Navigation of Remote Undersea Vehicles - Stanford...

Navigation of Remote Undersea Vehicles

Mark A. Zumberge Scripps Institution of Oceanography

November 2011 Stanford PNT Symposium

Outline


!! Requirements for undersea position and time measurements

!! ROVs and AUVs

!! Ocean acoustics

!! Short and long baseline acoustic navigation

!! Seafloor geodesy for crustal deformation

!! Time measurement in acoustics and seismology

Requirements for undersea positioning and time

!! Seismic velocity is between 3 and 5 km/s, and acoustic velocity is 1.5 km/s

!! Positions of seismometers and acoustic receivers are generally controllable to around 1 meter

!! Cameras won't see things much further away than 10 m

!! 0.1 to 1 ms in time and 0.1 to 1 m in position are desirable goals


Remotely Operated Vehicles

!! Tethered to the ship all the time

!! Umbilical provides power and video link

!! Consumes tens to hundreds of kilowatts of power for propulsion, lights, cameras, hydraulic manipulator arms

!! Remain within a few km of a ship


November 2011 Stanford PNT Symposium source: International Marine Contractors Association

Autonomous Under Vehicles

!! Autonomous: means not tethered to a ship

!! Run on batteries, so low power required

!! May travel for many tens of hours a speeds of a few knots

!! Used for !! high resolution bathymetric mapping

!! cable and pipeline route surveys

!! archaeological surveys


Ocean acoustics


travel time (s)

z (m

)Philippine Sea T1 !> T2

254 254.5 255 255.5 256 256.5 257 257.5

0

1000

2000

3000

4000

5000

6000

pow

er (d

B)

!35

!30

!25

!20

!15

!10

!5

0


Short baseline acoustic navigation

!! Short baseline acoustic navigation

!! A transducer array of order 0.5 m diameter is mounted on the hull of a vessel

!! It emits an acoustic signal that is received and retransmitted by a vehicle mounted transponder

!! The range to the transponder is determined by the acoustic travel time and the angles are determined by the array phase response


Hull mounted array


Source: Kongsberg diameter = 40 cm

November 2011 Stanford PNT Symposium Stanford PNT Symposium

Multiple GPS receivers and attitude sensors on the vessel provide reference frame information. Transducer array determines angles of signal arrivals w.r.t. the vessel. Large effort needed to survey transducer location w.r.t. to GPS receivers on vessel


Results of multiple position determineations with UISBL system in 1200 m water depth Rule of thumb for USBL navigation: precision is typically 0.2% of water depth (source: IMCA) New technologies: - spread spectrum - coded signals - pressure/depth info - sound speed profile

Long baseline acoustic navigation

!! Acoustic transponder array deployed on seafloor over several km area

!! Vehicle emits a signal which is returned by all the transponders in the net

!! Times of individual replies recorded

!! Position determined by trilateration


!! More effective in deep water (distance to ship irrelevant)

!! Can be deployed and remain in place for many years

!! Can cover large region


Merged inertial and acoustic navigation for AUV positioning



If the DVL continuously tracks the seafloor, the real-time navigation deviation is 0.05% of the total distance traveled. Research is ongoing to use maps of Earth's gravity field to help correct drift in inertial navigation

Geodesy for crustal deformation

!! For geophysical studies of tectonics, higher precision positioning is needed

- 1 cm in both height and lateral position


GPS-Acoustic positioning Precise kinematic GPS positioning Optical survey of phase center offsets

Acoustic range ship to PXP

H(GPS) = A + B

H(PXP) = C+(D + !)

Shipboard hydrophone is common spatial point observed both by GPS from shore and acoustic triangulation from seafloor transponders

Initial global position of seafloor array.

Shipboard configuration

Hydrophone inside instrument well

Contraction at the Nazca – South America plate

Height measurements with ambient seawater pressure


The uniformity of seawater density and the high precision available with quartz pressure gauges allows relative height measurements to 10 ppm, or 1 cm in 1 km

Axial Volcano

Oblique view of the seafloor around Axial Volcano (white area near the center). In this computer generated image blue areas are deep and white are shallow.

Height change vs time


1998 2000 2002 2004 2006 2008193.0

193.5

194.0

194.5AX01 (Magnesia)8.8 cm/yr

1998 2000 2002 2004 2006 2008

187.0

187.5

188.0

188.5AX04 (Bag City)4.8 cm/yr

1998 2000 2002 2004 2006 2008197.5

198.0

198.5

199.0 AX05 (Marker 33)6.2 cm/yr

1998 2000 2002 2004 2006 2008

185.5

186.0

186.5AX63 (Caldera center)12.7 cm/yr

Year

Heigh

t (m)

relat

ive to

AX6

6 MPR data (old)

linear fitexponential fit

MPR data (new)

Time measurement in acoustics and seismology

0 100 200 300 400 500!0.05

0

0.05

0.1

0.15clock mooring: dvla0

cloc

k er

ror (

s)

0 100 200 300 400 50010!5

10!4

10!3

10!2er

ror u

ncer

tain

ty (s

)

0 100 200 300 400 5000

2

4

6

2004 yearday

resi

dual

s (s

tand

ard

erro

r)

STAR Qu ! GPSSTAR Qu!RbDU Rb ! GPSDU!STAR Rb


Chip scale atomic clocks


0 0.5 1 1.5 2 2.5 3 3.5x 10!5

!1

!0.5

0

0.5

1

1.5 x 10!9 CSAC: median(f) ! 10Mhz = 0.000588(Hz)

days

! f /

f 0

100 101 102 103 104 10510!12

10!11

10!10

10!9

" (#

)

seconds

Questions?


Summary:

Routine position precision from acoustic navigation:

around 1 m

Geodetic quality of seafloor positioning:

around 1 cm

Global "Acoustic GPS" is under discussion

Navigation of Remote Undersea Vehicles - Stanford...

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