Please note that this site is an archive. The most up-to-date material is at: http://www.scar.org/researchgroups/geoscience/ .

SCAR GSSG - GIANT Program - Guidelines for Antarctic GPS monumentation " /> " />

Updated: 

Guidelines for Antarctic GPS monumentation - Edition 2


A PDF version of this document is available - [2.3Mb]

CONTENTS

Introduction
Australia
USA - UNAVCO
USA - National Geodetic Survey (NGS)
USA - HIGP (Mike Bevis)
USA - USGS (Ken Hudnut)
USA - Transantarctic Mountains Deformation (TAMDEF) project
Canada - Geodetic Survey Division, Natural Resources Canada
Canada - Western Canada Deformation Array (WCDA), Geological Survey
Germany - Jubany Station, King George Island
Germany - GAP 95
Argentina - Marambio Station
Italy - Victoria Land Network for crustal DEFormation control (VLNDEF)
Summary
References


Introduction

In Antarctica the requirement for monuments is unique. The snow-free rock areas often have exposures of solid bedrock but can also be covered by moraine debris and patterned soil polygons with permafrost.

Site selection of monuments on solid bedrock needs to be carefully examined to ensure that a "surface floater" rock (ie. one not attached to bedrock) is avoided.

These guidelines incorporate the ideas from several different countries and represent what we believe to be "best-practice" examples of monumentation for GPS occupations. We strongly recommend readers to use and adopt these guidelines when installing geodetic / geodynamic markers in Antarctica.

If readers are aware of other guidelines or best-practice examples for geodetic marker monumentation could they please inform the authors of this paper John Manning or Glenn Johnstone

These guidelines should also be read in conjunction with the SCAR Expert Group on Geospatial Information "Guidelines for Antarctic cGPS Reference Stations" (under development). Monumentation is only one aspect of installing and maintaining cGPS reference stations.


Australia

These notes are based on methods developed by the National Mapping Division (NMD) of Geoscience Australia. Bob Twilley from the Geodesy Group has authored the majority of this section.

The NMD permanent survey mark, used in Antarctic survey work, has been designed for long term stability with geodetic GPS observation considerations.

Description of mount

The mount is a 150mm diameter, 8mm thick stainless steel (non magnetic) plate, with a 15.875mm (5/8 inch) diameter Whitworth threaded hole in the centre. The top surface of the plate has a machined finish.

At evenly spaced (120 degree) locations around the plate and 10mm in from the edge there are 3, 6mm diameter holes drilled and threaded.

On the underside of the mounting plate a 12mm diameter stainless steel rod with collar and 15.875mm (5/8") Whitworth thread above the collar is screwed into the plate with the threaded spigot protruding 12mm above the top surface. The length of this rod can be variable and has a reverse thread on its other end to help prevent turning when fixed into rock.

Three threaded 6mm diameter rods to fit the holes in the outer edge of the plate are to be made from mild steel with a nut welded onto one end. The length of these rods should be of about the same length as the centre stainless steel rod. Three locking nuts to fit rod.

Close up of Australian geodetic marker, Law Base, Larsemann Hills

Fig. 1: Close up of Australian geodetic marker - Law Base, Larsemann Hills.

Relative size of the mark

Fig. 2: Relative size of the mark

Technical detail of mounting plate

Fig. 3: Technical detail of mounting plate

Method of installation

After selecting a solid rock location with good sky view for GPS observations proceed with the following:

Suggested equipment

  1. HILTI TE5A battery operated drill - 24 Volts and 350 Watts. Depending on rock type, 1 battery would last for 1 installation.
  2. 1 Spare battery. 1 manufactured circle bubble fitted to drill depth guide.
  3. 20mm diameter and 10mm diameter HILTI bits, plus spares. Small air brush with plastic hose.
  4. Circular bubble set into threaded collar.
  5. HILTI HIT HY150 2 parts epoxy resin with squeeze gun. 1 tube per installation.
  6. Bolt cutters.


USA - UNAVCO

UNAVCO - the University NAVSTAR Corsortium - which is part of the University Corporation for Atmospheric Research, based in Boulder, Colorado, has a comprehensive web site devoted to all aspects of GPS, including Site Planning and Reconnaissance Guidelines and GPS monumentation guidelines. Excerpts from the UNAVCO web site are as follows:

"Site Planning and Reconnaissance Guidelines"

This section covers such items for consideration as:

  1. Site selection
  2. Monumentation
  3. Power
  4. Communications
  5. Security

Full details can be found at: www.unavco.ucar.edu/project_support/permanent/recon.html

"GPS monumentation" guidelines

The following table provides a summary of various monument types used in the GPS community and under development and test at UNAVCO. All monuments require separate antenna mounts.

