156 Innovative C-band and X-band FM-CW radars to study boundary layer precipitation

Thursday, 29 September 2011
Grand Ballroom (William Penn Hotel)
Christopher R. Williams, CIRES/Univ. of Colorado, Boulder, CO

Using support from the University of Colorado at Boulder Cooperative Institute for Research in Environmental Sciences (CU / CIRES) Innovative Research Program, two inexpensive vertically pointing precipitation radars were developed to observe precipitation within the lowest 300 meters of the atmosphere. The C-band radar operated in the point-to-point Internet service frequency band (5.8 GHz) and the X-band radar operated in the police radar frequency band (10.5 GHz). The low transmitted power enabled the radar hardware costs for both radar systems to be less than US$ 12 000.

Both radars used the Linear Frequency Modulated Continuous Wave (LFMCW) technique to observe at a 5-m range resolution from near the surface to over 300 m. The Doppler processing at each range gate was achieved using two Fourier transforms (FFTs). The range-FFT converted the sweep voltages into discrete frequencies that corresponded to discrete ranges. The real and imaginary components of each complex frequency were re-labeled as the in-phase and quadrature voltages (I and Q). Then, at each range a Doppler-FFT converted the I and Q voltages from consecutive sweeps into Doppler velocity power spectra.

Another innovation of this project was that the parallel processing of the Cell Broadband Engine installed in a Sony Playstaion 3 was used to perform all FFT calculations as well as other radar signal processing (e.g., coherent integration and incoherent integration). Observations from a rain event identified precipitation variability at 1-s and 5-m resolution. For example, during a 20 second dwell, the reflectivity varied by over 10 dBZ indicating non-uniform precipitation during this dwell.

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