Transcript Multibeam Backscatter

TGPI 11/2003
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
POSMV
WinFrog
POSMV Control
ISIS
Delphmap
SeaBat
XTF File
POSMV Subnet
SeaBat Subnet
Main Vessel Subnet
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XTF Packets were created to hold the new
time stamps
X T F _ H E A D E R _ P O S _ R A W
_ N A V IG A T IO N
F ie ld
B y te
S ta tu s
C o m
m
e n t
0
M
M u s t b e
2
M
1 0 7
O ffs e t
W
O R D
B Y T E
M a g ic N u m
b e r
H e a d e r T y p e
s e t to
0 x F A C E
( h e x a d e c im
X T F _ H E A D E R _ P O S _ R A W
B Y T E
S u b C h a n n e lN u m
W
o r d
N u m
W
o r d
R e s e r v e d 1 [2 ]
D W
O R D
b e r
C h a n s T o F o llo w
N u m
B y t e s T h is R e c o r d
a l v a lu e )
=
3
U
U n u s e d . S e t to
0 .
4
U
U n u s e d . S e t to
0 .
6
U
U n u s e d . S e t to
0 .
1 0
M
M u s t
b e
6 4 .
( S iz e
o f
t h is
_ N A V IG A T IO N
p a c k e t
is
a lw a y s
6 4
b y te s )
W
Y e a r
1 4
M
F ix
y e a r
B Y T E
M o n th
1 6
M
F ix
m
B Y T E
D a y
1 7
M
F ix
d a y
B Y T E
H o u r
1 8
M
F ix
h o u r
B Y T E
M in u t e s
1 9
M
F ix
m
B Y T E
S e c o n d s
2 0
M
F ix
S e c o n d s
d e c im
2 1
M
( 0
2 3
M
W
O R D
O R D
D o u b le
a l s e c o n d s
R a w Y c o o r d in a t e
–
R a w
s ta m
R a w
o n th
in u t e
9 9 9 9 )
F ix
p o s it io n
p e d
n a v
t e n t h s
fr o m
o f
P O S R A W
o r
o th e r
t im
e
P O S R A W
o r
o th e r
t im
e
R a w X c o o r d in a t e
3 1
M
D o u b le
R a w A lt it u d e
3 9
O
A lt it u d e , c a n
F lo a t p it c h
4 7
O
P it c h , d e g r e e s , p o s it iv e
F lo a t r o ll
5 1
O
R o ll, d e g r e e s , p o s it iv e
F lo a t h e a v e
5 5
O
H e a v e , p o s it iv e
F lo a t h e a d in g
5 9
O
H e a d in g
B Y T E
6 3
U
U n u s e d . S e t to
R e s e r v e d 2
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p o s it io n
p e d
n a v
illis e c o n d s
s o u r c e .
D o u b le
s ta m
m
fr o m
s o u r c e .
h o ld
R T K
u p .
0
a lt it u d e
b o w
u p
p o r t u p
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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
410993.9454
410993.9854
410994.0254
410994.0654
410994.1054
410994.1454
Time 2
Delayed Heave
11027.9237
0.1604094
11027.9637
0.1564011
11028.0037
0.1508863
11028.0437
0.143916
11028.0837
0.1356362
11028.1237
0.1261356
Output Times
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Heave
Heave Time 1 Heave Time 2
0.1506919
410890.1424 10924.12078
0.1473659
410890.1824 10924.16077
0.1425089
410890.2224 10924.20077
0.1361792
410890.2624 10924.24077
0.128481
410890.3024 10924.28077
0.1195327
410890.3424 10924.32077
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. TrueHeave
0.4
0.3
0.2
0.1
0
200
205
210
215
220
225
230
-0.1
-0.2
Seconds
-0.3
-0.4
True Heave Delayed Heave
Real TimeHeave
Heave
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235
240
245
250
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Real Time Heave (3x)
TrueHeave (3x)
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Real Time Heave
TrueHeave
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How TrueHeave Affects Run-In Time
TrueHeave Applied
Real Time Heave
Applied
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Cook Inlet
556 sq km
Icy Bay
Portlock
Bank
305 sq km
Yakutat Bay
850 sq km
36 sq km
Albatross Bank
Glacier
Bay
27 sq km
Castle Bay
425 sq km
207 sq km
Northern
Clarence
Strait
Semidi
Islands
2875 sq km
290 sq km
UNCLOS
Cape
Ommaney
17160 sq km
Pribilof
Islands
280 sq km
Hazy
Islands
38 sq km
UNCLOS
395 sq km
9194 sq km
Aleutian Islands
2362 sq km
Chirikof
Island
Kenai
Fjords
Cape
Hinchenbrook
Pamplona
Spur
South
Yakutat
1488 sq km
535 sq km
1830 sq km
162 sq km
372 sq km
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Fairweather
219 sq km
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Data Samples: Alaska Surveys
Castle Bay
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Sun Illuminated Bathymetry
3x Vertical Exaggeration
3m bins, 4m – 50m depths
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Sun Illuminated Bathymetry
3x 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
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