Monument type

Weight
(lbs)

Cost
(US $)

Multipath

Stability

Thermal expansion

Installation

Usage

Other notes

Concrete Pillar

Note 1

Note 1

High (duplicates ground effects)

Good

Low

Deep anchors in bedrock or soil

NGS

Difficult and time consuming installation

Deeply Anchored GPS Monument (UCSD)

Note 1

Note 1

Low

Excellent

Very low

Deep anchors in bedrock or soil

Basin/Range (TB installed) and networks in CA (PFO)

Difficult and time consuming installation

INVAR* Rod with sleeve

Note 1

Note 1

Low

Good

Very low

Anchors in bedrock

Greenland permanent GPS station

INVAR* is expensive

NGS Sleeve type monument

Note 1

Note 1

Low

Excellent

Very low

Deep anchors in soil

NOAA/NGS

Difficult and time consuming

Stainless steel pin

2

5

N/A

Excellent

Stainless steel (7-8 x 10exp-6 in/in/deg F)

Bedrock only

Majority of GPS campaigns

Simple installation

* Invar 36 is a 36% nickel-iron alloy possessing a rate of thermal expansion approximately one-tenth that of carbon steel at temperatures up to 400°F(204°C). This alloy has been used for applications where dimensional changes due to temperature variation must be minimized such as in radio and electronic devices, aircraft controls, optical and laser system, etc.

Note 1. Can vary depending upon site conditions and amount of material.

Full details for monumentation can be found at: www.unavco.ucar.edu/project_support/permanent/monumentation/monumentation.html

Diagrams on various installations can be found at:

www.unavco.ucar.edu/project_support/permanent/monumentation/monument_table.html

Technical detail of UNAVCO's Invar design used in Greenland

Fig. 4: Technical detail of UNAVCO's Invar design used in Greenland


USA - National Geodetic Survey (NGS)

"Process Action Team 20 (PAT 20) was established by the National Geodetic Survey (NGS)…to develop design recommendations for a site monumentation system for future…operations.

The process of developing CORS monumentation design recommendations involved the investigation of various issues including: existing monumentation types, properties of potential monumentation materials, GPS signal reception factors, and [Continuously Operating Reference Station] CORS site environment. PAT 20 examined a wide range of existing monumentation scenarios that are in use throughout the world.

PAT 20 recommends the following monument design for most future National CORS installations: a step-tiered cylindrical concrete pier that is a minimum depth of 10 ft. (3.0 m) by a minimum diameter of 1.5 ft. (0.46 m) below ground level, 5 ft. (1.5 m) tall by 1 ft. (0.3 m) diameter above ground, with an antenna mount consisting of a traditional tribrach adapter attached to a non-metallic base that is integrated into the concrete pier. The Team believes that this design is suitable for a wide range of site conditions and that it has an excellent chance for long term endurance. This type of monument provides the high level of horizontal and vertical stability required for CORS applications. The monument’s shape and materials have a negligible impact on the quality of the GPS signals. The materials are readily available and affordable. The preparation of materials and the installation procedures re relatively straightforward and require only a limited amount of specialized equipment and technique. The antenna can be locked in a true north orientation and will be force-centered to a repeatable position whenever it is removed and replaced."

Source: National Continuously Operating Reference Station (National CORS) Site Monumentation Final Report", December 20, 2000

example of a US NGS National CORS installation

Fig. 5: Example of the US NGS National CORS installation


USA - HIGP (Mike Bevis)

Professor Michael Bevis is based at the Hawaii Institute of Geophysics and Planetology (HIGP), University of Hawai'i at Manoa. His research interests include crustal motion geodesy, neotectonics, glacial isostatic adjustment, sea level change, and GPS meteorology. He has many years experience with geodetic work in Antarctica and has developed his own type of geodetic marker. Below are the specifications and notes on installation.

"Machine shop specifications and tolerances:

All Dimensions ±1/64" (Except drill hole diameter) Use cylindrical stainless steel rod such as #304, which is reasonably machinable and highly corrosion resistant.

Cut the three grooves. We use a lathe tool 1/8" wide, and make two cuts per groove. Do not bother to make the base of the grooves really smooth. Use plenty of cutting oil to prevent chattering during groove cutting.

