A Broad-Band Noise Technique for Fast-Scanning Radar Observations of Clouds and Clutter Targets

This paper describes a relatively simple technique for suppressing interference fluctuations from precipitation and other cluttertype targets. The technique utilizes noise as a transmitted signal and receives the returns in a simple radiometer-type receiver. For noise of bandwidth B and an averaging time equal to transmitted pulselength T, the root-mean-square (rms) fluctuation in the return from a given volume in range is a fraction, ≃√/√BT of the mean return, down from a fractional value of unity for unaveraged single-frequency returns. Using this technique, a fast-scanning radar has been constructed which scans the hemisphere overhead every 20 s with a 2.2° beam. For this system, B = 30-40 MHz and T = 1 μs, and the error in the reflectivity estimate per transmitted pulse is ≃1-dB rms. Observations of precipitation returns using 300-MHz bandwidth noise are compared to simultaneous single-frequency observations to demonstrate the clutter reducing ability of the noise technique. For 300-MHz bandwidth noise transmissions and an averaging time of 1 μs, interference fluctuations are reduced by 25 dB from the single-frequency case, and the mean reflected signal is determined to within 0.3-dB rms in a single transmitted pulse.