The contractor should provide a MOVE® (or similar) analysis of the network(s) in order to be able to prove the network(s) meet the co-ordinate accuracy criteria, using the a priori values suggested by the company prior to mobilization, as well as during the survey to determine the effect of any equipment failure.
Orientation a long each streamer for the front acoustic network should be derived from the average of the first two active streamer compasses on the respective streamer. Orientation along each streamer for the tail acoustic network should be derived from the average of the last two active streamer compasses on the respective streamer, or from the rGPS positioning. Other appropriate procedures may be used with company approval.
The speed of sound in water at the streamer depth should be established and updated as specified by the company.
26. Streamer Compasses Criteria
| Direction Accuracy (1σ) | ± 0.5 degrees |
| Resolution | 0.35 degrees |
| Display | 0.1 degrees |
| Internal Gimballing: Roll | 360 degrees |
| Internal Gimballing: Pitch | at least 25 degrees |
| Acceptable On-Line Filtering: | sample every second and averaged over 7 seconds |
A unique serial number should be clearly engraved or marked in some other durable manner on an easily visible portion of the streamer compass housing.
The streamer compass configuration should be the same or very similar for each streamer. If operationally feasible, a given streamer compass should be mounted on the same streamer, at the same location, throughout the seismic acquisition.
The static biases for the streamer compasses which meet the specified tolerances set later in these guidelines, shall be set to zero (0) in the integrated navigation system and the post processing software, at the discretion of the company. The contractor should only use dynamic streamer compass verification values with the written approval of the company.
27. Streamer Depth Sensor Criteria
| Accuracy (1σ) | ± 0.2 metres |
| Resolution | 0.1 metres |
| Display | 0.1 metres |
28. Magnetic Variation for Streamer Compasses
| Model Used for Magnetic Variation Calculation | |
| Prospect Centre: Latitude | |
| Prospect Centre: Longitude | |
| Date Used for Computation | |
| Magnetic Variation Computed | degrees |
| Magnetic Secular Variation Computed | degrees |
| Agreement with most recent Admiralty Chart or other Independent Method | within 0.2 degrees |
| Magnetic Storm and Sun Spot Activity Reports | sent to vessel at least weekly, if significant |
29. Gyro Compass(es) Criteria
| Accuracy (1σ): Static | ± degrees |
| Accuracy (1σ): Dynamic | ± degrees |
| Resolution | 0.1 degrees |
| Display | 0.1 degrees |
| Alignment with Vessel Centre Line (securely fastened) | ± 0.2 degrees |
| Alignment: Repeaters | ± 0.2 degrees |
| Orientation for Navigation System | primary gyro compass |
30. Echo Sounder Criteria
| Depth | maximum water depth in prospect area |
| Accuracy | ± 1% of the water depth in area of operations |
| Units | metres |
| Graphic Resolution | 0.2 metres |
| Digital Resolution | 0.1 metres |
| Frequencies: at least 2 | 33 kHz and 210 kHz (or similar) |
| Recording Paper Speed and Scales | adjustable |
| Speed of Sound Setting | adjustable and continuously displayed |
| Transducer Draught Setting | adjustable |
| Event Mark | external and manual input |
| Output: Paper Record * | Yes (to be included with observer's log for each line) |
| Output: Digital | Yes |
| Heave Compensator** (Optional) | ± 0.5 centimeters or 5%, of measured range |
| Speed of Sound: Accuracy from T/S meter | ± 1 metre per second |
| Speed of Sound in Water Column: Valued Used (select)*** | standard / observed |
| Speed of Sound at Streamer Depth: Value Used *** | observed |
| Draught: Value Used (select) *** | standard / observed |
* All analogue records should be clearly and legibly annotated to include at least the following minimum information at the start and end of each line: date, time, line number, shot point and scale used.
** The heave compensator (if used ) should be installed in close proximity to the echo sounder transducer and should be rigidly fixed. The installation and operation of the heave compensator should be in accordance with the manufacturer's specifications.
*** The velocity of sound in water for the water column and at the streamer depth and the draught of the vessel(s) should be observed and updated as specified latter in these guidelines.
31. Marine Gravity Criteria
| Sample Rate for Gravity and Navigation | 1 second |
| Synchronization with Navigation timing | 1 second |
| Noise Envelope at 3 Minute Filter Horizontal | ± 0.5 mGal |
| Accelerations: Up to Force 4 or 25,000 mGal Up to Force 5 or 50,000 mGal Up to Force 6 or 75,000 mGal |
± 1.0 mGal ± 2.0 mGal |
| Maximum Filtered Accelerometer Noise | 4 level divisions |
| Heading Changes On Line | less than 1 degrees per minute, if operationally feasible |
| Speed Chances on Line | less than 1 knot per minute |
| Sensor Offset Position* | centre of vessel pitch, roll, and yaw axes |
*The marine gravity meter should be in a position where it will not be exposed to extremes of temperature or be knocked or damaged, but will allow easy access for maintenance. The equipment should be mounted such that it is sufficiently dampened not to be affected by floor transmitted high frequency vibrations.
