Presentation on theme: "Addis Ababa, Ethiopia, 02 May 2011 1 AFREF IGS Guidelines / Station Requirements Rui Fernandes DI-UBI, Univ. Beira Interior, Covilhã, Portugal. Instituto."— Presentation transcript:
Addis Ababa, Ethiopia, 02 May 2011 1 AFREF IGS Guidelines / Station Requirements Rui Fernandes DI-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 - Visibility Ideally: No obstruction above horizon in any direction. Acceptable: No significant obstructions above 10º in any direction. - Security Protection of antenna against robbery or vandalism acts. Reserved access to the receiver. - Electric Power Ideally: Access to reliable public electrical network. Alternative: Autonomous systems (e.g., solar panels). - Internet Ideally: Continuous and reliable access - Monument Stability Ideally: rigidly connected to the ground REQUIRED BY ALL APPLICATIONS DEPENDENT OF THE APPLICATION
Addis Ababa, Ethiopia, 02 May 2011 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 3
Addis Ababa, Ethiopia, 02 May 2011 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 4
Addis Ababa, Ethiopia, 02 May 2011 5 Requirements Monument Stability 2Km ApplicationLevel Tectonic Motions and Vertical MonitoringSub-centimeter Early Warning Systems (Tsunamis, Volcanoes) Sub-centimeter Centimeter Real-Time Products (Orbits, Surveying)Centimeter Reference Frames Sub-centimeter Centimeter Meteorological ApplicationsDecimeter Ionospheric MonitoringMeters Proper Self-Center Mounting Device is fundamental
Addis Ababa, Ethiopia, 02 May 2011 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 6
Addis Ababa, Ethiopia, 02 May 2011 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 7
Addis Ababa, Ethiopia, 02 May 2011 8 Requirements Permanent access to Internet 2Km ApplicationRequired?* Tectonic Motions and Vertical MonitoringNo (Local Storage) Ionospheric Monitoring Yes No (Local Storage) Reference FramesYes 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 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 measures 99%+ of expected data Cycle slips/observations <0.1% 10
Addis Ababa, Ethiopia, 02 May 2011 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 11
Addis Ababa, Ethiopia, 02 May 2011 GNSS Receivers: Commonly used models Commonly Used Models Trimble NetR8/NetR9 Topcon GB-1000/G3-A Leica GRX1200 Septentrio PolaRx Costs (US$) Street Price: $15k-30k Academic: $10k-15k Large Quantity: $10k-15k 12
Addis Ababa, Ethiopia, 02 May 2011 GNSS Antennas Antennas Stable, well defined phase pattern – consistent between like models Backplane that rejects multipath Absolute calibrations of antenna and radome pair Current best practice: Choke Ring design Radomes – avoid use if possible! Material should be homogeneous and of uniform dimension Hemispherical shape with centre of curvature at absolute L1/L2 phase centre Radome should be calibrated along with antenna Current best practice: do not use radome unless required for weather, debris or vandal protection 13
Addis Ababa, Ethiopia, 02 May 2011 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 14
Addis Ababa, Ethiopia, 02 May 2011 Issues concerning data availability Not Public Available e.g., Algeria, Angola No Internet e.g., Ethiopia Mozambique Channel Unreliable Internet e.g., Many locations (but the situation is improving) No IGS Conformal e.g., SCINDA 15
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