thales geosolutions pacific tgpi 11/2003 precise timing and trueheave® in multibeam acquisition and...

TGPI 11/2003

THALES GEOSOLUTIONS PACIFIC

Precise Timing and TrueHeave® in Multibeam Acquisition and Processing

Doug Lockhart, Thales GeoSolutions (Pacific) Inc

Dushan Arumugam, Thales GeoSolutions (Pacific) Inc

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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

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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

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Precise Timing—Selecting 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

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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.

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System Topology

UTC Serial String

Main Vessel Subnet

SeaBat Subnet

POSMV Subnet

POSMV

SeaBat

ISIS Delphmap WinFrog POSMV Control

XTF File

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XTF Packets were created to hold the new time stamps

XTF_HEADER_POS_RAW_NAVIGATION Field Byte

Offset Status Comment

WORD MagicNumber 0 M Must be set to 0xFACE (hexadecimal value) BYTE HeaderType 2 M 107 =

XTF_HEADER_POS_RAW_NAVIGATION BYTE SubChannelNumber 3 U Unused. Set to 0. Word NumChansToFollow 4 U Unused. Set to 0. Word Reserved1[2] 6 U Unused. Set to 0. DWORD NumBytesThisRecord 10 M Must be 64. (Size of this packet is always 64

bytes) WORD Year 14 M Fix year BYTE Month 16 M Fix month BYTE Day 17 M Fix day BYTE Hour 18 M Fix hour BYTE Minutes 19 M Fix minute BYTE Seconds 20 M Fix Seconds WORD decimal seconds 21 M (0 – 9999) Fix tenths of milliseconds Double RawYcoordinate 23 M Raw position from POSRAW or other time

stamped nav source. Double RawXcoordinate 31 M Raw position from POSRAW or other time

stamped nav source. Double RawAltitude 39 O Altitude, can hold RTK altitude Float pitch 47 O Pitch, degrees, positive bow up Float roll 51 O Roll, degrees, positive port up Float heave 55 O Heave, positive up. Float heading 59 O Heading BYTE Reserved2 63 U Unused. Set to 0

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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

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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

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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

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Roll Timing Error in Caris Subset Mode (simulated data)

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Roll Timing Error in Caris Subset Mode (real data)

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Roll Timing Error Removed

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Multiple Lines with Roll Timing Error

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Multiple Lines with Roll Timing Error Removed

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TrueHeave: What is it?Without interrupting the flow of the real time heave

1.Unfiltered heave data is stored in the POS/MV memory

2.After a few minutes, a zero phase filter is passed over the stored heave data

3.The delayed heave value and real time heave value are output together over the Ethernet

Time 1 Time 2 Delayed Heave Heave Heave Time 1 Heave Time 2410993.9454 11027.9237 0.1604094 0.1506919 410890.1424 10924.12078410993.9854 11027.9637 0.1564011 0.1473659 410890.1824 10924.16077410994.0254 11028.0037 0.1508863 0.1425089 410890.2224 10924.20077410994.0654 11028.0437 0.143916 0.1361792 410890.2624 10924.24077410994.1054 11028.0837 0.1356362 0.128481 410890.3024 10924.28077410994.1454 11028.1237 0.1261356 0.1195327 410890.3424 10924.32077

Output Times Heave values Valid Times

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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.

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Real Time Heave v. TrueHeaveM

eter

s

Seconds

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

200 205 210 215 220 225 230 235 240 245 250

Delayed Heave HeaveTrue Heave Real Time Heave

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Real Time Heave (3x)

TrueHeave (3x)

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Real Time HeaveTrueHeave

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How TrueHeave Affects Run-In Time

Real Time Heave Applied

TrueHeave Applied

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Cook Inlet556 sq km

PortlockBank

850 sq km

Albatross Bank

27 sq km

Castle Bay207 sq km

Semidi Islands

2875 sq km

UNCLOS17160 sq km

PribilofIslands

38 sq km

UNCLOS9194 sq km

Icy Bay305 sq km

Yakutat Bay36 sq km

Glacier Bay425 sq km

Northern Clarence Strait290 sq km

Cape Ommaney280 sq km

Hazy Islands395 sq km

Aleutian Islands2362 sq km

South Yakutat372 sq km

Pamplona Spur162 sq km

Kenai Fjords535 sq km

Chirikof Island1488 sq km

Fairweather219 sq km

Cape Hinchenbrook1830 sq km

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Data Samples: Alaska SurveysCastle Bay

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Sun Illuminated Bathymetry3x Vertical Exaggeration

3m bins, 4m – 50m depths

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Sun Illuminated Bathymetry3x Vertical Exaggeration

3m bins, 4m – 50m depths

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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.

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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

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Acknowledgments:

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

thales geosolutions pacific tgpi 11/2003 precise timing and trueheave® in multibeam acquisition and...

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