Data recording should commence 8 to 10 minutes before the start of a line or part of a line, and terminate at least 5 minutes after the end of the line or part of a line. Sufficient analogue data should be recorded to allow data recovery in the event of the failure of the digital data recording.
32. Marine Magnetometer Criteria
| Minimum Sensitivity Accuracy | ± 1 nT (1 nT = 1 gamma which was old measure ) |
| Sampling Rate | 2 seconds |
| Synchronization with Navigation Timing | 1 second |
| Noise Envelope | ± 2 nT |
| Signal to Noise Ratio | 25:1 |
| Towed Astern | at least 3 times vessel length (if operationally feasible) |
33. Speed Log and Acoustic Doppler Current Profiler Criteria
| Speed Log: Accuracy | ± 0.1 metres per second on each axis |
| Speed Log: Update Rate | at least once per minute |
| Acoustic Doppler Current Profiler: Update Rate | at least once per minute |
| Acoustic Doppler Current Profiler: Accuracy | ± 0.03 metres per second on each axis |
For the marine gravity, marine magnetometer, and acoustic Doppler current profiler the contractor should provide visual outputs as well as digital and analogue records. All analogue records (if provided) should be clearly and legibly annotated to include at least the following minimum in formation at the start and end of each line: date, time, line number, and shot point.
34. Minimum Positioning Spares Recommended
| Primary DCPS Positioning onboard including GPS receiver, demodulator, antenna and cabling, computer hardware and software | Secondary DCPS Positioning onboard including GPS receiver, demodulator, antenna and cabling, computer hardware and software |
|---|---|
| DCPS at each reference station GPS receiver, demodulator, modem and relay capability, antenna and cabling, computer hardware and software | 100% (in 'hot stand by mode') |
| Tailbuoy Vehicles including rGPS unit, telemetry link, power supply, antenna and cabling, computer hardware and software* | 50% of minimum number of active tailbuoys required (rounded up for odd numbers ) |
| Acoustic Positioning Transponders / Responders* | 25% |
| Acoustic Positioning: Batteries | new at mobilization (replaced within manufacturer's expected duration) |
| Streamer Compasses* | 50% |
| Streamer Compasses: Batteries | new at mobilization (replaced within manufacturer's expected duration) |
| Streamer Depth Controllers* | 50% |
| Streamer Depth Controllers: Batteries | new at mobilization (replaced within manufacturer's expected duration) |
| Laser positioning unit | 100% |
| Gyro compass | 100% |
| Navigation Data Logging units | 100% |
| Repair of Equipment: Maximum Period of Navigation Downtime (if operationally feasible) | 6 hours |
* These suggested percentages of spares may not be required for multi streamer surveys where it could be possible to cannibalize a streamer(s) to allow production to continue. In such cases provisions for such a possibility should be included in the contract.
35. Pre Survey Checks, Verifications and Calibrations of Positioning Systems – Timing
| DGPS Positioning Verification - Primary | during mobilization |
| DGPS Positioning Verification - Secondary | during mobilization |
| Primary and Secondary DGPS Reference Stations – GPS Health (Site) Audits | within 6 months of mobilization |
| rGPS Positioning Verification | all during mobilization |
| Laser Positioning Calibration | within 4 months of mobilization |
| Laser Positioning Calibration: Directions | both (same as for gyro compass(es)) |
| Laser Positioning Calibration: Long Projects | repeated at 6 months from start of survey |
| Acoustic Positioning: Inspection of hull mounted Transducer by Diver to clear marine growth from transducer) | during mobilization (if not accessible through gate valve) or at discretion of company |
| >Streamer Compasses: Manufacturer's Calibration | within 24 months of mobilization |
| >Streamer Compasses: Verification by contractor | within 24 months of mobilization |
| Streamer Depth Controllers: Calibration | all during mobilization |
| Gyro Compass(es) Calibration | within 4 months of mobilization |
| Gyro Compass(es) Calibration: Directions | both |
| Gyro Compass(es) Calibration: Long Projects | repeated at 6 months from start of survey |
| Echo Sounder Transducer Check: Inspection by Diver (to clear marine growth from transducer) |
during mobilization (if not accessible through gate valve) or at discretion of company |
| Echo Sounder Check: Lead Line Check | during mobilization or at discretion of company |
| Echo Sounder Check: Bar Check | prior to acquisition if operationally feasible |
| T/S Bridge or Seawater Sound Velocity Meter | within 12 months of mobilization |
| Speed of Sound in Water Column for Echo Sounder | at prospect centre and if operationally feasible, at corners of prospect prior to commencement |
| Speed of Sound in Water at Streamer Depth for Acoustic Positioning | in prospect prior to commencement |
| Marine Gravity (if applicable): As Required by Manufacturer | during mobilization, including alongside still reading |
| Marine Magnetometer (if applicable): As Required by Manufacturer | during mobilization |
| Speed Log (if applicable) Transducer Check: Inspection by Diver (to clear marine growth from transducer) |
during mobilization (if not accessible through gate valve) or at discretion of company |
| Acoustic Doppler Current Profiler (if applicable) Transducer Check: Inspection by Diver (to clear marine growth from transducer) |
during mobilization (if not accessible through gate valve) or at discretion of company |
| Results to be available prior to commencement of seismic acquisition | within 12 hours of commencement |
The company may request to be present at any or all of these checks, verifications and calibrations.
