West Antarctic Ice Sheet (WAIS) Airborne Gravimetry
About the Data
This dataset contains aerogravity data collected by the Support Office for Aerogeophysical Research (SOAR) as part of the West Antarctic Ice Sheet (WAIS) Airborne Gravimetry project at Lamont-Doherty Earth Observatory (LDEO) in collaboration with the University of Texas Institute for Geophysics (UTIG). Data were collected using a Bell Aerospace BGM-3 gravity meter and a LaCoste & Romberg "S" gravity meter modified by ZLS Corporation.
This page contains links to the aerogravity data at LDEO.
Data Information
The free-air gravity dataset was gridded using a spline function. Grid cell size is 1 x 1 km.
- 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:
This free-air gravity dataset 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.
Gravimeter System
The gravimeter was mounted at the center of gravity of the Twin Otter aircraft. The platform enclosure was bolted to the floor, and the sensor was shielded from vibration by rubber shock mounts within the platform assembly. The gravity instrumentation has included both a Bell Aerospace BGM-3 gravity meter and a LaCoste & Romberg "S" gravity meter modified by ZLS Corporation. The BGM-3 gravity meter was made available through an agreement between NSF and NAVO. For both gravimeters, the sensor was mounted on a two-axis, gyro-stabilized platform that aligns the sensitive axis of the accelerometer with the time-averaged local vertical.
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).