Earth gravity field for ice thickness data: LGB traverses 1989-95

Full description

The Lambert Glacier Basin (LGB) series of five oversnow traverses were conducted from 1989-95. LaCoste and Romberg gravity meters were used to record measurements of the Earth's gravity field approximately every 2 km along the 2014 km main traverse route from LGB00 (68.6543 S, 61.1201 E) near Mawson Station, to LGB72 (69.9209 S, 76.4933 E) near Davis Station. Gravity readings were also obtained at 5 km intervals along a 516 km upper western offset track (50 km parallel upslope from main route) from LGBUW485 (68.6458 S, 60.0272 E) to LGBUW000 (72.6508 S, 55.9275 E).

Raw data were stored as meter readings in field notebooks, transferred manually to spreadsheet files (MS Excel). Processed data were stored in spreadsheet files (MS Excel). The data available at the url below are stored in various formats.

Summary data (2 km spatial resolution) can be obtained from CRC Research Note No.27 'Ice Thicknesses and Surface and Bedrock Elevations from the Lambert Glacier Basin Traverses 1990-95'.

Documents providing archive details of the logbooks are available for download from the provided URL.

This work was completed as part of ASAC projects 3 and 2216.

Logbook(s):
- Gravity Meter Log 89/90
- LGBT Gravity #2 1992-93
- Glaciology Gravity Readings LGBT 1990-91

One of these documents has been scanned, and is available for download from the provided URL.
Glaciology Gravity Readings, LGBT 1990 - 91.pdf

Lineage

Progress Code: completed

Statement: The dataset is complete on a 2 km spatial resolution along the entire 2014 km of main LGB traverse route. The 5 km spatial resolution data along the north-west parallel offset route has not been processed. LaCoste and Romberg Model-G gravity meters were used to take field readings at a 2 km spatial resolution around the 2014 km of main LGB traverse route in Kemp Land, and at 5 km spatial resolution along 516 km of parallel offset (50 km upslope) route in the north-west corner of the basin. Reference readings to determine instrument tares and drift were taken (where possible) at the principal closure site for the traverse work (over a small brass plaque stamped 'BMR 7499.0160') in the Mt. Nelson seismic vault owned and maintained for Geoscience Australia (GA) by the Geology Department of the University of Tasmania. Where possible a second standard reading was taken immediately prior to departure on the Australian National Gravity Network Station ('ANGN 6491.0260') at Elizabeth Street Pier, Hobart, Tasmania. Raw gravity readings were converted to standard milligal units using lookup conversion tables calibrated for each instrument. The following corrections were then made to each reading: tare-drift from reference closure readings; an earth tide correction from standard algorithm; a free air correction to compensate for height above the geoid (using geographic location and elevations constrained by nearby geodetic GPS survey); and a latitude correction (latitude again GPS constrained). Fully adjusted gravity values were used to interpolate across ice thickness gaps in radio-echo sounding (RES) data using the standard Bouguer Anomaly formulae. The data have been constrained by repeat measurement at standard closure sites and by repeat field measurement over several sections of traverse track. Since the data have been used in differential mode (difference between readings 2 km apart) to interpolate across RES data gaps much of the gross errors were cancelled out in the analysis. Geographic locations for gravity readings were navigational GPS (30-100 m accuracy) constrained to overnight LGB station geodetic GPS fixes (1-5 m horizontal) every 30 km along the main traverse route, and of similar accuracy for the north-west parallel offset line.