DOI: 10.5285/bc870f9e-4200-4ae2-8db0-6cb80b870c09
title: Processed line aerogravity data over the Jutulstraumen rift area (2001/02 season)

description: A British Antarctic Survey Twin Otter and survey team acquired 15,500 line-km of aerogeophysical data during the 2001/02 Antarctic field season along a 1-km line spacing grid with tie-lines 8 km apart. Twenty-five flights were flown from the South African base SANAE, for a total of 100 survey hours. We present here the processed line aerogravity data acquired using a LaCoste & Romberg air-sea gravity meter S83 mounted in the BAS aerogeophysically equipped Twin Otter aircraft. Data are provided as XYZ ASCII line data. This high-resolution aerogeophysical survey was part of the "Magmatism as a Monitor of Gondwanabreak-up" project (MAMOG) of the British Antarctic Survey, which included new geochemical investigations, structural geology, geochronology, and AMS studies over western Dronning Maud Land.
description: Airborne gravity are presented in (Ferraccioli et al., 2005). The dataset available here includes all raw data and final free air gravity anomalies. Intermediate processing steps are not available for this dataset, but have been applied. All data is provided in the "by flight" database. 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 (Note these channel descriptions are for reference - intermediate processing values are not available). 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), are based on readings before and after each flight. Tie absolute gravity values for the survey (Base) were derived from land gravity measurements adjacent to the survey aircraft. Airborne absolute gravity values (Abs_grav) = Rec_grav- Still + Base 2/ Corrections to derive free air anomalies (disturbances) (Note these channel descriptions are for reference - intermediate processing values are not available). 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 (FAA) = the filtered free air gravity anomaly (mGal) faa_150 = Gridded Tie line data sampled back into database used for levelling. Lev_cor = levelling correction (mGal). FAA_lev = levelled free air gravity anomalies. FAA_up2964m = upward continued free air anomalies. Note no levelling has been applied to the free air gravity data. Channel description: Basic Channels 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 Lat Latitude WGS 1984 x x projected meters* y y projected meters* Height_WGS1984 Aircraft altitude (meters) in WGS 1984 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) Calculation Channels 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 (mGal) EotvosCor Eotvos correction (mGal) LatCor Latitude correction (mGal) FaCor Free air correction (mGal) HaccCor Horizontal acceleration correction (mGal) Free air Channels Free_air Un-filtered free air anomaly (mGal) FAA_Lev Levelled free air anomaly data (mGal) FAA_150 Filtered (150 second) free air anomaly (mGal) FAA_up2964m Upward continued free air anomaly to an altitude of 2964m (mGal) * Projected coordinates (x and y) are in Lambert conic conformal with two standard parallels defined as follows: Latitude of natural origin: -71 Longitude of natural origin: 0 Scale factor at natural origin -75.33333333333 False easting 0 False northing 2082760.109
description: The following parameters have no values: ST_Real, Beam_vel, RecGravity, Abs_grav, EotvosCor, LatCor, FaCor, HaccCor.