GGP Agreements

GGP is a project to improve the quality and quantity of vertical gravity signals at the Earth's surface that are recorded by existing and future SG installations. Through the GGP, SG installations are encouraged to record the gravity signal to minimum specified standard and to make their data available on a mutually agreed upon format to other GGP Groups and to the scientific community in general.

The recommendations that follow are the result of intensive, and sometimes very lively, discussions on the various possibilities for recording gravity signals. The input to these decisions was of course limited to those present at the meetings.

Data Recording Parameters

It is agreed:

  1. That the gravity signal should be recorded at high rate for (a) seismological purposes and (b) to permit data repair before decimation. High rate data is recorded usually between 1 and 10s; for the purposes of the GGP we will assume that data sampled more frequently that every 10s can be decimated to 10s for data exchange.
  2. The precision should be the equivalent of 0.1 ngal, which is 7.5 digits if the full bandwidth of the signal is to be recorded.
  3. The timing accuracy for each gravity sample should be 10 ms.

    [Note Added:] A semi-diurnal tidal wave (M2 of amplitude say 100 mgal has a maximum slew (derivative) of 0.0145 mgal/sec. At a sensitivity (gravity error) of 0.1 ngal, this slew translates into a timing (epoch) error of 6ms. In practise a 10 ms error is therefore not unreasonably stringent.
  4. The atmospheric pressure should be recorded at a minimum sampling interval of 10s at an accuracy equivalent to better than 0.1 mbar.
  5. This high rate 10s data is regarded as the GGP Raw Data.

It was left unresolved (a) from which GEP outlet (TIDE, MODE, 1s) the gravity signal was to be sampled and (b) the characteristics of the anti-aliasing filter prior to sampling. It is generally agreed the latter should be improved from the current IDA-based filter.

The Potsdam group (Neumeyer et al.) propose (a) that the atmospheric pressure should be recorded with the same recording parameters as the gravity signal (b) that the gravity data should be sampled from the gravity GEP outlet (if not available from the tide GEP outlet) and (c) that the antialiasing filter should be designed by GWR. This last point has been discussed and proposed by several other individuals.

The question of 1s versus 10s sampling rate has been actively discussed by a number of individuals, including Mansinha, Crossley, Richter, Z\"urn and Hinderer. The consensus seems to be forming that a 10s sampling rate is sufficient for all geophysical purposes (including normal mode studies), provided that a suitable anti-aliasing filter can be designed that does not cut off frequencies of seismological interest.

There is no a priori reason for every GGP group to record the gravity at the same rate or through the same filter, provided the resulting 10s data (GGP Raw Data for seismic studies) and 1m data (GGP Data for all other studies) are produced to a consistent standard (i.e. signal to noise ratio, frequency band). However there would be some benefit to the having a standard 10s anti-aliasing filter, designed by GWR that satisfied the scientific goals of GGP.

[Note Added:] This has already been proposed and discussed with GWR, (see elsewhere).

Data Exchange Format

It is agreed:

  1. Bearing in mind the need to balance the large amount of Raw Data collected by the GGP versus the need to allow flexibility in future processing, 1 min samples of gravity and local atmospheric pressure should be the standard GGP data for exchange.
  2. Separate files for each calendar month should be prepared as follows :
    1. FILE 1 - date, time, gravity, pressure (each minute)
    2. FILE 2 - date, time, water level, rainfall, tilts, temperature, humidity (each minute, or as available)
    3. FILE 3 - date, time, log file information (giving all the known disturbances, He refills, gaps etc., as necessary)
  3. All times are to be quoted as UTC (including leap seconds). All variables are to be quoted in the units in which the measurements are made, with the appropriate calibration factors given.
  4. Usually the signals are recorded in volts. For other purposes, the units to be adopted are mgal (gravity), mbar (pressure), m (rainfall, water level), °C (temperature) and SI for all other variables. The three data files for each month, as defined above (FILES 1-3), constitute the definition of GGP Data.

    [Note Added:] Peters (NOAA) suggests rainfall in cm, does anyone have strong opinions on this?
  5. That considering the widespread use and availability of the ETERNA program for tidal analysis (Wenzel, 1994b), the ETERNA, or more precisely the PRETERNA, data format (Wenzel, 1994a) should be adopted for data exchange as outlined by Wenzel (1994c). In this format, for example the gravity and pressure data (FILE 1) would appear as:

    Header information
    (station parameters, comments and parameters of the data
    acquisition, scale factors, etc.)
    date time gravity (volts) air pressure (volts)
    yyyymmdd hhmmss ggg.gggggg ppp.pppppp

    As indicted by Wenzel (1994b) "Step corrections (to be added to all subsequent data of the channel) may be input via a code 77777777 in columns 1..8 and a data gap may be input via a code 66666666 in columns 1..8. The end of the data series is marked by a 99999999 in columns 1..8". (Further details can be obtained from the GGP Secretariat or G. Wenzel).
  6. GGP participants should make available the GGP Raw Data to other GGP participants, when (see below), and if so requested.

