Interferometric SounderInterferometric Sounder

Hydrographic Survey LaunchHydrographic Survey Launch

AEH 174 MachaAEH 174 Macha

FS 20FS 20

Hydrographic Survey LaunchHydrographic Survey Launch

AEH 174 MachaAEH 174 Macha

FS 20FS 20

NAVOCEANO2004 July

SummarySummary

• AEH 174 Peruvian Hydrographic LaunchAEH 174 Peruvian Hydrographic Launch

• Interferometric sounderInterferometric sounder

• Projects relatedProjects related

Peruvian Hydrohraphic LaunchAEH 174 “MACHA”

ATLAS FANSWEEP 20

Peruvian Hydrographic Launch

ATLAS FANSWEEP-20

• 100 KHz• Máx. range 600 mts.• Coverage 12 times the vertical depth• 1440 beams per swath• Fore and aft angle 1,3°• Stabilization of roll, pitch, heave• Precision de ± 0,10 cm + 0,2 % of the depth

Depth Range - CoverageDepth Range - Coverage

Depth Range versus Coverage (100 kHz Version)

0 m

100 m

200 m

150 m

50 m

250 m

300 m

0 m

10

0 m

20

0 m

15

0 m

50

m

25

0 m

30

0 m

25

0 m

15

0 m

20

0 m

30

0 m

10

0 m

50

m

Mud Sand Rock

ATLAS FANSWEEP 20

• To establish parallel tracks each To establish parallel tracks each other , arranging of spacing other , arranging of spacing

• OHI (SP-44)OHI (SP-44)

TRACK 1

Z

6Z 6Z

4Z

Multibeam System SpecsMultibeam System Specs

EM 3000EM 3000 vs. Fansweep 20Fansweep 20 Frequency (kHz) 300 200Transducer single dual

or dual 35*35cmConfiguration Flat T FlatSource Level 215 227Power (kW) 0.6 2*1Pulse length (ms) 0.15 0.04Beamwidth (deg) 130*1.5 180*1.2

1.5*30Number of beams 127 20-1440Beam spacing (deg) 0.9Max ping rate (1/s) 25 12 Angular Coverage 130 160Swath Width 4.3xWD 11.3xWDAlong Track BW 1.5 1.2 

EM 3000EM 3000 vs. Fansweep 20Fansweep 20 Frequency (kHz) 300 200Transducer single dual

or dual 35*35cmConfiguration Flat T FlatSource Level 215 227Power (kW) 0.6 2*1Pulse length (ms) 0.15 0.04Beamwidth (deg) 130*1.5 180*1.2

1.5*30Number of beams 127 20-1440Beam spacing (deg) 0.9Max ping rate (1/s) 25 12 Angular Coverage 130 160Swath Width 4.3xWD 11.3xWDAlong Track BW 1.5 1.2 

Cost EstimatesCost Estimates

Hydrographic Launch AEH 174 MACHA with Fansweep 20Hydrographic Launch AEH 174 MACHA with Fansweep 20 Personnel 6 person crew Salary $ 50 $ 1,200 1 Vessel 4 days Leasing ~$2000 $ 8,000Fuel ~400 gallon/day Per Gal $3 $ 4,8001 Fansweep 20 Leasing ~$9000 $36,000

Total: $50,000

Hydrographic Launch AEH 174 MACHA with Fansweep 20Hydrographic Launch AEH 174 MACHA with Fansweep 20 Personnel 6 person crew Salary $ 50 $ 1,200 1 Vessel 4 days Leasing ~$2000 $ 8,000Fuel ~400 gallon/day Per Gal $3 $ 4,8001 Fansweep 20 Leasing ~$9000 $36,000

Total: $50,000

SystemsSystems

• Conventional systems to date use either the principle of Conventional systems to date use either the principle of beamforming, sometimes combined with phase beamforming, sometimes combined with phase measurement, or the interferometric phase measurement, or the interferometric phase measurement principle. The basis for both methods is a measurement principle. The basis for both methods is a signal processing procedure which measures sound signal processing procedure which measures sound travelling times and transmitting or receiving angles travelling times and transmitting or receiving angles relative to a hydroacoustic transducer and determines relative to a hydroacoustic transducer and determines from these the depth and position of a point being from these the depth and position of a point being measured on the bottom, doing so relative to the normal measured on the bottom, doing so relative to the normal to the transducer. Both conventional methods have their to the transducer. Both conventional methods have their special characteristics.special characteristics.

