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Satellite geodesy (ge-2112)

Applications

E. Schrama

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Applications• Global Positioning System

– Precise point positioning services

– Detection of platetectonics

– estimation of wet tropospheric delay

• International Earth Rotation Service– Earth rotation parameters + LOD

– Interpretation of these Earth rotation variables (AAM)

• Satellite altimetry– status 2002, where are we, how did it emerge, results

• Results from gravity missions

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GPS: precise point positioning

• Concept of differencing– Single differencing– Double differencing– Triple differencing

• Software– Bernse software– GIPSY JPL– Other software

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Concept of differencing• In the GPS system, many observations are made at the “same” time by

difference receivers.

• All receivers collect pseudo range data, carrier phase data and navigation messages

• The Pseudo range navigation allows you to get a approximate solution for receiver coordinates (approx 3 m)

• More importantly is that the pseudo range navigation solution allows to synchronize all receiver clocks to the (approx 10 nano seconds, nsec).

• The pseudo-range solution requires orbit information

• The dual frequency concept results in ionospheric free ranges and carrier phase estimates

• From this point on we start to work with “differencing techniques”,

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Broadcast Ephemeris GPS

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Broadcast ephemeris GPS (2)

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Single differences

SAT(1) SAT(2)

RCV(a)

r1a r2

a

Single Difference = r1a - r2

a

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Double differences

SAT(1) SAT(2)

RCV(a)

r1a

r2a

Double Difference = (r1a - r2

a) - (r1b-r2

b)

r2b

r1b RCV(b)

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Difference data processing

• Single differences (as shown two sheets before this one) are insensitive to receiver clock errors

• Double differences are insensitieve to all receiver and satellite clock errors

• Triple differences (= differences of double differences at consequetive epochs) reveal jumps in carrier phase data.

• Differencing techniques as described above result in observation equations that allow one to solve for coordinate delta’s (improvements)

• Available software to do this: GIPSY (JPL) + Bernese SW

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GPS to observe deformation around a vulcano on Hawaii

Ref: http://www.unavco.org/research_science/science_highlights/kilauea/kilauea.html

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Plate Tektonics

Source: Unavco Brochure

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GPS: Wet troposphere (cm)

http://www.gst.ucar.edu/gpsrg/realtime.html

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Ionosphere from GPS (TEC)

http://www.gst.ucar.edu/gpsrg/realtime.html

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IERS Earth rotation parameters

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X-pole solution

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Y-pole solution

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IERS: Length of day variations

The atmosphere (left) and the ocean tides (right) correlate with space geodetic observations of the length of day (LOD) source: NASA

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Satellite Altimetry

By means of a nadir looking radar we measure the reflection of short pulse in the footprint. This footprint is about 4 to 8 kilometer in diameter.

Source: JPL

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Pulse reflection

time

power

time

power

Sent

Received

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Radar footprint simulation

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Significant wave height (JPL)

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Scalar wind speed (JPL)

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Ionospheric delay (JPL)

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Radiometric water vapor (JPL)

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Technical evolution• SKYLAB 1972 NASA 20 m

• GEOS-3 1975-1978 NASA 3 m

• SEASAT 1978 NASA 2 m

• GEOSAT 1985-1990 US Navy 30 cm

• ERS-1 1991-1996 ESA 4-10 cm

• ERS-2 1995- ESA 4 cm

• T/P 1992- NASA/CNES 2 - 3 cm

• GFO 2000- US Navy

• JASON 2001- NASA/CNES 2 - 3 cm

• ENVISAT 2002- ESA

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Geosat (1985-1990)

ERS-1 1991-1996ERS-2

1995-

Recent and operational systems

Topex/Poseidon 1992 -

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Doris tracking network

Source: CNES

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ERS-1/2 tracking + cal/val

Source: DEOS

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T/P sampling

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120

119

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Topex/Poseidon groundtrack

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Mesoscale Variability

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Gulf stream (altimeter)

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Thermal image Gulf stream

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Permanent currents

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Schematic overview ocean currents

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Ship observations (1)

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To show how difficult it sometimes is at sea (2)

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More Detail in Gulf Steam

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Four Seasons from Altimetry

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El Niño Southern Oscillation

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Speed Kelvin/Rossby waves

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Kelvin and Rossby wavesEquator: 2.8 m/s 20 N: 8.5 cm/s

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Pacific decadal oscillation

1977-1999 Since 1999

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Examples of ocean tides

This shows a 7 meter tidal height difference in Brittany France (Pentrez Plage)

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M2 tide observed by altimeter

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Tides in the South China Sea

M2 wave

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K1 tidal component (23h 56m)

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Tide constants along the shores

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Tidal energy dissipation

-3 0 -2 0 -10 0 1 0 2 0 3 0 m W / m2

R R a y, G S F C

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Gravity from satellite altimetry

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January 98 August 98

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Quickscat

You can also observe wind speed AND direction from space with a so-called scatterometer. (A different instrument that looks and works much like a radar altimeter.)

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Tutorial quickscat

under the radarSide lobes

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Global windfield patterns

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Extreme wind conditions (Hurricane DORA)

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ICE/wind

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Decade of the Geopotentials

• CHAMP: a satellite equipped with acceleromters and a spaceborn version of GPS

• GRACE: two CHAMP flying after one another

• GOCE: four “champs” inside a satellite

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CHAMP 1

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CHAMP 2

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CHAMP launch

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CHAMP 4

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CHAMP 5

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Gravity field improvement

0 50 100 150 200 250 30010

-5

10-4

10-3

10-2

10-1

100

degree l

met

ercumulative geoid error