36. Checks, Verifications and Calibrations of Positioning Systems – During Acquisition
| DGPS Positioning | comparison of network solution with each DGPS Reference Station for each line or part of a line |
| DGPS Positioning - Primary versus Secondary | comparison for each line or part of a line |
| Laser Positioning Check: To Fixed Target onboard | daily or at discretion of company |
| Laser Positioning Check: via Post Processed Comparisons | weekly |
| Laser Positioning Distance Check versus rGPS | during deployment and recovery of streamer(s) within 200 metres of stern |
| Laser Positioning Position Check versus Acoustic Positioning | during deployment and recovery of streamer(s) within 200 metres of stern |
| Streamer Compasses: Dynamic Biases (for appropriate shot point interval consistent with the method of calculation) | for each line or part of a line |
| Streamer Depth Sensors: Calibration Check | all replacements to be checked before deployment |
| Gyro Compass(es): Check On Line | for each line or part of a line |
| Gyro Compass(es): Check by Transit Bearings, Sun Shots, or other methods | when appropriate |
| Speed of Sound in Water Column for Echo Sounder | weekly; changed when differs by 2 metre per second or sooner if changes in seas conditions warrant |
| Speed of Sound in Water at Streamer Depth for Acoustic Positioning | weekly; changed when differs by 2 metre per second or sooner if changes in sea conditions warrant |
| Vessel Draught | weekly during calm sea conditions; changed when differs by 0.5 metres |
| Marine Gravity (if applicable): As required by Manufacturer |
daily checks, including still readings during any port calls |
The company may request to be present at any or all of these checks, verifications and calibrations.
37. Post Survey Checks, Verifications and Calibrations of Positioning Systems – Timing
| DGPS Positioning Verification - Primary | at discretion of company |
| DGPS Positioning Verification - Secondary | at discretion of company |
| rGPS Positioning: Verification | at discretion of company |
| Laser Positioning: Calibration | period since previous verification greater than twice period stated above, or at discretion of company |
| Streamer Compasses: Verification by contractor | period since previous verification greater than twice period stated above, or at discretion of company |
| Streamer Depth Sensors: Calibration | at discretion of company |
| Gyro Compass(es): Calibration | period since previous verification greater than twice period stated above, or at discretion of company |
| Speed of Sound in Water Column for Echo Sounder | in prospect at end of survey |
| Echo Sounder: Lead Line Check | during demobilization or at discretion of company |
| Echo Sounder: Bar Check | during demobilization or at discretion of company |
| Marine Gravity (if applicable): As required by Manufacturer |
during demobilization |
| Marine Gravity (if applicable): Land Tie (select) | Yes / No |
| Preliminary Results to be available | prior to end of demobilization |
The company may request to be present at any or all of these checks, verifications and calibrations.
