2 Calibration of a Multibeam System HYSWEEP®Calibration of a Multibeam SystemPat asked to include USACE regs. for patch testing. I don’t see them here.Patch Testing Single and Dual Head Multibeam Systems.Also: Patch Testing Laser Scanners.
3 Multibeam Patch Testing A Patch Test DeterminesCorrection to Roll mounting angle.Correction to Pitch mounting angle.Correction to Yaw mounting angle.GPS Latency (time delay).Bad roll calibration resulting in a 6’ vertical difference in the outside beamsUSACE Requirements for Patch Testing (EM )Patch tests are performed after initial installation, and periodically thereafter if sensors are modified, to quantify any residual biases from the initial system alignment.
4 Alignment Errors Roll: Pitch: Yaw: Sonar and MRU alignment relative to horizontal.Causes large depth errors at outer beams.Pitch:Sonar and MRU alignment relative to horizontal.Causes depth and position errors across the swath.Yaw:Sonar and Gyro alignment relative to boat frame.Causes position errors.
5 GPS Latency Error Latency: Is Latency testing required? Delay between position fix and sounding dataarrival time.Can cause positional errorsError is independent of multibeam system.Is Latency testing required?Hardly Ever. Positioning systems and most newer Multibeam systems, both send data with UTC time tags that remove latency.Available as a “reality check”.5
6 Patch Test Location Roll Test: Latency, Pitch and Yaw Tests: Look for an area that is reasonably flat.Along the center of a dredged channel should be OK.Anchorages are good too.Latency, Pitch and Yaw Tests:Look for an area with variable bottom terrain.The side slope of a dredged channel will work. A flowing current may make this difficult to stay on line.Pipeline crossings are excellent!Nice graphic! Line separation? 1x depth at shallow end as you stated in another slide? 1½ x depth?—I thought that’s what Pat said.The entire patch test can be done right here.
7 Survey Lines – Single Head Roll Test:Line A-B. Reciprocal lines, flat bottom, survey speed.Pitch Test:Line C-D. Reciprocal lines, variable bottom, survey speed.Yaw Test:Lines C-D and E-F. Offset lines, same direction, variable bottom, survey speed.Nice graphic! Line separation? 1x depth at shallow end as you stated in another slide? 1½ x depth?—I thought that’s what Pat said.Latency Test:Line C-D. Same direction, variable bottom, high speed then low speed.7
8 Pitch, Yaw and Latency Tests over a Slope Survey Lines – Single HeadPitch, Yaw and Latency Tests over a SlopePitch Test:Line C-D. Reciprocal lines, variable bottom, survey speed.Yaw Test:Lines C-D and E-F. Offset lines, same direction, variable bottom, survey speed.Separation = Mid Depth = (Top of Slope + Bottom of Slope ) / 2.Nice graphic! Line separation? 1x depth at shallow end as you stated in another slide? 1½ x depth?—I thought that’s what Pat said.Latency Test:Line C-D. Same direction, variable bottom, high speed then low speed.8
9 Survey Lines – Dual Head Roll TestDifferent line geometry to overlap port and starboard heads separately.Requires 3 survey lines instead of 2.Lines A and B overlap starboard head.Lines B and C overlap port head.Some dual head systems in engineered mounting frames can be treated as single head. Check with the sonar company.Pitch, Yaw and Latency TestsSome engineered frames can be treated as single head.Others can not. Check with the sonar company for their procedures.Nice graphic! Line separation? 1x depth at shallow end as you stated in another slide? 1½ x depth?—I thought that’s what Pat said.Overlap: Green = Port Head.Red = Starboard Head.9
10 Survey Lines – Laser Scanner The best patch area is a parking lot with light posts!Line pairs A-C or B-D can be compared for all alignments: roll, pitch and yaw.If your boat isn’t trailerable, you will need something similar on the water.Nice graphic! Line separation? 1x depth at shallow end as you stated in another slide? 1½ x depth?—I thought that’s what Pat said.Parking lot survey linesHYPACK® data from Optech ILRIS scanning laser.10
11 Some Things to Avoid Avoid Patch Testing with Bad positioning Use RTK GPS whenever possible.Assuming 3’ DGPS shift in 40’ of waterLatency Test: +/- 0.4 seconds.Pitch Test: +/- 4.4 degrees.Yaw Test: +/- 4.3 degrees.Avoid Patch Testing in Very Shallow WaterPatch testing becomes more reliable as the water gets deeper.Test in the deepest area available.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.Nice graphic! Line separation? 1x depth at shallow end as you stated in another slide? 1½ x depth?—I thought that’s what Pat said.11
12 Patch Test Processing In MBMAX32 Starting the Patch Test Load survey lines in pairs (the two ‘Pitch’ test lines for example).Edit through to Area Based Editing. Auto cell size in Matrix Setup works well.Starting the Patch TestThe Patch Test works against a cross section cut through the survey lines.Use “Wrench” icon to manually cut the section.Roll section: Across track, flat area.Pitch section: Along track, over nadir.Yaw Section: Along track, half way between lines.Latency section: Along track, over nadir.Added GPS latency also to HYPACK® Hardware.
13 How It Works Numerical 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!Added GPS latency also to HYPACK® Hardware.Good FitCross sections overlay well.Error is at the minimum point.Poor FitCross sections overlay poorly.Large error.13
14 Patch Test Window – Part 1 ResultsRead test results here.Select TestPick the tab corresponding to the test you want to run.Select Sonar HeadFor dual head systems, select head 1 or 2ControlModify Test SettingsError GraphX axis is angle or time adjustment.Y axis is the error; difference between cross sections.Cross SectionsRed is the first line, green is the second.Added GPS latency also to HYPACK® Hardware.OverrideSelect Next or Previous adjustment.Vertical AdjustmentMoves the first line up or down if needed.14
15 Patch Test Window – Part 2 Patch Test HistoryAverage Results with Uncertainty.Use the average instead of the individual tests.Survey InformationComments from the data files.Step SelectionsDefault Angle / Time Steps. Can be over-ridden in the Control section.Coarse: Use this to get ‘close’.Medium: Usually appropriate for DGPS.Fine: Usually appropriate for RTK GPS.Save TestSaves test result in an RTF document.Added GPS latency also to HYPACK® Hardware.15
16 Example: MB Roll Tests Single Head Dual 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 HeadAcross track section.In this example, different result are seen for heads 1 and 2.“Decent” sounds subjective…maybe “clear” , “clean” or “distinct”?Roll Test Head 1Roll Test Head 216
17 Example: MB Pitch/Yaw Tests Pitch TestPatch Test Section is cut directly over nadir.Good overlap, good error curve.Angle step of 1.0 degrees using DGPS. Better resolution if RTK.Yaw TestPatch 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.“Decent” sounds subjective…maybe “clear” , “clean” or “distinct”?17
18 Example: Laser Scanner 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.Roll Test: Adjustment to match up pavement cross sections.“Decent” sounds subjective…maybe “clear” , “clean” or “distinct”?Pitch Test: Adjustments to make the pole vertical.Yaw Test: Adjustments to align the base of the pole.18
19 Testing Order and Repetition Order of Processing makes a DifferenceFind 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.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.“Decent” sounds subjective…maybe “clear” , “clean” or “distinct”?19
20 Results Test Results (from the Patch Test window) Some Error Curves Good.Not as Good. U-shaped error curve is preferred. But not always possible.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.“Decent” sounds subjective…maybe “clear” , “clean” or “distinct”?20