reading gps time series plots

Reading GPS Time

Series PlotsRoger Groom, UNAVCO Master Teaching-in-Residence

Shelley Olds UNAVCO

GPS Basics

• Need 3 satellite signals to locate the receiver in 3D space

• 4th satellite used for time accuracy

• Calculate position within sub-centimeter

Anatomy of a GPS Station

GPS antenna inside of dome, solidly attached into the ground with braces. If the ground moves, the station moves.

Solar panel for power

Equipment enclosure • GPS receiver• Power/batteries• Communications/ radio/ modem• Data storage/ memory

Movement of GPS stations

GPS station positions change as plates move.

How will these stations’ positions change

relative to one another?

Processed GPS Data

SBCC GPS STATION

• Located near Mission Viejo, CA • Position data collected every 30

seconds• One position estimate developed

for each day North East Vertical

Date North (mm) East (mm)Vertical

(mm)

1/1/2004 -37.67 36.57 2.33

1/2/2004 -38.04 35.73 5.63

1/3/2004 -37.16 35.83 4.69

1/4/2004 -37.34 36.34 5.36

1/5/2004 -37.59 36.44 9.11

… … … …

1/1/2005 -9.43 9.63 2.36

1/1/2006 16.48 -18.09 7.35

1/1/2007 45.98 -43.42 -6.43

Starting with the basics: GPS Time Series Plot

Y-axis:• North (N/S)• East (E/W)• Height (up/down)

(sometimes called Vertical)

• In millimeters

X-axis: Date of the measurement In 10ths of year or months

Red data points are rapid position estimates

Units of measurement

• X AxisTypically in 10ths of year

• Y AxisUsually millimeters (but always check)

Gaps in Data

Causes• Power outages• Snow coverage• Equipment failure• Vandalism• Wildlife• Etc.

Gum drop GPS station

Build a gum-drop model of a GPS Monument 1 gum drop for the receiver = GPS Receiver 4 toothpicks (3 legs, one center post) = Monument braces 3 small Playdoh feet = Cement Small piece of transparency paper = ‘see-through’ Earth’s plate

Gum-drop stations in action

DateNorth(mm)

East(mm)

Height (mm)

2000 0 0 02001 1 1 02002 2 2 02003 3 3 02004 4 4 02005 5 5 0

… … …

What direction is GPS monument A moving?

GPS Monument A

5432102000 2001 2002 2003 2004 2005

Time (years)

Nor

th (m

m)

DateNorth Position

(mm)2000 02001 12002 22003 32004 42005 5

… …

GPS Monument A

Plotting the GPS Position over time: North

North vs Time

543210

Time (years)

Nor

th (m

m)

DateNorth Position

(mm)2000 02001 12002 22003 32004 42005 5

… …

GPS Monument A

Plotting the GPS Position over time: North

North vs Time

2000 2001 2002 2003 2004 2005

543210

Time (years)

Eas

t (m

m)

DateEast Position

(mm)2000 02001 12002 22003 32004 42005 5

… …

GPS Monument A

Plotting the GPS Position over time: East

East vs Time

2000 2001 2002 2003 2004 2005

543210

Time (years)

Hei

ght (

mm

)

DateHeight(mm)

2000 02001 02002 02003 02004 02005 0

… …

GPS Monument A

Plotting the GPS Position over time: Height

Height vs Time

2000 2001 2002 2003 2004 2005

Summary

• Positive slope (numbers getting larger)North-south time

series: The station is moving north

East-west time series: The station is moving east

Height time series: The station is moving up

Nor

th (m

m)

Eas

t (m

m)

Hei

ght

(mm

)

Time

DateNorth(mm)

East(mm)

19992000

01

01

2001 2 22002 3 32003 4 42005 5 5

… … …

Plot North and East togetherGPS Monument A

• Plot the location of the GPS station each year. • Draw an arrow from the first data point to the last data point.• Move your gum-drop GPS monument from year 2000’s position toward

2005’s position. What direction is your GPS monument moving?

