DOI: 10.5285/5388db62-4a5e-4072-9b01-3a65785d80a0
title: Processed line aerogravity data over Northern Palmer Land, Antarctic Peninsula (2002/03 season)

description: Over 20,000 km of new aerogravity data were acquired over Palmer Land during the 2002-2003 Antarctic campaign. Profile lines were oriented E-W with N-S tie lines. Line spacing was 5 km, tie lines were 25 km apart and nominal flight altitude was 2800 m. Differential, carrier phase, kinematic GPS processing methods provided the vertical and horizontal accelerations, which dominate the raw aerogravity signal. Levelled airborne gravity data have mean accuracies of 3 mGal. 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.
description: SPARC airborne gravity data and details of survey design and data processing are presented in Ferraccioli et al (2006). The dataset available here includes channels from raw through to filtered and upward continued free air anomalies, where data was recoverable. Data processing steps are outlined below Processing steps: 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 38 mGal per second. Beam velocity (Beam_vel) is derived from raw beam position (RB) assuming a centred difference approximation. Relative gravity (rec_grav) = (Spr_tens_real+((beam_vel)*k_fac)+CC)*scale_value, k_fac=30, meter scale value =0.9966. Still readings (Still) are in mGal and were calculating assuming a 2nd order best fit to the approximately linear drift of the meter observed at the tie down points. 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), with a 3 point mean filter applied after differencing to reduce short wavelength noise. 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 (Faacont) was produced by upward continuing free air data from the collected flight altitude to 2800 m. 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, 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) 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 EotvosCor Eotvos correction LatCor Latitude correction FaCor Free air correction HaccCor Horizontal acceleration correction Free air Channels Faa Un-filtered free air anomaly FAAup Upward continued free air anomaly to altitude 2800 m *Projected coordinates (x and y) are in Polar stereographic 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 Positioning for the SPARC survey uses kinematic differential GPS. Processing was carried out using GPSurvey software. Differential positioning used fixed base stations at each of the operational camps (Ferraccioli et al., 2006). Positions are calculated for the phase centre