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    Re: Fatal interaction betweeu yacht and ferry.
    From: Gary LaPook
    Date: 2007 May 07, 15:59 -0700

    Gary wrote:
     George, that was a scintillating observation.
    On May 7, 1:50 pm, "George Huxtable" 
    > The radar reflection from a boat, illuminated by a coherent signal (which
    > radar is), is the sum of all the reflections, that return toward the radar
    > scanner, from all the different bits of the boat, summed up togeter. And
    > when you sum them, you have to take account of the phase shift in each case,
    > from each bit of boat, because the double-distance, from scanner to
    > reflecting surface back to scanner, is different for each bit. The detected
    > returned power, the integral of them all, will depend critically on the
    > boat's geometry and the angle of the boat's attitude to the beam. There's
    > nothing to prevent that returned signal summing up to zero, or near-zero, at
    > a particular attitude, simply because that jumble of returned signals
    > happens to cancel out to zero, a null-reflection, because of those differing
    > phase shifts. Luckily, a small yaw in the boat, or changing direction from
    > the radar antenna, will make it visible again. That's one reason for the
    > complexity of radar image behaviour; the way they tend to "twinkle".
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