multi beam calibration

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Multi-beam Calibration Quick Guide

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To ensure maximum reliability and accuracy from the system, the system and externallyconnected sensors should be calibrated before the start of a new survey or within six months ofthe last calibration.

The built in SIS utility is used to process data from a calibration survey, usually consisting of oneor more sets of overlapping lines as described below.The data should be processed by the depth utility, and a depth profile displayed with data fromonly a narrow corridor you define. This allows a comparison of the data collected on any twolines. Offsets may be found entering corrections into the system and reprocessing the lines toobserve the effect of the correction.

Determining a suitable location

On a flat area, only roll error will cause significant depth errors. Thus if the survey is to be run ina reasonably flat area, it may be sufficient to perform roll calibration only.Usually however a full calibration is required.

The ideal calibration area is partly flat and partly a fairly steep slope with little change in depthacross track, and with a distinct feature such as a peak (wreck) or hollow in the flat area.

In summary roll requires a flat area with all other calibrations conducted over a slope, peak /hollow (preferably a wreck) location. Calibration should be conducted in fine seas whereverpossible.

Finding a location

Open the Multi-beam calibration file from -S:\Surveying_DVD_APR_2012\Surveying_CD_New\GIS Information\MBES_CalSites_Wrecksor scale off a position from relevant chart.

Load the DXF into the V5 Online system and log multi-beam data over the location. Once therehas been confirmation that the wreck position is correct, a more accurate position can bederived from SIS or Caris to generate the lines.

Zoom into the relevant wreckthat you wish to use.This can now be exported as aDXF & opened in V5.


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Create Calibration lines

Open Line plan utilities > Computations > Compute wreck grid

Enter position of wreck

Orientation (Wx dependent)

Compute sonar lines andoffset (dependent on waterdepth) > this will be used torun the alignment lines

Once the lines are generated, they maystill require further orientation andextending (Lines are only 200m long atthis time)


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Rotate lines

Line plan utilities >

Extend lines

Computations > Lines > Rotate

Select all lines >

Rotate around the target position asrequired

Computations > Lines > Cut >

Extend/Crop


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SV Dip

Prior to commencing the first line, a new sound velocity profile will be required > Stop the shipclose to the location and conduct a full down and up cast SV Dip.Normally an XBT would not suffice, although if there is a time constraint, check with CR, PC,Office etc.

Once the profile is loaded into the SIS PC (Along with V5 generated absorbent coefficient files),append the SV profile PDF to the final report

Select all lines >

Extend SOL

Select all lines >

Extend EOL


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Offsets

Take a note of the previous calibration values.

Locations screen grab

Angular offsets screen grab

Run a BIST and save as .

Screen shot can beappended into the finalreport

Full patch test:Set to zero

Verification:Leave previous results


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Line running

Line running order should be conducted in the following sequence if possible

Roll (Flat seabed)Pitch (Sloped area)Time delay (Wreck)Heading (Offset from wreck)

Generally the lines that have been made will suffice, although additional lines may be required.

Roll :Same line run in opposite directions run at samespeed (eg: 6 Knots) over a flat seabed.

Pitch :Same line run in opposite directionsat same speed (eg: 6 Knots) over a sloped area.

Time delay :Same line run in same direction at different

speeds (eg: 6 & 10 Knots), over a feature

Horizontal Alignment (Yaw) :Two lines offset from feature run at same

speeds (Eg: 6Knots), with feature visible inouter beams

Slope

Flat seabed

Positions of interest to create corridor:See below


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Calibration SIS settings

If possible, conduct the patch test/verification using the same settings in the SIS runtimeparameters menu as the next project. Similar (Or deeper) depths to the next project would also bebeneficial.

Table below shows depth ranges and maximum swathe width.Check with system specifications for maximum angles.

Running lines

Load lines into V5, start running calibration lines >If time permits, follow the next steps once each of the calibration sections have been completed.If there are time constraints, run all lines then follow the next steps >

SIS Calibration

SIS:

Select > Calibration from drop down menu


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SIS screen will then display the calibration view

The lines that are required to be checked will need selecting in the SIS display

Select the (C) Calibrationbutton to enable selectionof lines and calibrationcorridor

SIS display will automatically zoom tothe lines that have been logged withinthe survey

* If more than one survey in thesystem, select from the right hand dropdown menu

Select to stop the screenfollowing the vessel


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Press control and right mouse click on the main display >

Control left mouse click to select the lines

Press control and right mouse click on the main display >

To draw the corridor > Control and left mouse click at the start and the end points of the corridor.

Display will show the corridor of the selected lines

Screen will appear >

Select ship tracks

Lines will highlight yellow >

Now a corridor needs to becreated to view correctionsrequired

Screen will appear >

Select Create corridor


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Example: Roll (Flat seabed across track)

Yellow lines = Selected lines

Slice displayed incalibration depth view

Verification: Installation values willbe read from the raw data files

Patch test: Figures will be zero,awaiting a correction to be applied

Insert correction value >Apply >

Check depth view for best adjustment

Store

Calibration corridor


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Corridors

Corridors are to be generated in certain areas of the line, see below

Roll

One line run twice (in opposite directions) at the same speed, over a flat area

Pitch

Same two lines can be used (If they cover a sloped area)

Calibration:Select both linesCreate corridorperpendicular across thetrack

Calibration:Select both linesCreate corridor along thetrack over the slope


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Time Delay

Same line run twice (In the same direction) at different speeds over a feature

Horizontal Alignment (Yaw)

