MIRAI MR12-05 Leg3 Gravity

Last Modified: 2019-07-23
: MR12-05 Leg3
: Processed (DMO)-Corrected
: JAMSTEC
: Absolute gravity
:
OCEANS > MARINE GEOPHYSICS > MARINE GRAVITY FIELD
SOLID EARTH > GEODETICS/GRAVITY > GRAVITY

For Using Data

Data Management Office
See Terms and Conditions about constrain of use.
See Terms and Conditions about data citation.

2013-01-07 02:00 – 2013-02-13 11:58

Instrument:
Shipboard gravimeter
Instrument:
Microgravimeter (MR11-06 - )
The data provided here are quality-controlled absolute gravity data and free-air anomalies. The absolute gravity data are a combination of relative gravity data measured by the shipboard gravity meter and the absolute gravity data of the ports in departure and arrival. Drift corrections and the Eoetvoes corrections were done before converting into absolute gravity. As a quality control, low reliability data were removed (see Quality control of data for the judging criteria). The absolute gravity values of the ports are referenced to those of the Japan Gravity Standardization Net of the Geographical Survey Institute of Japan.
  1. (1) Shipboard gravity meter
    2. The system consists of two main assemblies; the gyro-stabilized platform including the gravity sensor and the data handling & control system.
    Manufacturer： LaCoste & Romberg
    Model： S-116
    Measuring range： 12,000 mGal
    Accuracy： 1.0 mGal
    Drift rate： < 3.0 mGal/month
    Installation： Gravity meter room
    Reference:「Model "S" Air-Sea Dynamic Gravity Meter SystemⅡ」 INSTRUCTION MANUAL LaCoste and Romberg Gravity Meters, Inc. 2004
  2. (2) Portable gravity meter
    3. The portable gravity meter consists of two modules; the data acquisition/control module and the gravity sensor module. The gravity sensor is enclosed in a thermostatically controlled vacuum chamber. The portable gravity meter is used to calculate the absolute gravity of the port with reference to the gravity station of the Japan Gravity Standardization Net of the Geographical Survey Institute of Japan.
    Manufacturer： SCINTREX
    Model： CG-5
    Measurement range： 8,000 mGal
    Standard deviation： 0.005 mGal
    Drift rate： < 0.02 mGal/day
    Reference:“CG-5 OPERATION MANUAL”, SCINTREX
Date (UTC) Port Absolute gravity (mGal) Sea level (cm) Draft shipboard (cm) Absolute gravity at sensor position (mGal) Reading of shipboard gravity meter (mGal)
2012/11/04 01:13:00
 SEKINEHAMA
980371.93 261
 625
 980372.95 12611.57
2013/03/29 02:33:00
 SEKINEHAMA 980371.93
 323
 575
 980373.03 12610.35
According to the filter process of the gravity meter system, the gravity data has a time lag of 120 seconds between the measurement and its output. After adjustment of this lag time, the following corrections and calculations were performed.

