# Data Reduction

Data reduction steps included the subtraction of the vertical acceleration of the aircraft (A_{aircraft}) from the gravity measurement (A

_{measured}). The Eötvös correction for airborne measurements was calculated to compensate for measuring gravity from a moving platform on a rotating Earth and was added to the measurement. The anomalous gravity was determined by then subtracting the predicted gravity for that latitude at the ellipsoid (G

_{theo}) and adding the free-air correction (FAC) to correct the predicted gravity to the altitude of the aircraft. These corrections combine to yield the free-air anomaly (FAA): FAA = A

_{measured}– A

_{aircraft}+ Eötvös + FAC – G

_{theo}Aggressive low-pass filtering is required to minimize the high amplitude noise that remains in the free-air anomaly even after corrections are applied. Noise attenuation was optimized by a cosine taper applied as a filter in the frequency domain that begins its roll off at 0 Hz (dc) and reaches infinite attenuation at 0.006 Hz. Crossover errors have been calculated at profile intersections and an appropriate dc shift and drift rate have been applied to the profiles in order to minimize the overall standard deviation in a least square sense. The accuracy of the airborne gravity data was estimated from the evaluation of crossover errors (± 2.98 mGal) and the evaluation of repeat measurements (± 1.39 mGal). The spatial resolution is 5.5 km. Gravity measurements have been tied to the International Gravity Standardization Network (IGSN-71) at McMurdo Station (BLDG57, position 77.8477°S, 166.6820°E).

The picture below shows the free-air gravity data using a histogram equalized color table and an illumination to reveal smaller details.## The free-air gravity data set was gridded using a spline function. Grid cell size is 1 × 1 km.

Free-Air Gravity DataFile format is 3 column ASCII file with x [km] y [km] z [mGal] for the projected data and longitude [°] latitude [°] z [mGal] for the files with geographical coordinates. You can choose between gzipped compressed versions (highly recommended) and uncompressed ASCII files:

Projection InformationProjection type Lambert conformal conic A axis radius 6378.137 B axis radius 6356.752 Reference longitude -105.0 Reference latitude -82.5 First standard parallel -81.5 Second standard parallel -83.5 False easting 343.122675 False northing 203.86649 Map projection unit kilometer Download compressed data sets

- Projected gravity data (compressed with gzip, 1.7 MB)
- Longitude-Latitude gravity data (compressed with gzip, 3.6 MB)
This free-air gravity data set has been described in Bell et al., Airborne gravity and precise positioning for geologic applications,Journal of Geophysical Research,Vol. 104, No B7, 15281-15292, 1999. If you use the data please refer to this publication.