A British Antarctic Survey Twin Otter and survey team acquired 8,300 line-km of aerogeophysics data during the Austral summer of 1998/99. Gravity and radio-echo data were acquired simultaneously with the magnetic data at a compromise constant barometric height of 2,200 m, which provides a terrain clearance of 100 m over the highest peaks. Two separate surveys were conducted; one at 5 km line spacing (tie lines at 20 km) over and stretching beyond the southern extent of the Forrestal range (main survey), and one at 2 km line spacing (tie lines at 8 km) covering the Dufek Massif (detailed survey).
Ashtech Z12 dual frequency GPS receivers were used for survey navigation. Pseudorange data were supplied to a Picodas PNAV navigation interface computer, which was used to guide the pilot along the pre-planned survey lines. The actual flight path was recovered, using carrier-phase, continuous, kinematic GPS processing techniques. All pseudorange navigation data were recorded at 1 Hz on a Picodas PDAS 1000, PC-based data acquisition system.
We present here the processed line aerogravity data collected using Lacoste and Romberg air-sea gravity meter S83.
Data are provided as XYZ ASCII line data.
Aerogeophysics, Aerogravity, Antarctica
|ISO Topic Categories:||
|Name||Dr P. C Jones|
|Organisation||British Antarctic Survey|
Ferris, J.K., Johnson, A.C., Storey, B.C., 1998. Form and extent of the Dufek intrusion, Antarctica, from newly compiled aeromagnetic data. Earth and Planetary Science Letters, 154 185-202. https://doi.org/10.1016/S0012-821X(97)00165-9
Ferris, J.K., Storey, B.C., Vaughan, A.P.M., Kyle, P.R., Jones, P.C., 2003. The Dufek and Forrestal intrusions, Antarctica: a centre for Ferrar Large Igneous Province dike emplacement? Geophysical Research Letters 30 DOI: 10.1029/2002GL016719
Hackney, R.I. & Featherstone, W.E., 2003. Geodetic versus geophysical perspectives of the gravity anomaly, Geophys. J. Int., 154, 35-43.
Holt, J.W., Richter, T.G., Kempf, S.D. & Morse, D.L., 2006. Airborne gravity over Lake Vostok and adjacent highlands of East Antarctica, Geochem. Geophys. Geosyst., 7, doi:10.1029/2005GC001177.
|Quality:||No values are given for St_Real, Beam_vel , Abs_grav, VaccCor, EotvosCor, LatCor, FaCor, and HaccCor. This intermediate information is not available for this legacy data.|
|Lineage:||The dataset available here includes channels from raw through to filtered free air anomalies, populated where processing steps could be recovered from older databases. Basic details on survey design are presented in Ferris et al., (1998, 2003).
Raw data from L&R meter #S83 includes:
Channel names in brackets
Spring tension (ST) meter units
Cross coupling (CC) meter units
Raw beam position (RB) mV
Cross axis accelerometer output (XACC) mV
Long Axis accelerometer output (LACC) mV
Gravity processing steps were as follows:
1/ Calculate observed gravity.
True spring tension (ST_real) is calculated from the posted spring tension (ST) correcting for the fact that for this survey the true spring tension approaches the posted value at 40 mGal per second.
Beam velocity (Beam_vel) is derived from raw beam position (RB) assuming a centred difference approximation.
Relative gravity (rec_grav) = ((ST_real+CC)*0.9966)+(Beam_velocity*k_fac), k_fac=60/2.04, meter scale value =0.9966.
Still readings are in mGal (Still), and were calculated assuming a linear best fit to the drift of the airborne meter observed at base stations at Mario Zucchelli, Talos Dome, Dome C, and C3 (Jordan et al., 2007). Tie absolute gravity values for the survey (Base) were derived from land gravity measurements adjacent to the survey aircraft (Jordan et al., 2007).
Airborne absolute gravity values (Abs_grav) = Rec_grav- Still + Base
2/ Corrections to derive free air anomalies (disturbances).
Vertical acceleration (VaccCor) is calculated as 2nd derivative of flight altitude (Height_WGS1984)
Eotvos correction (EotvosCor) follows (Harlan, 1968).
Latitude correction (LatCor) = 978.03185(1+0.005278895 sin2Lat- 0.000023462 sin4Lat) (IUGG 1967).
Free air correction (FaCor) = 0.3086*Height_WGS1984. NOTE subsequent free air values are defined as gravity disturbances in geodesy, as they are referred to the ellipsoid (Hackney and Featherstone, 2003).
