SUMMARY
Table 1.1: Summary Introduction
Survey Date: 22 May 2021. All times Local (UTC+2)
Location: Skagerrak, Denmark. WGS-84 position: 58°04’44.98”N,
009°43’21.95”E, WD: 350 m
Weather Conditions: Wind: WSW 4/5, Sea state 3, Waves height: 0.8 – 1.1m
Coordinate System: Datum: ETRS89. Projection: UTM Zone 32N, CM 9°W
Personnel: Ricardo Williams, Vincenzo Cedro
Equipment
Kongsberg HiPAP 501 USBL SW H 4.3.5.5 Kongsberg APOS WinHPRU Version 6.8.2.3 Kongsberg cNODE Maxi (S/N 119518 B18) Fugro StarPack (DGPS 3 G4+)
iXblue Hydrins
Sequence of Events
Before departure to the survey site, the cNode Maxi transponder was tested over the side to verify acoustic connection and battery capacity. Fugro Pioneer then transited to Skagerrak and arrived at 09:50. After a toolbox talk, an SVP was carried out and the HiPAP pole was deployed. The cNode Maxi was deployed to the seabed with clump weights (approx.
125kg) at 12:00. The extended 4-cardinal points survey procedure commenced at 13:00 and finished at 18:00, results were then computed. An offset spin verification was carried out between 21:00 and 00:30 overnight with a couple of hours break for poor weather conditions. Thereafter the vessel stood by, awaiting first light. At 07:30 a toolbox was conducted for the recovery. The transponder was released from the seabed with the hydrostatic release and recovered to Fugro Pioneer at 08:00.
Conclusion
The HiPAP USBL system on board Fugro Pioneer was successfully calibrated for Roll, Pitch and Orientation. Calibration results were confirmed by a USBL verification.
Fugro Pioneer USBL Calibration Report
FP_USBL_Cal_22-05-2021 | Fugro Pioneer USBL Calibration Report | Issue DRAFT Rev 00
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1. PREPARATION
1.1 Attitude and Heading
The Hydrins was providing corrected pitch, roll and heading to the HiPAP system. The Hydrins was corrected for attitudes and was aligned with the vessel reference frame. The Hydrins lever arms were set for the HiPAP reference position.
Figure 1.1: Hydrins alignments
Figure 1.2: HiPAP Attitude sensors in APOS
Fugro Pioneer USBL Calibration Report
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1.2 Offsets
USBL transceiver offsets were measured by laser scanner in dry dock during construction in 2014, both in the raised and deployed (lowered) position. The deployed offsets were entered into the APOS transceiver configuration.
The DGPS and motion data received by the HiPAP system were already CRP referenced so there was no need to enter offsets in APOS.
Table 1.1: Calibration Offsets
Name X Y Z Remarks
HiPAP raised 3.91 3.56 -4.31 To CRP
HiPAP deployed 3.91 3.56 -7.05 To CRP
DGPS 3 -0.754 3.995 12.134 To CRP
The USBL calibration was completed using the “Installation” parameters calculated by the previous USBL adjustment (on 2020.01.19 at Fraserburgh).
Figure 1.3: HiPAP Transceiver offsets in APOS (Installation parameters prior to new Calibration)
The calibrated Hull Unit Depth offset (the laser measure) was verified. The HiPAP pole was lowered to its full position.
Fugro Pioneer USBL Calibration Report
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Figure 1.4: HiPAP hull unit depth offset
1.3 Sound Velocity Profile
An SVP was carried out on arrival to the calibration site and entered into APOS and EA400 single beam echosounder.
Figure 1.5: Active SVP in APOS
Fugro Pioneer USBL Calibration Report
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2. ACQUISITION
2.1 Transponder Position
The B18 cNODE Maxi transponder was deployed to the seabed. Once settled, the mean position of the instrument was calculated using StarfixNG. This position was used to centre the cardinal points pattern. The average position read as: 542626E, 6437751N.
2.2 Water Depth and Transponder Height
The EA400 echosounder displayed a seabed water depth of 345.5 m at transponder location.
The height from the seabed clump weight to the B18 transponder head was 3.0m. The transponder Z values were referenced to water line. Water line to CRP was 2.5m.
2.3 Transducer Alignment Properties
The acceptance criteria for Expected Accuracy were set in APOS (both for Acoustics and dGPS measurements).