543210

1 2 3 4 5

north

east

DateNorth(mm)

East(mm)

19992000

01

01

2001 2 22002 3 32003 4 42005 5 5

… … …

Step 2) What direction is GPS monument A moving?

GPS Monument A



54321

1 2 3 4 5

north

east

What direction is GPS monument B moving?

DateNorth(mm)

East(mm)

2000 0 02001 -1 -22002 -2 -42003 -3 -62004 -4 -82005 -5 -10

GPS Monument B

Focus on the data for the North data• Is Monument B moving in a more positive or negative direction?• What direction is GPS Monument B moving? North or South?

Now, focus on the data for the East data• Is Monument B moving in a more positive or negative direction?• What direction is GPS Monument B moving? East or West?

Plotting North and East Positions Together



GPS Monument B

-1-2-3-4-5

-5 -4 -3 -2 -1

north

east

Date (Year) North (mm) East (mm)2000 0 02001 -1 -22002 -2 -4

2003 -3 -62004 -4 -82005 -5 -10

-1-2-3-4-5

-5 -4 -3 -2 -1

north

east




GPS Monument BDate (Year) North (mm) East (mm)

2000 0 02001 -1 -22002 -2 -4

2003 -3 -62004 -4 -82005 -5 -10

-1-2-3-4-5

-5 -4 -3 -2 -1

north

east




GPS Monument BDate (Year) North (mm) East (mm)

2000 0 02001 -1 -22002 -2 -4

2003 -3 -62004 -4 -82005 -5 -10

-1-2-3-4-5

-5 -4 -3 -2 -1

north

east

Moving south and west

Negative slopeNorth-south time

series: The station is moving south

East-west time series: The station is moving west

Height time series: The station is moving down

Nor

th (m

m)

Eas

t (m

m)

Hei

ght (

mm

)

Time

What direction is this GPS station moving?

Zero slope

Is the GPS station moving?

Time

Nor

th (m

m)

Time

What direction is this GPS station moving?

Zero slope

The station isn’t moving.

How is GPS monument BURN moving?

Time

Nor

th (m

m)

Time

Which car matches the graphs?

WhatDirection?

________

Which car? (letter)

________

North

Time (Hours)

Nor

th (m

iles)

East

Eas

t (m

iles)

Time (Hours)

1)

AB

C

E

D

North


WhatDirection?

North-Northeast

Which car? (letter)

_Car A__

1)

AB

C

E

D

North

North

Time (Hours)

Nor

th (m

iles)

East

Eas

t (m

iles)

Time (Hours)


WhatDirection?

_______

Which car? (letter)

________

North

Time (Hours)

Nor

th (m

iles)

East

Eas

t (m

iles)

Time (Hours)

2)

AB

C

E

D

North


WhatDirection?

_South_

Which car? (letter)

__Car C__

North

Time (Hours)

Nor

th (m

iles)

East

Eas

t (m

iles)

Time (Hours)

2)

AB

C

E

D

North


WhatDirection?

______

Which car? (letter)

________

North

Time (Hours)

Nor

th (m

iles)

East

Eas

t (m

iles)

Time (Hours)

3)

AB

C

E

D

North


WhatDirection?

Northwest_

Which car? (letter)

___Car B_

3)

AB

C

E

D

North

North

Time (Hours)

Nor

th (m

iles)

East

Eas

t (m

iles)

Time (Hours)


What direction is Car E moving?

__________

4)

AB

C

E

D

North

North

Time (Hours)

Nor

th (m

iles)

East

Eas

t (m

iles)

Time (Hours)

Draw the North and East Graphs


What direction is Car E moving?

___East___

4)

AB

C

E

D

North

North

Time (Hours)

Nor

th (m

iles)

East

Eas

t (m

iles)

Time (Hours)



What direction is Car D moving?

_____________

5)

AB

C

E

D

North

North

Time (Hours)

Nor

th (m

iles)

East

Eas

t (m

iles)

Time (Hours)



What direction is Car D moving?

Southeast

5)

AB

C

E

D

North

North

Time (Hours)

Nor

th (m

iles)

East

Eas

t (m

iles)

Time (Hours)


Reference Key

What does GPS tell us about Iceland ?

