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Automatic interference cleaning exercises on Wera FMCW radar signals


Yves Barbin, Pierre Broche, Jean-Charles de Maistre, Philippe Forget et Joël Gaggelli

CNRS & University du Sud Toulon Var, LSEET-LEPI, BP20132, F-83957 LA GARDE, France


The most interesting frequencies for long range HF Surface Wave Radar (low attenuation) are also propagated by strong ionospheric reflexions and are, then, very suitable for very long range communications, international broadcasting programs and over-the-horizon radio detection systems. As a result, strong interferring signals are observed within the frequency band used by the HF surface wave radars and are the main cause for performance limitations in range and time coverage.

This paper, related to the one presented by K.-W. Gurgel, presents a four steps approach to reduce the impact of Radio Frequency Interference (RFI):

  1. Precampaign local survey leading to the selection of a frequency band B0. B0 should be several times much larger (few hundred kHz) than the required effective radar band B1(typically 50 kHz).
  2. Before each measurement cycle (i.e. every half hour), preacquisition scanning of B0 (~2 minutes) and immediate selection of the "best" effective radar sub band B1 within B0.
  3. Off line responses rejection. An acquisition is multipulse or multichirp based (typically 2048 or 4096 chirps with Wera).  Interferences might not last over the total measurement cycle. With combined interferences detection and a statistical threshold criteria, some of the "worst" responses (chirp responses) can be rejected without much current map distortion (lacunary time sampling).
  4. Off line signal "cleaning" inside the elementary Chirp responses. Narrow bandwidth interferences within a chirp response can be modelled and detected. Although linear subtracting method is too difficult to achieve, partial signal substitution within the chirp response achieves good and robust results.
This combined approach is applied to the "Golfe du Lion" LSEET-LEPI radar campaign.
Local Contact: (Klaus-Werner Gurgel)