© j.e. hughes clarke, omg/unb swath sonar training 2008swath sonar training 2009 femme 2009 -...

© J.E. Hughes Clarke, OMG/UNB

Swath Sonar Training 2008Swath Sonar Training 2009 FEMME 2009 - Lisbon

Assessing target detection capability using single and dual

swath sonars with high definition beam forming

John E. Hughes Clarke(1)

David Fabre(1) , Rebecca Martinolich(1) and Melvin Broadus(2) Peter Milner and Ernest Sargent(3)

(1) Ocean Mapping Group, University of New Brunswick (2) US Naval Oceanographic Office , MS, USA

(3) Canadian Hydrographic Service – Pacific, Sidney, BC



USNS Bowditch and SumnerEM710 - 0.5°x1.0° - dual swath - 37m depth 0.5, 1.0 and 2.0m cubesEM122 - 1.0°x1.0° - dual swath - 4980m 40m high, 300wide knolls

CCGS VectorEM710 - 0.5°x1.0° - dual swath - 40m depth 1 and 2m boulders.

40m

60°

Most demandinginterpretation of

IHO target detection:

Special and 12.5% and 5%

Cube equivalents

across +/-60+° sectorat survey speed

8-10 knots

The requirement: 2.5%Z cube equivalents



Principal Controls on Topographic Resolution:

1 - Sampling Density

2 – Bottom Detection Method



Comparison of sounding density as a function of angular sector

12 knots, 20m of water, 1° beam spacing

+/-45° sector +/-60° sector +/-75° sector



100 knots (for clarity)

1 Transmit sector

3 Transmit sectors

8 Transmit sectors

How to Implement Dual Swath



(+/-70°) at 10 knotsdual swathe at 5 Hz (10Hz effective)

1 Transmit

sector

3 Transmit sectors

8 Transmit sectors



EM7100.5°x1.0°dual swath

WaterColumnImaging

USNS Bowditchtarget detection

trials2.0m,1.0 mand 0.5m

Steel mesh cubes32-37m of water



2mcube

1mcube

0.5mcube

EM710 0.5°x1.0° dual swath Water Column ImagingUSNS Bowditch, June 2008 - Target detection trials

Released with the permission of U.S. Naval Oceanographic Office



T01

1

2

T02

3

T03

4

T04

5

T05

6

T06

“Duel” Swath – 6 Ping Cycle

81kHz

97kHz 89kHz

73kHz

73kHz81kHz

EM710Very Shallow Mode

0.3ms pulse(~3.3kHz bandwidth)

0°

+30°

+60°

-30°

-60°



2.0mcube

EM710 0.5°tx x 1.0°rcDual-swath +/-60° - 6 knots

7m

30m

USNS Bowditch – July 2008 - Saipan trialsReleased with the permission of NavOceano

SUN ILLUMINATED DTM (0.25m resolution

25m x25m view)

BACKSCATTERMOSAIC

(-10 to -35 dB)ALONG TRACKACROSS TRACKWATERCOLUMN

ANIMATION (10m x 10m view)

50°

30°

0°



1.0mcube

EM710 0.5°tx x 1.0°rcDual-swath +/-60° - 6 knots

7m

30m

USNS Bowditch – July 2008 - Saipan trialsReleased with the permission of NavOceano

SUN ILLUMINATED DTM (0.25m resolution

25m x25m view)

BACKSCATTERMOSAIC

(-10 to -35 dB)ALONG TRACKACROSS TRACKWATERCOLUMN

ANIMATION (10m x 10m view)

50°

30°

0°



Savary Island – Glacial Erratic Boulder FieldsIntertidal to at least 90m.

UsingNaturally-Occuring

Boulders asTest Targets

60m

60m

50m



Naturally-occurring boulders rarely have an aspect ratio approaching 1

to 1



1m boulder – 40m – 10 knotsEM710 0.5°x1.0° - dual swath CCGS VECTOR April 2009

10° 0° 40° 45°60°

WATERCOLUMNANIMATION

(10m x 10m view)

SUN ILLUM.DTM (0.25m res.25m x25m view)

ACROSS TRACKvert. lines = 1mhoriz.bar = 1m

ALONG TRACKvert. lines = 1mhoriz.bar = 1m


Swath Sonar Training 2008Swath Sonar Training 2009 FEMME 2009 - Lisbon20° 35° 45° 50°60°

2m boulder – 40m – 10 knotsEM710 0.5°x1.0° - dual swath CCGS VECTOR April 2009

WATERCOLUMNANIMATION

(10m x 10m view)

SUN ILLUM.DTM (0.25m res.25m x25m view)

ACROSS TRACKvert. lines = 1mhoriz.bar = 1m

ALONG TRACKvert. lines = 1mhoriz.bar = 1m



The “footprint” depends on beam width and depth

ACROSS

ALO

NG

Does HDBF have any real benefit?

