Monumentation Recommendations

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Monumentation Design and Implementation Recommendations

Table 1: Considerations for Monumentation

Desired Monument Characteristics Parameters Affecting Monument Characteristics of a Good Monumentation Site Good Practice in Design of Monument
  • Stability with time
  • Stable to a certain degree of accuracy
  • Zero interaction with signal
  • Low cost
  • Simple design
  • Ease of installation
  • Corrosion resistance
  • Long term survivability
  • Climate
  • Impact
  • Frost Action
  • Shrinking and swelling of soil rock due to changes in moisture content
  • Soil expansion and contraction
  • Slope Instability
  • Compression of Soils
  • Presence of cavities due to karstic formations, such as found in dolomitic regions
  • Erosion
  • Diurnal and Seasonal Temperature variations
  • Human Tampering
  • Radio Frequency Interference
  • Presence of faults
  • Joints, fractures, and shear zones.
  • Water Table Level
  • Obstructions
  • Presence of bedrock and its type and condition
  • Vandalism
  • Shallow bedrock of high quality
  • Clear horizon
  • Safe from vandalism
  • Clear of reflecting surfaces (fences, metal poles etc.)
  • Not too far from receiver
  • Ease of access
  • Data accessibility via internet or phone line
  • Continuous electric power
  • No local crustal instabilities
  • Controlled vegetation (growing horizon elevators)
  • Minimize multipath signals by choosing optimal above ground width and antenna height above ground level.
  • Test the multipath environment and the radio frequency interference present at the chosen site before installation of monument.
  • Minimize resonance cavities by minimizing empty space between top of monument and antenna.
  • Minimize amount of metal in close proximity of antenna.
  • Design monument to be higher than snowfall levels.
  • Choose depth of monument anchor such that it is unaffected by frost action.
  • Use materials with low coefficients of thermal expansion when high temperature variations are expected (Invar for example).
  • Attach to solid bedrock for extremely stable foundation.
  • Avoid mounting the GPS antenna within 24.4cm (9.6in), or exact multiples of this distance, of a potentially reflecting horizontal surface.
  • Increase visibility of antenna above obstructions.
  • Implement insulation when thermal expansion is a concern.
  • Prepare lightning surge protection.
  • Install vertical and horizontal stability measurement instruments (tiltmeters, inclinometers, strainmeters) when high accuracy (sub-mm level) is desired.
  • Avoid nearby high voltage power lines.



Table 2: Types of monuments and examples of each

Monument Type Description Organizations Characteristics  
Pier C-Bar Reinforced Concrete National Geodetic Society (NGS)
  • Wide range of applications
  • Benign signal environment
  • High level of position stability
  • Inexpensive
  • Repeatability in antenna positioning
  • Long Term Survivability
Rebar Reinforced Concrete
  • Bay Area Regional Deformation (BARD)
  • Western Canada Deformation Array (WCDA)
  • University NAVSTAR Consortium (UNAVCO)
  • Most commonly used monument type
H-beam New Mexico State Highway and Transportation Department
  • Excellent Stability
Helical United States Geological Survey (USGS)
  • Excellent Vertical and Horizontal Stability
Rod Stainless Steel WCDA
  • Long Term Stability
  • Minimal effects from temporal solar radiant heating
Metal Rod Brace
  • Southern California Integrated GPS Network (SCIGN)
  • Basin and Range Geodetic Network (BARGEN)
  • Pacific Northwest Geodetic Array (PANGA)
 
Invar rod encased in concrete UNAVCO
  • Good Stability
  • Very low thermal expansion
  • Low multipath signals
Mast Rohn Tower U.S. Coast Guard
  • Large heights can be used to reduce obstructions
  • Concrete monuments used to anchor masts
Stainless Steel GPS Earth Observation Network of Japan (GEONET)
Chain Link Fence Post
  • National Oceanic and Atmospheric Administration's (NOAA)
  • Forecast Systems Laboratory (FSL)
  • Inadvisable for geodetic purposes, consider other monumentation choices
Building Rooftop
  • Texas Department of Transportation's (TXDOT)
  • Regional Reference Points (RRP)
  • SATLOC
  • Inadvisable for geodetic purposes due to instabilities; consider other monumentation choices
  • If unavoidable, choose a load-bearing wall on a low-elevation building -Foundation of building must be stable
  • Larger buildings have more instability
  • Use vertical and horizontal stability measuring instruments to keep track of the movement of the building
Wall Mounted
  • Institute of Geophysics and Planetary Physics of the University of California, San Diego (IGPP-UCSD)

 

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