GRAVITY FIELD PRODUCTS
Riccardo Barzaghi
c/o Politecnico di Milano, ITALY
GGOS Days Cambridge MA, USA, October 24-28, 2016
The questions
What are the products?
What are the applications?
Who are the users?
How do we define the requirements for the products (spacial, temporal, etc.)?
How do we meld these with the geometric reference frame?
What measurements are required?
Gravity Field observations&products
Absolute gravity
IAG resolution #2 (Prague 2015) for the establishment of a global absolutegravity reference system (JWG 2.1)
(1) Worldwide set of AG instruments realise the standard
(2) Combination with SG realise a continuous timely coverage (permanent observations)
(3) Network of gravity stations establishes the link between gravity and geometric positions
(4) Availability of world-wide AG / SG observations leads to a new importance and use of the data (GGOS requirement)
Absolute gravity: establishment of an international gravity reference frame
Gravity Field observations&products
Relative gravity (ground based, aerogravimetry, at sea)
Gravity Field observations&products
Relative gravity data are inhomogeneous either in density and precision(old data are not even properly georepherenced)
andfrequently restricted
5’×5’ Δg data availability (EGM2008) (gravity at sea from radaraltimetry)
12.0% of Land
42.9% of Land
45.1% of Land
Gravity and Gradiometry from dedicated satellite missions
Gravity Field observations&products
Global coverage and nearly homogeneous precisionUnrestricted data
Monthly variation of the gravity anomaly (mgal) in the Amazon River from GRACE (2004)
Gravity Field observations&products
Satellite only Global Geopotential Models to d/o 280 (GOCE)
Geoid and DOT at sea from altimetry
Gravity Field observations&products
Global coverage and nearly homogeneous precisionUnrestricted data
Gravity Field observations&products
Free air gravity anomaliesfrom satellite altimetry: the DTU models
DOT estimate from e.g. SSH(DTU) and N(GOCE):the GULF Stream current velocity
Potential differences
Gravity Field observations&products
WB
-WA
= - gdnA
B
ò
i) spirit leveling&gravity
i) optical clocks
DW
c2=
Df
f
δnAB
Any estimated/observed functional of the anomalous potential T(local-regional-global) like e.g.
i) Geoid undulation N
ii) Gravity anomalies Δg (free-air, Bouguer anomalies, Helmert anomalies…)
iii) Deflection of the vertical (ξ,η)
Gravity Field observations&products
Gravity Field related products
DTM/DSM
Earth Tides
Gravity Field observations&products
Gravity Field observations&products
DATA TYPE GLOBAL DISTRIBUTION METADATA HOMOGEOUS PRECISION
Absolute gravity Y/N Y Y
Relative gravity Y Y/N N
Gravity from satellite Y Y Y
Potential differences Y Y/N N
Est./Obs. Functional of T Y/N Y/N N
Related products Y Y Y/N
i) Gravity corrections to leveling increments
Technical applications: surveying&navigation
ii) Height conversion
Gravity Field products: users&applications
WB
-WA
= - gdnA
B
ò
H @ h- N
iii) Inertial Navigation (e.g. for aerial photogrammetry and LIDAR)
Gravity Field products: users&applications
Technical applications: surveying&navigation
DOV Û (x ,h)
Gravity Field products: users&applications
(a) Geophysics: gravity inversion at local and global scale
Scientific applications
Moho depth from GOCE
3D density estimate from gravity
(b) Oceanography: MSS/MDT
(c) Hydrology: time varying gravity at local and global scale
MSS over the Mediterranean Sea (DTU2013)Global MDT
local scale investigation(MEMS can be used too)
(d) Height systems unification (IHRS/IHRF)
(e) Gravity and atomic clocks
Required measurements
(i) global and dense coverage
(ii) homogeneous precision
(iii) different data kinds
(iv) metadata information
The “official” IAG GGM
GGM for what?
Scientific tasks Technical tasks
No stringent need to adopt an offcial IAG GGM
Need to adoptan offcial IAG GGM
How to define the “official” GGM?