TAMDEF-I Project (TransAntarctic Mountains Deformation

Monitoring Network)

L. Hothem (1) and M. Willis (1,2)

(1) U.S. Geological Survey

(2) Byrd Polar Research Center, Ohio State University

Antarctic Geodesy Symposium, AGS’01, Saint Petersburg, Russia, 18-20 July 2001

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South Victoria Land TransAntarctic Mountains DEFormation

Monitoring (TAMDEF-I) project

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In November 1996, the Byrd Polar Research In November 1996, the Byrd Polar Research Center/Ohio State University, jointly with the US Center/Ohio State University, jointly with the US Geological Survey, began work on establishing a Geological Survey, began work on establishing a network of about 30 stations located at sites in the network of about 30 stations located at sites in the South Victoria Land region of the Transantarctic South Victoria Land region of the Transantarctic Mountains. Mountains.

The 4The 4thth and last in series of GPS observing and last in series of GPS observing campaigns for this phase of the studies was campaigns for this phase of the studies was completed in the December 1999-January 2000 field completed in the December 1999-January 2000 field season. High quality data were obtained in each of season. High quality data were obtained in each of the 4 observing campaigns. the 4 observing campaigns.

ObjectiveObjective: test predictions of leading models for ice : test predictions of leading models for ice sheet change and tectonismsheet change and tectonism

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Transantarctic Mountains Deformation Monitoring Project (TAMDEF)

South Victoria Land

• Cooperative project - Ohio State University and USGS

• Three GPS observing campaigns completed– 1996-97, 97-98, 98-99, and 99-00 field seasons

• Objective: test predictions of leading models for ice sheet change and tectonism

• Other geodetic measurements:– International GPS Service (IGS) stations in and near

Antarctica– Absolute gravity– Tide gages

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Transantarctic Mountains Deformation Monitoring Project

(TAMDEF)South Victoria Land

• TAMDEF-I -- Four GPS Observing Campaigns – 1-year intervals– Field seasons: 1996-97, 97-98, 98-99, and 99-2000

• Measure rock motion - 3-dimensional– Expected signals are:

1. Glacial rebound2. Tectonic3. Volcanic

– Directions and patterns of these motions mostly distinct– GPS measurements designed to discriminate among them– Test predictions of leading models for ice sheet change

and tectonism• Long-term project

– TAMDEF-II is planned

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GPS surveys formed geometrical elements generally at three spatial scales

• Long baselines (100 to 400 km) that span the features most expected to show motion. Simultaneous tracking time is at least 2 days, often 7 days.– Station at Cape Roberts (ROB0) occupied continuously during

each of the 4 observing campaigns.– Some other stations with continuous data sets spanning periods

of up to 15 days.

• Short baselines (10 to 25 km) crossing suspected fault zones. Simultaneous tracking time 2 to 24 hours.

• Very short baselines (0.05 to 0.20 km) at each site (footprint array) to test for local motion due to such processes as frost action. Simultaneous tracking time is generally 60 minutes.

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BTL

ARR

ROB

TAMDEF Station

Absolute Gravity Station

Other GPS Reference Stations

Local fault surveys

MCM4ERR

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To obtain high accuracy or mm-level GPS measurements where biases are adequately modeled or minimized and which are free of blunders due to human error, requires careful planning and successful execution of the field methodologies employed.

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(1) Special pins set in rock outcrop

(2) Established a set of reference points, “footprint” array, at each site to monitor stability of the primary monument

(3) Used specially designed “fixed-height” level mounts to ensure at a high confidence level, sub-mm repeatability for the relationship of antenna reference point (ARP) to the monument reference point

(4) Employed late model GPS receivers with Dorne Margolin model choke ring antennas

(5) Collected multiple-day 24-hour data sets simultaneously at 8 to 12 stations

Field ProceduresField Procedures

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Threaded stainless steel 20-cm rodglued into hole drilled in bedrock

TAMDEF Monuments

Nylon cap toprotect threads

Plastic marker stampedwith 4-character station name

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Attaching and leveling the antenna mount

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Special “Fixed-Height” Level Mount for

TAMDEF Monuments

Station ARR0 located adjacent to IGS station MCM4.

At each station of the TAMDEF network, relationship of Antenna Reference Point (ARP) to station mark (bottom of divot for stainless steel pin) is repeatable for each setup at the sub-mm level.

ARP

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Arrival Heights (ARR)TAMDEF Network

IGSStationMCM4

TAMDEF

StationARR0

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IGS Station - “MCM4”McMurdo Station - Operational since January 1994

MCM4 ARR0

MCM4 withraydome cover

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GPS Equipment

Ashtech Z12Trimble SSE and SSi

Receiver Models

Antenna Models

Ashtech & Trimble Dorne Margolin Choke Rings

Footprint Array for ARR

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Cape Roberts (ROB)

Footprint Array for ROB

ROB0

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Station ROB0

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Cape RobertsTide Station(Installed 1991)

co-located withTAMDEF Station

ROB0(Established

November 1996)

Install permanentGPS/GLONASS

observing stationduring 2000-2001

field season

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Bettle Peak (BTL)Footprint array

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TAMDEF Station “ERE”Mount Erebus, Antarctica

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Reliable Power Supply Essential for Continuous Data Collection

Transport Caseand

Site storage for GPSreceiver and two

40 amp-hour gel-cellbatteries

30-watt solarpanel generating

system

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Details on Field Procedures • Sites selected with relatively clear horizon

– No obstructions above 10– Minimal obstructions above 5

• Mask angle for data collection = 5• Data collection sampling rate:

– Daily (24-hour) data sets = 30-sec or 15-sec – Footprint surveys = 5-sec

• Data management– All “raw” data translated into RINEX format– Categorized by station location and day of operation– Compressed and stored on CD-ROMs

• Documentation for site and each occupation– Description of geology at each site– Satellite sky view– Model and serial numbers of GPS equipment used– Duration of site occupation

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Quality Analysis & Data Processing

• Data quality analysis– TEQC Toolkit by UNAVCO

• 24-hour data sets– “Precise point positions” computed by use of

JPL/NASA’s automated GIPSY-OASIS II package– “Differential positions” computed by use of National

Geodetic Survey/NOAA’s PAGES package– All processed using IGS orbital coordinate data

• Footprint array surveys– Software packages used include

• GPSurvey V2.3• Ashtech GPPS• Magellan AOS

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SUMMARY

• Methodology employed for TAMDEF GPS observing campaigns was successful overall in meeting goals for:– data free of errors due to blunders– minimizing multipath effects – multiple-day data sets relatively free of gaps