S 1

1
Graphics files in directories d\nico\proj\GOCE\g
raphics\ d\nico\proj\GOCE\GranadaIIreport\graphi
cs d\images\geo
Gravity Field and Steady-State Ocean Circulation
Explorer (GOCE)
2
Issues of Concern
Ice Sheet Melting
Earthquakes volcanic activities
Thermohaline ocean circulation heat transport
Sea level change
Global unification of height system
3
International Programme

• International Lithosphere Programme (ILP)
• Int. Decade of Natural Disaster Reduction
  (IDNDR)
• International Association of Geodesy (IAG)
• World Climate Research Programme (WCRP)
• - GEWEX
• - WOCE/CLIVAR
• - GCOS/GOOS
• - ACSYS/CLIC
• International Geosphere/Biosphere Program (IGBP)
• - LOICZ
• Intergovernmental Oceanographic Commission (IOC)
• - GLOSS

Earthquakes and Volcanic Activities Global
Unification of Height System Thermohaline
Ocean Circulation and Transport of Heat. Ice
Sheet Melting Sea Level Change
4
Research Goals

• Solid Earth Physics anomalous density
  structure of lithosphere and upper mantle
• Oceanography determination of dynamic ocean
  topography
• Ice Sheets improved knowledge of ice sheet
  balance
• Geodesy unified height systems, levelling by
  GPS
• and from the above improved Sea Level Change
  Studies

5
Mission Objectives

• determine the Earths gravity field with an
  accuracy of
• 1 mgal (1 mgal 10-5 m/s2 )
• determine the geoid ( equipotential surface for
  a hypothetical ocean at rest) with an accuracy of
  1 cm
• achieve this at length scales down to L 100 km
• (degree and order 200)

6
Presentation Outline

• Mission Rationale
• Science Application
• Mission Design
• Performance
• Conclusions

7
Mission Rationale Limitations of Existing
Gravity Field Data

• terrestrial gravity anomalies
• large unsurveyed areas, heterogeneous data,
  offsets and biases
• geoid mapping via satellite altimetry
• not acceptable for oceanography
• satellite orbit analysis
• - only large spatial scales are satisfactory
  - heterogeneous data
• - error correlation

8
gravdensBGI.gif
Mission Rationale Incomplete Data Coverage
9
geoid_altim2.ppt
Mission Rationale Limitation with Satellite
Altimetry
10
egm.bw.eps
Mission Rationale Signal Accuracy versus Spatial
Scales
11
Mission Rationale Spaceborne Gravity Field
Methods

• Satellite-to-Satellite Tracking in High-Low
  Mode
• SST-hl
• Satellite-to-Satellite Tracking in Low-Low Mode
• SST-ll
• Satellite Gravity Gradiometry
• SGG

12
sst_hl.eps
Mission Rationale SST - hl
SST - hl
13
sst_ll.eps
Mission Rationale Combined SST - ll and SST - hl
SST - ll
14
gradiometry.eps
Mission Rationale Combined SGG and SST - hl
SST - hl
15
Mission Rationale Gravity Field Satellite Design
Criteria

• Orbit as low as possible and near polar
• Uninterrupted tracking in 3-D
• Isolation of gravitational signal
• Amplification of gravitational signal by
  principle of differentiation

16
Mission Rationale GOCE versus Design Criteria

• Orbit altitude 250 km and sun-synchronous
  (inc. 96.5)
• Uninterrupted and 3-D high-low tracking with
  GPS satellites relative to ground network
• Drag-free system and elimination of residual
  drag common mode rejection
• Gravity signal amplification by gradiometry
  (differential accelerometry)
• in addition all component gradiometer

17
goce_eqn.jpg
Mission Rationale Full Tensor Gradiometer
Measurements
acceleration differentiation
gravity gradient
angular acceleration
angular velocities
18
satellit.ppt
Mission Rationale Instrument Concept
angular forces
translational forces

GPS/GLONASS SST -hl
star sensors


A
B
GRAVITY GRADIOMETER
measures
GRAVITY GRADIENTS
angular accelerations
common mode accelerations
angular control
drag control
19
CGG_fill_bw.eps CGG_plainx.eps CGG_overlayx.eps
Mission Rationale Uniqueness
SGG achieves highest attainable resolution SGG
and SST-ll are complementary
20
vik.bw.eps
Mission Rationale The 3-D structure of the
Gravity Field
21
Mission Rationale The 3 -D structure of the Error
Coefficient
22
GIGGOS.doc (.eps)
Mission Rationale The Interdisciplinary Research
Solid Earth Physics
Earth System Model - ocean - ice sheet -
lithosphere - mantle - core
Geodesy
Sea Level Change
Cryosphere
Oceanography