No new offsets were set for the GPS Antenna offset as the position sent to APOS was already the vessel CRP, with correct offsets. No Gyro rotation was entered as the heading sent to APOS from Hydrins is already corrected.
Only the Transducer inclinations parameter group was selected for calculation. The previous calibration values were set as initial values. High 1-sigma accuracy values (15) were set for each of the three inclination parameters. This allowed roll, pitch and gear to be freely computed by APOS.
In Calculation, the Auto exclude option was enabled and Automatic compensation for tidal variations was switched on. The Tidal Range in the calibration area was 0.2m.
Fugro Pioneer USBL Calibration Report
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Figure 2.1: Transducer Alignment properties
2.4 Acquisition Method
StarfixNG was used to create the waypoints for vessel navigation, The Extended Cardinal Points calibration method was used for Calibration. The four Cardinal points were established at 140m from the deployed transponder and data was acquired on reciprocal headings for each location.
The vessel used dynamic positioning to hold the HiPAP transceiver stationary over the cardinal waypoint, on a 30° and 210° heading. 600 readings at 1.0 second intervals were taken. Complete logging at one location took 10 minutes. This procedure was repeated for all four cardinal waypoints.
The vessel then moved above the transponder location, and whilst stationary, recorded 600 readings at each of the four orientations, 035°, 125°, 215° and 305° heading. A pause in acquisition was required as prevailing weather conditions made station keeping difficult.
Fugro Pioneer USBL Calibration Report
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Figure 2.2: Calibration waypoints pattern
Fugro Pioneer USBL Calibration Report
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3. CALCULATIONS 3.1 Measurements
At the end of acquisition, a total of 1591 readings had been recorded. The figure below shows the raw, uncorrected measurements and the corrected position (Measurements were auto-excluded by APOS and are marked as red Symbols).
Figure 3.1: Measured Transponder position
Figure 3.2: Measured Transponder Depth
Fugro Pioneer USBL Calibration Report
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4. COMPUTED RESULTS
4.1 Transducer Alignment results
The transducer alignment results, calculated by APOS, were based on 1521 observation.
Table 4.1: Transducer alignment results
Name Calculated SD Initial (previous calibration)
Roll 0.07° 0.01° 0.04°
Pitch -0.01° 0.01° -0.07°
Orientation 269.77° 0.02° 269.78°
Figure 4.1: Calculated Parameters
Fugro Pioneer USBL Calibration Report
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Figure 4.2: Applied results in APOS
Fugro Pioneer USBL Calibration Report
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5. POST CALIBRATION VERIFICATION (Spin Test)
After the calibration, the newly calculated values were updated in the APOS system (Figure 4.2).
Verification SPIN Test was then completed in APOS and StarfixNG. Four sets of 300 observations were recorded over the verification waypoint at 035°, 125°, 215° and 305° vessel heading respectively.
The plots below show the beacon position for the verification sessions. The groupings are tight and within the expected tolerance. This demonstrates reliability of the new USBL calibration results updated in APOS.
Figure 5.1: Scatter Plots of Spin Test Verification (before and after Calibration)
Fugro Pioneer USBL Calibration Report
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Figure 5.2: Cardinal Point Calibration completed in NG
As an additional check, the Cardinal point calibration was run to calculate calibration parameters for pitch roll and Heading in NG to compare both results. These results are presented below. They show a negligible difference and were not applied in StarfixNG as all correction will be applied in APOS.
Table 5.1: NG Calibration Results Attitude Corrections
Pitch [°] 0.00 -0.03 ± 0.00
Roll [°] 0.00 0.06 ± 0.00
Orientation [°] 0.00 -0.03 ± 0.01
Observations Accepted: 6336 Observations Rejected: 131
6. WALK Away Test
Following the Spin Test verification, a walk away test was performed. This is a simple test where the vessel recorded transponder positions while travelling away from the transponder on a constant heading. This was completed in order to confirm that the alignment values obtained from the calibration were effective and that the range is accurately being measured by the USBL system.
Error! Reference source not found. shows Scatter plots of the Walk Away test before and after the alibration; this confirms the accuracy of the calibration as the Beacon position did not move while the vessel was moving away from the BC (700 m approximately). The weather conditions during this test