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GPS for H 2 0 ???

GPS for H 2 0 ???. Greg W. Keel P.Eng. Parallel Geo-Services Inc. (250) 753-0050 gkeel@nanaimo.ark.com. Introduction. Why does GWA need to know about GPS? Basic concepts of GPS Corrected Vs Uncorrected GPS positioning Different types of GPS equipment

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GPS for H 2 0 ???

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  1. GPS for H20 ??? Greg W. Keel P.Eng. Parallel Geo-Services Inc. (250) 753-0050 gkeel@nanaimo.ark.com

  2. Introduction • Why does GWA need to know about GPS? • Basic concepts of GPS • Corrected Vs Uncorrected GPS positioning • Different types of GPS equipment • MWLAP cross-reference pilot project in Okanagan • Q & A ???

  3. Why GPS for GWA ? • Well and facility location is important for: • inventory of what facilities exist and where they are, • emergency response, • spatial understanding of water resources • Accurate well elevations can be used to help understand the aquifer • If properly applied...GPS can reliably establish horizontal locations and elevations

  4. GPS Basic Concepts - Intro • GPS: Global Positioning System = NAVSTAR • US military designed, built, maintained…$20B • Always has been dual-use (military / civilian) • Initial concepts developed in early 1970s • First satellites launched in 1978 • 1980s: development of equipment / software / methodologies (limited satellites available) • 1986: Space Shuttle disaster delays GPS • early 1990s: GPS fully operational (Gulf War #1) • 2000: Selective Availability (SA) shut off…changes civilian accuracy from 100m to <10m (horizontal 95%)

  5. GPS Basic Concepts - 2 • Continuous positioning anywhere on earth • 3D Position, Velocity, Time • 24 satellites, inclined orbits 20,000km high • Military tracks each satellite: known positions (ephemeris) • User’s GPS receiver tracks codes broadcast by each satellite, determines distance (pseudo-range) by measuring the transmission time and scaling by the speed of light • With 4 pseudo-ranges, plus their ephemeris, user’s GPS receiver can compute instantaneous 3D position by trilateration (geometric intersection of distances) • 3 terms for this methodology: single-point, autonomous, or uncorrected GPS positioning.

  6. GPS Basic Concepts - 3 • Uncorrected GPS positioning has achievable accuracies (95%): horizontal <10m, and vertical <15m • WARNING: LOW POSITIONAL INTEGRITY ! • any errors…small or large…will affect the user’s computed position (and you probably will not know it) • reliable positioning (e.g. for a public database) requires better positional integrity - checking - the simplest way to do this with GPS is to apply differential corrections from a nearby GPS base station • any instantaneous errors “seen” at the GPS base station are formed into corrections and applied to the “rover” GPS measurements • DGPS rover positional integrity and accuracy are improved (95%) : horizontal <1m, and vertical <1.5m

  7. GPS Equipment - Navigation receivers • Navigation receivers for casual use • Examples handheld receivers: garmin, lowrance, magellan, etc. • Cost: $150 - $500+ • Good navigation features • May accept DGPS corrections • May have built-in WAAS (form of DGPS for aviation) - not practical • Limited control of measurement quality and positioning filters - not suitable for reliable positioning

  8. GPS Equipment - Professional DGPS • Professional DGPS receiver • Examples: Ashtech, Leica, Novatel, Trimble, etc • 3 components: antenna, receiver, datalogger • Costs: $5,000 - $15,000+ • Intelligent data capture - GIS ready • Advanced control of measurements and position filters…can be “tuned” for different accuracies / environments (e.g. for MWLAP cross-referencing pilot)

  9. GPS Equipment - Survey grade • Survey-grade instruments • Carrier-phase measurements produce very precise relative baselines (few mm) • Can be applied “static” or “kinematic” as long as the tracking conditions are good (mostly open) • Most expensive ($25,000+), and most demanding form of GPS.

  10. MWLAP cross-referencing pilot • >250 water systems in Okanagan • Golder and Associates • Inventory & locations: • wells / intakes • storage facilities • treatment facilities • monitoring sites Equipment: Trimble Pro-XR with CDGPS real-time differential corrections. Data collection parameters designed to reliably achieve <5m horizontal and vertical accuracies (actual accuracies are better).

  11. MWLAP cross-referencing pilot • Summaries to-date: • >300 wells/intakes • >370 monitoring sites • >130 treatment facilities • >180 storage facilities • GPS data is emailed to Parallel Geo-Services for check / edit / export in final formats, then returned to Golder for entry to DWIMP database. • Offsets applied when it is not possible / practical to place the GPS antenna on the center of the feature (see next slide).

  12. Questions... • Greg W. Keel P.Eng. • Parallel Geo-Services Inc. • (250) 753-0050 • gkeel@nanaimo.ark.com

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