Two lines offset from contact (Contact in outer-beams) run in the same direction at the samespeed

Calibration:Select both linesCreate corridor along thetrack over the contact

Centre line

Calibration:Select both linesCreate corridor along thetrack over the contact


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Set corrections

Open installation parameters in SIS & select > Sensor setup > Angular offsets

Verify the corrections that have been applied and select OK to activate the new settings intothe system

On completion of the corrections being set,ensure that store is selected


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Verification lines

Caris

Load lines into Caris and apply predicted tides. Check for any spurious data

Settings applied to the SIS will need to be verified >

From the original lines generated, run the mainline again (bothdirections) and a perpendicular line (both directions) as aminimum. Time permitting; it would be viable to orientate someadditional lines with a 45 offset and run at variable speeds.

Verification lines:

= Minimum

= If time permits

Original lines


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Run another BIST, append to the report for reference.Ensure that all screen grabs, relevant information are appended to the calibration report. Reportis to be saved into the ships reference folder (& digitally) and sent to the office for verification.

* Note: These are not Gardline generated notes, theyve been written as a guide only. Anyqueries etc, seek advice from the office

Happy cals shippers, JB

Calibration in Caris

Notes below have been taken from UKHOEM systems can be calibrated using the Caris software package rather/as well as the SIScalibration utility.

1. Introduction

This document is designed to provide some basic guidance in the use of the calibration tool ofCaris HIPS. The tool does have more functionality than is covered here. The Caris HIPS V6.0manual provides a good explanation of the calibration tool in chapter 21 and should be referredto as required.

A multibeam calibration consists of a check on the possible errors in the multibeam systemprimarily for; Latency, Pitch, Roll and Yaw. The method of using the calibration tool is similarfor each of these checks. It is assumed that the reader has an understanding of the requirementsof a multibeam calibration.


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2. Calibration Tool: Latency

Import the lines for the patch test into Caris HIPS in the usual way and apply tides if you havethem, if not using the zerotide file will do, and merge the data.

1. Select the two lines used for latency/timing calibration in the project window of HIPS.2. Select: Tools/Calibration from the main menus, which brings up the screen shown below:

3. Starting with window 1 left click on the corner of the yellow box and resize it to coverthe required data. It is also possible to move the yellow box by left clicking on its centreand dragging. Repeat this for window 2, which is effectively a zoom in of window1.

4. Right click on window 3 and select: Define subset.

1

2 3


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5. Use the size and rotation controls to position the yellow box in window 3 over the areaof the data most suited for the calibration. Make sure the box is rotated parallel to thedirection of the survey lines.

6. Right click in the yellow box in window 3. It should become filled with hashed bluelines.

7. Close the subset definition window and left click on the blue area in window 3. Itshould turn yellow hashed. Then right click on the yellow hashed area in window 3 andselect calibration from the menu. The screen should look similar to the one below:


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8. Adjust the small yellow box in window 2 to take the best slice through the data for thetype of calibration you are checking (latency, pitch, roll or yaw). E.g for latency and pitchthis will be a thin slice along the vessel track in the NaDir region of the swath:

9. A view of the slice taken through the data is displayed in window 3. Adjust the slidersin the depth scale window to expand the scale and best visualise the data in window 3.

10. Right click in window 3 and select calibration from the menu. (Any corrections alreadyentered in the vessel config file will be shown in the calibration window.)

11. Adjust the Nav: time error setting to correct for any mismatch in the data. For examplein the image below the 2 lines should be adjusted until they overlap.

12. Keep a record of the result for the Nav: time error.13. Click the quit button on the calibration window.14. Right click in window 2 and select editing complete15. Exit the calibration tool.16. Do Not update the vessel config file yet.

3. Calibration Tool: Pitch

1. Select the two lines used for pitch calibration in the project window of HIPS.


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2. Repeat steps 2 to 10 in section 2.3. Enter the Nav: time error obtained in section 2.4. Adjust the Transducer 1: Pitch setting to correct for any mismatch in the data.5. Keep a record of the result for the Transducer 1: Pitch error.6. Repeat steps 13 to 16 in section 2.

4. Calibration Tool: Roll

1. Select the two lines used for roll calibration in the project window of HIPS.2. Repeat steps 2 to 10 in section 2.3. Enter the Nav: time error obtained in section 2 and the Transducer 1: Pitch error

obtained in section 3.4. Adjust the Transducer 1: Roll setting to correct for any mismatch in the data.5. Keep a record of the result for the Transducer 1: Roll error.6. Repeat steps 13 to 16 in section 2.

5. Calibration Tool: Yaw

1. Select the two lines used for yaw calibration in the project window of HIPS.2. Repeat steps 2 to 10 in section 2.3. Enter the Nav: time error obtained in section 2, the Transducer 1: Pitch error obtained

in section 3 and the Transducer 1: Roll error obtained in section 4.4. Adjust the Transducer 1: yaw setting to correct for any mismatch in the data.5. Keep a record of the result for the Transducer 1: Yaw error.6. Repeat steps 13 to 16 in section 2.

6. Updating the vessel config file

Once the Latency, Pitch, Roll and Yaw errors have been obtained, the vessel configuration filecan then be updated with the correct values and the survey lines re-merged. It is then worthchecking the data to make sure the values have been applied correctly.

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