Horizontal acceleration correction (HaccCor). For this survey the approximation of (Swain, 1996) was used, assuming a damping factor of 0.707, and a platform period of 4 minutes.
3/ Free air anomaly and filtering.
Free air anomaly (Free_air) = Abs_grav-VaccCor+EotvosCor+FaCor-LatCor-(0.5*HaccCor)
Filtered free air anomaly (FAA_filt) used 9 km 1/2 wavelength space domain kernel filter (Holt et al., 2006).
Final free air data (FAA_clip) was produced by manually masking turns, start and end of lines, and other regions of noisy data.
Upward continued free air anomaly (FAA_2400m) was produced by upward continuing each line segment from the collected flight altitude to 2400 m, the highest altitude in the survey.
Note no levelling has been applied to the free air gravity data.
Date UTC date (YYYY/MM/DD)
Time UTC time (HH:MM:SS.SS)
FlightID Sequential flight number and survey ID e.g. W12
Line_name Line Number e.g. LW200.1:12
Lon Longitude WGS 1984, for processing see readme
Lat Latitude WGS 1984, for processing see readme
x x projected meters*
y y projected meters*
Height_WGS1984 Aircraft altitude (meters) in WGS 1984, for processing see location data page
Raw gravity Channels
ST Spring Tension (meter units)
CC Cross Coupling (meter units)
RB Raw beam position (Mv)
XACC Cross axis accelerometer (Mv)
LACC Long axis accelerometer (Mv)
Still Airborne meter still reading value (mGal)
Base Absolute gravity reference, from land gravity (mGal)
St_real True Spring tension value (meter units)
Beam_vel Gravity meter beam velocity (Mv/sec)
Rec_grav Recalculated relative gravity (mGal)
Abs_grav Calculated absolute gravity (mGal)
VaccCor Vertical acceleration correction
EotvosCor Eotvos correction
LatCor Latitude correction
FaCor Free air correction
HaccCor Horizontal acceleration correction
Free air Channels
Free_air Un-filtered free air anomaly
FAA_filt Filtered free air anomaly
*Projected coordinates (x and y) are in Lambert conic conformal with two standard parallels defined as follows:
Latitude of false origin: -80
Longitude of false origin: 80
Latitude of 1st standard parallel -83
Latitude of 2nd standard parallel -77
False easting 2000000
False northing 2000000
Positioning for the Dufek survey uses Ashtech Z12 dual frequency GPS recievers (Ferris et al, 2003). Positions are calculated for the phase centre of the aircraft antenna. All positions (Lat, lon and height) are referred to the WGS1984 ellipsoid.
|Data Set Creator||Jones, P.C.|
|Data Set Title||Processed line aerogravity data over the Dufek Massif, Pensacola Mountains (1997/99 season)|
|Data Set Release Date||2020|
|Data Set Publisher||Polar Data Centre,Natural Environment Research Council,UK Research & Innovation|
|Other Citation Details||shortdoi:10/d546|
|Horizontal Resolution Range||30 meters - < 100 meters|
|Vertical Resolution Range||N/A|
|Temporal Resolution Range||N/A|
|Detailed Location||Dufek Massif|
|Detailed Location||Pensacola Mountains|
|Distribution Media||Online Internet (HTTP)|
|Distribution Size||73 MB|
|Data Storage:||This dataset constains 1 ASCII XYZ file:
- DUFEK_GravByFlight.XYZ ~73MB
|Use Constraints:||This data is covered by a UK Open Government Licence (http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/) Further by downloading this data the user acknowledges that they agree with the NERC data policy (http://www.nerc.ac.uk/research/sites/data/policy.asp), and the following conditions:
1. To cite the data in any publication as follows:
Jones, P. C. (2020). Processed line aerogravity data over the Dufek Massif, Pensacola Mountains (1997/99 season) (Version 1.0) [Data set]. UK Polar Data Centre, Natural Environment Research Council, UK Research & Innovation. https://doi.org/10.5285/6BF4FF06-31C4-41F4-B88C-6378122B77D5
2. The user recognizes the limitations of data. Use of the data is at the users' own risk, and there is no warranty as to the quality or accuracy of any data, or the fitness of the data for your intended use. The data are not necessarily fully quality assured and cannot be expected to be free from measurement uncertainty, systematic biases, or errors of interpretation or analysis, and may include inaccuracies in error margins quoted with the data.