TOWFISH DRIVER

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TOWFISH DRIVER
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Towfish

• The towfish is used to localized à towed sensor
  without USBL posit, sidescan sonar,
  magnetometer..
• The towfish driver allows an accuracy estimated
  position of the mobile by merging different
  information and filtering navigation of the boat.
• In a hardware configuration several mobile could
  be create, a Towfish driver could be associate to
  each mobile.
• If two mobiles are created, the sidescan sonar
  mobile should be the first in the configuration,
  the shared memory root the first mobile position
  to the Sidescan survey program.

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Towfish Merge Information
Horizontal distance
Layback Calculated
A-Frame Offset
Z Offset
Depth
Cable out x Catenary factor
Depth Boat
Altitude
Towfish driver setting Sidescan Survey
Information Survey Information Towfish
Driver Calculation
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Towfish Filter and smooth Boat navigation

• In real time the driver makes a calculation of
  the mobile position by applying filter and
  latency on the boat heading.
• The estimated calculation of the mobile is close
  the reality.

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Setting up a Towfish Driver

• In Hardware, add the driver to position your main
  vessel
• GPS.DLL in this example.
• Create a 2 mobile for your towfish position.
• Named Sidescan in this example.
• Select a driver to position the towfish.
• Towfish.DLL
• Select Sidescan Survey in System (check Include
  box for Sidescan Survey)

Note If you are towing a sidescan, you need to create the mobile in Hardware before selecting the sidescan option
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Configuration Sample

• Configuration with a sidescan sonar and
  Magnetometer.

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Connection Block Diagram With SS
Your computer
HYPACK SURVEY
SIDE SCAN SURVEY
POSITION, HEADING MEMORY SHARED Sensor
Altitude Depth value
Mobile position
Hypack Mobile
GPS
Side Scan Sonar
Pulley

• Towfish driver calculated in Real Time the
  position of the mobile.
• Information is passed between the two modules
  using the shared memory.

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Set up

• Cable out input source
• Layback Method calculation
• Number of segment
• Pulleys Offset in Boat referential.
• Record method if connection with the pulley is
  lost

• Catenary factor value ie
• K0.9 pour 100m cable out the cable out value
  calculated is 90m.
• Depth Source if advanced formula is used for
  calculation.
• If Depth Source Fish Depth use to select the
  Depth value
• -Shallow fish fish at the surface
• -Deep fish deep under the boat
• -Depth Sensor/Altitude Sensor coming from the
  selected channel

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Set up

• DO NOT USE GENERIC OFFSET.

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Layback method calculation HYPACK
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Layback method calculation T. Backer
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Layback method calculation SHOM
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Layback method calculation SHOM

• Basic Method
• Do not apply Pythagoras Calculation only the
  multiplication of the catenary factor and the
  cable out.
• The result will be the Layback.

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Layback method calculation SHOM

• Classic Method.
• Pythagoras with values coming from.
• Hardware
• Catenary factor,
• Z pulley.
• Survey
• Cable Out.
• Sidescan Survey
• Sensor immersion
• Boat Depth Altitude or Depth sensor

• For a good calculation
• Zero pressure sensor should be done on
  subsurface.
• Zero Pulley should be done at the pulley.
• If (Iz)²gt(k.L) then an alarm is displayed in
  real time.

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Layback method calculation SHOM

• Specific Method is equivalent to Classic Method.
• This method is more adapted
• when the pulley Z offset is important.
• When the surveyor want to do the zero pulley at
  the surface.

• For a good calculation
• Zero pressure sensor should be done on
  subsurface.
• Zero Pulley should be done on subsurface.
• If (Iz)²gt(k.L) then an alarm is displayed in
  real time.

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Layback method calculation SHOM

• If (Iz)²gt(k.L) then an alarm is displayed in
  real time.

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Cable out input Method

• Several counting pulley could provide
  automatically the cable out information via a
  serial connection or shared memory.

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The towfishs immersion for Sidescan.

• Two possibilities
• Depth sensor on fish, then select Sidescan
  interface and Depth Sensor.
• There is no Depth Sensor on the sidescan then the
  immersion is approximate calculation.
• SS DepthBoat Depth- SS Altitude

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The towfishs immersion for other sensor

• Some towed sensor as Magnetometer could provide
  depth information.
• Depth Source
• Enable Mobile Depth
• Fish Depth
• Enable Depth Sensor
• Fish Depth Channel
• Select the input Channel

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Towfish Survey Window

• Display Tab
• Display all the different information

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Towfish Survey Window

• Cable Out and altitude graph

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Towfish Survey Window

• Visual Graph

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Towfish Survey Window

• Variables Display

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Cable out Manual Input

• In Manual Mode, cable out could be set by
• Using arrow
• Input in the dialog box
• The Cable out Adjustment
• If a counting pulley is using the cable could
  slide on the sheave, if cable mark has been done
  then surveyor could adjust the cable out value.

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How improve the estimated position

• 1-mark you cable (10m,15m,20m..) to control the
  information delivered by the pulley.
• 2-when you put back the fish on boat check the
  coherence of the zero pulley you did when you put
  the towfisn in the water.
• 3-If it is a long survey it could interesting
  during the day to do again the zero pulley.
• These actions will improve the estimated
  position of the fish, note that a transvers
  current could decrease the position.

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Calculated the Catenary Factor for SS

• 1-Do the same line in the two ways on a
  remarquable obstruction.
• 2-In Hyscan make a target on these obstructions
  for each line
• 3-Measure the distance between the two targets
  divide per 2 or the average of the distance
  between the obstruction and the target,
• It is the Error E

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Calculated the Catenary Factor for SS

• 4-In Hyscan load the two lines and activate
  spredsheet
• 5-Clic on the obstruction the spreadsheet will
  display the value

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Calculated the Catenary Factor for SS

• 6- Take the information in the spreadsheet.
• Layback Logged is the calculation did by towfish
  driver
• Cable out (L)
• Depth sensor immersion (I)
• Pulley Offset (Z) from Hardware
• 7- Calculate the correct K factor.

The K factor depends of the survey speed and the
cable out value. For the same system the k value
could be different for 20 m cable out and 150m
cable out.