Cut a bevel on bottom (approx. 45°), and center drill the top end.

Technical specifications for the Bevis pin

Fig. 6: Technical specifications for the Bevis pin

Next mill a flat surface onto the lower shank of the pin, and the top 3/8" notch, then rotate roughly 180° and mill the other notch. Mill down approx. .055" in each case,

Next mill a flat surface onto the lower shank of the pin, and the top 3/8" notch, then rotate roughly 180° and mill the other notch. Mill down approx. .055" in each case, as shown below:

General view of the Bevis pin

Fig. 7: General view of the Bevis pin

Note added in 1998: Tech 2000 now makes these pins with a slightly conical hole to optimize

their use with the Tech 2000 GPS antenna mast (a fixed-height spike mount leveled under tension).

Installation of Stainless Steel Pins as Geodetic Markers

Note: These instructions assume you are using version 2 of the 6" x 1/2" diam. Stainless steel pins developed at NCSU. See the separate document on pin specifications and fabrication details [above].

First, stamp the station name on the top of the pin. Four letter names are standard. We use 1/8" rotary stamp kits for this purpose. We have devised a steel tube fitted to a footplate to hold the pin steady during stamping. Stamp the name around the hole taking up about half of the pin's top.

At a site with competent bedrock (not a boulder!) find an area in which to install the pin. Choose a local high, so the pin will rarely sit in a pool of water. Drill a hole with a rotary hammer drill and a 1/2" carbide hammer bit. We can recommend the following drills: the Ryobi ER-160 (gasoline-powered), the Bosch 7/8" Rotary Hammer model 11207VS and the Hilti TE-22 (both of which require a portable generator to power them, via a heavy extension cord) and for remote areas where it is not easy to bring gasoline or a generator the cordless battery powered Hilti TE-10A with several pre-charged battery packs. All these drills use SDS bits. We prefer bits with 8" of drilling length. 10" & 12" lengths are more common, but involve extra weight & cost.

The hole should be about 1/2" deeper than the pin, as shown in the schematic section, left. The preferred method is to achieve a friction fit between the pin and the rock. This is usually possible using a 1/2" drill bit. The hole tends to widen near the top because the bit pivots about its tip early in the drilling. Drill the hole, and blow all dust out of the hole with a long flexible tube.

See how far the pin will fall into the hole. If the top 1/2"-3/4" of the pin sticks out of the hole then a good fit should be possible. If more than 1" sticks out it will probably be too hard to insert the pin, and you should consider plan B. If the pin falls all the way down into the hole then a friction fit is impossible, and you must epoxy the pin into place. After a little practice all will be obvious. Practice at home, not in the field! You will notice the same bit drilling different sized holes in different types of rock.

Given a suitable hole proceed as follows. Remove the pin. Squirt a little Hilti C-100 epoxy into the hole, and charge the grooves in the pin with the epoxy. We recommend latex gloves so you can use your fingers. Hammer the pin into the hole until it is flush with the rock surface. Use a suitably shaped piece of aluminum between the pin and the hammer to prevent damage to the pin. The epoxy should squirt out of the hole. With practice you use just the right amount of epoxy to prevent waste. No air spaces

Schematic diagram of Bevis pin being installed

Fig 8: Schematic diagram of Bevis pin being installed

PLAN A: Friction fitted and Epoxied should remain in the hole.

PLAN B: Epoxied. If the rock is such that the hole is too tight for the pin, use a 5/8" bit to drill a wider hole, and simply epoxy the pin in place.

Notes: Be sure to use Hilti C-100 epoxy - it is reliable and widely available. Take plenty of spare carbide bits for the drill. If you have to press down hard on a drill the bit is too blunt! Mike Bevis and Eric Kendrick (20 May 92)

Note added in 1998: If you intend to use the Tech2000 antenna mast with this marker, it is a good idea to have the pin 'bottom out' on the rock, since the mast exerts strong downwards force on the pin. This requires a little extra care during the drilling. If the hole is longer than the pin then at a minimum you must ensure that this space is completely full of epoxy."