Sample detectedSample detected

Latitud 12° 03.72’Longitud 77° 09.50’

Sunk Boat20 Noviembre 2001

Sampled detectedSampled detected

Latitud 12° 03.72’Longitud 77° 09.50’

Disadvantages of interferometric Disadvantages of interferometric sounder; sounder; • Typically slower along-track ping rate (pings port - listens, then Typically slower along-track ping rate (pings port - listens, then

pings starboard), making it difficult to achieve IHO target detection pings starboard), making it difficult to achieve IHO target detection requirements (by bathymetric means) at normal survey speeds. requirements (by bathymetric means) at normal survey speeds.

• From our experience, interferometric systems do not detect the From our experience, interferometric systems do not detect the seabed as robustly as beam forming systems (i.e. more noise and seabed as robustly as beam forming systems (i.e. more noise and higher standard deviation). higher standard deviation).

• From our experience, interferometric systems are not as good at From our experience, interferometric systems are not as good at detecting structures rising steeply from the seabed (i.e. dock walls, detecting structures rising steeply from the seabed (i.e. dock walls, sand waves, some rocks).  This is due to an apparent inability to sand waves, some rocks).  This is due to an apparent inability to resolve two echoes arriving at the same time from different resolve two echoes arriving at the same time from different directions within the same beam.  Some modern systems claim to directions within the same beam.  Some modern systems claim to get around this. get around this.

• With beamforming systems, it is easier to steer and compensate for With beamforming systems, it is easier to steer and compensate for vessel motion. vessel motion.

Advantages of interferometric Advantages of interferometric sounder:sounder:

• Good pseudo sidescan (usually better that Good pseudo sidescan (usually better that beamforming backscatter) this can assist target beamforming backscatter) this can assist target detection detection

• Good across-track sounding density (but not in Good across-track sounding density (but not in nadir) nadir)

• Wider swath widths (if high along-track ping rate Wider swath widths (if high along-track ping rate not required) not required)

• Typically cheaper than beamforming systems Typically cheaper than beamforming systems

Project - Survey SpecificationsProject - Survey Specifications

Planning Specifications Specifications greater due to several external factors

Water level Heave Water column stability

Planning Specifications Specifications greater due to several external factors

Water level Heave Water column stability

Surveys on Rivers Surveys on Rivers

• Peru has more than 20 rivers Peru has more than 20 rivers able to be navigate, they have able to be navigate, they have an around extension of 16000 an around extension of 16000 Km.Km.

• So far ,more than half of them So far ,more than half of them have been surveyed ,with have been surveyed ,with Single beam echosounder onto Single beam echosounder onto the thalweg channel. the thalweg channel.

• The Peruviam Hydrographic The Peruviam Hydrographic Office has the goal to acquire Office has the goal to acquire a Multibeam Echosounder for a Multibeam Echosounder for Riverine Surveys.Riverine Surveys.

ConcernsConcerns

• The main issue with the Fansweep is the poor ratio between data The main issue with the Fansweep is the poor ratio between data acquisition and data processing.  The processing software acquisition and data processing.  The processing software supplied by Atlas was slow and manually intensive.  There have supplied by Atlas was slow and manually intensive.  There have also been some obstacles due to hardware problems over the also been some obstacles due to hardware problems over the years. Input from Atlas seemed to be required, as the setups years. Input from Atlas seemed to be required, as the setups were not totally transparent.  For example, there were some were not totally transparent.  For example, there were some complex calibration procedures and the help menu is not complex calibration procedures and the help menu is not available.  It is worth remembering however that the DHN available.  It is worth remembering however that the DHN procurement began in 2001, so things may have improved in procurement began in 2001, so things may have improved in recent times.recent times.

• It is also worth remembering that the number of beams in a It is also worth remembering that the number of beams in a beamforming system is not comparable to the number of beamforming system is not comparable to the number of datapoints in an interferometric system (the system is just datapoints in an interferometric system (the system is just resampling), so we should be cautious about the sales pitch resampling), so we should be cautious about the sales pitch "more soundings"."more soundings".

Interferometric SounderInterferometric Sounder

Hydrographic Survey LaunchHydrographic Survey Launch

AEH 174 MachaAEH 174 Macha

FS 20FS 20

Hydrographic Survey LaunchHydrographic Survey Launch

AEH 174 MachaAEH 174 Macha

FS 20FS 20