It was left unresolved (a) the exact format for each data file, including headers and (b) the medium (INTERNET, diskettes, etc.) by which the exchange should take place.

Data Availability

It is agreed that GGP Data (both 1 min and 10s, if requested) should be available to other GGP Participants within 1 year of its collection.

It was left unresolved:

(a) the extent to which data repair was to be performed on the Raw Data prior to decimation to 1 minute, or on the data repair to be performed on the 1 minute data itself

(b) the specifications of the decimation filter used to prepare 1 minute data from Raw Data

(c) the data format for the exchange of GGP Raw Data

(d) the definition of a GGP Participant and provision of GGP Data to non-GGP participants

(e) the publishing of scientific papers based on the use of GGP Data.

The Potsdam Group suggests a zero phase shift filter with a corner period between about 300s and 1000s. This is consistent with filters currently in use in several installations.

[Note Added]: We suggest that in response to the unresolved issues, the following policies could be adopted:

(a) For GGP Raw Data (10s), if data is recorded more frequently than every 10s, it would be sensible to remove spikes and offsets prior to decimation to 10s. For GGP Data (1m), it is assumed that spikes, offsets, disturbances and gaps are repaired prior to decimation to 1 min. Any tides or atmospheric pressure corrections that are removed or involved in the repair process are restored prior to decimation.

(b) The decimation filter should preserve the amplitude of signals to a 3hr period within 0.1% of its DC level with no phase shift.

(c) The data format for the exchange of 10s data could also be PRETERNA, i.e. one 10s sample per line (or per time epoch).

(d) Each SG Group could nominate one individual to receive the GGP data. Each Group would have to establish who would have access to the priveledged data within the 1 year time interval. It is probable that those involved in collecting the data or supporting the local projects might be recipients of the data.

(e) The publication of papers based on cooperative studies is sometimes a delicate issue. Certainly the source of GGP data should always be explicitly acknowledged in any publication that uses the data. Within the restricted time period, perhaps potential authors should post their publication intentions to a GGP Bulletin Board for feedback and compromise with their colleagues.

Closing Remarks

Perhaps the most contentious issue left at the present time is that of the GGP Data Centre. There are valid arguments for a Network Centre (as proposed by Aldridge and Jensen), a Data Centre in the form of a Storage Centre and a Data Centre in the form of a Data Processing Centre. Clearly each of these addresses different needs and requires different resources.

To date, we have agreed to set up an International GGP Data (Storage and Distribution) Centre in Canada, but this will be without the facilities for Data Processing that are perhaps required. Peters suggests that a Data Centre should be able to accept data in any format and massage it into a standard format for storage and distribution to the community. This is in principle a worthwhile goal, but given the current limitations in resources, none of the SG groups have offered this level of manpower commitment. As a comparison, ICET, for example, requires a standard data format.

On the other hand the possibility of passing GGP data to an multi-purpose international data centre (such as GFZ) carries with it the concern that the data will not be processed according to GGP requirements and that with the relatively small amount of data involved, an elaborate system is unwarranted. We are however grateful for the interest shown by the Potsdam group in GGP data.

The real problem is that we have no funding for a GGP Data Centre, but as suggested by our Japanese colleagues, the existence of a Data Centre may be used to attract funding. It is relatively easy to set up a Mosaic, WWW or Gopher access to GGP Data and given the explosion of INTERNET use, most SG groups are now able to take advantage of this way of accessing data.

Aside from this problem, the GGP Observing Period is still set to commence in July 1995. We will be keeping close contact with the SG Groups over the next 6 months to see if this start time is still realistic.


Beroza & Jordan, 1990, J. Geophys. Res. 95, 2485-2510.

Richter, B. & Wenzel, Step Response Calibration

Richter, B. & Wenzel, IFAG Lift.

Sato, T., K. Shibuya, K. Okano, K. Kaminuma and M. Ooe, 1993, Obervations of Earth tides and free oscillations with a superconducting gravimter at Syowa station (Status Report), Proc. NIPR Symp. Antart. Geosci., 6, 17-25.