38. Checks, Verifications and Calibrations of Positioning Systems - Acceptable Results
| DGPS Positioning Verification - Land Survey Methods versus DGPS network solution (for the same instant in time) | less than 3 metres average radial difference, standard deviation less than 2 metres |
| DGPS Positioning Verification - Land Survey Methods versus each DGPS reference station position (for the same instant in time) | less than 3 metres average radial difference, standard deviation less than 2 metres |
| Accuracy of Known Points used for Land Survey Comparison on WGS84 datum (if used) |
± 0.3 metres or better |
| Accuracy of Known Points used for Land Survey Comparison on Local Datum (if used) |
± 0.3 metres or better |
| Accuracy of Land Survey Distance measurement | at least ± 0.2 metres |
| Accuracy of Land Survey Direction measurement | at least ± 0.02 metres |
| DGPS Positioning Verification - Integrity Check Method versus DGPS network solution |
less than 2 metres average radial difference, standard deviation less than 2 metres |
| DGPS Positioning Verification - Integrity Check Method versus DGPS network solution Scatter Plot |
tight plot around mean position |
| Secondary DGPS Positioning Verification (alongside) | same as Primary, or average radial difference with Primary less than 3 metres |
| rGPS Positioning Verification - Land Survey Methods versus each rGPS position | less than 3 metres average radial difference, standard deviation less than 2 metres |
| rGPS Positioning Verification - Re-radiation Method versus each rGPS unit |
less than 1 metre average standard deviation less than 1 metre |
| Laser Positioning Calibration: Distance (for the same instant in time) |
less than 2 metres, standard deviation less than 0.5 metres; absolute difference between observations in 2 directions less than 0.7 metres |
| Laser Positioning Calibration: Direction (for the same instant in time) |
less than 2 degrees, standard deviation less than 0.2 degrees: absolute difference between observations in 2 directions less than 0.6 degrees |
| Laser Positioning: Agreement with Previous Results | distance within 1.0 metres, direction within 0.4 degrees |
| Laser Positioning Check: To Fixed Target onboard | distance within 0.5 metres, direction within 0.2 degrees |
| Laser Positioning Check: via Post Processed Comparisons | distance within 0.7 metres, direction within 0.6 degrees |
| Laser Positioning: Distance Check versus rGPS during deployment and recovery | less than 2 metres average radial difference |
| Laser Positioning: Position Check versus Acoustic Positioning during deployment and recovery | less than 3 metres average radial difference |
| Streamer Compasses: Verification by contractor | manufactures preset (A, B and C) values should be unaltered from the values derived during the most recent manufacturer's calibration |
| each static bias less than 0.5 degrees of either sign, provided that for each compass the size is the same | |
| each average static bias less than 0.5 degrees | |
| 2% tested for roll at ± 5, ± 10, and ± 15 degrees and pitch at ± 5 and ± 10 degrees; each bias less than 0.85 degrees of either sign, provided that for each compass the size is the same | |
| Streamer Depth Sensors: Calibration on Deck | depth error less than 0.2 metres |
| Gyro Compass(es): Calibration* | standard deviation less than 0.1 degrees; absolute difference between observations in 2 directions less than 0.4 degrees |
| Accuracy of Azimuth Baseline used for Gyro Compass(es) Calibration | ± 0.05 degrees |
| Gyro Compass(es) Calibration: Agreement with Compass(es) Calibration | within 0.6 degrees |
| Echo Sounder Check: Lead Line Check (taking into consideration possible debris alongside) |
less than 0.5 metres between echo sounder and lead line check |
| Echo Sounder Check: Bar Check | less than 0.3 metres between bar and echo sounder |
| Marine Gravity (if applicable): Daily and Post Survey | as per manufacturers specifications |
| Marine Gravity (if applicable): Still Reading | similar results to previous, less than 1 mGal drift per month since last reading |
| Marine Magnetometer (if applicable): Connected to Test Module Sensor | less than ± 2 nT after at least 2 hours; readings should drift over time |
*If the gyro compass correction is larger than 1.5 degrees of either sign, consideration could be given to slewing the gyro compass and repeating the observations.
39. Checks, Verifications and Calibrations of Positioning Systems - Acceptable On Line Results
| DGPS Positioning comparison of network solution with each DGPS Reference Station for each line or part of a line* |
less than 3 metres average radial difference |
| less than ± 2 metres difference in Eastings | |
| less than ± 2 metres difference in Northings | |
| DGPS Positioning - Primary versus Secondary** | less than 3.5 metres average radial difference |
| Streamer Compasses: Dynamic Biases (for appropriate shot point interval consistent with the method of calculation) | less than 0.8 degree (1.2 degrees for front and tail compasses) of either sign |
| Gyro Compass(es): Check On Line* | absolute difference between each gyro compass for each line less than 1.0 degrees |
*These checks could be used as quality control tools and not necessarily as rejection criteria.
** This should be a necessary condition when switching between the two systems when the primary DGPS temporarily fails. If this condition is not met, production should cease until the DGPS positioning improves, and an explanation is provided by the contractor to the satisfaction of the company.
