Patch TestingPatch Testing

HYPACK 2013HYPACK 2013

HYSWEEPHYSWEEP®®

Calibration of a Multibeam SystemCalibration of a Multibeam System

• Patch Testing Single and Dual Head Multibeam Systems.Patch Testing Single and Dual Head Multibeam Systems.

• Also: Patch Testing Laser Scanners.Also: Patch Testing Laser Scanners.

Multibeam Patch TestingMultibeam Patch Testing

Bad roll calibration resulting in a 6’ vertical difference in the outside beams

A Patch Test DeterminesA Patch Test Determines•Correction to Correction to RollRoll mounting angle.mounting angle.

•Correction to Correction to PitchPitch mounting angle. mounting angle.

•Correction to Correction to YawYaw mounting angle.mounting angle.

•GPS GPS LatencyLatency (time delay).(time delay).

USACE Requirements for Patch Testing (EM1110-2-1003)USACE Requirements for Patch Testing (EM1110-2-1003)•Patch tests are performed after initial installation, and periodically thereafter if sensors are modified, to quantify any residual biases from the initial system alignment.

Alignment ErrorsAlignment Errors

Roll: Roll: • Sonar Sonar andand MRU alignment MRU alignment relative to relative to

horizontal.horizontal.• Causes Causes large depth errorslarge depth errors at outer beams. at outer beams.

Yaw:Yaw:• Sonar Sonar andand Gyro alignment Gyro alignment relative to boat relative to boat

frame.frame.• CausesCauses position errorsposition errors. .

Pitch:Pitch:• Sonar Sonar andand MRU alignment MRU alignment relative to relative to

horizontal.horizontal.• Causes Causes depth and position errorsdepth and position errors across the across the

swath.swath.

GPS Latency ErrorGPS Latency Error

Latency:Latency: • Delay Delay between position fix and sounding databetween position fix and sounding data arrival time.arrival time.• Can cause Can cause positional errorspositional errors• Error is independent of multibeam system.Error is independent of multibeam system.

Is Latency testing required?Is Latency testing required? • Hardly Ever.Hardly Ever. Positioning systems and most newer Multibeam systems, Positioning systems and most newer Multibeam systems,

both send data with both send data with UTC time tags that remove latency.UTC time tags that remove latency.• Available as a Available as a “reality check”.“reality check”.

Roll Test:Roll Test:• Look for an area that is Look for an area that is reasonably flatreasonably flat..• Along the center of a Along the center of a dredged channel dredged channel should be OK. should be OK.• AnchoragesAnchorages are good too. are good too.

Patch Test LocationPatch Test Location

Latency, Pitch and Yaw Tests:Latency, Pitch and Yaw Tests:• Look for an area with Look for an area with variable bottom variable bottom

terrainterrain..• TheThe side slopeside slope of a dredged channel of a dredged channel

will work. A flowing current may will work. A flowing current may make this difficult to stay on line.make this difficult to stay on line.

• Pipeline crossingsPipeline crossings are excellent!are excellent!

The entire patch test can be done right here.

Survey Lines – Single HeadSurvey Lines – Single Head

Roll Test:Roll Test:• Line A-B. Reciprocal lines, flat bottom, Line A-B. Reciprocal lines, flat bottom,

survey speed.survey speed.

Pitch Test:Pitch Test:• Line C-D. Reciprocal lines, variable bottom, Line C-D. Reciprocal lines, variable bottom,

survey speed.survey speed.

Yaw Test:Yaw Test:• Lines C-D and E-F. Offset lines, Lines C-D and E-F. Offset lines,

same direction, variable bottom, same direction, variable bottom, survey speed.survey speed.

Latency Test:Latency Test:• Line C-D. Same direction, variable Line C-D. Same direction, variable

bottom, high speed then low bottom, high speed then low speed.speed.

Survey Lines – Single HeadSurvey Lines – Single Head

Pitch, Yaw and Latency Tests over a SlopePitch, Yaw and Latency Tests over a Slope

Pitch Test:Pitch Test:• Line C-D. Reciprocal lines, variable Line C-D. Reciprocal lines, variable

bottom, survey speed.bottom, survey speed.

Yaw Test:Yaw Test:• Lines C-D and E-F. Offset lines, Lines C-D and E-F. Offset lines,

same direction, variable bottom, same direction, variable bottom, survey speed.survey speed.

• Separation = Mid Depth = (Top of Separation = Mid Depth = (Top of Slope + Bottom of Slope ) / 2.Slope + Bottom of Slope ) / 2.

Latency Test:Latency Test:• Line C-D. Same direction, variable bottom, high speed then low speed.Line C-D. Same direction, variable bottom, high speed then low speed.

Survey Lines – Dual HeadSurvey Lines – Dual Head

Overlap: Green = Port Head.

Red = Starboard Head.

Roll TestRoll Test• Different line geometry to Different line geometry to overlap port overlap port

andand starboard heads starboard heads separately.separately.• Requires Requires 3 survey lines instead of 2.3 survey lines instead of 2.• Lines A and B overlap Lines A and B overlap starboardstarboard head.head.• Lines B and C overlap Lines B and C overlap portport head.head.• Some dual head systems in Some dual head systems in engineered engineered

mounting framesmounting frames can be treated as can be treated as single headsingle head. . Check with the sonar Check with the sonar company.company.

Pitch, Yaw and Latency Pitch, Yaw and Latency TestsTests

• Some engineered frames can be treated as single head.

• Others can not. Check with the sonar company for their procedures.

Survey Lines – Laser ScannerSurvey Lines – Laser Scanner

HYPACK® data from Optech ILRIS scanning laser.

The best patch area is a parking lot with light posts!The best patch area is a parking lot with light posts!• Line pairs A-C or B-D can be compared for all Line pairs A-C or B-D can be compared for all

alignments: alignments: roll, pitch and yaw. roll, pitch and yaw.

Parking lot survey lines

If your boat isn’t trailerable, you will If your boat isn’t trailerable, you will need something similar on the water.need something similar on the water.

Do not view Patch Testing as EXACT! Do not view Patch Testing as EXACT! •See DGPS uncertainties above.

•Run each test at least twice to confirm results.

•Multiple tests will be averaged in post processing.

Avoid Patch Testing with Bad Avoid Patch Testing with Bad positioningpositioning•Use RTK GPS whenever possible.Use RTK GPS whenever possible.

•Assuming 3’ DGPS shift in 40’ of waterAssuming 3’ DGPS shift in 40’ of waterLatency Test:Latency Test: +/- 0.4 seconds.+/- 0.4 seconds.Pitch Test:Pitch Test: +/- 4.4 degrees.+/- 4.4 degrees.Yaw Test:Yaw Test: +/- 4.3 degrees.+/- 4.3 degrees.

Some Things to AvoidSome Things to Avoid

Avoid Patch Testing in Avoid Patch Testing in Very Shallow WaterVery Shallow Water•Patch testing becomes Patch testing becomes more reliable as the water more reliable as the water gets deeper.gets deeper.

•Test in the Test in the deepest area deepest area availableavailable..

In MBMAX32In MBMAX32•Load survey lines in Load survey lines in pairspairs (the two ‘Pitch’ test lines for example).(the two ‘Pitch’ test lines for example).

•Edit through to Edit through to Area Based Editing.Area Based Editing. Auto cell sizeAuto cell size in Matrix Setup works well.in Matrix Setup works well.

Starting the Patch TestStarting the Patch Test•The Patch Test works against a The Patch Test works against a cross cross sectionsection cut through the survey lines.cut through the survey lines.

•Use “Wrench” icon to Use “Wrench” icon to manually manually cut the cut the section.section.

•Roll section:Roll section: Across track, flat area.Across track, flat area.

•Pitch sectionPitch section: : Along track, over nadir.Along track, over nadir.

•Yaw SectionYaw Section:: Along track, half way Along track, half way between lines.between lines.

•Latency sectionLatency section: : Along track, over nadir.Along track, over nadir.

Patch Test ProcessingPatch Test Processing

How It WorksHow It Works

Good FitGood Fit•Cross sections overlay well.•Error is at the minimum point.

Poor FitPoor Fit•Cross sections overlay poorly.•Large error.

Numerical MethodNumerical Method•The cross sections are calculated at various The cross sections are calculated at various angle offsetsangle offsets. . For example; pitch For example; pitch offset from -10 to 10 degrees at one degree steps.offset from -10 to 10 degrees at one degree steps.