  1. (1) Drift correction
    2. D = ((Vge-Vgs)-(Age-Ags))/(Te-Ts)
    D: Drift value (mGal/day)
    Vgs: The shipboard gravity at the start of the cruise (mGal)
    Vge: The shipboard gravity at the end of the cruise (mGal)
    Ags: The absolute gravity at the shipboard sensor position at the start of the cruise (mGal)
    Age: The absolute gravity at the shipboard sensor position at the end of the cruise (mGal)
    Ts: The start time of the cruise (day)
    Te: The end time of the cruise (day)
  2. (2) Eoetvoes correction
    3. E = 7.503*S*cos(φ)*sin(α)+0.004154*S^2
    E: Eoetvoes correction (mGal)
    S: Ground speed of the ship (knot)
    φ: Latitude (radian)
    α: Course of the ship (radian、measured clockwise from the north)
    Reference: Blakely,R.J., Potential theory in gravity & magnetic applications, Cambridge University Press,New York,441pp,1995
    * The navigation data such as S,φand αare the 4-min average values. Before average processing, following data were removed from each dataset. If the number of data used for a 4-min average calculation did not include more than 50% of good data, the processed average value was considered as a missing value.
    ･ Time error (inversion of time, continuation of same timestamps)
    ･ Ship speed exceeding 20knot
    ･ Course of the ship except 0-360°
  3. (3) Calculation of the absolute gravity
    4. G = Ags+(Vg-Vgs)-D*(T-Ts)+E-H*(β-4π*k*ρw)
    G: The absolute gravity at sea surface (mGal)
     Ags: The absolute gravity at the shipboard sensor position at the start of the cruise (mGal)
     Vgs: The shipboard gravity at the start of the cruise (mGal)
     Vg: The shipboard gravity at the measurement time (mGal)
     D: Drift value (mGal/day)
     Ts: The start time of the cruise (day)
     T: The measurement time (day)
     E: Eoetvoes correction (mGal)
     H: Height from sea surface of the shipboard sensor position (m)
     β: Free-air gradient 0.3086 (mGal/m)
     k: Gravitational constant
     ρw: Density of sea water
     4π*k*ρw=0.0864
  4. (4) Calculation of the Free-air anomaly
    5. Gf = G -γ+δ
    Gf: The Free-air anomaly (mGal)
    G: Absolute gravity at sea surface (mGal)
    γ: Normal gravity(mGal)
    *The normal gravity formula of the Geodetic Reference System 1980
    γ=978032.67715(1+0.0052790414sin^2φ+0.0000232718sin^4φ+0.0000001262sin^6φ+0.0000000007*sin^8φ)
    δ: Atmospheric correction at sea surface
    δ=0.87-0.0000965*0(mGal)
  5. (5) Output of the data
    6. Time (UTC)
    Latitude (degree)
    Longitude (degree)
    Processed absolute gravity at sea surface (mGal)
    Free-air anomaly (mGal)
Following criteria were used for removal of low reliability data:
⋅ Abrupt free-air anomaly change exceeding 10mGal/km
⋅ Change in Eoetvoes correction exceeding 3mGal/min
⋅ Ground speed of the ship below 3knot
(1) File naming rule: Cruise ID_corr.grv
(2) Sampling rate: ten seconds
(3) Geodetic system: WGS84
(4) If you would like the raw data set, please contact us from "Contact Us" above.
: MR12-05 Leg3
: Processed (DMO)-Corrected
: JAMSTEC
: Absolute gravity
:
OCEANS > MARINE GEOPHYSICS > MARINE GRAVITY FIELD
SOLID EARTH > GEODETICS/GRAVITY > GRAVITY

Observation Map

Imagery reproduced from ...

Figures

Data List

  File names
MR12-05_leg3_corr.grv
: MR12-05 Leg3
: Processed (DMO)-Corrected
: JAMSTEC

Gravity Corrected

No. Column Content Format Unit Remarks
1 1 - 8 Date i4,i2,i2 YYYYMMDD (UTC)
2 10 -15 Time i2,i2,i2 hhmmss (UTC)
3 17 -25 Latitude f9.5 degree No sign for the northern hemisphere.
Negative for the southern hemisphere.
4 27 -36 Longitude f10.5 degree No sign for eastern hemisphere.
Negative for the western hemisphere.
5 38 -45 Absolute gravity f8.1 mGal
6 48 -53 Free-air anomaly f6.1 mGal

Related Information

Enlarge Image

MR12-05 Leg3

Ship Name: MIRAI

Period: 2013-01-05 - 2013-02-15

Chief Scientist: Hiroshi Uchida (JAMSTEC)

Proposal Title:
WOCE-revisit in the western Pacific and Southern oceans
Verification of new chemical tracers for studying ocean general circulation
Distribution and ecology of pelagic sea skaters and their response to environmental factors
Optical characteristics of aerosos on oceans observed by shipboard skyradiometer
Mapping stable oxygen isotope ratio on the Indian and Pacific sectors of the Southern Ocean
Distribution of water vapor isotope ratio on oceans
Study on ocean general circulation and heat/freshwater transport and their variability in the Pacific and Southern oceans using Argo floats
Carbon dioxyde and volatile organic matter influencing the climate system in the Southern Ocean
Clarification of Lyra seamount formation processes
Circulation of global warming gases related to marine biomass using isotopes
Standarization of geophysical data and application to ocean floor dynamics
Temporal and spatial distribution of optical characteristics of clouds and aerosols on oceans

Update History

2019-07-23
An observation data was registerd.
2014-08-12
An observation data was registerd.
2014-02-17
An observation data was registerd.
2013-11-05
An observation data was registerd.