AP-MTT Seminar - Monday, Oct. 21, 2013
"High-Resolution Wind-Field Retrieval on an Active-Array Radar"
Presented by Dr. Vijay Venkatesh
US Department of Energy Atmospheric Radiation Measurement (ARM) Climate Research Facility
Date: 1:00 - 2:00 PM Monday, October 21, 2013
Place: MRC Conference Room, ElectroScience Laboratory, 1330 Kinnear Rd, Columbus, OH
Abstract: Over the past several decades, several single Doppler radar wind-field retrieval techniques that rely on the scanning capabilities of weather radars have been developed. These methods must trade angular-resolution to retrieve the wind-field. This work focuses on a possible mechanism for high- resolution wind-field retrieval using an active phased-array radar. Segmenting the array-face into displaced apertures multiplexed in time, we investigate retrievals of mean wind along the aperture separation by correlating received voltages. The basic idea is that laminar scatterer advection along the antenna separation causes the received signal at one sub-array to be a delayed copy of the signal at the other sub-array.
The methodology employed herein comprises of Monte-Carlo simulations and analysis of real data collected with an active phased-array radar system. First, Monte-Carlo based simulations of back- scattered electric fields at the antenna array elements are employed to optimize the array segmentation. This system optimization is accomplished by minimizing the propagated uncertainty from errors due to RMS turbulent velocity and thermal noise. We show that the designed X-band system exhibits nearly an order of magnitude lower retrieval uncertainty than the S-band implementation on the National Weather Radar Testbed (NWRT). This is by virtue of obtaining independent samples more rapidly and a relatively wider beam. Second, RF beamforming errors are evaluated. Based on simulations and measurements, we demonstrate a field-repeatable method to measure relative phase- center displacement using precipitation echo statistics. These results, along with antenna pattern measurements, suggest that highly overlapping apertures are most immune to RF beamforming errors. In large part, this is because element-level phase compensation error residues for highly overlapping apertures are well correlated and do not affect subsequent retrievals. Third, wind-field retrievals using the segmented array face are shown to be in qualitative and quantitative agreement with existing coarser- resolution methods. In conjunction with traditional Doppler measurements, these are the highest angular-resolution single weather radar wind-field retrievals demonstrated to date. Although initial results on a stratiform precipitation dataset are encouraging, it appears possible that the techniques developed are limited to cases with relatively low wind-speeds.
Bio: Dr. Vijay Venkatesh is a Radar Engineer for the US Department of Energy Atmospheric Radiation Measurement (ARM) Climate Research Facility. In this role, he is employed with the Pacific Northwest National Lab (PNNL) to develop procedures/software for long-term calibration of a network of C- to W-band radars for Climate Research. Prior to this, Dr. Venkatesh was with the University of Massachusetts Microwave Remote Sensing Lab (MIRSL).