Sea ice clutter was measured using an X-band radar which is located at the city of Mombetsu in Hokkaido. The pulsewidth of the radar was 80 nsec. To sample by 40 nsec and record digitally, an emitter coupled logic (ECL) was used as a high-speed IC. The sampled data were first transferred to 64 Kbyte dynamic memory board and next to a 5 inch floppy disk through an 8 bit micro-computer. These data were processed by a 16 bit micro-computer. As a result, it is shown that the amplitude of sea ice obeys a Weibull disturibution with shape parameters of c0.50 to 1.65. Thus, the amplitude statistics deviate from the well-known Rayleigh distribution of c2.0, in which a logarithmic/constant false alarm rate (LOG/CFAR) circuit is useful. Therefore, it is concluded that the new Weibull/CFAR should be considered to suppress sea ice clutter.

In a radar system, it is well known that the conventional and logarithmic CFAR techniques after a square-law detector are effective for Rayleigh clutter. To apply these CFAR techniques to practical radar systems with a linear detector, the false-alarm probability was calculated by a Monte Carlo simulation on a computer for a finite number of samples N. It is concluded that the conventional CFAR receiver is superior to the logarithmic CFAR receiver.

We have already measured ground clutter using an X-band and L-band radars. Here, ground clutter was first measured using a millimeter wave radar with the frequency of 34.86 GHz, which is located on the campus of the University of Electro-Communications. The pulsewidth of the radar was 30 ns. Thus the spatial resolution was as small as 4.5 m. We have found that the clutter amplitude distribution obeys a Weibull distribution with shape parameter of c0.497 to 0.675 at depression angles of 0.8 to 1.9 deg., when reflectors are ordinary terrain and such structures as landing strips at airport and buildings. To improve target detectability in such Weibull-distributed ground clutter, Weibull constant false alarm rate (CFAR) system will be required.

Ground clutter from irregular surfaces was measured using an L-band long range air-route surveillance radar (ARSR) at very low grazing angles, between 0.13 and 0.25. It is shown that the ground clutter amplitude statistics themselves do not always follow a Weibull distribution, but rather the residual amplitude after the double canceller moving target indicator (MTI) obeys a Weibull distribution. Therefore, the unsuppressed residual ground clutter will be suppressed by means of Weibull CFAR processors.

Weibull-distributed ground, sea, sea-ice and weather clutter were measured in Japan for various radar resolutions and wavebands. Weibull clutter and its suppression techniques are reviewed. Especially, Weibull CFAR in two-dimensional clutter rejection system is emphasized.

Ground clutter from cultivated land was measured using an L-band long range air-route surveillance radar (ARSR) at very low grazing angles, between 0.21 and 0.32. It is shown that the Weibull-distributed ground clutter obeys a Weibull distribution in the frequency domain after processing by the discrete Fourier transform (DFT). Thus the new Weibull-CFAR should be considered to suppress such clutter in the frequency domain.