motivation experiences made with unigrace, ecgn, ngos and others steadily growing number of absolute...

NKG Working Group for Geodynamics Copenhagen, 23 –24 April, 2008 1

AGrav - Establishing a Database for Absolute Gravity Observations

Herbert Wilmes, Hartmut Wziontek, Reinhard Falk Federal Agency for Cartography and Geodesy, Frankfurt (BKG)

Sylvain Bonvalot Bureau Gravimétrique International, Toulouse (BGI)

NKG Working Group for Geodynamics Copenhagen, Denmark, 23 – 24 April 2008


Motivation• Experiences made with UNIGRACE, ECGN, NGOS and others• Steadily growing number of absolute gravimeters and absolute gravity

measurements• Demand for an overview about existing locations, observations,

instruments and institutions involved• New questions from “GGOS”, “Global change” “Mass transports” etc. • Cooperation and coordination of measurements• Absolute gravity data from a period of about 20 years available and

“potentially in danger”


Growing number of absolute gravimeters

Owners:

Value of the data grows! Long-term availability of absolute gravity data ?

Distribution of FG5 gravimeters

0

2

4

6

8

10

12

14

No o

f ins

trum

ents

Asia(18)

Europe(23)

America(7)

Australia(1)

(Status 2006)

• Metrological,• Geodetic, • Geologic and• Geophysical Institutions

Complemented by other instrument types: e.g. JILA-G, A10, IMGC, GABL, Faller etc.


AG observations by BKG,

1993 - 2006

Observations with FG5 absolute

gravimeters

Contribution to a global gravity network


Absolute gravimetry network (NGA)

(National Geospatial Intelligence Agency, USA)

Need more co-located observatories (VLBI, Laser, GPS, abs.grav., …)Many regional initiatives - ECGN/Europe, NGOS/Nordic ..) ..

Courtesy: S. Kenyon


AGrav - Absolute Gravity database

AGrav - Absolute Gravity database

Global database of absolute gravity measurements:

Definition of standards for data exchange Free exchange of meta-data:

Who measured where and when? Provision of contact information Sharing gravity values among contributing groups Map based web-interface to access meta-data and/or processing

results Collaboration: BKG and BGI, 2 mirror sites:

Frankfurt: http://agrav.bkg.bund.deToulouse: http://bgi.dtp.obs-mip.fr

http://agrav.bkg.bund.de/





http://bgi.dtp.obs-mip.fr/agrav/











International Gravimetric Bureau

Absolute Gravity DatabaseBKG database prototype installed & tested at BGI (S. Bonvalot, visit of H. Wziontek – Oct. 2007) – Additional

functionalitiesWorldwide data collection in progress at BGI

Two mirror sites : BGI & BKG


Agrav User Interface: Web-based Application (2)

Access to meta-database or detailed processing results with one user interface: Complete data access:

• Access restricted to contributing groups• Meta data and gravity values if available) • complete processing details


Data Exchange Format

Definitions: • Observation epoch: Period of an instrument set up and continuous data acquisition. Short interruptions due to technical demands are allowed. More than one processing result per observation epoch is possible and a final gravity value can be given outside automated processing schemes. • Location: One or more gravimetric points/monuments in close spatial relationship with equal environmental (atmospheric, hydrologic) conditions. Usually the distance between such points should not be greater than a few 100m

Required information:• Meta-information

- location: site name, coordinates- instrument: type, serial number and additional properties- period of the observation epoch

• Observation and processing details: - gravity value, error estimates- applied reduction models- vertical gravity gradient

• Simple structure ASCII format• to be created without additional effort

For FG5 and A10 users project-files created with the “Absolute Gravity Data Acquisition and Processing Software” (g-Soft) by Micro-g/LaCoste already meet these requirements!

Since most of the AG operators use g-Soft, the preparation is a by-product of standard processing, no additional is necessary! Other users can generate such a file easily.

“g”-Software project file


Data Upload (1)

Insertion of new data by the user• data under direct control of the user, the user decides whether only meta data should be made available or the gravity value • no additional personnel necessary

Web-form was developed to upload new or update existing data. Project-files are processed by a Perl-script on the server.

Step 1: Definition of the Location (Site)• choice of an existing station from the listor• definition of a new station Consistency check: Combination of country code / site code must be unique!

Step 2: Definition of the Point/Monument at the specified Location (Site)• choice of an existing point from the listor• definition of a new point Now project files can be chosen for the particular point! Decision, to upload meta data or the complete data.


Data Upload (2)

The project files are uploaded to the server and information stored in the data-base. If meta-data was chosen, all gravity related information is deleted. Script output helps to identify possible inconsistencies. The data can be edited manually after upload.

Problems of this approach: • Assignment of consistent site codes in responsibility of the user alone! Inconsistencies must must be avoided!• No conventions for site codes, teams use their own naming schemes!• Site- and point-codes not distinguished in project file


Conclusions

• Growing number of absolute gravity measurements• Demand of an overview about existing locations, observations, instruments and institutions

For both purposes, a relational database was designed and implemented and has reached the operational status now.

Prospectively, the database will contribute to the realisation of an international gravity reference and serve as a basis for geophysical interpretation of absolute gravity on a global scale.

Database can ensure the long-term availability of absolute gravity data for e.g. the maintenance of reference frames or the monitoring of global change processes.

Database available for the NGOS community to include AG data and work with the database as individual institution or as a group.

Comments and proposals are welcome!

motivation experiences made with unigrace, ecgn, ngos and others steadily growing number of absolute...

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