EQUI-ANGULAR

Independent Beam Footprints

EQUI-DISTANT

Just picking beam centre

Partially Independent Beam Footprints

+ High Definition Beam Forming

Non Independent Beam Footprints

tm tn

Across track resolutionBased on time-sampling



? Centre ?Amplitude Detection:A: Peak based on running averageB: Centre of Mass based on window about A

Estimated Noise Level

AB

Phase Detection:C: intersection based on linear or quadratic regression through window from B D: IF low residual for C, reduce window by 10% and repeatE: IF low residual for D ….F: If low residual for E. ….…until < 5 samples or high residual

FE D

C

? Centre ?

B2A2



What is “High Definition Beamforming” ?

If the S/N is sufficient to use a small subset of the phase slope, can choose multiple points on the curve (0, -/4, /4, /2, 3/4 etc..)

ONLY possible if no layover within beam

footprint



Comparing Field Trial ResultsWith a Numerical Model

•Specify targets to resolve•amplitude•wavelength•backscatter angular response

•of region•of target

1 - Field Trials:•Solutions + Water Column

2 - Modelling:•Know sonar configuration:

•Beam widths/spacing•Source Level w,r,t. Noise•Pulse Length•Pulse Repetition rate•Bottom Detection Methodology



10 knots - 40m+/-65°

Shot cycle – 5Hz1m per cycle

(10 Hz – dual swath0.5 m per cycle)

5 shots

RESON 71251.0°tx. – 0.5°Rc.

single swath

EM7100.5°tx. – 1.0 Rc.

dual swath

EM7101.0°tx. – 1.0 Rc.

dual swath

EM7101.0°tx. – 2.0 Rc.

dual swath

EM7102.0°tx. – 2.0 Rc.

single swath

1.0m fore-aft

2.8m across track

~1.0° spacing1.0m fore-aft

1.4m across track

~0.5° spacing 2.0m fore-aft

2.8m across track

~1.0° spacing

0.5m fore-aft

1.4m across track

~0.5° spacing1.0m fore-aft

0.7m across track

~0.5° spacing

SONAR MODEL GEOMETRIES



Propagating Annulus Time Slices

Tx. Rc. Product+ seabed BS AR Differential Phase

Zero PhasePhase Wrap

Phase Wrap



TARGET GEOMETRY

1m and 2m Pseudo-Boulders

at 40m depth

5 swaths50cm spacing along track

0.5° beam spacing

2m radius

1m height

1m radius

1m height

10°45°

60°



Peak Detection WMT Detection

Full Beam Phase Detection Within Beam Phase Sweep

1x1x1 m “boulder”40m – 10° incidence0.5°x1.0° - dual swath

+/-65° - 10 knots.






+/-65° - 10 knots.



The equivalent of a 1m cube at 40m (2.5% of depth) at 5000m is a 125m "cubic" object.

In ~4870m of water lie two knolls:

knoll A - "gaussian" shape, ~400m wide at base - ~50m high knoll B - "gaussian" shape, ~300m wide at base - ~35m high

Deep Water (~5000m) Target Detection

EM122 1° x1°8km6km

4km2km

125m

5m contours



0000m0°

2000m22°

4000m39°

6000m50°

8000m58°

EM122 - 5000m – 8 knots.



0000m0°

2000m22°

4000m39°

0000m0°

EM122 - 5000m – 8 knots.

+/- 45° +/- 25°



Summary A

2.5% cubes are achievable

– BUT requires:

A - High and Even Sounding Density:

•at 10 knots, requires – dual-swath •No point in dual swath if no multiple sectors.

•No point if not multi-sector pitch and yaw stabilized.

Barely 3 strikeson a 1m3



Summary BB - Bottom Detection:

•As across-track dimension larger than required resolution, rely heavily on HDBF.

– only useful at lower grazing angles (no layover)

•Where target aspect ratio is too high, will track common slant range (peak or WMT detect) over sector significantly wider than physical beam width.

- O.5° Rc (7125 – superior).

Within Beam Phase Sweep

Peak Detection



Now that we actually “detect” 2.5% cubes...

The next challenge is to resolve their shape

Q’s ?

© j.e. hughes clarke, omg/unb swath sonar training 2008swath sonar training 2009 femme 2009 -...

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