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  • The Spinning Mango Of Death
    Posted by Bill Sweetman 1:09 PM on Feb 04, 2011

    Raytheon has received a low-rate initial production contract for the APY-10 radar that equips Boeing's P-8A Poseidon, the Navy's replacement for the veteran P-3 Orion. (Mike Fabey updates on the P-8A in the latest issue of DTI.)

    In a phone conference on Thursday, Raytheon business development manager Brad Hopper noted that the APY-10 will include a special mode for detecting submarine periscopes.

    This was interesting, since at one time the Navy had said in budget documents that it was going to leave the Automatic Radar Periscope Detection and Discrimination (ARPDD) mode off the P-8A radar, and concentrate on developing that capability for the MH-60R helicopter's Telephonics APS-147 and the mast-mounted Northrop Grumman SPS-74(V) radar for Nimitz-class carriers (logically, since those are the tallest masts in the group).

    ARPDD is the result of a very long development program involving the Navy-oriented Johns Hopkins Applied Physics Laboratory as well as Raytheon (previously Texas Instruments).

    The challenge is to pick out a small, stealth-treated, slow-moving object out of sea clutter - and moreover, one that is transient. Now that periscopes have high-definition TV sensors that equal the acuity of direct optics, the submarine can pop up the mast, make one scan and drop it back into the water. The crew can then review the scene at leisure and zoom in digitally on potential targets.

    How ARPDD is supposed to work is classified, but a 1997 JHL paper provides some clues. The basic technique involves the ability to track thousands of targets, and then sift through those tracks and eliminate those that don’t look or behave like periscopes.

    The goal at the time was no more than one false alarm (that is, a false periscope declaration) per sortie. High range resolution cuts down on clutter within each detection cell, while high scan rates (up to 300 rpm) make it possible to accurately measure very small target movements.

    This requires three characteristics from the radar: very fast processing using unique algorithms; good clutter rejection; and a high scan rate. Interestingly, mechanically scanned radars are better at rejecting ocean clutter than active electronically scanned arrays (AESAs) in the current state of the art, so the APY-10 remains the last hold-out of the airborne M-scan. (It also looks as if the APY-10 has a 180-degree scan angle, which a fixed AESA can't approach.)

    blog post photo

    Another unique feature of the APY-10 is that the antenna is shrouded in a yellow Lexan ball, so that it looks as if the P-8A's nose accommodates a giant mango. The shroud reduces aerodynamic drag as the radar spins in ARPDD mode.

    The APY-10 could be retrofitted to a P-3, Raytheon says, but so far, customers looking to update Orions (Pakistan, Thailand, Taiwan and Norway) have not had the same high-end requirement and have used the lower-cost SeaVue system.

    Tags: ar99, radar, raytheon, p-8a

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