Seama, N., Y. Fukuda and J. Segawa, 1993, Superconducting gravimeter observations at Kakioka, Japan, {\em J. Geomag. Geolectr., 45, 1383-1394

Tamura, Y. et al. 1993, Geophys. J. Int.

Warburton, R. & Brinton, E., 1994, Recent developments in GWR Instruments' superconducting gravimeters, paper submitted to Second Workshop on Non-Tidal Gravity Changes : Intercomparison between absolute and superconducting gravimeters, Walferdange, Luxembourg, September 6-8, 1994

Wenzel, H.-G., 1994a, PRETERNA - a preprocessor for digitally recorded tidal data. Bulletin d'Information Mar\'ees Terrertres, 118, 8722-8734, Bruxelles.

Wenzel, H.-G., 1994b, ETERNA - an Earth tide analysis package for the personal computer, Submitted to Bulletin Geodesique.

Wenzel, H.-G., 1994c, Format and Structure for the exchange of high precision tidal data, Paper presented at the meeting of the Working Group on High Precision Tidal Data Processing, August 30 - September 2, Bonn, Germany.


Tables and Figures

Table 1. SG Station Locations
(plotted on Figures 2 and 3)

Code Instrument Location Lat °N Long °E Height(m) Status
MI GWR T001 Miami, USA 28.48 ? 289.84 ?   N
BE GWR T003 ROB Belgium 50.7986 4.3581 98 A
WU GWR T004 Wuhan, China 30.53 114.30   A
ST GWR T005 Strasbourg, France 48.6222 7.6850   A
WE GWR T006 Wettzell, FRG 49.1458 12.8794 612 A
ES GWR T007 Esashi, Japan 39.148 141.335 393 A
BR GWR T008 Braunschweig, FRG 52.1331 10.4004 -553 A
KY GWR T009 Kyoto, Japan 35.0 135.786 57.6 A
KY GWR T010 Kyoto, Japan 35.0 135.786 57.6 A
KA GWR T011 Kakioka, Japan 36.233 140.183 31.7 A
CA GWR T012 Cantley, Canada 45.5850 284.1929 269 A
BL GWR T015 Bologna, Italy 44.29 11.20 24 A
SY GWR T016 Syowa, Antarctica 69.0 39.6   A
TH GWR T017 Thessalonika, Greece 40.38 22.56   ?
PO GWR T018 Potsdam, FRG 52.3806 13.0682 81 A
ME GWR T020 Metsahovi, Finland 60.2172 21.3958 55.6 A
BO GWR T001 Boulder, USA 40.09 245.99   A
BO GWR T0?? Boulder, USA 40.09 245.99   N
SD GWR T0?? San Diego, USA 32.8 242.70   B
MB GWR T0?? Membach, Belgium 50.617 6.00 250 N
UC UCSD SGA San Diego, USA 32.8 242.70   B
FA UCSD SGB Fairbanks, USA 64.51 212.57   A

A = Probable GGP Site
B = Operational intermittently, or in use for non-GGP purposes
N = New Station or new instrument to be installed
? = No confirmation of status

Table 2. GGP Start Times

Instrument Location Begin GGP Recording
GWR T001 Miami, USA 1995
GWR T003 ROB Belgium ROB Belgium & Now - 10s later
GWR T004 Wuhan, China Wuhan, China & New site - July 1995
GWR T005 Strasbourg, France Data Acquisition Upgrade - 1995
GWR T006 Wettzell, FRG Now
GWR T007 Esashi, Japan Now
GWR T008 Braunschweig, FRG  
GWR T009 Kyoto, Japan Fall 1994
GWR T010 Kyoto, Japan Now
GWR T011 Kakioka, Japan Now
GWR T012 Cantley, Canada Fall 1994
GWR T015 Bologna, Italy ?
GWR T016 Syowa, Antarctica Now/Data Delay
GWR T017 Thessalonika, Greece  
GWR T018 Potsdam, FRG Now - new site 1995?
GWR T020 Metsahovi, Finland Started August 1994
GWR T001 Boulder, USA Fall 1994
GWR T0?? Boulder, USA  
GWR T0?? San Diego, USA  
GWR T0?? Membach, Belgium New Site 1995
UCSD SGA San Diego, USA  
UCSD SGB Fairbanks, USA Now

