Geoscience Reference
In-Depth Information
Fig. 3. Altitude profile of Doppler spectra (a) before and (b) after applying clutter mitigation
algorithm (Nishimura et al., 2010). Colors show the backscattered power in an arbitrary unit.
CRI is also able to be used for clutter mitigation. Fig. 3 is an example of clutter mitigation.
Measurement data were collected by the receiving antenna array of the Equatorial
Atmosphere Radar (EAR), which were temporally installed for multistatic radar
observations. The EAR is installed at West Sumatra, Indonesia and is operated with a center
frequency of 47-MHz and peak output power of 100 kW (Fukao et al., 2003). Strong returns
centered at 0 m s -1 in Fig. 3a are signals returned from the ground (i.e., ground clutter), and
have to be removed in order to estimate spectral moments correctly. By applying the clutter
mitigation algorithm developed by Nishimura et al (2010), the clutter signals are
successfully removed (Fig. 3b). Nishimura et al. (2010) attained the clutter mitigation by
combining the directional-constrained minimization of power with constrained norm
(DCMP-CN; see Kamio et al. (2004) for details) and an algorithm that compensates
electromagnetic coupling between antennas and the ground. The compensation was carried
out because the electromagnetic coupling can cause a phase error of atmospheric echoes
received by antenna arrays, and the phase error can lead to degradation of desired
atmospheric echoes in the output of the adaptive clutter mitigation process.
In the case shown by Nishimura et al. (2010), each antenna element has an identical antenna
gain. When a high-gain antenna is used for transmission and reception of scattering from
atmospheric targets, using auxiliary antennas which are used only for receiving ground
clutters is effective for clutter mitigation. In order to realize clutter mitigation using the main
antenna of the MU radar and auxiliary antennas, Kamio et al. (2004) modified the DCMP-
CN method. In the modified method, the weight of main antenna is kept to 1 in order to
keep the main lobe pattern, and the weights of auxiliary antennas are optimized in order to
minimize the received power from side lobes.
Moving biological targets like birds and insects can cause a large error of wind velocity
measured by wind profiling radars (e.g., Vaughn, 1985; Wilczak et al., 1995). Using CRI,
moving clutter is able to be suppressed. From the CRI measurement using TEP, Cheong et
al. (2006) succeeded in separating clear-air echoes and the biological scattering which was
moving in the grating-lobe region, and demonstrated that the separation of biological
scattering greatly reduced the error of wind velocity estimates. Chen et al. (2007) also
applied CRI to data measured by multiple antenna profiler radar (MAPR) of National
Search WWH ::




Custom Search