Shipboard differential magnetometer survey is carried out separately or simultaneously with reflection 2D seismic survey, gravimeter survey and on the same lines. On completion of onboard checks of magnetometer, it will be deployed overboard with the use of special winch and will then be towed with floating cable at a fixed distance from the vessel. Magnetic survey will be acquired using one magnetometer (in the differential regime)
Magnetic survey will be acquired using SeaSpy2 magnetometer by Marine Magnetics (Canada). Sensors ensure highest absolute accuracy of any magnetometer, 0.1 nT. Sensitivity of SeaSpy2 sensors is unrivaled as well – better, than 0.01 nT.
Key technical specifications of SeaSpy2 magnetometer::
|Manufacturer||Marine Magnetics corp. Canada|
|Measurement resolution, sec||0,1 – 0,25|
|Absolute accuracy, nT||0,1|
|Range, nT||18 000 - 120 000|
The initial data are recorded with 2 sec sampling rate in ASCII text file:
- time (Greenwich time) (in seconds) from beginning of the day
- readings of Earth’s magnetic field sensors Т1
SeaSpy is a fully digitized system. Magnetometer signal is measured within the towed sensor where the signal is strongest and least affected by outer environment.
Magnetometer data record will be carried out continually using Sea LINK software and recorded in a computer text file with extension *.mag in ASCII format, (in the format adopted by equipment manufacturer).
Horizontal positioning is carried out from GPS receivers installed on board the vessel, from where the data arrives to the laboratory in NMEA0183 format (GGA or RMC protocol ) via RS-232 interface with sampling of 1 sec. Record of magnetic survey conditions is made in the logbook from gyrocompass repeaters and log.