REYK

HOFN

GPS Monument REYKN

orth

(mm

)E

ast (

mm

)

What direction is Monument REYK moving?

GPS Monument HOFNN

orth

(mm

)E

ast (

mm

)

What direction is Monument HOFN moving?

What directions are Monument REYK and HOFN moving?

REYKHOFN

Nor

th (m

m)

Eas

t (m

m)

Nor

th (m

m)

Eas

t (m

m)

towards each other, away from each other, or in the same direction?

REYK HOFN

How quickly is REYK moving?

Average position on 1/1/1997 = ______ mmAverage position on 1/1/2007 = ______ mm

Speed of REYK north = ___ mm / 10 years = ____ / yr to the North or South

Nor

th (m

m)

How quickly is REYK moving?

Average position on 1/1/1997 = _-135__ mmAverage position on 1/1/2007 = __70____ mm

Speed of REYK north = (70 - -135) mm / 10 years = 205 mm/ 10 yr = 20.5 mm / yr to the North

Calculate the speed of REYK for in the east-west direction and the speed of HOFN for both north-south and east-west directions (hint, use 1998 and 2008 for HOFN).

Nor

th (m

m)

How are quickly are REYK and HOFN moving?

Nor

th (m

m)

Eas

t (m

m)

Nor

th (m

m)

Eas

t (m

m)

REYK HOFN

REYK North = 20.5___ mm/year

REYK EAST = -11.0 __ mm/year

HOFN North = 15.0 ____ mm/year

HOFN EAST = 13.0 __ mm/year

Plotting vectors: north

• Number each axis using the same scale.• Vector: magnitude and direction

Tail is the GPS monument location Length of arrow is the magnitude Shows direction on a map

• GPS Monument REYK has moved 20.5 mm to the North per year• On your graph paper, each block represents 1 mm.

Draw a vector arrow 20.5 blocks along the north axis.

Plotting vectors: east

• Now draw a vector arrow -11.0 blocks (mm) along the East axis:

Adding the vectors together• To add the vectors together,

Re-draw the East arrow by placing its tail at the arrow head of the North arrow

Then draw a new vector from the tail of the North vector to the arrow head of the East vector.

GPS Monument C moves at: √20.52 + -112 = 23 mm / yr to the WNW

Draw the vectors on your map

What is happening to Iceland?

Icelandic rift eruption(Photo: National Geographic Magazine)

Vestmanneyjar, Heimaey, Iceland January 1973.

Source: USGS

Sites of surface eruptions

http://upload.wikimedia.org/wikipedia/commons/a/ab/Iceland_Mid-Atlantic_Ridge_Fig16.gif

The fracture pictured here occurs over the Mid-Atlantic Ridge. The photo by R. Stull was taken immediately after the largest earthquake in the area since 1917.

www.calstatela.edu/dept/geology/HotSpots.htm

http://www.calstatela.edu/dept/geology/HotSpots.htm

ICELAND

Mid-Atlantic Ridge

Conclusion

What you can do:• Explain the components of GPS data. • Determine velocity vectors from GPS

time series plots• Identify uses of GPS in applications

other than driving and hiking.

Other tools to explore

• UNAVCO GPS, Earthquake, Volcano Viewerhttp://geon.unavco.org/unavco/GEV.php

• Google Earth: Learn about Plate Tectonicshttp://geon.unavco.org/unavco/GE/Learn_about_

Plate_Tectonics.kmz

• IRIS Earthquake Browserhttp://www.iris.washington.edu/servlet/eventserv

er/map.do

59

http://geon.unavco.org/unavco/GEV.php

http://geon.unavco.org/unavco/GE/Learn_about_Plate_Tectonics.kmz

http://geon.unavco.org/unavco/GE/Learn_about_Plate_Tectonics.kmz

http://www.iris.washington.edu/servlet/eventserver/map.do

http://www.iris.washington.edu/servlet/eventserver/map.do

Thank you

Contact: Shelley Oldsolds unavco.org

http://www.unavco.org/

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reading gps time series plots

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