HYSWEEP Calibration of a Multibeam System Running a

® HYSWEEP Calibration of a Multibeam System Running a Patch Test on Single and Dual Head Multibeam Systems PROJECT: SAMPLE PATCH TEST SINGLE HEAD 10/30/2020 HYPACK® 2006 1

Patch Testing a Multibeam System Demonstrates: The errors resulting from a mounting offset of the sonar head, and the motion sensor and gyrocompass. The errors resulting from uncompensated GPS latency. How to run a Patch Test survey. Why Patch Test? To avoid profiles like this! 10/30/2020 HYPACK® 2006 2

USACE requirements for Patch Tests Patch tests are performed after initial installation, and periodically thereafter if sensors are modified, to quantify any residual biases from the initial system alignment. During this calibration series, four separate tests are performed to determine residual alignment biases for: - Position Time Delay (Latency) - Pitch Offset - Roll Offset - Yaw/Azimuthal Offset From EM 1110 -2 -1003 USACE standards 10/30/2020 HYPACK® 2006 3

Roll Misalignment Roll: Sonar and MRU alignment relative to vertical. Can cause large depth and position errors at outer beams. 10/30/2020 HYPACK® 2006 4

Pitch Misalignment Pitch: Sonar and MRU alignment relative to vertical. Can cause depth and position errors across the swath. 10/30/2020 HYPACK® 2006 5

Yaw Misalignment Yaw: Sonar and MRU alignment relative to vertical. Can cause depth and position errors across the swath. 10/30/2020 HYPACK® 2006 6

GPS Latency Error Latency The delay between position fix and transmission. Will cause positional errors. Error is independent of Multibeam system 10/30/2020 HYPACK® 2006 7

The process 1. Create the Lines in HYPACK® (*. LNW file). Need to create 3 lines. 2. Run the survey lines in the correct direction and speed. 3. Process each pair of lines through the MULTIBEAM EDITOR to Phase 3. 4. Run the Patch Test Tool to run the calibration test. Automatic or Manual. 5. Check results. Run the test again for confidence. 6. Enter the corrected values in the hardware set-up. – HYSWEEP® HARDWARE HYPACK® Navigation (Latency) and Sounder (Roll, Pitch, Yaw) 10/30/2020 HYPACK® 2006 8

Hints for a successful patch test Run the test in the deepest section of the survey area. Run lines at normal survey speed (except for latency). Run each test twice to confirm results. Take the time specifically for the test before you begin surveying. Repeat the test if the mount is moved. 10/30/2020 HYPACK® 2006 9

Patch Test Warnings While collecting data, keep an eye on GPS quality. If HDOP > 2, do your patch testing another time. Slight position errors result in patch test errors. Do lots of testing and use the average result. Never change mounting offsets based on a single test. 10/30/2020 HYPACK® 2006 10

Uncertainties due to DGPS Approximations assuming 3’ DGPS shift in 40’ of water: Latency Test: +/- 0. 4 seconds Pitch Test: +/- 4. 4 degrees Yaw Test: +/- 4. 3 degrees 10/30/2020 HYPACK® 2006 11

Single Head Patch Test Survey Roll: LINE A-B – Reciprocal lines, flat bottom Pitch: LINE C-D – Reciprocal lines, sloping bottom. Yaw: LINE C-D, E-F – Offset lines, sloping bottom. Latency: LINE C-D – Same line and direction, differing speed, sloping bottom. – Beware of settlement differences at different speeds. 10/30/2020 HYPACK® 2006 12

Dual Head Patch Test Survey Different line geometry to overlap head 1 and 2 separately. Roll, pitch and yaw tests require 3 lines instead of 2. Port Head tested by lines 1 and 2. Starboard Head tested by lines 2 and 3. 10/30/2020 HYPACK® 2006 14

Dual Head Patch Test Similar to single head, but additional survey line is needed to account for offset. If the sonar is in an engineering mount – fixed angles – then the Patch Test can be considered a single head. Many Atlas, Seabeam and Simrad dual head systems are mounted in a rigid frame with calibration angles known. These can be treated as single head multibeam systems. Transducers separated – Use Dual Head Patch Test 10/30/2020 Transducers in Engineering mount – Use Single Head Patch Test HYPACK® 2006 15

Patch Test Processing: How it Works In Phase 3 of MULTIBEAM EDITOR. Processing starts with a cross section through the survey lines. Calculates bottom at different mounting angles to find best fit. Bad fit Good fit 10/30/2020 HYPACK® 2006 16

Begin Processing in MULTIBEAM EDITOR 1. 2. 3. 4. 5. Launch MULTIBEAM EDITOR. Load files two at a time. Apply tide correction, offsets and other corrections as needed. Edit the data. In Phase 3, start the Patch Test. Note: For Dual Head systems, select head 1, head 2 or both as required. 10/30/2020 HYPACK® 2006 17

Running the Patch Test Module Run Patch Test one of two ways: Basic: Run from the MULTIBEAM EDITOR menu – program cuts section automatically. Advanced: Use Patch Test tool in Survey Window to cut test section yourself. 10/30/2020 HYPACK® 2006 19

Roll Test Result: +0. 10 degree adjustment (0. 1 resolution in shallow water). Good overlap in cross sections. Decent “UShaped” error curve = good confidence in results. Click here to start test. 10/30/2020 HYPACK® 2006 20

Roll Test, Heads 1 and 2 Results: Head 1: +1. 10 degree adjustment. Head 2: -1. 90 degree adjustment. Decent U-Shaped error curve in both cases. 10/30/2020 HYPACK® 2006 21

Pitch Test Result: +1. 0 degree adjustment (1. 0 resolution in shallow water). 10/30/2020 HYPACK® 2006 22

Dual Head Pitch Test Usually identical to single head pitch test. Select both heads. 10/30/2020 HYPACK® 2006 23

Yaw Test Result: +1. 0 degree adjustment (1. 0 resolution in shallow water). 10/30/2020 HYPACK® 2006 24

Latency Test Single Head Result: -0. 1 second adjustment (0. 1 resolution). Ragged error curve = low confidence in final results. Dual Head: Identical to single head latency test. 10/30/2020 HYPACK® 2006 26

Bad data results Watch out for data that doesn’t produce the “normal” curve. Check sensor offsets in the MULTIBEAM EDITOR. Examine the data for suspicious points. Select another portion of the line. Re-run the data. Good data What Bad data will look like 10/30/2020 HYPACK® 2006 27

Patch Test in Action AUTOMATIC PATCH TEST 10/30/2020 MANUAL PATCH TEST HYPACK® 2006 28

Reading the Results Adjustment: Recommended mounting offset or latency change. Initial Offset: Mounting offset or latency setting at time of Patch Test survey. Final Offset: New mounting offset or latency based on Patch Test result. 10/30/2020 HYPACK® 2006 29