OR/14/014 Part 2: Survey logistics
|Beamish D and White J. 2014. TellusSW: airborne geophysical data and processing report . British Geological Survey Internal Report, OR/14/014.|
Aircraft and equipment
Aircraft and Geophysical on-board equipment
|Operator||:||CGG AIRBORNE SURVEY|
|Survey Speed||:||140 knots|
|Magnetometer (x3)||:||Scintrex CS-3 single cell caesium vapour, wing pod(s) and/or tail stinger installation, sensitivity = 0.01 nT , sampling rate = 0.5 s, ambient range 20 000 to 100 000 nT. The general noise envelope was kept below 0.5 nT.|
|Radar Altimeter||:||Honeywell KRA405B|
|Electronic Navigation||:||Novatel OEMV-3 & Omnistar DGPS|
Base Station Equipment
|Magnetometer||:||Scintrex CS-3 single cell caesium vapour, mounted in a magnetically quiet area, measuring the total intensity of the earth’s magnetic field in units of 0.01 nT at intervals of 0.5 sec, within a noise envelope of 0.20 nT.|
|GPS Receiver||:||NovAtel OEM4, measuring all GPS channels, for up to 12 satellites.|
|Computer||:||Laptop, Pentium model.|
|Data Logger||:||CF1, SBBS (single board base station).|
Data Processing equipment
|Printer||:||Portable inkjet printer.|
|DVD writer Drive||:||Internal DVD+RW format.|
|Hard Drive||:||1024 GB Removable hard drive.|
Survey aquisition progress
PROJECT ACQUISITION FIGURES
|Total survey line kilometres Accepted|
|Total Flying Hours|
PROJECT DOWNTIME FIGURES
|Total days flown|
|Lost days due to Weather Influence|
|Lost days due to Excessive Diurnal activity|
|Lost days due to Aircraft Mechanical Issues|
|Lost days due to Electronical Issues|
|Lost days due to Data/System Noise|
|Lost days due to sickness, injuries or other HSEQ Incidents|
|Lost days due to mandatory Pilot Down Days|
|Lost days due to Logistics
(Permits, security, fuel shortages, unrest)
|4.25 (2 Days Total Invoice able)|
|Lost days due to 3rd Party Influence|
Tests and calibration
Important checks were performed before, during and after the data acquisition stage to ensure that the data quality was in keeping with the survey specifications. The following outlines the Quality Control measures conducted throughout the acquisition phase of the survey.
The difference between the time a reading is taken and the time it is stored, due to computer processing time and position of the different sensors relative to the GPS antenna was determined in the field. See Appendix 3 Tests and calibrations results for the lag value of the different geophysical systems.
Magnetic tests and calibration
MAGNETOMETER COMPENSATION (FOM)
The compensation procedure involved the flying, at altitude, over a magnetically quiet area, undertaking aircraft manoeuvres, rolls ± 10°, pitches ± 5° and yaws ± 5°, along headings parallel to the traverse and control line trends. A fluxgate magnetometer monitored these manoeuvre noise effects and the compensator accumulated the results. The compensator returned a Figure of Merit (FOM) value, results of which are presented in Appendix 3 Tests and calibrations results .
Before the commencement of the survey several lines were flown at standard speed and flying height in opposite directions over a suitable, well controlled magnetic anomaly to establish the parallax of the system (spatial relationship between GPS and magnetometer readings).
The system noise was measured and recorded at the project site before the survey started, see Appendix 3 Tests and calibrations results .
The results of the heading test are presented in Appendix 3 Tests and calibrations results .
The radar altimeter was calibrated at the start of the survey. See tabulated results in Appendix 3 Tests and calibrations results .
Quality control of production data
At the completion of each day’s flying an initial review of the data was performed in the field. This process was primarily to ensure all the equipment was functioning properly and enables the crew to immediately ascertain that production can resume the following day. This process does not necessarily determine if the data were within specifications. Priority was given to getting the data back to the office where a more thorough analysis of the data was performed. A list of the steps of the initial field review of the data follows:
- All digital files were confirmed to be readable and free of defects.
- The integrity of the airborne data was checked through statistical analysis and graphically viewed in profile form. Any null values or unreasonable noise levels were identified.
- All altimeter and positional data were checked for any inconsistency, invalid values and spikes.
- The base station files were examined for validity and continuity. The data extent was confirmed to cover the entire acquisition period.
- The diurnal data were examined for any noise events or spiking.
- Flight path video files were visually checked for quality and to confirm the full coverage for the survey flight.
- Duplicate backups of all digital files were created.
Data checking and editing
All acquired data were thoroughly checked at each field base prior to delivery to the Johannesburg processing centre, including checking of line and flight numbers and spike checking in all major data channels. Upon receipt of the data in Johannesburg, these procedures were repeated, beginning again from the raw (untouched) data and providing a backup check of data quality.
The line data was checked for noise, flight path separation, height deviation, gaps and spikes using in-house CGG ATLAS software. The magnetic diurnal was checked and later corrected as described in Part 3: Data Processing .
All lines passed the basic QC check.
Line spacing control
Standard quality control routines were applied to highlight deviations from the planned flight path that exceed survey specification. These are accepted if a valid safety or other acceptable reason for the deviation is given in the flight log.
The survey was acquired on a drape surface. The figure 'Map of the height deviation from planned drape' in Appendix 3 Tests and calibrations results presents the deviation from the planned drape.