40. Rejection Criteria - Acceptable Data for Each Line or Part of a Line
| DGPS Positioning: Primary or Secondary | 100% |
| Shot Point Interval: Nominal (over any 200 shot point sliding window) | ± 1% and not more than 7 consecutive shot points |
| Shot Point Interval: Mean* | nominal ± 0.02 metres |
| Shot Point Interval: Standard Deviation | less than 2.0% of nominal |
| rGPS Positioning | 95% and not more than 20 consecutive shot points |
| Laser Positioning | 95% and not more than 20 consecutive shot points |
| Acoustic Positioning for One or More Streamers | loss for not more than 20 consecutive shot points |
| For each Front Acoustic Range | 70% of range data with in a 3 metre window centered on nominal range |
| Reflected Acoustic Ranges | 5% of total number of acoustic ranges in each acoustic network |
| Streamer Compasses | 95% and not more than 20 consecutive shot points |
| For each Streamer Compass where one of the following derived from the time series plots or statistics may apply: | less than 0.8 degrees from best linear fit of data over 250 metres either side of the event |
| average value less than 0.8 degrees from adjacent compasses on same streamer | |
| differences of the standard deviation (DSD or Dstd ) between adjacent compasses on the same streamer less than 0.7 degrees | |
| calculated dynamic bias unacceptable for 5 or more lines or parts of lines in same direction | |
| Streamer Depth Sensors | not more than 10 consecutive shot points rejected between any two adjacent sensors, or between the front and tail of any streamer |
| Echo Sounder: Operational Downtime | more than 1 hour |
| Source Depth | not more than 10 consecutive shot points rejected |
| Marine Gravity (if applicable) if either: | horizontal accelerations in excess of 60,000 mGal peak to peak on either axis |
| cross coupling readings in excess of ± 20 mGal | |
| Marine Magnetometer (if applicable) | greater than 10 nT peak to peak |
| Network Adjustment: Variance Covariance Matrix in Front Network | each attribute less than 5 metres for 95% of shot points in line or part of a line |
| Near Trace Radial Offset: Variation | less than 2 metres, unless such variations are a result of tides and currents influencing the towing characteristics, or other physical causes |
* Inline shot to shot spikes over 2.5 metres should correlate with shot point time interval spikes. Cross line spikes over 4 metres should be investigated to ensure filtering parameters are set up correctly for the data, or any other problems.
Post processed navigation data should be used in the acceptance or rejections of lines. This means that a line may be accepted in real time but subsequently rejected due to problems highlighted during processing.
41. Survey, Navigation and Positioning Misfire Criteria
| DCPS Positioning: Primary and Secondary | any loss or unacceptable DCPS for both systems simultaneously |
| Tailbuoy rGPS Positioning: Acceptable Number | falls below minimum |
| Sub Array rGPS or Front (gun) Float rGPS | falls below minimum; rectified prior to start of next line |
| Positioning: Acceptable Number | |
| Laser Positioning* | no data available, if operationally feasible rectified prior to start of next line |
| Acoustic Positioning for One or More Steamers** | no data available |
| Streamer Compasses: Streamer Rejected | if on same streamer, 3 or more or any 2 adjacent streamer compasses rejected |
| Echo Sounder | exceeds minimum downtime criteria |
* Missing laser positioning (if used) data caused by fog, rain and sea conditions should be considered beyond the control of the contractor. Redundancy in the front network should take this into consideration if the these conditions are expected regularly during the 3D survey.
** Missing acoustic positioning data may be interpolated provided the vessel was on a steady course, there were no significant feather changes (less than 2 degrees), and existing sea state allowed suitable interpolation to be carried out at discretion of the company.
Continuation could be allowed depending on performance of supporting systems and redundancy during the line and at discretion of the company. Acquisition could continue provided the following criteria are met for each system:
- Loss of tailbuoy rGPS positioning - all other acoustic ranges in the tail network (not including those to the unacceptable active tailbuoy(s) l should be acceptable.
- Loss of sub array rGPS positioning or of front (gun) float - reliable and consistent laser and acoustic positioning data is available to position the affected centre of source(s).
- Loss of acoustic positioning to sub array(s) - reliable and consistent rGPS and laser positioning data is available to position the affected centre of source(s).
- Loss of laser positioning to the sub array(s) - reliable and consistent rGPS and acoustic positioning data is available to position the affected centre of source(s).
- Loss of acoustic positioning for one or more streamers - there were no variations in the streamer feather angle(s), and there were no sudden heading changes during the effected period.
42. Survey, Navigation and Positioning Line Termination Criteria
A line or part of a line should be terminated if the survey, navigation and positioning misfire criteria in the preceding tables are not met for anyone of the following systems for the number of consecutive shot points given below, unless continuation is approved by the company.
| DCPS Positioning: Primary and Secondary | not more than 5 consecutive shot points |
| Tailbuoy rGPS Positioning | not more than 20 consecutive shot points |
| Sub Array rGPS Positioning | not more than 20 consecutive shot points |
| Front (Gun) Float rGPS Positioning | not more than 20 consecutive shot points |
| Laser Positioning | not more than 20 consecutive shot points |
| Acoustic Positioning | not more than 12 consecutive shot points |
| Streamer Compasses | not more than 20 consecutive shot points |
| Gyro Compass | not more than 20 consecutive shot points |
| Echo Sounder | not more than 100 consecutive shot points |
| Binning: On-Line | not available for over 500 metres |
| Full Nominal Coverage | less than 85% |
| Continuous Misfires (for same source) | 8 or more of the shot points |
| Misfires Over Consecutive Shot Points | not more than 10 in 20 shot points |
| not more than 20 in 100 shot points | |
| Misfires for Any Line or Part of a Line | 4% |
| Misfires for Prospect | 2% |
43. Interrupted Line Continuation
| Shot Point Overlap for Start and End of Reshoot | 10 shot points (at no charge to company) | |
| Minimum Reshoot Length | active streamer length | |
| Number of Edits in Any Line or Part of a Line | maximum of 3 separate edits, cumulative total less than 25% of the complete planned line | |
| Minimum Number of Segments per Line | less than 20 km | 2 |
| 20 to 35 km | 3 | |
| 35 to 50 km | 4 | |
| greater than 50 km | at discretion of company | |
Reshoots should be acquired in the same direction as the original lines unless approved otherwise by the company. In fills should be also acquired in the same direction as the original lines, except at swathe boundaries, unless approved otherwise by the company.
