GPS for H 2 0 ???

GPS for H20 ???

Greg W. Keel P.Eng.

Parallel Geo-Services Inc.

(250) 753-0050

[email protected]

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 ???

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

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%)

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.

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

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

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)

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.

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).

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).

Questions...

Greg W. Keel P.Eng. Parallel Geo-Services Inc. (250) 753-0050 [email protected]