Addis Ababa, Ethiopia, 02 May 2011 1 AFREF IGS Guidelines / Station Requirements Rui Fernandes...
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Transcript of Addis Ababa, Ethiopia, 02 May 2011 1 AFREF IGS Guidelines / Station Requirements Rui Fernandes...
Addis Ababa, Ethiopia, 02 May 2011 1
AFREFIGS Guidelines / Station Requirements
Rui FernandesDI-UBI, Univ. Beira Interior, Covilhã, Portugal.
Instituto Geofísico D. Luíz, Lisboa, Portugal.
DEOS, Delft Univ. of Technology, The Netherlands.
Addis Ababa, Ethiopia, 02 May 2011 2
Requirements – Site Selection The Big Five (criteria)
2Km
- VisibilityIdeally: No obstruction above horizon in any direction.Acceptable: No significant obstructions above 10º in any direction.
- SecurityProtection of antenna against robbery or vandalism acts.Reserved access to the receiver.
- Electric PowerIdeally: Access to reliable public electrical network.Alternative: Autonomous systems (e.g., solar panels).
- InternetIdeally: Continuous and reliable access
- Monument StabilityIdeally: rigidly connected to the ground
REQUIRED BY ALL APPLICATIONS
DEPENDENT OF THE APPLICATION
Addis Ababa, Ethiopia, 02 May 2011 3
Monumentation and mount
Monuments and Site Stability
• Bedrock foundation preferred, but rooftops sometimes the only option
• Short and deep drilled braced monuments are preferred by many
• Pillars are easier to build and good under the right conditions – top of pillar effects on GNSS signal
• Reference marks and site / monument stability surveys are desired at core stations
Antenna Mounts• Securely attach antenna to
monument/tamper resistant• Ability to centre, level and orient
antenna in azimuth• Reduce potential for multipath by
minimizing surface area • Current best practice: SCIGN mount
or similar
Addis Ababa, Ethiopia, 02 May 2011 4
Location
Site security, ownership and permission
• Location must be viable over long term
Horizon mask• Rule of thumb: minimize obstructions
above 10°
Multipath• Rule of thumb: site should be at least 15
metres from reflective sources• Antenna height: at ground seems good,
but observed multipath high at some sites with ~0.5 m height
• Avoid creating cavity between ground plane and monument top
Addis Ababa, Ethiopia, 02 May 2011 5
Requirements Monument Stability
2Km
Application Level
Tectonic Motions and Vertical MonitoringSub-
centimeter
Early Warning Systems (Tsunamis, Volcanoes)
Sub-centimeterCentimeter
Real-Time Products (Orbits, Surveying) Centimeter
Reference FramesSub-
centimeterCentimeter
Meteorological Applications Decimeter
Ionospheric Monitoring MetersProper Self-Center Mounting Device is fundamental
Addis Ababa, Ethiopia, 02 May 2011 6
Power and protection
Power Systems• AC power with battery back-up is preferred• DC solar systems are feasible where AC is
unavailable• Power budget is typically 6-20 W,
depending on receiver model and communications
Lightning protection• Options for antenna, power and
communication connections
Enclosures• Climate controlled building is best• Securely house all station equipment
Addis Ababa, Ethiopia, 02 May 2011 7
Communication and ancillary
Communications • Communications solution depends on
data requirement• Options range from mobile networks to
broadband satellite• Use of public Internet (DSL) is generally
preferred
Ancillary Sensors• Meteorological – surface pressure,
humidity and temperature at the GNSS antenna are required for water vapour measurements
Addis Ababa, Ethiopia, 02 May 2011 8
Requirements Permanent access to Internet
2Km
ApplicationRequired?
*
Tectonic Motions and Vertical Monitoring No (Local Storage)
Ionospheric MonitoringYes
No (Local Storage)
Reference Frames Yes
Early Warning Systems (Tsunamis, Volcanoes)
Yes
Real-Time Products (Orbits, Surveying) Yes* In order to properly monitor the station remotely and
automatically, the internet access is always desirable.
Addis Ababa, Ethiopia, 02 May 2011
9
Communication requirement
Level 1: •15-30 second sampling, daily to hourly retrieval, many hours latency•Precise orbits, reference frame, tectonics, ground based PWV/climate
Level 2: •15-30 second sampling, 10-60 minute retrieval, 10-60 minute latency•Ground based PWV/forecasting, ionosphere, space based PWV
Level 3: •10 Hz to 1 second sampling, streamed or small batch retrieval, several minutes latency, guaranteed delivery•Seismology (ground shaking and large event detection), tsunami warning, photogrammetry/airborne LIDAR•Real-time kinematic
Addis Ababa, Ethiopia, 02 May 2011 10
GNSS Receivers: Tracking Performance
General: Dual frequency, many independent channels, up to 50Hz sampling, ~ 1 mm phase
precision
GNSS observables Current:
GPS L1 C/A, L1&L2 P, L1&L2 phase (mandatory)GPS L2C, L5 (most modern receivers)
GLONASS L1 C/A Code, L1&L2 P, L1&L2 phase (most modern receivers)
Galileo – 2012+ (expected)
Performance measures99%+ of expected data
Cycle slips/observations <0.1%
Addis Ababa, Ethiopia, 02 May 2011 11
GNSS Receivers: Features• Power consumption 3-10 W• Memory up to many GB• Multiple I/O ports• Log and output multiple formats simultaneously• Raw, RINEX, BINEX, RTCM SC104, etc. • Command and control interface• Built in server technology supports http and ftp over TCP• Configuration over network by uploading configuration file• Serial commands and custom interface applications• Environmental specifications: -40 to +60 C, humidity
sealed• Power management• Ability to cycle power remotely and automatic restart in same
configuration after power loss • Ability to log and stream data from external sensors
(met, tilt)• Code and carrier multipath rejection and ability to
disable• External timing frequency input• Reliability: Mean Time Between Failure (MTBF) ~60,000
hours
Addis Ababa, Ethiopia, 02 May 2011 12
GNSS Receivers: Commonly used models
Commonly Used Models
Trimble NetR8/NetR9Topcon GB-1000/G3-A
Leica GRX1200Septentrio PolaRx
Costs (US$)Street Price: $15k-30kAcademic: $10k-15k
Large Quantity: $10k-15k
Addis Ababa, Ethiopia, 02 May 2011 13
GNSS Antennas
AntennasStable, well defined phase pattern – consistent between like modelsBackplane that rejects multipathAbsolute calibrations of antenna and radome pairCurrent best practice: Choke Ring design
Radomes – avoid use if possible!Material should be homogeneous and of uniform dimensionHemispherical shape with centre of curvature at absolute L1/L2 phase centre Radome should be calibrated along with antennaCurrent best practice: do not use radome unless required for weather, debris or vandal protection
Addis Ababa, Ethiopia, 02 May 2011 14
General AFREF station requirements
• Continuously operating• no end in operation expected• Communications• continuous internet access• Very stable monument• Availability of the data• data distributed freely in near real-time• Safe and secure instrument housing• Multipath-free installation site• Clear horizon to low elevation angles• Reliable electricity supply or UPS
Addis Ababa, Ethiopia, 02 May 2011 15
Issues concerning data availability
Not Public Available
e.g., Algeria, Angola
No Internete.g., EthiopiaMozambique Channel
Unreliable Internete.g.,
Many locations (but the situation is improving)
No IGS Conformale.g.,
SCINDA