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Precise Timing and TrueHeave in Multibeam Acquisition and Processing

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Castle Bay. 207 sq km. Semidi. Islands. 2875 sq km. UNCLOS. 17160 ... Castle Bay. TGPI 11/2003. THALES GEOSOLUTIONS PACIFIC. 24 /28. Sun Illuminated Bathymetry ... – PowerPoint PPT presentation

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Title: Precise Timing and TrueHeave in Multibeam Acquisition and Processing


1
Precise Timing and TrueHeave in Multibeam
Acquisition and Processing
  • Doug Lockhart, Thales GeoSolutions (Pacific) Inc
  • Dushan Arumugam, Thales GeoSolutions (Pacific) Inc

2
Objective Enable precise timing and TrueHeave
  • Timing overview Why timing is important
  • Precise timing
  • Selecting an epoch
  • Supported Sub-Systems
  • System topology
  • Modified patch test procedures
  • TrueHeave acquisition and processing
  • Timing and TrueHeave economic benefits

3
Why is Timing Important?
  • Multibeam Bathymetry is created from a number of
    data elements
  • Sounder ranges and angles
  • Position
  • Pitch, Roll, Heave
  • Heading
  • Data elements are merged using time as a common
    index
  • Timing errors and variable latencies will result
    in a miss match or irregular merge of the data
    elements
  • The bad merge will produce a sounding calculation
    that is both horizontally and vertically
    inaccurate

4
Precise TimingSelecting an Epoch
  • Time stamp data when it is created, not when it
    is logged.
  • Select a standard epoch.
  • PC millisecond timers define their own epoch and
    are not standard
  • Use a single clock/epoch to time stamp all data.
  • Position, attitude, and heading are time stamped
    in the POSMV on the UTC epoch
  • TrueHeave data can be time stamped by the POSMV
    on the UTC or GPS time

5
Supported Sub-Systems
  • Precise Timing and TrueHeave have been
    implemented on the following systems by TGPI
  • Reson SeaBat
  • Applanix POS/MV
  • TritonElics ISIS (XTF)
  • Caris HIPS
  • Other implementations are possible.

6
System Topology
7
XTF Packets were created to hold the new time
stamps
8
Precise Timing TrueHeave Acquisition
  • Logged in XTF by TEI ISIS
  • Position, Heading and Attitude data time stamped
    in POS/MV on UTC epoch
  • Bathy data Time Stamped in SeaBat using POSMV UTC
    serial string
  • Logged by POS/MV Controller
  • TrueHeave data time stamped within the POS/MV on
    UTC epoch
  • TrueHeave data is logged throughout the survey
    day, independent of line changes

9
Precise Timing TrueHeave Processing
  • XTF files are converted into HDCS format by Caris
  • Options in the XTF converter let the user
    selected the XTF packets containing the new timing

10
Modified Patch Test Procedures
  • Acquisition
  • Line pairs for Pitch, Roll and Yaw are required
  • Pitch, Roll and Yaw lines are processed as usual
  • Navigation Latency lines are not required
  • Navigation latency can be determined from any
    single line
  • Processing
  • Pitch, Roll and Yaw are processed as usual
  • Navigation latency is determined by examining
    roll timing error
  • Roll timing error is negated and applied to the
    ping time, accounting for all navigation and
    attitude latencies

11
Roll Timing Error in Caris Subset Mode
(simulated data)
12
Roll Timing Error in Caris Subset Mode (real data)
13
Roll Timing Error Removed
14
Multiple Lines with Roll Timing Error
15
Multiple Lines with Roll Timing Error Removed
16
TrueHeave What is it?
  • Without interrupting the flow of the real time
    heave
  • Unfiltered heave data is stored in the POS/MV
    memory
  • After a few minutes, a zero phase filter is
    passed over the stored heave data
  • The delayed heave value and real time heave value
    are output together over the Ethernet

Heave values
Output Times
Valid Times
17
TrueHeave Processing
  • Caris allows the user to browse and select raw
    POS/MV files containing TrueHeave data.
  • The heave record in the HDCS format can be
    replaced with the TrueHeave or real time heave
    record.

18
Real Time Heave v. TrueHeave
Meters
19
Real Time Heave (3x)
TrueHeave (3x)
20
Real Time HeaveTrueHeave
21
How TrueHeave Affects Run-In Time
22
(No Transcript)
23
Data Samples Alaska SurveysCastle Bay
24
Sun Illuminated Bathymetry3x Vertical
Exaggeration3m bins, 4m 50m depths
25
Sun Illuminated Bathymetry3x Vertical
Exaggeration3m bins, 4m 50m depths
26
Precise Timing Benefits
  • Reducing timing errors results in more room in
    the error budget for other errors such as Tides
    SVP
  • Mechanically induced artifacts are easier to
    diagnose when timing errors are small
  • Increased operational weather window. No survey
    time was lost due to excessive vessel motion in
    Alaska this summer.

27
TrueHeave Benefits
  • Reduced heave component in error budget,
    particularly during long period swell
  • Shorter turn times, line changes, and easier
    shoreline surveys
  • Realized savings from a single survey
  • Prince William Sound
  • Estimate turn times for real time heave filter -
    10 min
  • Actual turn time - 4-5 min
  • Lines - 1293
  • Total turn time - 107.75 hrs (at 5 min) 4.5
    days
  • Time saved on turns 4.5 days

28
Acknowledgments
  • NOAA Our existing large Alaska survey contract
    allows us to invest internally on RD efforts
    like this that ultimately benefit our operations,
    NOAA and the hydrographic community.
  • Applanix Rob Corcoran implemented TrueHeave in
    the POS/MV and provided valuable technical
    assistance
  • TritonElics Inc Caris Software providers made
    quick updates to their software to support the
    new timing and TrueHeave
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