Multistatic Radar Observation of a Fine-Scale Wind Field with a Coupling-Compensated Adaptive Array Technique

Abstract

As part of the Coupling Processes in the Equatorial Atmosphere (CPEA-II) Campaign, multistatic radar observations of local wind field were conducted using the Equatorial Atmosphere Radar and two auxiliary receiver arrays in West Sumatra, Indonesia, in December 2005. For obtaining velocity estimates from atmospheric echoes received by the two small arrays that have a high sidelobe level due to their small e¤ective aperture, an adaptive clutter rejection process is required. Because of the existence of electromagnetic coupling between antennas and the ground, the relative phase, in terms of an echo received by separate antennas, cannot be accurately predicted only with given positions of antennas and the target volume. The phase error leads to degradation of desired atmospheric echoes in the output of the adaptive clutter rejection process. In order to compensate for the mutual coupling e¤ect, we proposed a method to estimate the phase error corresponding to several directions in which atmospheric echoes were observed with particularly high signal-to-noise ratio (SNR). The estimates were interpolated at every necessary directional point using linear fit, thereby resulting in a successful removal of ground clutters without a serious loss of SNR. With this method, we have obtained a partial data set of the wind field. The wind field in the lower troposphere shows small-scale fluctuations on a horizontal scale of @500 m. We also present an attempt to interpret the fluctuation in a composite of multiple plane waves, employing a nonorthogonal decomposition method using a generalized inverse.

New Observations by Wind Profiling Radars

“…From a CRI measurement by TEP, Pollard et al (2000) demonstrated that horizontal distribution of refractive index structure function is able to be measured. (Nishimura et al, 2010). Colors show the backscattered power in an arbitrary unit.…”

“…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).…”

“…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.…”