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?