Andrew Mc Lean Kelvin Barraclough Gisborne Secondary College

Andrew Mc. Lean Kelvin Barraclough Gisborne Secondary College

What is GPS? • 24 + satellites

What is GPS? • 24 + satellites • Several ground stations

What is GPS? • 24 + satellites • Several ground stations • GPS receiver

Satellites • Altitude ≈ 20200 km

Satellites • Altitude ≈ 20200 km • Period 12 hours

Satellites • Altitude ≈ 20200 km • Period 12 hours • At least 4 visible everywhere

Satellites • • Altitude ≈ 20200 km Period 12 hours At least 4 visible everywhere Solar powered, ≈ 50 W transmitter

Satellites • • • Altitude ≈ 20200 km Period 12 hours At least 4 visible everywhere Solar powered, ≈ 50 W transmitter Transmit on 1575. 42 MHz

Satellites • • • Altitude ≈ 20200 km Period 12 hours At least 4 visible everywhere Solar powered, ≈ 50 W transmitter Transmit on 1575. 42 MHz Fitted with atomic clocks

Satellites • • Altitude ≈ 20200 km Period 12 hours At least 4 visible everywhere Solar powered, ≈ 50 W transmitter Transmit on 1575. 42 MHz Fitted with atomic clocks Lifespan ≈ 10 years

Ground Stations • I master station, four remote

Ground Stations • I master station, four remote • Monitor satellites and send back accurate orbital and time data

The Signal • The “almanac”. Approximate position of all satellites, transmitted and stored in the GPS.

The Signal • The “almanac”. Approximate position of all satellites, transmitted and stored in the GPS. • The “ephemeris”. Accurate data of individual satellite position.

The Signal • The “almanac”. Approximate position of all satellites, transmitted and stored in the GPS. • The “ephemeris”. Accurate data of individual satellite position. • The “pseudo random code”. Effectively, an accurate time signal

The Signal • The “almanac”. Approximate position of all satellites, transmitted and stored in the GPS. • The “ephemeris”. Accurate data of individual satellite position. • The “pseudo random code”. Effectively, an accurate time signal • Turned off while satellite orbit is adjusted

Satellite positions 27400 km 20200 km

Signal times 0. 091 s 0. 067 s

Establishing position

Establishing position

Establishing position • If receiver had a good enough clock – • Two satellites – somewhere on a circle

Establishing position • If receiver had a good enough clock – • Two satellites – somewhere on a circle • 3 rd satellite – cuts this circle twice, but usually one solution is obvious

Establishing position • If receiver had a good enough clock – • Two satellites – somewhere on a circle • 3 rd satellite – cuts this circle twice, but usually one solution is obvious • 4 th satellite – removes ambiguity

Establishing position • With a small, cheap clock -

Establishing position • With a small, cheap clock – • 3 satellites give 2 D fix

Establishing position • With a small, cheap clock – • 3 satellites give 2 D fix • 4 satellites give 3 D fix

Accuracy • Given clear view of sky typically 5 – 10 m

Receivers • Aren’t equal

Receivers • Aren’t equal • Need “good view” of sky

Possible information • Position

Possible information • Position • Distance travelled

Possible information • Position • Distance travelled • Speed

Possible information • • Position Distance travelled Speed Direction

Possible information • • • Position Distance travelled Speed Direction Altitude

Gathering data – “low tech”

30 25 20 15 Series 1 10 5 0 0 5 10 15 20 25 30 35 40 45 50

Gathering data – “hi tech” • Almost all GPS receivers can be connected to a computer to transfer data

Suitable software (1) • “Ozi. Explorer”

Suitable software (1) • “Ozi. Explorer” • $130

Suitable software (1) • “Ozi. Explorer” • $130 • Uses raster mapping

Suitable software (1) • • “Ozi. Explorer” $130 Uses raster mapping Suitable for all brands of GPS

Suitable software (1) • • • “Ozi. Explorer” $130 Uses raster mapping Suitable for all brands of GPS Transferring data from Ozi is awkward

Suitable software (2) • Garmin “Mapsource”

Suitable software (2) • Garmin “Mapsource” • Free with Garmin GPS

Suitable software (2) • Garmin “Mapsource” • Free with Garmin GPS • Uses Vector mapping

Suitable software (2) • • Garmin “Mapsource” Free with Garmin GPS Uses Vector mapping Allows easy transfer of data to other programs (eg Excel)

Some possibilities • • Real aircraft - loop the loop Model aircraft Racing cars, dragsters, motorbikes Skydivers, bungee jumpers Yacht racing Theme park rides Relative motion on moving ship

Cost? • • Cheap GPS ≈ $100 Garmin GPS Map 60 CSx ≈ $470 Ozi. Explorer $130 Oztopo maps for Garmin (all of Australia) $229