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
This combined approach is applied to the "Golfe du Lion" LSEET-LEPI radar campaign.
- 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).
- 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.
- 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).
- 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.