These documents can be obtained from the WWW at:

Stainless Steel Monument Pin Machine Shop Specifications www.unavco.ucar.edu/project_support/permanent/monumentation/pin1.pdf

Stainless Steel Monument Pin Installation Instructions, www.unavco.ucar.edu/project_support/permanent/monumentation/pin2.pdf

Contact details:

Professor Michael Bevis
Email: bevis@soest.hawaii.edu
Office: POST 814B
Phone Number: +1 (808) 956-7864
Fax Number: +1 (808) 956-3188
University of Hawai'i at Manoa
Hawaii Institute of Geophysics and Planetology
2525 Correa Rd.
Honolulu, Hawaii 96822
USA


USA - USGS (Ken Hudnut)

Ken Hudnut works for the Geologic Division of USGS. He has an extensive web page devoted to various aspects of geodetic monumentation and installation including:

This can be found at: pasadena.wr.usgs.gov/office/hudnut/hudnut/rock_pin.html

"In some cases, there are good reasons to install a fixed, forced-centering GPS antenna mount in rock. For this purpose, the rock pin design by Mike Bevis (at SOEST, HIGP) has been modified from the original (see previous section above). The installation of the pin itself is done in much the same way as for a Bevis pin. This page describes our modifications to the Bevis Pin design, how we install such pins, and things to consider during the selection of a good piece of rock to install such a pin into.

The continuous GPS station with the lowest random-walk type monument noise within the Southern California Integrated GPS Network (SCIGN) is of this type (Y. Bock et al., 1995 - Fall AGU talk; ["Analysis of Continuous GPS Measurements in the Los Angeles Basin: Techniques and Initial Results"]). It is located at Lake Mathews, and is called station MATH. Although it is a somewhat different (higher mounting point) pin design than the subsequently designed one shown here, the selection of bedrock was made taking into account all of the factors discussed below. Also, it was installed as described below.

This is the least expensive way to install a highly stable monument for a GPS network. The largest challenge in doing this properly is in selecting a good piece of bedrock, so a discussion of this step is included here. Even if you plan to use a different type of pin, post, or mast antenna mount in bedrock, some of this section may be useful to you. If you are considering using this pin, you should also be aware of the tests indicating problems of using low (0.5 meter) antenna mounting heights, and these are discussed here as well."

Technical specifications of Hudnut pin (modification of the Bevis pin)

Fig 9: Technical specifications of Hudnut pin (modification of the Bevis pin)

Contact details:

Dr. Kenneth W. Hudnut.
Geophysicist
United States Geological Service, Geologic Division
Western Region Earthquake Hazards Team
Email: hudnut@usgs.gov
Office Phone: +1 (626) 583-7232
Office Fax: +1 (626) 583-7827


USA - Transantarctic Mountains Deformation (TAMDEF) project

"The TAMDEF project is a joint USGS and OSU program to measure crustal motion in the Transantarctic Mountains of Southern Victoria Land.

We use precision GPS measurements separated by several years to test the predicted rates of motion. The first four seasons of measurement have been completed so far in this, the most extensive ice-free area on the Antarctic continent.

We are based for the austral summer at McMurdo Station (770 50'S, 1660 39'E), the largest National Science Foundation base on the Antarctic Continent. Using helicopters we fly out to sites where we have installed high-quality geodetic style pins into exposed bedrock. We deploy antennas onto these pins according to a pattern designed to highlight rock motion due to ice loading, tectonics and volcanic loading. We leave the equipment on site, unattended for between 3 and 21 days, depending on the weather.

Four field seasons have been completed so far. The first year set up 23 of the sites we use. The second season we installed a further 4. We installed a 28th site on the peak of Mt Erebus during the 1998-1999 field-season. During the 1999-2000 season we reoccupied almost all sites with help of both the USGS and the Italian Antarctic Program (PRANRA)."

Methods and Placement

"The monument sites are selected principally for good quality of bedrock exposure, with other concerns being the ease of helicopter access and satellite sky-view. Dual-frequency 12-channel receivers with choke-ring antennas designed to exclude L1 multi-path are used. The receivers are kept in insulated boxes and powered from 30W solar panels and 40 amp-hour gel-cell batteries. Stations are occupied for between 3 and 14 days. The antennas are mounted on force-centered fixed-height (0.0794m) mounts that are fixed to threaded steel rods embedded into the bedrock." A very detailed picture series showing installation of one marker can be found at: www.geology.ohio-state.edu/~willis/arr8images.html.

"Every site includes a small array to test for local motion. The intent is to detect noise from locally occurring frost heave and related processes. Each micro-footprint consist of at least three markers arranged in a radial fashion between 20 and 250 meters away from the center point. These monuments are occupied during a 'static survey' of between one and two hours. "

Figure 10 shows an example of the pin and tribrach antenna mounting system that has been developed and used by the TAMDEF research team.

