|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
- Exposure to:
- 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
- Diurnal and Seasonal Temperature variations
- Human Tampering
- Radio Frequency Interference
- Presence of faults
- Joints, fractures, and shear zones.
- Water Table Level
- Presence of bedrock and its type and condition
- 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.