Data: West Antarctic Ice Sheet Airborne Gravimetry

Data Reduction

Data reduction steps included the subtraction of the vertical acceleration of the aircraft (Aaircraft)  from the gravity measurement (Ameasured).  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 (Gtheo) 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 = Ameasured – Aaircraft + Eötvös + FAC – Gtheo 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).

Free-Air Gravity Data

The free-air gravity data set was gridded using a spline function. Grid cell size is 1 × 1 km.
Projection Information
Projection 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
File 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:
Download compressed data sets
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.
The picture below shows the free-air gravity data using a histogram equalized color table and an illumination to reveal smaller details. Free-air gravity map