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1. To cite the data in any publication as follows:

https://doi.org/10.5270/esa-8ffoo3e - PolarGap: "Filling the GOCE polar gap in Antarctica and ASIRAS flight around South Pole"

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.

Methodology:

The airborne gravity measurements from the LCR gravimeter S-83 were corrected for aircraft dynamic movement using precise point positioning (ppp) GPS solutions following the methodology of Olesen et al 2002. Gravity from the iMAR RQH sensor was processed using a Kalman filtering approach to provide independent gravity estimates (Becker et al 2015). These independent estimates of the gravity field were combined using a Technical University of Denmark (DTU) in-house draping approach. This ensures that the long-wavelength, bias-stable LCR data are optimally merged with the more linear, but drifting, results of the iMAR RQH sensor.

The processing parameters for the LCR gravity data included a 130-150 sec 2nd order Butterworth along-track filtering, corresponding to a spacing on the ground of ca. 6 km. The flight elevations were generally low level (1200 ft AGL), but occasionally higher due to fog or low-level clouds; flight altitudes varied between 2.9 and 4.3 km.

The overall accuracy of the airborne processing was 2.2 mGal r.m.s., as inferred from 129-xover points, not taking into account the difference in heights at the cross-over points. This is a highly satisfactory result, given the rough conditions (field camps and temperatures down to -30degC), and the fact that the BAS Twin-Otter did not have an autopilot, which is usually a requirement for high-quality, bias-free aerogravity. No cross-over adjustment was performed on the data, so the data level of every single line is determined only by the gravimeter "apron" values, i.e. the stationary readings before or after flights. The gravity ties used to define absolute gravity values constraining the survey level were done with LCR land gravimeters G-784 (BAS) and G-867 (DTU), linked to earlier surveys and reference stations at McMurdo and Rothera, and adjusted in a least-squares process.

The aerogravity data set includes the following channels:

Fiducial: line_no*10000+running no

latitude_decimal_degrees: DD.DDDDD

longitude_decimal_degrees: DDD.DDDDD

ellipsoidal_height_m: Elevation referenced to WGS1984 ellipsoid (m)

gravity_disturbance_mGal: Gravity variations corrected to the WGS1984 ellipsoid (mGal)

gravity_anomaly_mGal: Free air gravity anomalies corrected to the GOCE R5 geoid (mGal)

Data collection:

Data was collected using the BAS aerogeophysicaly equipped twin otter VP-FBL. Two gravity systems were used: A ZLS-modified Lacoste and Romberg (LCR) gravimeter S-83 which is a stabilised platform type sensor, and a high grade inertial navigation unit, iMAR RQH-1003, provided by TU Darmstadt, which acted as a so-called strapdown gravity sensor. Data from both these instruments was merged to give an optimal final product.

Data quality:

The gravity anomalies showed crossover errors with 2.2 mGal r.m.s., as inferred from 129-intersections. No levelling or additional adjustment was carried out.

Data resolution:

The radial design of the survey makes defining a specific resolution problematic. Line spacing at the survey edges was 90 km, reducing towards South Pole. The along track resolution is 6 km half-width based on the imposed filtering.