44. Required Statistical Testing Values for Network Solution
| Probability of Test (Β) | 20% |
| Power of the Test (1 - Β) | 80% |
| Level of Significance (α) for the W-test | 1% |
| Level of Confidence (1 - α) for the W-test | 99% |
The calculation of the source and receiver group co-ordinates should be based upon the least squares adjustment and include full statistical testing. The preferred testing method for all observables is by applying Baarda statistical testing for outliner detection. The preferred processing approach is an integrated adjustment whereby all observables are processed in one integral network adjustment per event. Alternatively, processing may be based on a sequential adjustment of partial networks.
45. Suggested a priori Standard Deviations (1σ)
| Vessel Offsets and Baselines | |
| Towed Offsets and Baselines | |
| Vessel DGPS Positioning: Easting | |
| Vessel DGPS Positioning: Northing | |
| rGPS Range to Front (Gun) Float(s) | |
| rGPS Bearing to Front (Gun) Float(s) | |
| rGPS Range to Tailbuoy(s) | |
| rGPS Bearing to Tailbuoy(s) | |
| Laser Range | |
| Laser Bearing | |
| Streamer Compasses | |
| Streamer Compasses: First and Last | |
| Acoustic Ranges | |
| Gyro Compass(es) | |
| Course Made Good (if used) |
The same or similar a priori values should be met, and should be used in order to achieve the a posterior values required. Different contractor's will use different values.
What is important is that the 'relative' weighting between the observations should be correct. Based on the post processed results of the first 5 accepted lines, these parameters should be either confirmed or reviewed to better fit the actual data performance. The confirmed or updated parameters to be used for the post-processing of all lines acquired during the survey, should be agreed in writing by both the contractor and the company.
For each line or part of a line, the Unit Variance for each network should lie about a value of 1 ± 0.3. However, since the observables are filtered and possible correlations between them are disregarded, the Unit Variance may not be one. A pessimistic set of a priori values would reduce the Unit Variance value towards zero. It is preferable to concentrate on the consistency of the Unit Variance over the survey area, and over the line analyzed in particular. Peculiar variation(s) of the Unit Variance from the average for the prospect should be systematically investigated.
46. Acceptable Network Comparisons with Calculated Offset Positions
| Comparison between Network Solution and Positions | Tolerance | Acceptable Fixes for Each |
|---|---|---|
| Derived from Vessel Offsets, Laybacks, and | Line or Part of a Line | |
| Streamer Compasses for: | ||
| Sources and Front Acoustic Sensors | ± 3 metres (radial) | 95% |
| Tail Acoustic Sensors | ± 7 metres (cross-line) | 95% |
| Tail Acoustic Sensors | ± 2 metres (in-line) | 95% |
For each streamer, the tailbuoy misclosure angle should not be greater than 0.5 degrees. The tailbuoy misclosure angle is the derived angle from the head of each streamer between the positioning solution for the streamer tailbuoy (whether actively positioned or not) derived from offsets and the streamer compasses, and the tailbuoy rGPS position. The results for each streamer should be sorted by line direction, and for averages over 0.3 degrees the magnetic variation should be further analyzed. Regardless of the line direction, the derived magnetic declination from the tailbuoy misclosure angles should be of the same algebraic sign, and should be consistent over a localized area (although some differences may be observed in large prospects over volcanic strata) .
