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Precise Timing and TrueHeave ® in Multibeam Acquisition and Processing. Doug Lockhart, Thales GeoSolutions (Pacific) Inc Dushan Arumugam, Thales GeoSolutions (Pacific) Inc. Timing overview: Why timing is important Precise timing Selecting an epoch Supported Sub-Systems System topology

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precise timing and trueheave in multibeam acquisition and processing
TGPI 11/2003

Precise Timing and TrueHeave® in Multibeam Acquisition and Processing

Doug Lockhart, Thales GeoSolutions (Pacific) Inc

Dushan Arumugam, Thales GeoSolutions (Pacific) Inc

objective enable precise timing and trueheave
TGPI 11/2003

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

Objective: Enable precise timing and TrueHeave
why is timing important
TGPI 11/2003

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

Why is Timing Important?
precise timing selecting an epoch
TGPI 11/2003

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

Precise Timing—Selecting an Epoch
supported sub systems
TGPI 11/2003

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.

Supported Sub-Systems
precise timing trueheave acquisition
TGPI 11/2003

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

Precise Timing & TrueHeave Acquisition
precise timing trueheave processing
TGPI 11/2003

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

Precise Timing & TrueHeave Processing
modified patch test procedures
TGPI 11/2003

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

Modified Patch Test Procedures
trueheave what is it
TGPI 11/2003

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

TrueHeave: What is it?

Heave values

Output Times

Valid Times

trueheave processing
TGPI 11/2003

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.

TrueHeave Processing
real time heave v trueheave
TGPI 11/2003

Seconds

True Heave Real Time Heave

Real Time Heave v. TrueHeave

Meters

how trueheave affects run in time
TGPI 11/2003

TrueHeave Applied

Real Time Heave Applied

How TrueHeave Affects Run-In Time
slide22
TGPI 11/2003

Cook Inlet

556 sq km

Portlock

Bank

850 sq km

Albatross Bank

27 sq km

Castle Bay

207 sq km

Semidi

Islands

2875 sq km

UNCLOS

17160 sq km

Pribilof

Islands

38 sq km

UNCLOS

9194 sq km

Icy Bay

305 sq km

Yakutat Bay

36 sq km

Glacier

Bay

425 sq km

Northern Clarence Strait

290 sq km

Cape Ommaney

280 sq km

Hazy Islands

395 sq km

Aleutian Islands

2362 sq km

Cape Hinchenbrook

1830 sq km

Chirikof

Island

1488 sq km

Kenai

Fjords

535 sq km

Pamplona

Spur

162 sq km

South

Yakutat

372 sq km

Fairweather

219 sq km

precise timing benefits
TGPI 11/2003

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.

Precise Timing Benefits
trueheave benefits
TGPI 11/2003

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

TrueHeave Benefits
acknowledgments
TGPI 11/2003

NOAA:Our existing large Alaska survey contract allows us to invest internally on R&D 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

Acknowledgments: