PATCH TESTINGPATCH TESTINGHYSWEEPHYSWEEP®®

HYSWEEPHYSWEEP®®

Calibration of a Multibeam SystemCalibration of a Multibeam System

04/20/23 HYPACK® 2009 Training Seminar 2

PROJECT: SAMPLE PATCH TEST SINGLE HEADPROJECT: SAMPLE PATCH TEST SINGLE HEAD

Running a Patch Test on Single and Dual Running a Patch Test on Single and Dual Head Multibeam SystemsHead Multibeam Systems

Patch Testing a Multibeam SystemPatch Testing a Multibeam System

04/20/23HYPACK® 2009 Training Seminar 3

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

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

•Correction to pitch mounting angle.

•Correction to yaw mounting angle.

•GPS latency (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.

Errors Relating to the Multibeam Errors Relating to the Multibeam Roll: Roll: • Sonar and MRU alignmentSonar and MRU alignment relative to relative to

vertical.vertical.• Can cause Can cause large depth errorslarge depth errors at outer at outer

beams.beams.

Pitch:Pitch:• Sonar and MRU alignmentSonar and MRU alignment relative to relative to

vertical.vertical.• Can cause Can cause depth and position errorsdepth and position errors

across the swath.across the swath.

Yaw:Yaw:• Sonar and Gyro alignmentSonar and Gyro alignment relative to relative to

boat frame.boat frame.• Can cause Can cause position errorsposition errors..

04/20/23HYPACK® 2009 Training Seminar 4

GPS Latency ErrorGPS Latency Error

04/20/23HYPACK® 2009 Training Seminar 5

Latency: Latency: • Delay Delay between position fix and data arrival between position fix and data arrival

time.time.• Can cause Can cause positional errorspositional errors• Error is independent of multibeam system.Error is independent of multibeam system.

Patch Test SurveyPatch Test Survey• Roll: Line A-BRoll: Line A-B

- - Reciprocal lines, flat bottom. Survey speed.Reciprocal lines, flat bottom. Survey speed. • Pitch: Line C-DPitch: Line C-D

– Reciprocal lines, sloping bottom. Survey speed.Reciprocal lines, sloping bottom. Survey speed.• Yaw: Lines C-D, E-FYaw: Lines C-D, E-F

– Offset lines, sloping bottom. Survey speed.Offset lines, sloping bottom. Survey speed.• Latency: Line C-DLatency: Line C-D

– Same line and direction, differing speed, sloping Same line and direction, differing speed, sloping bottom. Watch for settlement differences.bottom. Watch for settlement differences.

04/20/23HYPACK® 2009 Training Seminar 6

Dual Head•Different geometry to overlap port and starboard heads separately.

•Roll, pitch and yaw tests require 3 lines instead of 2.

•Some dual head systems in engineered mounting frames can be treated as single head.

Survey Hints and WarningsSurvey Hints and Warnings

04/20/23HYPACK® 2009 Training Seminar 7

Hints:Hints:

•Test in the deepest section of the survey area.

•Except for latency, run lines at your normal survey speed.

•Run each test twice to confirm results. Average multiple tests for final results.

DGPS Warning:DGPS Warning:

•Make sure you have good GPS positioning. Slight position error lead to patch test errors.

•If HDOP is high, perhaps best to patch testing another time.

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

Patch Test ProcessingPatch Test Processing

04/20/23 HYPACK® 2009 Training Seminar 8

In MBMAXIn MBMAX

•Load survey lines in pairs (the two pitch lines for example).

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

Starting the Patch TestStarting the Patch Test

•The patch test works against a cross section cut through the survey lines.

•Use Tools menu to automatically cut a section or,

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

How It WorksHow It Works

04/20/23 HYPACK® 2009 Training Seminar 9

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 angle offsets. For example; pitch offset from -10 to 10 degrees at one degree steps.

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

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

The Patch Test WindowThe Patch Test Window

04/20/23 HYPACK® 2009 Training Seminar 10

Select Test

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

Select Sonar Head

•For dual head systems, select head 1 or 2

Results

•Read test results here.

Cross Sections

•Red is the first line, green is the second.

Error Graph

•X axis is angle or time adjustment.

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

Vertical Adjustment

•Moves the first line up or down if needed.

Override

•Select Next or Previous adjustment.

04/20/23HYPACK® 2009 Training Seminar 11

Single HeadSingle Head

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

•Good overlap in cross sections.

•Good “U-Shaped” error curve.

Dual HeadDual Head

•Totally different result for each head.

Roll TestRoll Test

04/20/23HYPACK® 2009 Training Seminar 12

Pitch, Yaw, LatencyPitch, Yaw, Latency

•Angle step of 1.0 degrees using DGPS for pitch and yaw. Better resolution if RTK.

•Time step of 0.1 second using DGPS for latency test. Better resolution if RTK.

Order of Processing:Order of Processing:

•Find the latency offset first

•Apply latency, then do the pitch test.

•Apply pitch, then do the roll test.

•Apply roll, then finish with the yaw test.

Other TestsOther Tests

04/20/23HYPACK® 2009 Training Seminar 13

Test Results (from the patch test Test Results (from the patch test window)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. Bad. Bad. Should see a U-shaped error curve.

Some Error Curves

Patch Test in ActionPatch Test in Action

04/20/23 HYPACK® 2009 Training Seminar 14

Automatic Patch TestAutomatic Patch Test