47. Acceptable Residuals
| rGPS Range to Front (Gun) Float(s) | less than 1 metres | |
| rGPS Bearing to Front (Gun) Float(s) | less than 0.2 degrees | |
| rGPS Range to Tailbuoy(s) | less than 1 m | (for 300 m streamers, pro- |
| rGPS Bearing to Tailbuoy(s) | less than 0.3° | rated for other configurations) |
| Tailbuoy In-Line Misclosure | less than 3.0 metres | |
| Laser Positioning (if used): Range | less than 0.7 metres | |
| Laser Positioning (if used): Direction | less than 0.6 degrees | |
| Acoustic Positioning: Ranges | less than 0.5 metres | |
| Gyro Compass(es) | less than 0.5 degrees | |
48. Navigation Recording and Post Processing Parameters
| TIME to be used for all data logging and reporting | |||
| STANDARD PORT with reference (for tidal information) | |||
| Survey, Navigation and Positioning Statistical Data Format | Microsoft Excel® / Lotus 1-2-3® | ||
| (select software version and specify media) | Media: | ||
| Format: | Media: | Copy to: | |
|---|---|---|---|
| Raw Navigation Data Format* | UKOOA P2/91 | Client | |
| Number of Acquired Lines per Tape | |||
| Tape Naming Format: Raw** | |||
| Final Post Processed Data Format | UKOOA P1/90 | Client, Seismic | |
| Processing | |||
| Contractor | |||
| Number of Post Processed Lines per Tape | |||
| Tape Naming Format: Post Processed** | |||
| Final Post Processed Data Available for On Line Binning Display | within 12 hours of completion of a line or part of a line | ||
| Final Post Processed Data Format for Vessel Position Files*** | UKOOAP1 /90 | Client | |
| Final Post Processed Data Format for Vessel Position Files | UKOOAP1 /90 | Client | |
| and Reduced Bathymetry One header and all V and E records. | |||
| Final Post Processed Data Format for CMP data (Generally | UKOOA P1 /90 | Client | |
| the position between centre source and the first record.) | |||
| Marine Gravity Data if applicable: | Lotus 1-2-3® | Client, Gravity | |
| Standard digital Lacoste - Romberg Format | Compatible | Processing | |
| Contractor | |||
| Marine Magnetometer (if applicable) | Client | ||
| Acoustic Doppler Current Profiler (if applicable) | |||
* Raw data only with no filtering or smoothing applied to the data.
** The contractor may have a standard tape naming format which may be suitable.
*** Generally with one header and all V records, although may be required as all V records with individual headers.
The contractor should ensure that there are no discrepancies between the survey, navigation and positioning logging and records, and the seismic acquisition logging and records. All positioning data should be co-registered with all other data in both time and sequence number formats in order to permit unambiguous correlation with the seismic record data. The contractor should ensure that all positioning post-processing and co-registration with the seismic records is completed onboard, unless agreed otherwise in writing with the company.
All raw data should be recorded to disk or other medium for all survey, navigation and positioning systems. All records for one position fix should be referred to the same instant in time (generally gun firing). Deskewing to the time of gun firing should be carried out by means of extrapolation or interpolation from a consecutive number of samples. Proof of correct deskewing technique will be required by the company.
The most recent unfiltered time-tagged laser positioning data should be available to the integrated navigation system. Old readings should be clearly identified and rejected from the network adjustment.
The contractor should provide, for each line or part of a line, a log showing the status of the positioning systems; any irregularities, changes or failures should be noted as they occur. These logs and quality control logs and time series plots for every system and sensor used onboard should be included with the navigation data
The company should be allowed to view all onscreen data and any hard copy outputs at any time. Copies of this information should be provided if requested by the company.
49. Navigation Post Processing for Third Party Quality Control
| Format: | Media: | Within: | |
|---|---|---|---|
| Raw Navigation Data Format | UKOOA P2/ 91 | 5 hours | |
| Final Post Processed Data Format | UKOOA P1/90 | 9 hours |
Data should be available, if required, within the period specified, from the completion of a line or part of a line, otherwise acquisition should cease. The time period could also be specified relative to the expected acquisition time for the typical line length of the survey.
Access should be provided to a separate contractor's navigation work station to allow the company representatives to inspect the raw and post processed data for each line or part of a line at any time.
50. Survey, Navigation and Positioning Statistical Data Required for Each Line
| Line Name | first and last shot point |
| Primary DGPS | maximum HDOP, maximum PDOP, average HDOP, average computed height, DGPS reference stations used |
| Secondary DGPS | maximum HDOP, maximum PDOP, average HDOP, average computed height, DGPS reference stations used |
| Average difference comparisons with primary in Easting and Northing (or Along and Across) | |
| Laser positioning | unacceptable data that was not used for complete line |
| Acoustic positioning | unacceptable data that was not used for complete line |
| Streamer compasses | unacceptable data that was not used for complete line, or shot point range of any streamer compass data which was not acceptable for more than 20 shot points compass(es) which failed the calculated dynamic bias test |
| Gyro Compass(es) | performance comment with regard to oscillations average difference comparisons with primary gyro compasses |
| Echo Sounder | speed of sound in water column used and observed |
| Fully Integrated | results of statistical testing for whole network |
| Networks | results of statistical testing for each observable or observation type |
| average unit variance, average degrees of freedom, average residuals for each observable | |
| comparison of on-line and off-line results | |
| average separations for sub-arrays, and centre of sources | |
| average streamer front, middle (if used) and tail separations between each adjacent pair (e.g., between streamers 1 and 2, streamers 2 and 3, etc.) | |
| average angular tailbuoy misclosure (rotation) and average in-line and cross-line misclosures for each streamer | |
| average shot point interval, shot point interval test based on distance and time | |
| absolute error ellipses for selected CMP locations specified by the company | |
| effect of undetected errors in the observations, of the size of the MOE (marginal detectable error), for each observation on the CMP co-ord inates (e.g., external reliability) | |
| Shot Points | all edits declared survey, navigation and positioning misfires, or seismic misfires, as well as any trace edits |
Edits could be included in final P1 / 90 version provided that the procedure does not adversely effect the integration of the navigation and seismic data during seismic processing.
