AiA In Australia 2015 GPS Accuracy And RR/RP Integration

GPS Characteristics WinRiver II uses GGA and VTG strings ZDA string used to set time in some cases Single (L1) vs Dual (L1/L2) Frequency GLONASS – potentially more satellites to use Integrated vs Separate Receiver/Antenna Vector (Heading) Capability

GPS Accuracy Probability based – CEP = 50% confidence – RMS = 65% – 2dRMS = 95% HDOP, VDOP, PDOP Accuracy vs Precision – Accuracy = true position – Precision = repeatability – For measuring discharge, Precision >> Accuracy

Differential Correction Sources SBAS – Satellite Based Augmentation Service – WAAS, EGNOS, MSAS, GAGAN – Free – Not available worldwide (i.e. in Australia and NZ) Beacon – Limited Coverage, primarily coastal – Free – User must locate and tune desired station

RTK (Real-Time Kinematic) – Rover + Base (or RTK network) – Absolute accuracy depends on Base position – Dual Frequency -> operational advantages OmniStar – Latitude < 60 deg N/S – VBS, XP, HP – Subscription based – Not supported by current Hemisphere GPS firmware but systems with compatible firmware and existing subscriptions are expected to continue working Starfire, C-Nav, TerraStar – Similar to OmniStar, but from different providers – Not currently supported by Hemisphere

GPS Usage Considerations Selection of Differential source – Availability at site – Equipment and subscription costs All require good compass calibration – ADCP data is relative to magnetic north – GPS data is relative to geodetic north – Magvar aligns magnetic to geodetic Site Considerations

PocketMax 3 Plot

Simple Comparison

Loop Closure Errors

Why Integrated GPS? Advantages – Single input to WinRiver II – Less potential for GPS data latency – Simpler integration, esp. with float Disadvantages – No separate GPS text file – Troubleshooting more difficult – Can’t set ADCP time from GPS

How It Works RS-232 NMEA output from GPS Must configure RR with baud rate; RP has auto-detect capability Standard NMEA header(s) GGA, VTG messages only for position/speed Suggested: 9600 baud Excess GPS data ignored/discarded RR: GPS only – no Heading or Depth input RP: Will capture Heading and Depth inputs

WinRiver II Wizard

GPS Interface Kit Contents GPS interface cable(s) – Cable configuration depends on GPS system – In-hull cable(s) with bulkhead connector – External cable(s) GPS Mounting Bracket(s) Hardware Single (additional) hull penetration

RiverRay Float

RiverRay Float Harness

RiverRay Serial/Power Cable

Integrated Antenna/Receiver Simplest system Mount GPS above ADCP Two-piece wiring harness kit – In-hull: MicroChange to bulkhead conn. – External: Bulkhead to GPS – Both cables carry data + power

Separate Antenna/Receiver Receiver in Hull Better protection for receiver and lower center of gravity Mount Antenna above ADCP Three-piece wiring kit – In Hull: MicroChange to GPS receiver – In Hull: GPS antenna to bulkhead conn. – External: Bulkhead to Antenna

Separate Antenna/Receiver Receiver Outside Hull Receiver more exposed, higher C.G. Mount Antenna above ADCP Three-piece wiring kit – In Hull: MicroChange to bulkhead conn. – External: Bulkhead to GPS receiver – External: GPS to Antenna

Questions?