Figure 1 - Surface Gravity Signals

Figure 2 - Global SG Stations

Figure 3 - European SG Stations

Appendix A - Abbreviations Used in this Document

Acronym Expansion
CSGI Canadian Superconducting Gravimeter Installation
FLINN Fiducial Laboratories for an International Natural Science Network
GFZ GeoForschungsZentrum (Potsdam)
GGP Global Geodynamics Project (this proposal)
GLRS Geodynamics Laser Ranging System (proposed by NASA)
GSC Geological Survey of Canada
GWR Goodkind Warburton and Reinemann (SG manufacturers, California)
IAG International Association of Geodesy
IASPEI International Association of Seismology and Physics of the Earth's Interior
ICET International Centre for Earth Tides (Brussels)
IERS International Earth Rotation Service (Paris)
ICG International Commission on the Geoid (IAG)
IGC International Gravity Commission (IAG)
IUGG International Union of Geodesy and Geophysics
NAOM National Astronomical Observatory of Japan, Mizusawa
NASA National Aeronautics and Space Administration
NIPR National Institute of Polar Research (Tokyo)
NOAA National Oceanographic and Atmospheric Agency (Boulder)
ORI Ocean Research Institute (Tokyo)
SEDI Study of the Earth's Deep Interior (IUGG)
SG Superconducting Gravimeter
SLR Satellite Laser Ranging
VLBI Very Long Baseline Interferometry

Appendix B - The stance of Japanese SCG Group for the data exchange under the GGP

Japanese SCG Group is ready to provide the SCG data obtained at Japanese four stations including Syowa Station for the GGP. All the data can be sent by FTP. According to the agreement made at the GGP meeting at Whistler Mountains, the GGP data to be sent from Japan will be 1 minute SCG \& pressure data, and the document file concerning the descriptions of the data.

As a premise to provide the Japanese SCG data, we, the members of Japanese SCG Group, consider that all the GGP data be exchanged through a GGP Data Centre, which is expected to be set up in a certain country where there is at least one active GGP member. We consider it indispensible to set up the GGP Data Center for fair and smooth management of data exchange. Moreover setting up the GGP Data Center might be useful for getting the endorsement from an authorised organisation such as IAG to implement the objectives of the GGP, which have already been proposed in March, 1990 (Aldridge et al., 1990).

Concerning this, we agree that the Japanese GGP data shall be sent through a subcenter in Japan and we also receive the GGP data from the other countries through this subcenter.

A. The duties of the center.

The duties of the center might be:

  1. collecting the GGP data from worldwide GGP members and archiving them,
  2. circulating the data information and preparing the GGP data files for the request from all the other GGP members and the scientists involved under the GGP data policy,
  3. updating regularly the GGP data management files which could be made accessible by any registered users,
  4. publishing regularly news letters and/or activity reports,
  5. coordinating workshops relevant to the GGP, if it is possible.

The news letter and/or activity report might include the following items, for example:

(a) a log of the available GGP data
(b) research topics using the GGP data and related ones,
(c) information on the exchange of SCG raw data

B. Financial support.

It is impossible by Japanese regulations to support the operational funds of the GGP Data Center that is managed in a foreign country. However, we are seeking for the possibility whether we can prepare resources to invite foreign researchers for the GGP objectives.

Submitted by: T. Sato and S. Takemoto, Walferdange, September 1994.

Appendix C - GGP Mailing List/Steering Committee

Prof. Keith Aldridge, Department of Earth \& Atmospheric Science, York University, 4700 Keele Street, North York, Ontario, M3J lP3 CANADA. Tel : +1-416-736-5529 Fax : +1-416-736-5817 Email :

Prof. Dimitrios Arabelos, Dept. of Geodesy \& Surveying, University of Thessaloniki, Univ. Box 474, GR-54006 Thessalonika, GREECE. Tel : +30-31-2693 Fax : +30-31-203587 Email : -

Dr. Paolo Baldi, Dipartimento Di Fisica, Settore Di Geofisica, Universita Delfi Studi Di Bologna, Viale Berti Pichat 8, 40127 Bologna, ITALY. Tel : +39-51-243-586 Fax : +39-51-250-106 Email : -

Prof. David J. Crossley, Department of Earth \& Planetary Sciences, McGill University, 3450 University St., Montr\'{e}al, Qu\'{e}bec H3A 2A7, CANADA. Tel : +1-514-398-4886 Fax : +1-514-398-4680 Email :

Dr. Bernard Ducarme, Observatoire Royal de Belgique, 3 Avenue Circulaire, ll80 Bruxelles, BELGIUM. Tel : +322-373-02-48 Fax : +322-374-98-22 Email :

Prof. John Goodkind}, Department of Physics, B-019, University of California, La Jolla, San Diego, California 92093, USA. Tel : +1-619-534-2716 Fax : +1-619-534-0173 Email : -