51. Final Navigation Deliverables
| Film | Paper | Scales | Copies | Within | |
|---|---|---|---|---|---|
| Raw Navigation Data | 1 | 2 weeks | |||
| Final Post Processed Navigation Data | 2 | 2 weeks | |||
| Final Post Processed Data for Vessel Positions | 1 | 2 weeks | |||
| Final Post Processed Data for CDP Positions | 1 | 2 weeks | |||
| Shot Point Location Map (select) | Yes / No | 1:25 000 | 4 | 2 weeks | |
| Plotting and Labeling Intervals | 10 and 100 | ||||
| Shot Point Location Map (select) | Yes / No | 1:50 000 | 4 | 2 weeks | |
| Plotting and Labeling Intervals (metres) | 50 and 500 | ||||
| Large Scale Antenna Position Maps (select) | Yes/No | 1: | 4 | 2 weeks | |
| Large Scale Coverage Maps (select) | Yes/No | 1: | 4 | 2 weeks | |
| Water Depth Map(s) corrected for draught, speed of sound and tides (select) | Yes/No | 1: | 4 | 2 weeks | |
| Water Depth Contour Map(s) (select) | Yes / No | 1: | 4 | 2 weeks | |
| Water Depth Contour Interval (select) | Yes / No | 10 metres | |||
| Final Navigation Report (specify numbers of copies) | n /a | Yes | n /a | ||
| Copy of Report on diskette (select) | Word® / Word-perfect® | ||||
| Marine Gravity Data (if applicable) | 2 | 1 month | |||
| Marine Magnetometer Data (if applicable) | 1 | 2 weeks | |||
| Acoustic Doppler Current Profiler Data (if applicable) | 1 | 2 weeks | |||
| Spatial Plots (see next Table) | Yes | A4 and A3 | 4 | by demob | |
| Field Navigation Tapes | kept until seismic processing completed | ||||
| Echo Sounder Trace Records | included with observers logs for each line or part of line | ||||
| On Line Navigation Printouts and Track Plots | kept until seismic processing completed | ||||
Final deliverables should be provided within the period specified from the completion of the survey
52. Required Spatial Plots
Different spatial plots are given under three separate topics.
| Coverage | Seismic Acquisition | Positioning |
|---|---|---|
| Coverage plots without flexed binning | In-line misclosure for each Streamer | dN: Primary v Secondary DGPS |
| Coverage plots with flexed binning | Average rotation angle for all streamers | dE: Primary v Secondary DGPS |
| Count displays for all hits in each bin including any duplicates | Average feather angle for all streamers | Primary positioning system height |
| Uniqueness offset coverage plots for each sub-line | Contoured water depth | Primary positioning PDOP |
| Centre source separation | Primary positioning HDOP | |
| Adjacent fro t streamer separations | Secondary positioning PDOP |
53. Required Navigation Personnel – Minimum Number and Minimum Experience
| Minimum Number | Minimum Experience | |
|---|---|---|
| Chief Navigator | 1 | 3 years |
| Shift Leader(s) | 2 | 2 years |
| Navigator(s) | 2 | 1 year |
| Navigation Data Processor(s) (if provided ) | 1 | 2 years |
The numbers and experience of the navigation personnel will differ from contractor to contractor. Flexibility will be required by both the company and the contractor. The requirement being to ensure that the company is provided with competent contractor personnel, as well as the necessary opportunities are provided for the contractor's personnel to gain experience.
54. Navigation Data Shipments Details
| Addresses: | |
|---|---|
| Raw Navigation Data Tapes | |
| Post Processed Navigation Data Tapes | |
| Maps and Reports | |
| Marine Gravity Processing Contractor | |
| Marine Magnetometer Processing Contractor |
The above suggested survey, navigation and positioning guidelines for 3D marine seismic survey specifications are considered by the author to be practical or best practice values which should be achievable. As much as possible all of the multitude of parameters involved have been described, although that does not eliminate the possibility that something could have been overlooked. Also criteria which are relevant to particular contractor systems have not been described. New developments and technological improvements may make some of the above criteria redundant. Users of these guidelines may wish to vary any of the values and other criteria suggested due to commercial and operational considerations, and via negotiations to clarify or re-define possibly problematic criteria.
Acknowledgements
HSCIL has carried out 3D survey consulting assignments as the Client Navigation Representative for over 25 companies, while supervising a variety of contractors. This background and over 20 years of experience has allowed HSCIL to produce these guidelines. The author wishes to thank the personnel of several contractors, and other colleagues for their suggestions and comments.
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