GPS for H20

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GPS for H20 ???

• Greg W. Keel P.Eng.
• Parallel Geo-Services Inc.
• [phone]
• gkeel_at_nanaimo.ark.com

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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 ???

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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

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GPS Basic Concepts - Intro

• GPS Global Positioning System NAVSTAR
• US military designed, built, maintained20B
• 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
  offchanges civilian accuracy from 100m to lt10m
  (horizontal 95)

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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)
• Users 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,
  users 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.

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GPS Basic Concepts - 3

• Uncorrected GPS positioning has achievable
  accuracies (95) horizontal lt10m, and vertical
  lt15m
• WARNING LOW POSITIONAL INTEGRITY !
• any errorssmall or largewill affect the users
  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 lt1m, and vertical
  lt1.5m

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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

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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
  filterscan be tuned for different accuracies /
  environments (e.g. for MWLAP cross-referencing
  pilot)

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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.

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MWLAP cross-referencing pilot

• gt250 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 lt5m
horizontal and vertical accuracies (actual
accuracies are better).
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MWLAP cross-referencing pilot

• Summaries to-date
• gt300 wells/intakes
• gt370 monitoring sites
• gt130 treatment facilities
• gt180 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).

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Questions...

• Greg W. Keel P.Eng.
• Parallel Geo-Services Inc.
• [phone]
• gkeel_at_nanaimo.ark.com