TAMDEF geodetic mark & antenna mount

Fig.10: TAMDEF geodetic mark & antenna mount


Canada - Geodetic Survey Division, Natural Resources Canada

Taken from National Resources Canada, Geodetic Survey Division (1992), "Guidelines and Specifications for GPS Surveys", Release 2.1, December 1992.

"GPS provides a three-dimensional position. This characteristic should be reflected in the type of monument selected to mark the station. Because of the economics of establishing a new position by GPS versus the cost of constructing a sophisticated concrete structure to support the marker, standard concrete monuments (either cylindrical or pyramidal in shape) are no longer considered necessary except for specific projects. With this in mind, Table 1 indicates by order of preference the type of markers that should be used. A detailed description of these markers is presented in appendix C [of the report, see References for full description]. This list is not exhaustive and therefore, the project authority may authorize alternate markers."

MARKER TYPE

COMMENTS

1) tablet or bolt marker in bedrock, or large existing concrete structure

acceptable for any accuracy of survey

2) NRC type deep bench mark consisting of a steel pipe driven to refusal and protected by an outer galvanized steel pipe. The datum point is attached at the top of the inner pipe and the annular space between the pipes is filled with heavy oil. A covered well filled with crushed stone provides additional horizontal stability and protection Note: Markers of this type, installed prior to 1988, require the addition of a horizontal stabilizer cap to prevent wobbling of the inner pipe.

acceptable for any accuracy of survey

3) 3-D marker consisting of a datum point attached to steel rod sections (1.6 cm in diameter) driven to refusal. A covered well filled with tamped crushed stone provides additional horizontal stability and protection.

acceptable for any accuracy of survey

4) Helix pipe marker consisting of a brass cap attached to a 2.4 metre long section of square tubing with a steel helix spiral welded about 15 cm from the bottom end. A covered well filled with crushed stone provides additional horizontal stability and protection.

acceptable for any accuracy of survey

5) post marker consisting of a reinforcing steel rod with identification cap

Acceptable for surveys of accuracies of 57 ppm or better if used in permafrost or in weathered or soft rock (shale); and acceptable in any kind of soil for surveys of lower accuracies

Table 1: Recommended markers for GPS surveys.


Canada - Western Canada Deformation Array (WCDA), Geological Survey

The Western Canada Deformation Array (WCDA) is a permanent GPS tracker network established by the Geological Survey of Canada as part of the Canadian National Earthquake Hazards Program. The following information has been taken from their website in relation to monumentation of its markers:

"At present all WCDA sites are equipped with AOA Dorne Margolin choke ring antennas mounted on forced centre monuments. The stability of the GPS antenna is paramount to ensure that a tectonic signal and not a monument displacement signal is derived.

Up until 1998 all WCDA monumentation utilized concrete piers. With the exception of station FLIN, the monument construction utilized steel reinforcement rods within the concrete with additional steel reinforcement in the bedrock to depths of up to 3 metres. These concrete piers are topped with a levelled, brass force centering plate to permit unambiguous placement of the GPS antenna. Initially 0.5 or 1.0 mm circular shims were used to permit orientation of the antenna while still maintaining a tight threading of the antenna to the base plate. It was found that improvements were required in order to guarantee correct orientation as well as to facilitate access to the RF connector. A 10 cm high aluminum antenna base with a stainless steel insert, designed by the Geodetic Survey Division, NRCan, was therefore introduced. This base permits orientation of the antenna as well as easier access to the RF connector.

Station FLIN was established as part of a joint NRCan / NASA post-glacial rebound study. Given that the vertical component is especially critical and given the annual temperature variation expected (-40 to +40 degrees Celsius) this pier was constructed using special materials. A 4.5 metre Invar rod is grouted 3m in the bedrock. The top 1.5m of the rod is housed in a PVC sleeve inside of a special super-plasticized, high fly ash concrete mix with non-reactive aggregate and polypropylene fibres developed at NRCan’s CANMET laboratories. The concrete is anchored to a depth of 60 cm in the bedrock. A UNAVCO mount is used to attach and orient the antenna."

Schematic diagram of WCDA marker

Fig. 11: Schematic diagram of WCDA marker

Source: Schmidt, et. al


Germany - Jubany Station, King George Island

"The permanent marking of the GPS survey point was done with a central marker and three witness points in a distance between 10 to 30 m from "DAL1". The center bench mark consists of a brass cylinder, which is fixed on bedrock. It is possible to screw a tribrach with an adaptor and the GPS antenna directly on the marker. The top of the marker has the inscription "GAP 1995" and is covered by a cylindrical cover brass plate.

