MIRAI MR08-04 Shipboard Three Component Magnetometer (STCM)

The data provided is for corrected three component geomagnetic field anomalies. Three-axes flux-gate sensors with ring-cored coils were fixed on the roof of the bridge.
They measure the following items :
The effect of ship motion was eliminated by roll and pitch data which was provided by a tilt sensor. The apparent magnetic influence can be detected through a "Figure of 8 turn"(a pair of clockwise and anti-clockwise turns) on each cruise. If no Figure of 8 turn on the cruise was completed, the latest Figure of 8 turn from the previous cruise was applied (see section 4.). As a quality control, data of low reliability was removed (see section 5. for quality control criteria). Synthetic geomagnetic field values were calculated from IGRF models.

1. (1) Magnetometer
Manufacturer : Tierra Technica Ltd.
Type : SFG1214
Measurement range : ±100,000 nT
Accuracy : less than 100 nT
Resolution : 1 nT
Location : Dry Laboratory


2. (2) Magnetic Sensor
Manufacturer : Tierra Technica Ltd.
Form : flux-gate sensors with ring-cored coils
Location : Foremast


3. (3) Attitude sensor and Gyro compass
Manufacturer : IXBLUE
Type : PHINS
Accuracy(Roll, Pitch) : 0.01 degree
Accuracy(Gyro) : 0.01 degree *Secant(Lat.)
Location : In the doppler radar dome

The following corrections and calculations were performed.

(1) Ship magnetization correction
   Hob = ARPYF + Hp ---(i)
  Hob: Observed magnetic field vector (Ship coordinates)
  A: Effect of induced magnetization of the ship
  R: Matrix of rotation due to the roll
  P: Matrix of rotation due to the pitch
  Y: Matrix of rotation due to the heading
  F: Geomagnetic field vector
  Hp: Ship's permanent magnetic moment

Following the equation(i), we calculate the geomagnetic field F.
    RPYF = BHob + Hbp ---(ii)
  B: coefficient of Figure of 8 turn
  Hbp: Permanent magnetic field vector of the ship

Reference: Isezaki,N., A new shipboard three-component magnetometer, GEOPHYSICS. VOL.51,NO10(1986);P1992-1998

(2) International Geomagnetic Reference Field (IGRF)
  Synthetic geomagnetic field values are calculated from IGRF 11th Generation models by using navigation data ; latitude, longitude and date.
  Reference:IAGA Division V-MOD Geomagnetic Field Modeling[http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html]

(3) Calculation of the geomagnetic field anomaly
    An = F - Figrf
  An: Geomagnetic field anomaly vector
  F: Geomagnetic field vector
  Figrf: Synthetic geomagnetic field vector from IGRF

(4) Quality control of data
  Following criteria were used for removal of data of low reliability:

      ･Time error (inversion of time, continuation of same timestamps)

      ･Summation of the difference of heading by one second exceeding 20 degree per 5 minutes

      ･Ground speed of the ship below 3knot or exceeding 20knot

      ･X, Y, or Z component of geomagnetic field anomaly exceeding ±4000nT

(5) Filtering of the geomagnetic field anomaly
  Due to the residual undulation of the ship, a 120 second length Gaussian filter was applied for each component of the geomagnetic field anomaly data.

(6) Output of the data
  Time (UTC)
  Latitude (degree)
  Longitude (degree)
  X: Northward (positive on the north) component of geomagnetic field anomaly (nT)
  Y: Eastward (positive on the east) component of geomagnetic field anomaly (nT)
  Z: Vertical (positive for downward) component of geomagnetic field anomaly (nT)
  T: Absolute value of geomagnetic field anomaly (nT)

		|	0.9959	0.0360	0.0298	|			|	2234.6950	|
B	=	|	-0.0388	1.0601	-0.0024	|	Hbp	=	|	-261.5415	|
		|	0.0378	0.0055	0.9396	|			|	1613.8566	|

(1) File naming rule: Cruise ID_corr.stcm
(2) Sampling rate: 10 seconds
(3) Geodetic system: WGS84
(4) If you would like the raw data set, please contact us from "Contact Us" above.