered
by small-sized cloud particles, are an indispensable means to measure microphysical
properties of clouds (Kollias et al., 2007). Laser radars (lidars), which transmit laser light
and receive echoes scattered by atmospheric molecules, aerosols, and hydrometeors, are
useful to measure not only various physical quantities in the clear air but also particles
and hydrometeors in the atmosphere (Wandinger, 2005). Recent measurements using
collocated wind profiling radars and millimeter-wave radars/lidars have gained new
insights of turbulence and cloud processes. The measurement results are presented in
section 3.
Fig. 1. Conceptual drawing of CRI. The blue-colored volume on the right shows the resolution
without CRI (i.e., the angular resolution is determined by the antenna beam width), and the
red-colored volumes show the angular resolution improvement attained by CRI.
2. Imaging techniques to enhance radar resolutions
Though development of the radar interferometry techniques have decades of history,
CRI and RIM, which have been intensively developed for the last decade, are presented