An AC-powered Trimble Office Support Module 2 (OSM2) is attached to the PWR - I/O connector. In case of power failure, a battery connected to the receiver is used for power supply. The battery charging output is on PWR 2&3. The receiver electronics are housed in the meteorology shed. A Trimble choke ring antenna with a Dorne-Margolin element is connected to the receiver in order to reduce multipath effects which may be caused by the reflection of satellite signals from the ground. A Trimble conical cover over the antenna prevents snow accumulation, reduces antenna wear, and discourages animals from sitting on it. This radome mounts on a metal plate located under the antenna. A 80 m long of 7/8 inch foam low loss cable connects the GPS antenna to the receiver. The monumentation consists of a concrete pillar which is grounded on a rock outcrop

The GPS system was installed on March 5, 1997, and is operated as a stand-alone-system during the Antarctic winter. In operation, the GPS receivers are programmed to track up to a maximum of twelve visible GPS satellites above 100 elevation angle with an recording interval of 15 seconds. Once a day, a program on a PC establishes a data link to the receiver, downloads the previous 24 hours of data and deletes the file on the receiver. After retrieval, the data file is compressed and transferred to an archival directory on the PC. A data transfer for the post processing in Germany is only possible during the Antarctic summer season. "

Antenna and GPS monument at Jubany base, King George Island

Fig. 12: Antenna and GPS monument at Jubany base, King George Island

Source: Pohl, M., Schöne, T., Zakrajsek A.F., and Schenke, H.W. (unpublished) "GPS Observations at Jubany/Dallmann", February 2000, op.gfz-potsdam.de/staff/schoene/abs14_schoene.html


Germany - GAP 95 project

"The quality of geodetic deformation results depends on an absolutely reliable, stable and recoverable monumentation of the sites. The monumentation has to be fixed with the most stable parts of ground in the neighbourhood of the area under consideration, in general on bedrock. The requirements for the GPS bench marks in the region of the Antarctic Peninsula and at the border of the whole continent are as follows:

• the markers have to consist of a material with long lifetime expectation,

• the binder between marker and bedrock must be solid and has to protect the bedrock against water to avoid frost damage over a temperature range from -40°C up to +30°C,

• it must be possible to center any GPS antenna with sub-mm accuracy,

• the marker should have a thread to tighten the GPS antenna using a tribrach,

• the bedrock in the vicinity of the marker should not have crevices, therefore a geological expertise is indispensable,

• the position of the antenna must supply optimal conditions to receive GPS signals (attention to signal shading in the range above the minimum elevation and to multipath effects),

• the installation of 3 reference markers in a distance of 5 m to 20 m for recovering, identification and, in the worst case, for reinstalling the center marker.

Additionally a sequence of operations was developed to drill a hole of Æ 16 mm in solid bedrock under in situ conditions. A so-called "drill hammer" working with 36 V DC built-in accumulators and a power of 350 W was found out as best suited for the given task.

The marker shown in detail in Fig. 13 was used as the center bench mark at all newly monumented sites in the Antarctic Peninsula region including Gibbs Island and Signy Island as well as the Forster station region and Falkland Islands. The marker itself consists of a brass cylinder with a threaded bolt of stainless steel below, a thread on the top to support a tribrach with adapter and GPS antenna, and two holes to insert security bolts to avoid malicious destruction. A dowel of stainless steel was driven into a hole of the bedrock, drilled by the mentioned drill hammer. The marker was screwed into this dowel with a certain torque. To achieve a well vertically directed drill hole, which is necessary to get a vertical orientation of the GPS antenna, a bull’s eye level was attached to the drill hammer and always observed while drilling. After the marker was screwed into the steel dowel, the two holes of the security bolts were drilled into the bedrock and the bolts were driven into these holes under additional use of dowels of synthetic material. Before the dowels were driven into the bedrock, the special binder was filled into the drill holes to protect them against water penetration. The circular top of the marker is bearing the inscription

GAP
1995

and is covered by a cylindrical cover plate of brass of the same diameter like the marker itself. The cover plate is screwed on the marker top between the measurement epochs. Between the top of the marker and the cover plate a teflon disk is inserted to avoid corrosion at this place.

