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    Re: USNS Bowditch - also Slocum!
    From: Lu Abel
    Date: 2016 Dec 18, 01:13 +0000
    The US Navy also has driven the development of very sophisticated inertial navigation sensors.  They are the primary navigation systems for submarines and, as I understand it from a former Navy officer, even surface ships are equipped with them as a backup and alternate to GPS.

    Whether a underwater drone which could be lost or even stolen as in this case would be equipped with the best of our best inertial systems is beyond my pay grade...



    From: Don Seltzer <NoReply_Seltzer@fer3.com>
    To: luabel{at}ymail.com
    Sent: Saturday, December 17, 2016 4:43 PM
    Subject: [NavList] Re: USNS Bowditch - also Slocum!

    Here is an abstract that addresses the question:

    The Slocum Electric Glider is a buoyancy driven Autonomous Underwater Vehicle (AUV) capable of long term deployments typically lasting four to six weeks. During missions execution, the vehicle makes use of the Global Positioning System (GPS) to navigate to its commanded waypoints. GPS, however, can only be used while the vehicle is at the surface. While underwater, the glider uses a simple dead reckoning (DR) algorithm to estimate its location and does not find its true position again until its next periodic surfacing. The Slocum Glider's dead reckoning algorithm estimates its position based on speed and heading calculations; they are derived from measurements from onboard sensors. Specifically, speed is determined by the depth rate change and pitch angle over a period of time. Since there is limited sensory input to the algorithm, the vehicle's estimated global position can differ significantly from its true position. Precise location information is important when collecting spatiotemporal sensitive sensor data and for vehicle navigation. In this paper, we will explore the benefits that can be gained if the dead reckoning algorithm makes use of a Doppler Velocity Log (DVL) to improve a vehicle's location estimates. Initial results based on a deployment equipped with the DVL on a Slocum Glider show promising results.

    Don Seltzer

    On Sat, Dec 17, 2016 at 7:03 PM, Gary LaPook <NoReply_LaPook@fer3.com> wrote:
    The reason I brought this up is because of the name "Bowditch," a name near and dear to us and, I am sure, the ship didn't have that name just by accident. But, now that we are talking about the "Slocum" I am curious how these navigate since I assume that they can't receive GPS signals while deep in the ocean. Anybody here know how this is done?
    gl



       
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