Post on 30-Apr-2020
Navigation of Remote Undersea Vehicles
Mark A. Zumberge Scripps Institution of Oceanography
November 2011 Stanford PNT Symposium
Outline
November 2011 Stanford PNT Symposium
!! 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
November 2011 Stanford PNT Symposium
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
November 2011 Stanford PNT Symposium
November 2011 Stanford PNT Symposium
November 2011 Stanford PNT Symposium
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
November 2011 Stanford PNT Symposium
November 2011 Stanford PNT Symposium
November 2011 Stanford PNT Symposium
November 2011 Stanford PNT Symposium
November 2011 Stanford PNT Symposium
Ocean acoustics
November 2011 Stanford PNT Symposium
November 2011 Stanford PNT Symposium
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
November 2011 Stanford PNT Symposium
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
November 2011 Stanford PNT Symposium
Hull mounted array
November 2011 Stanford PNT Symposium
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
November 2011 Stanford PNT Symposium
November 2011 Stanford PNT Symposium
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
November 2011 Stanford PNT Symposium
November 2011 Stanford PNT Symposium
!! More effective in deep water (distance to ship irrelevant)
!! Can be deployed and remain in place for many years
!! Can cover large region
November 2011 Stanford PNT Symposium
Merged inertial and acoustic navigation for AUV positioning
November 2011 Stanford PNT Symposium
November 2011 Stanford PNT Symposium
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
November 2011 Stanford PNT Symposium
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
November 2011 Stanford PNT Symposium
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.
November 2011 Stanford PNT Symposium
November 2011 Stanford PNT Symposium
Height change vs time
November 2011 Stanford PNT Symposium
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
November 2011 Stanford PNT Symposium
Chip scale atomic clocks
November 2011 Stanford PNT Symposium
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?
November 2011 Stanford PNT Symposium
Summary:
Routine position precision from acoustic navigation:
around 1 m
Geodetic quality of seafloor positioning:
around 1 cm
Global "Acoustic GPS" is under discussion