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Patch Testing HYPACK 2013. HYSWEEP ® Calibration of a Multibeam System Patch Testing Single and Dual Head Multibeam Systems. Patch Testing Single and.

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Presentation on theme: "Patch Testing HYPACK 2013. HYSWEEP ® Calibration of a Multibeam System Patch Testing Single and Dual Head Multibeam Systems. Patch Testing Single and."— Presentation transcript:

1 Patch Testing HYPACK 2013

2 HYSWEEP ® Calibration 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.

3 Multibeam Patch Testing Bad roll calibration resulting in a 6 vertical difference in the outside beams A Patch Test Determines Correction to Roll mounting angle.Correction to Roll mounting angle. Correction to Pitch mounting angle.Correction to Pitch mounting angle. Correction to Yaw mounting angle.Correction to Yaw mounting angle. GPS Latency (time delay).GPS Latency (time delay). USACE 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: Sonar and MRU alignment relative to Sonar and MRU alignment relative tohorizontal. Causes large depth errors at outer beams. Causes large depth errors at outer beams. Yaw: Sonar and Gyro alignment relative to boat frame. Sonar and Gyro alignment relative to boat frame. Causes position errors. Causes position errors. Pitch: Sonar and MRU alignment relative to horizontal. Sonar and MRU alignment relative to horizontal. Causes depth and position errors across the swath. Causes depth and position errors across the swath.

5 GPS Latency Error Latency: Delay between position fix and sounding data Delay between position fix and sounding data arrival time. arrival time. Can cause positional errors Can cause positional errors Error is independent of multibeam system. Error 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. Hardly Ever. Positioning systems and most newer Multibeam systems, both send data with UTC time tags that remove latency. Available as a reality check. Available as a reality check.

6 Roll Test: Look for an area that is reasonably flat. Look for an area that is reasonably flat. Along the center of a dredged channel should be OK. Along the center of a dredged channel should be OK. Anchorages are good too. Anchorages are good too. Patch Test Location Latency, Pitch and Yaw Tests: Look for an area with variable bottom terrain. 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. The side slope of a dredged channel will work. A flowing current may make this difficult to stay on line. Pipeline crossings are excellent! Pipeline crossings are excellent! 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. Line A-B. Reciprocal lines, flat bottom, survey speed. Pitch Test: Line C-D. Reciprocal lines, variable bottom, survey speed. 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. Lines C-D and E-F. Offset lines, same direction, variable bottom, survey speed. 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.

8 Survey Lines – Single Head Pitch, Yaw and Latency Tests over a Slope Pitch Test: Line C-D. Reciprocal lines, variable bottom, survey speed. 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. Lines C-D and E-F. Offset lines, same direction, variable bottom, survey speed. Separation = Mid Depth = (Top of Slope + Bottom of Slope ) / 2. Separation = Mid Depth = (Top of Slope + Bottom of Slope ) / 2. 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.

9 Survey Lines – Dual Head Overlap: Green = Port Head. Red = Starboard Head. Roll Test Different line geometry to overlap port and starboard heads separately. Different line geometry to overlap port and starboard heads separately. Requires 3 survey lines instead of 2. Requires 3 survey lines instead of 2. Lines A and B overlap starboard head. Lines A and B overlap starboard head. Lines B and C overlap port 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. Some dual head systems in engineered mounting frames can be treated as single head. Check with the sonar company. Pitch, Yaw and Latency Tests Some engineered frames can be treated as single head. Others can not. Check with the sonar company for their procedures.

10 Survey Lines – Laser Scanner HYPACK® data from Optech ILRIS scanning laser. 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. Line pairs A-C or B-D can be compared for all alignments: roll, pitch and yaw. Parking lot survey lines If your boat isnt trailerable, you will need something similar on the water.

11 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 positioning Use RTK GPS whenever possible.Use RTK GPS whenever possible. Assuming 3 DGPS shift in 40 of waterAssuming 3 DGPS shift in 40 of water Latency Test: +/- 0.4 seconds. Latency Test: +/- 0.4 seconds. Pitch Test: +/- 4.4 degrees. Pitch Test: +/- 4.4 degrees. Yaw Test: +/- 4.3 degrees. Yaw Test: +/- 4.3 degrees. Some Things to Avoid Avoid Patch Testing in Very Shallow Water Patch testing becomes more reliable as the water gets deeper.Patch testing becomes more reliable as the water gets deeper. Test in the deepest area available.Test in the deepest area available.

12 In MBMAX32 Load survey lines in pairs (the two Pitch test lines for example).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.Edit through to Area Based Editing. Auto cell size in Matrix Setup works well. Starting the Patch Test The Patch Test works against a cross section cut through the survey lines.The Patch Test works against a cross section cut through the survey lines. Use Wrench icon to manually cut the section.Use Wrench icon to manually cut the section. Roll section: Across track, flat area.Roll section: Across track, flat area. Pitch section: Along track, over nadir.Pitch section: Along track, over nadir. Yaw Section: Along track, half way between lines.Yaw Section: Along track, half way between lines. Latency section: Along track, over nadir.Latency section: Along track, over nadir. Patch Test Processing

13 How It Works Good Fit Cross sections overlay well. Error is at the minimum point. Poor Fit Cross sections overlay poorly. Large error. Numerical Method The cross sections are calculated at various angle offsets. For example; pitch offset from -10 to 10 degrees at one degree steps.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.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!Minimum error is usually the correct offset. But not always!

14 Select Test Pick the tab corresponding to the test you want to run.Pick the tab corresponding to the test you want to run. Select Sonar Head For dual head systems, select head 1 or 2For dual head systems, select head 1 or 2 Results Read test results here.Read test results here. Cross Sections Red is the first line, green is the second.Red is the first line, green is the second. Error Graph X axis is angle or time adjustment.X axis is angle or time adjustment. Y axis is the error; difference between cross sections.Y axis is the error; difference between cross sections. Vertical Adjustment Moves the first line up or down if needed.Moves the first line up or down if needed. Override Select Next or Previous adjustment.Select Next or Previous adjustment. Patch Test Window – Part 1 Control Modify Test SettingsModify Test Settings

15 Survey Information Comments from the data files.Comments from the data files. Step Selections Default Angle / Time Steps. Can be over-ridden in the Control section.Default Angle / Time Steps. Can be over-ridden in the Control section. Coarse: Use this to get close.Coarse: Use this to get close. Medium: Usually appropriate for DGPS.Medium: Usually appropriate for DGPS. Fine: Usually appropriate for RTK GPS.Fine: Usually appropriate for RTK GPS. Patch Test Window – Part 2 Save Test Saves test result in an RTF document.Saves test result in an RTF document. Patch Test History Average Results with Uncertainty.Average Results with Uncertainty. Use the average instead of the individual tests.Use the average instead of the individual tests.

16 Single 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 Head Across track section. In this example, different result are seen for heads 1 and 2. Example: MB Roll Tests Roll Test Head 1 Roll Test Head 2

17 Pitch 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 Tests Yaw 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.

18 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 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.

19 Order 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 Repetition 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.

20 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.ResultsGood. Not as Good. Not as Good. U-shaped error curve is preferred. But not always possible. Some Error Curves

21 Sample Single Head Patch Test


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