GAP 95 marker

Fig.13: GAP 95 marker

The above-mentioned three reference markers were monumented with brass disks of 20 mm diameter and a thickness of 5 mm. The mounting of the reference markers was performed by drilling in bedrock, use of dowels, driving a bolt into the dowel and using the same binder as employed to fix and protect the center marker.

After the observation period was finished and the antenna removed, the cover plate was screwed on the center marker and a cairn of about 0.5 m height was erected over the marker. The cairn is to protect the bench mark against climate influence, e.g. to avoid large temperature differences by sun radiation generating surface tension of the bedrock and crevices, and against malicious destruction by people.

The control measurement of the three reference markers in relation to each other and to the center marker was made by a short GPS session of about one hour getting an accuracy of better than 2 mm."

Source: Heck, B., Kutterer, H., Lindner, K. and Mayer, M. (1996) "Application of Spectral and Sensitivity Analysis Including Systematic Effects for the Design and Analysis of GPS Networks".


Argentina - Marambio station

"Unlike other Antarctic locations where appropriate rock outcrops allowed a metallic piece with 5/8" thread to be glued with epoxy directly into a hole made in the rock, Marambio Island presented an additional challenge due to its permafrost soil. Since Marambio station is the most frequently visited Argentine Antarctic station due to its aerial link capabilities, a solution was worked out to include it into the new high precision geodetic network. A stainless steel metallic structure was specially designed for the "MAR1" site and anchored 2.5 m deep, well below the permafrost active layer which was estimated in the 0.5 m range.

Site Selection

Human activities, radio-interference and soil erosion of the permafrost in the surroundings of the station buildings were taken into account while looking for a new site. "MAR1" was selected some 2 km away from the VOR location, with a similar height to that of Marambio's higher plateau (some 200 m a.s.l.).

A field-camp with autonomous energy supply is normally set up at MAR1. Wind generated electrical power is available most of the time during summer campaigns.

There are no obstacles of any kind above a 10º elevation mask and the site is expected to be preserved free from physical obstacles as well as from radio interference for a long period.

Geodetic Monument

The monument was erected by placing a stainless steel cylinder tube 3 m long, 2 mm thick and 0.17 m in diameter into a hole 2.5 m deep on a flat dome with good water drainage capabilities and with no evidence of surface features normally related to permafrost instability. Several stainless steel pieces had been welded radially around the lower part and to the bottom of the tube for fixing purposes. Reinforced concrete was poured into the hole in order to obtain a 0.4 m high solid basement at the bottom. After the basement was solid enough, the hole was progressively filled with several layers of permafrost material (stones removed), in order to preserve the local soil characteristics as far as possible. Finally, the tube was filled up with sand for thermal insulation.

The benchmark consists of a stainless steel circular antimagnetic plate, 300 mm in diameter and 12.5 mm thick, attached to the top of the cylinder using three metallic devices with leveling capability. There is a 5/8" [15.875mm] stainless steel screw emerging from the center of the plate for instrument fixing purposes. The top surface of the plate lies 0.65 m above the ground.

Although eventual monument instability could become hard to distinguish from local crustal deformation, MAR1 is expected to start providing reliable GPS-derived site velocities after the forthcoming SCAR Epoch 98 GPS Campaign, three years after its installation and initial survey."

Source: Zakrajsek A.F., and Peretti, A. (1997) "Geodetic Monumentation in Antarctic Permafrost, Marambio (Seymour) Island"


Italy - Victoria Land Network for crustal DEFormation control (VLNDEF)

VLNDEF project started in 1999 with the aim to measure a network for the study of regional geodynamics of northern Victoria Land.

In 1999-2000 and 2000-01 Italian expeditions, a network of 25 stations with an average distance of 70 km covering the area from Terra Nova Bay, Italian station in Antarctica, to the northern Oates Coast on Pacific ocean, about 700 km long and about 300 km large, was established and surveyed.

The network design and station locations are based on principal faults of the area pointed out by most recent tectonics studies. The research activity is made within GIANT (Geodetic Infrastructure of ANTarctica) program and ANTEC (ANtarctic neoTECtonics) Group of Specialists of SCAR.

The network coordinates are defined in most recent ITRF 2000 system through the emanation from GPS permanent station TNB1. TNB1 was included in SCAR GPS Epoch measurement campaigns and, consequently, connected to the IGS network in 2000. VLNDEF includes the first Italian reference network about 5000 square km around Terra Nova Bay, and a small network for Mt. Melbourne volcano monitoring. The reference network was surveyed three times, while the detailed network was surveyed five times.

