The Decade of the Geopotential - techniques to observe the gravity field from space

(1)

The Decade of the Geopotential –

techniques to observe the gravity

field from space

Matthias Weigelt Tonie van Dam Olivier Francis

(2)

Geophysical implications of the gravity field

2

(3)

Gravity field modelling

3

with gravitational constant times mass of the Earth radius of the Earth

spherical coordinates of the calculation point Legendre function

degree, order

(unknown) spherical harmonic coefficients

(4)

Gravity field modelling

4

with gravitational constant times mass of the Earth radius of the Earth

spherical coordinates of the calculation point Legendre function

degree, order

(unknown) spherical harmonic coefficients

(5)

5

Snm - order m - C

nm

degree n

Spherical harmonic spectrum of ITG-GRACE2010s

-80 -60 -40 -20 0 20 40 60 80

0

20

40

60

80

-12 -11 -10 -9 -8 -7

Spherical -6

harmonic

representation

degree-RMS

Spectral representation

(6)

6

Snm - order m - C

nm

degree n

Spherical harmonic spectrum of ITG-GRACE2010s

-80 -60 -40 -20 0 20 40 60 80

0

20

40

60

80

-12 -11 -10 -9 -8 -7

Spherical -6

harmonic

representation

degree-RMS

Spectral representation

(7)

Pre CHAMP era

(8)

Space geodetic observation techniques

courtesy Oliver Baur

SLR:

Optical:

courtesy NOAA BC-4

(9)

1966:

Development of the gravity field precision and resolution

(10)

1972:

Development of the gravity field precision and resolution

(11)

1976:

Development of the gravity field precision and resolution

(12)

1982

^:

Development of the gravity field precision and resolution

(13)

1987:

Development of the gravity field precision and resolution

(14)

1990:

Development of the gravity field precision and resolution

(15)

1996:

Development of the gravity field precision and resolution

(16)

The Decade of the Geopotentials -

the concepts

(17)

Satellite missions

17

High-low SST

Low-low SST

Gradiometry

CHAMP

GRACE GOCE

(18)

CHAMP

(19)

Satellite system CHAMP

CHAMP = CHAllenging Minisatellite Payload

• Initial orbit height: ~ 485 km

• Inclination: ~ 87.5°

• Key technologies:

– GPS

– Accelerometer – (Magnetometers)

• Observation quantity:

– Position by GPS

– Non-gravitational forces by accelerometers

(20)

Newton‘s equation of motion

(21)

Newton‘s equation of motion

→

(22)

Newton‘s equation of motion

→ →

(23)

Newton‘s equation of motion

→ →

Observation: (position)

(24)

Newton‘s equation of motion

→ →

Differentiation: (acceleration)

(25)

Newton‘s equation of motion

→ →

(26)

Newton‘s equation of motion

→ →

(27)

Newton‘s equation of motion

→ →

(28)

2010:

GAIN due to CHAMP

(29)

GRACE

(30)

Satellite system GRACE

GRACE = Gravity Recovery and Climate Experiment

• Initial orbit height: ~ 485 km

• Inclination: ~ 89°

• Key technologies:

– GPS

– accelerometer

– K-Band ranging system

• Observation quantity:

– distance (range)

– change of distance (range rate)

30

© CSR, UTexas

(31)

Geometry of the GRACE system

31

Differentiation Integration

Rummel et al. 1978

(32)

2013:

GAIN due to GRACE

(33)

2013:

GAIN due to GRACE and GOCE

(34)

2013:

GAIN due to GRACE: time variable gravity (TVG)

(35)

Achievements

in terms of the TVG

(36)

Spatio-temporal resolution ?

10^-3 10^-2 10^-1 10⁰ 10¹ 10² 10³ 10⁴ 10⁵

10⁰ 10¹ 10² 10³ 10⁴ 10⁵

10000km

1000km

100km

10km

1km

sea ice

vulcanos

PGR

ocean currents ice mass balance solid

Earth and ocean

tides

lithosphere mantle tectonics

postseismicdeformation

coseismic deformation

groundwater snow soil moisture

runoff water balance storage balance

sea - level

quasi-staticocean circulation

atmosphere

(37)

Spatio-temporal resolution ?

10^-3 10^-2 10^-1 10⁰ 10¹ 10² 10³ 10⁴ 10⁵

10⁰ 10¹ 10² 10³ 10⁴ 10⁵

10000km

1000km

100km

10km

1km

sea ice

vulcanos

PGR

Earth and ocean

tides

sea - level

atmosphere

GRACE

(38)

Spatio-temporal resolution ?

10^-3 10^-2 10^-1 10⁰ 10¹ 10² 10³ 10⁴ 10⁵

10⁰ 10¹ 10² 10³ 10⁴ 10⁵

10000km

1000km

100km

10km

1km

sea ice

vulcanos

PGR

Earth and ocean

tides

sea - level

atmosphere

GRACE

(39)

Spatio-temporal resolution ?

10^-3 10^-2 10^-1 10⁰ 10¹ 10² 10³ 10⁴ 10⁵

10⁰ 10¹ 10² 10³ 10⁴ 10⁵

10000km

1000km

100km

10km

1km

sea ice

vulcanos

PGR

Earth and ocean

tides

sea - level

atmosphere

GRACE CHAMP

(40)

Change in water storage

40

GRACE GFZ Rel. 4 High-low SST

(41)

Water is stressed …

41

• Water balance in India (Rodell et al., Nature, vol. 460, 2009)

(42)

The Future

(43)

GRACE und GRACE Follow-On (GFO)

43

Low-low

• K-Band + Laser

• GPS

• Accelerometer

year

(44)

GRACE und GRACE Follow-On (GFO)

44

Low-low

• K-Band + Laser

• GPS

• Accelerometer

year

up to 4 year data gap

(45)

Bridging the gap …

45

High-low

GOCE

year

(46)

Bridging the gap …

46

High-low

GOCE GOCE

year

(47)

Bridging the gap …

47

High-low

GOCE GOCE

SWARM

year

(48)

Beyond GRACE Follow-On

10^-3 10^-2 10^-1 10⁰ 10¹ 10² 10³ 10⁴ 10⁵

10⁰ 10¹ 10² 10³ 10⁴ 10⁵

10000km

1000km

100km

10km

1km

sea ice

vulcanos

PGR

Earth and ocean

tides

sea - level

atmosphere

GRACE CHAMP

(49)

Beyond GRACE Follow-On

10^-3 10^-2 10^-1 10⁰ 10¹ 10² 10³ 10⁴ 10⁵

10⁰ 10¹ 10² 10³ 10⁴ 10⁵

10000km

1000km

100km

10km

1km

sea ice

vulcanos

PGR

Earth and ocean

tides

sea - level

atmosphere

GRACE CHAMP

(50)

Summary

• The decade of the potential yield an improvement

in the gravity field by three orders of magnitude.

• Time variable gravity can be observed for the first

time with a monthly sampling.

• Ongoing strive for higher spatial and temporal

resolution (with a likely setback in the coming

years).

(51)

Thank you

Matthias Weigelt Tonie van Dam Olivier Francis

(52)