•An An error valueerror value is calculated at each offset. Error = average depth difference is calculated at each offset. Error = average depth difference between cross sections.between cross sections.

•Minimum errorMinimum error is usually the is usually the correct offsetcorrect offset. . But not always!But not always!

Select TestSelect Test

•Pick the tab corresponding Pick the tab corresponding to the test you want to run.to the test you want to run.

Select Sonar Select Sonar HeadHead

•For dual head For dual head systems, select systems, select head 1 or 2head 1 or 2

ResultsResults

•Read test results here.Read test results here.

Cross Cross SectionsSections

•RedRed is the is the first line, first line, greengreen is the is the second.second.

Error GraphError Graph

•X axisX axis is angle or is angle or time adjustment.time adjustment.

•Y axisY axis is the error; is the error; difference between difference between cross sections.cross sections.

Vertical AdjustmentVertical Adjustment

•Moves the first line up or down if needed.Moves the first line up or down if needed.

OverrideOverride

•Select Next or Select Next or Previous adjustment.Previous adjustment.

Patch Test Window – Part 1Patch Test Window – Part 1

ControlControl•Modify Modify Test Test SettingsSettings

Survey InformationSurvey Information

•Comments from the data files.Comments from the data files.

Step SelectionsStep Selections

•Default Angle / Time Steps.Default Angle / Time Steps. Can Can be over-ridden in the Control be over-ridden in the Control section.section.

•CoarseCoarse: Use this to get ‘close’.: Use this to get ‘close’.

•MediumMedium: Usually appropriate : Usually appropriate for for DGPSDGPS..

•FineFine:: Usually appropriate for Usually appropriate for RTK GPSRTK GPS..

Patch Test Window – Part 2Patch Test Window – Part 2

Save TestSave Test

•Saves test result Saves test result in an RTF in an RTF document.document.

Patch Test HistoryPatch Test History•AverageAverage Results with Results with UncertaintyUncertainty..

•Use the averageUse the average instead of instead of the individual tests.the individual tests.

Single HeadSingle Head•Patch Test Section is cut across track.

•Angle step of 0.1 degree. Can go to 0.05 or better.

•Good overlap in cross sections.

•Good “U-Shaped” error curve.Dual HeadDual Head•Across track section.

•In this example, different result are seen for heads 1 and 2.

Example: MB Roll TestsExample: MB Roll Tests

Roll Test Head 1 Roll Test Head 2

Pitch TestPitch Test

•Patch Test Section is cut directly over nadir.

•Good overlap, good error curve.

•Angle step of 1.0 degrees using DGPS. Better resolution if RTK.

Example: MB Pitch/Yaw TestsExample: MB Pitch/Yaw Tests

Yaw TestYaw Test

•Patch Test Section is cut half way between track lines.

•Good overlap, good error curve.

•Angle step of 1.0 degrees using DGPS. Better resolution if RTK.

Patch Test Cross Sections:Patch Test Cross Sections:

•Roll Test: Cut test section across track over the pavement.

•Pitch and Yaw Tests: Cut test section along track over the pole.

•May be hard to get a good U-shaped error curve. Use Next/Previous to adjust manually.

Example: Laser ScannerExample: Laser Scanner

Roll Test: Adjustment to match up pavement cross sections.

Pitch Test: Adjustments to make the pole vertical. Yaw Test: Adjustments to align the

base of the pole.

Order of Processing makes a DifferenceOrder of Processing makes a Difference•Find the Latency offset first. (If Latency Test is necessary.)

•Apply latency, then do the Pitch test.

•Apply pitch, then do the Roll test.

•Apply roll, then finish with the Yaw test.

Testing Order and RepetitionTesting Order and Repetition

Do It Again!Do It Again!•After finding initial results, repeat the testing.

•Use the same order – Pitch, then Roll, then Yaw.

•The second run gives tighter results.

Test Results (from the Patch Test window)Test Results (from the Patch Test window)•Adjustment: Patch test change to initial offset.

•Initial Offset: Offset before patch test. (From HYSWEEP® Hardware.)

•Final Offset: Offset after Patch Test. To be included in average for update to HYSWEEP® Hardware.

ResultsResults

Good.Good.

Not as Good. Not as Good. U-shaped error curve is preferred. But not always possible.

Some Error Curves

Sample Single Head Patch TestSample Single Head Patch Test