Dr. Jacques Hinderer, G\'eodynamique Interne, Institut de Physique du Globe, 5 rue Ren\'e Descartes, 67084 Strasbourg, FRANCE. Tel : + Fax : + Email :

Prof. H.-T. Hsu, Institute of Geodesy \& Geophysics, Chinese Academy of Sciences, 54 Xu Dong Road, Wuchang, Hubei 430077, P.R. CHINA. Tel : +86-27-6816006 Fax : +86-27-7811080 Email :

Prof. Gerhardt Jentzsch, Institut f\"ur Geophysik, Technische Universit\"at Clausthal, Arnold-Sommerfeld Strasse 1, Postfach 1253, Clausthal-Zellerfeld D-38678, F.R.GERMANY. Tel : +49-5323-722641 Fax : +49-5323-722320 Email :

Dr. Jussi Kääriänen, Geodeettinen Laitos, Finnish Geodetic Institute, Ilmalankatu 1A, SF-00240 Helsinki, FINLAND. Tel : +358-0-410433 Fax : +358-0-414946 Email :

Dr. Tony Lambert, Geophysics Division, Geological Survey of Canada, 3, Observatory Crescent, Ottawa, Ontario K1A 0Y3, CANADA. Tel : +1-613-995-5446 Fax : +1-613-952-8987 Email :

Prof. Lalu Mansinha, Department of Geophysics, University of Western Ontario, Biology and Geophysics Building, London, Ontario, N6A 5B7, CANADA. Tel : +1-519-661-3145 Fax : +1-519-661-3198 Email :

Prof. Jim Merriam, Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan F7N 0W0, CANADA. Tel : +1-306-966-5716 Fax : +1-306-966-8593 Email :

Dr. J\"urgen Neumeyer, Rezente Kinematik und Dynamik der Erde, GeoForschungsZentrum Potsdam, Telegrafenberg A17, D-14473 Potsdam, F.R.GERMANY. Tel : 49-331-288-1135 Fax : +49-331-288-1111 Email :

Dr. George Peter, National Oceanic and Atmospheric Administration, N/OES13 SSMC4 STA8210, 1305 East-West Highway, Silver Spring, Maryland 20910, USA. Tel : +1-301-713-2856 Fax : +1-301-713-4475 Email :

Dr. Christian Poitevin, Centre de G\'{e}ophysique Interne, Observatoire Royal de Belgique, 3 Avenue Circulaire, ll80 Bruxelles, BELGIUM. Tel : +322-373-02-11 Fax : +322-374-98-22 Email :

Dr. Bernd Richter, Institut fur Angewandte Geodasie, Richard Strauss-Allee 11, D-6000 Frankfurt, F.R.GERMANY. Tel : +49-331-316-600 Fax : +49-331-316-602

Dr. Knut Rothing, State Mapping Authority, Geodetic Institute, Kartverksvn, N-3500 Honefoss, NORWAY. Tel : +47-32-11-81-00 Fax : +47-32-11-81-01 Email :

Dr. Tadahiro Sato, National Astronomical Observatory, Hoshigaoka-cyo, Mizusawa-shi, Iwate-ken 023, JAPAN. Tel : 81-197-22-7137 Fax : +81-197-22-2715

Dr. Peter Schwintzer, Rezente Kinematik und Dynamik der Erde, GeoForschungsZentrum Potsdam, Telegrafenberg A17, D-14473 Potsdam, F.R.GERMANY. Tel : +49-331-288-1130 Fax : +49-331-288-1111 Email :

Prof. Jiro Segawa, Ocean Research Institute, University of Tokyo, 15-1, 1-Chome, Minamidai, Nakano-ku, 164 Tokyo, JAPAN. Tel : +81-376-1251 Fax : +81-337-56716 Email : -

Prof. Kazuo Shibuya, National Institute of Polar Research, Kaga 1-9-10, Itabashi-ku, Tokyo 173, Tel : +81-3-3962-4789 Fax : +81-3-3962-5741 Email :

Prof. Shuzo Takemoto, Department of Geophysics, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto 606-01, JAPAN. Tel : +81-75-753-3912 Fax : +81-75-711-1374 Email :

Dr. Yoshiaki Tamura, National Astronomical Observatory, Hoshigaoka-cho, Mizusawa, Iwate-ken 023, JAPAN. Tel : +81-197-22-7131 Fax : +81-197-22-3410 Email :

Dr. Richard Warburton, 10623 Roselle Street, San Diego, California 92121, USA. Tel : +1-619-452-7655 Fax : +1-619-452-6965 Email : -

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