The data were processed with different software, more recently with Bernese and Gipsy.

Monumentation description

When the area of benchmark installation had been chosen, the materialization was realised using a driller and a resine to fix the still benchmark. The vertex verticality was controled using a spherical level. A solution, where the forced centering is completely guarenteed in different antenna collocation in time, with a sufficient verticality control, was prefered instead of a monumentation where some device is needed for perfect verticality control.

In fact the goal is crustal deformation determination and the most important thing is to control the re-installation of the antennas in exactly the same horizontal and vertical position everytime the mark is occupied.

Fig. 14: VLNDEF marker monumentation

Fig. 15: Example of VLNDEF station summary sheet

Source: Capra, A., (2002) personal communication


Summary

The general consensus between most of these points of view is that there are a number of suitable monumentation techniques available for use in the Antarctic. GPS marker monumentation used will depend upon the type of terrain and situation in which the marker needs to be placed.

The SCAR Expert Group on Geospatial Information strongly recommends, for the majority of Antarctic GPS geodetic markers, using the Australian or TAMDEF installations for geodynamic points.


References

Bevis, M. (1992) " Machine Shop Specifications", North Carolina State University, North Carolina, www.unavco.ucar.edu/project_support/equipment/permanent_station/monumentation/pin1.pdf

Bevis, M. and Kendrick, E. (1992) " Installation of Stainless Steel Pins as Geodetic Markers", North Carolina State University, North Carolina, www.unavco.ucar.edu/project_support/equipment/permanent_station/monumentation/pin2.pdf

Capra, A., (2002), University of Bologna, Italy, personal communication

Floyd, R.P. (1978) "Geodetic Bench Marks", National Geodetic Survey, NOAA Manual NOS NGS 1, Rockville, Maryland, USA. www.ngs.noaa.gov/PUBS_LIB/GeodeticBMs.pdf

Heck, B., Kutterer, H., Lindner, K. and Mayer, M. (1996) "Application of Spectral and Sensitivity Analysis Including Systematic Effects for the Design and Analysis of GPS Networks". pp. 54-55, from "The Geodetic Antarctic Project GAP95 - German Contributions to the SCAR 95 Epoch Campaign", edited by Reinhard Dietrich, Deutsche Geodätische Kommission, München. ISBN 3 7696 8586 6

Hudnut, K.W., (1996) "The Fixed-Mount Rock Pin: Site Selection, Design and Installation", USGS Geologic Division, pasadena.wr.usgs.gov/office/hudnut/hudnut/rock_pin.html

National Resources Canada, Geodetic Survey Division (1992), "Guidelines and Specifications for GPS Surveys", Release 2.1, December 1992, Ottawa, Canada. www.geod.nrcan.gc.ca/site/index_e/products_e/publications_e/GuidelinesSpecifications.pdf

National Resources Canada, Geological Survey of Canada, (2001), "Western Canada Deformation Array (WCDA)", Sydney, British Columbia, Canada. www.pgc.nrcan.gc.ca/geodyn/wcda.htm

Pohl, M., Schöne, T., Zakrajsek A.F., and Schenke, H.W. (unpublished) "GPS Observations at Jubany/Dallmann" op.gfz-potsdam.de/staff/schoene/abs14_schoene.html

Schmidt, M., Dragert, H., Hill, W., and Courtier, N., (2001) "New GPS Monument Design for Permanent GPS Installations in the Western Canada Deformation Array", Geological Survey of Canada, Natural Resources Canada, Sydney, British Columbia, Canada www.pgc.nrcan.gc.ca/geodyn/docs/monument/concrete.html

Twilley, R. (unpublished), "Antarctic GPS Antenna Mount for Geodynamic observations", June 1999, National Mapping Division, Geoscience Australia.

US National Geodetic Survey, Process Action Team 20, (unpublished) "National Continuously Operating Reference Station (National CORS) Site Monumentation Final Report", December 20, 2000

Willis, M., Wilson, T., Whillans, I., Hothem, L. and Glover, B., (1999) "Transantarctic Mountains Deformation Project", Ohio State University, Ohio, USA, www.geology.ohio-state.edu/~willis/

Zakrajsek A.F., and Peretti, A. (1997) "Geodetic Monumentation in Antarctic Permafrost, Marambio (Seymour) Island" Actas XIX Reunión Científica, Asociación Argentina de Geodesia y Geofísica, San Juan, 1997